**In Press**
Enfield, D.B. Evolution and historical perspective of the 1997-1998 El Niño-Southern Oscillation event. Bulletin of Marine Science (in press).
The ocean thermal history of the 1997-98 El Niño episode is described in detail, with emphasis on developments along the equator and eastern Pacific coastlines. The temporal evolution of the warming and its causes are traced from the western Pacific, past the Galapagos Islands, and on to the subpolar gyres off North and South America. Along the equator, the event was characterized by a subsurface warm anomaly that slowly made its way from west to east across the Pacific from mid-1996 until early 1997, whence it triggered the onset of surface anomalies at the eastern terminus of the equatorial waveguide. The thermocline depression off Ecuador intensified from mid-1997 through the end of the year, culminating in a mature phase with maximum sea surface temperature anomalies (SSTA) around November-December 1997. The event gradually abated thereafter until the beginning of the subsequent cool phase (La Niña) was detected in July 1998. Following their arrivals at the eastern boundary, equatorial Kelvin waves proceeded poleward into both hemispheres as coastal trapped waves, carrying the thermocline depression signal with them along with associated nutrient deficiencies and ecosystem impacts. The poleward propagation of SSTA was more uniform and faster south of the equator, reaching south-central Chile with amplitudes of 2°C or greater. North of the equator the propagation was discontinuous, with decreased anomalies south of 20°N and a revival of SSTA in excess of 2°C, north of there, but with considerably larger time lags than observed off Chile. The possible reasons for these interhemispheric differences are discussed.
Wang, C. On the ENSO mechanisms. Advances in Atmospheric Science (in press).
The El Niño-Southern Oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific Ocean-atmosphere interactions. The oscillatory nature of ENSO requires both positive and negative ocean-atmosphere feedbacks. The positive feedback is dated back to Bjerknes' hypothesis in the 1960s, and different negative feedbacks have been proposed since the 1980s associated with the delayed oscillator, the western Pacific oscillator, the recharge-discharge oscillator, and the advective-reflective oscillator. The delayed oscillator assumes that wave reflection at the western boundary provides a negative feedback for the coupled system to oscillate. The western Pacific oscillator emphasizes equatorial wind in the western Pacific that provides a negative feedback for the coupled system. The recharge-discharge oscillator argues that discharge and recharge of equatorial heat content causes the coupled system to oscillate. The advective-reflective oscillator emphasizes the importance of zonal advection associated with wave reflection at both the western and eastern boundaries. All of these physics are summarized in a unified ENSO oscillator. The delayed oscillator, the western Pacific oscillator, the recharge-discharge oscillator, and the advective-reflective oscillator can be extracted as special cases of the unified oscillator. As suggested by this unified oscillator, all of the previous ENSO oscillator mechanisms may be operating in nature.
Wang, C., and R.H. Weisberg. Ocean circulation influences on SST in the equatorial cental Pacific. Journal of Geophysical Research (in press).
Velocity data from an array of acoustic Doppler current profilers moored about 0, 140°W from May 1990 through June 1991 during the Tropical Instability Wave Experiment are used in conjunction with Tropical Atmosphere Ocean array data and a blended sea surface temperature (SST) product to study the processes that control SST variations. The horizontal velocity data allow us to calculate the vertical velocity component by vertically integrating the continuity equation. Given the three-dimensional temperature flux divergence, we examine the role of the ocean circulation on SST. Upwelling and downwelling are found to be associated with cooling and warming, respectively, suggesting that a vertical velocity component of either sign affects SST. Both the temperature flux divergence and advective formulations for the ocean circulations influence in the temperature budget show times when the ocean circulation appears to provide the primary control on SST and times when this is not the case, with the flux divergence formulation performing better than the advective formulation. Statistically, within a bandwidth encompassing the tropical instability waves and the intraseasonal variations, roughly half of the SST variation is accounted for by the ocean circulation. These results are encouraging, given that data sets with different spatial and temporal scales have been used. They suggest that future field experimentation which utilizes a flux divergence array with velocity and temperature data sampled at the same spatial and temporal scales will yield quantitatively improved results. The analyses also show that the ocean circulation on average provides a cooling effect requiring the net surface heat flux to be positive on average to maintain the mean background state. The cooling effect is mainly controlled by mean ocean circulation and temperature fields.
**2001**
Daly, K.L., W.O. Smith, G.C. Johnson, G.R. DiTullio, D.R. Jones, C.W. Mordy, R.A. Feely, D.A. Hansell, and J.-Z. Zhang. Hydrography, nutrients, and carbon pools in the Pacific sector of the Southern Ocean: Implications for carbon flux. Journal of Geophysical Research, 106(C4):7107-7124 (2001).
We investigated the hydrography, nutrients, and dissolved and particulate carbon pools in the western Pacific sector of the Antarctic Circumpolar Current (ACC) during austral summer 1996 to assess the region's role in the carbon cycle. Low fCO2 values along two transects indicated that much of the study area was a sink for atmospheric CO2. The fCO2 values were lowest near the Polar Front (PF) and the Subtropical Front (STF), concomitant with maxima of chlorophyll a and particulate and dissolved organic carbon. The largest biomass accumulations did not occur at fronts, which had high surface geostrophic velocities (20-51 cm s-1), but in relatively low velocity regions near fronts or in an eddy. Thus, vertical motion and horizontal advection associated with fronts may have replenished nutrients in surface waters but also dispersed phytoplankton. Although surface waters north of the PF have been characterized as a "high nutrient-low chlorophyll" region, low silicic acid (Si) concentrations (2-4 µM) may limit production of large diatoms and therefore the potential carbon flux. Low concentrations (4-10 µM Si) at depths of winter mixing constrain the level of Si replenishment to surface waters. It has been suggested that an increase in aeolian iron north of the PF may increase primary productivity and carbon export. Our results, however, indicate that while diatom growth and carbon export may be enhanced, the extent ultimately would be limited by the vertical supply of Si. South of the PF, the primary mechanism by which carbon is exported to deep water appears to be through diatom flux. We suggest that north of the PF, particulate and dissolved carbon may be exported primarily to intermediate depths through subduction and diapycnal mixing associated with Subantarctic Mode Water and Antarctic Intermediate Water formation. These physical-biological interactions and Si dynamics should be included in future biogeochemical models to provide a more accurate prediction of carbon flux.
Enfield, D.B., and A.M. Mestas-Nunez. Interannual to multidecadal climate variability and its relationship to global sea surface temperatures. In: Interhemispheric Climate Linkages, V. Markgraf (ed.). Academic Press, 17-29 (ISBN 0124726704) (2001).
As a benchmark to help profile paleoclimates across the Americas we develop an overview of what is known of modern climate variability on a planetary scale, with emphasis on climate manifestations in the Western Hemisphere. From instrumental observations taken as early as the mid-19th century, we look at both atmospheric and oceanic variables and consider their relationships on timescales ranging from interannual to multidecadal. We focus on three of the most important climate modes: the interannual El Niño-Southern Oscillation (ENSO), the interdecadal Pacific Decadal Oscillation (PDO), and the multidecadal North Atlantic Oscillation (NAO). The variable of greatest interest is sea surface temperature (SST) because it is arguably the least understood of the atmospheric boundary conditions for prehistoric climates and yet one of the most critical for effecting atmospheric model simulations of those climates. The analysis begins by computing a global distribution of the trend in SST, which turns out to be highly non-uniform, with characteristics that may reflect low-frequency changes in shallow water mass formation. We then compute a global, canonical mode for ENSO that preserves the amplitude and phase structures of interannual ENSO variability worldwide. The ranking of the modal amplitudes of ENSO events differs from the absolute amplitudes obtained by indexing SST data directly. This reflects the importance of the (non-ENSO) decadal-multidecadal climate modes in modifying the intensity of ENSO-related ocean warmings. Comparing the global mode between the ends of the 19th and 20th centuries, we see essentially no difference in amplitudes and frequency of ENSO on the global warming timescale, although such changes have occurred on shorter, multidecadal timescales. Upon removal of the global ENSO mode from the data, the residual variability is subjected to two different analyses that extract very similar spatio-temporal patterns of SST for the PDO- and NAO-like climate modes. The climate variations with longer timescales (PDO, NAO) together account for about the same amount of variance as ENSO, globally, and in some regions, e.g., the northeastern North Pacific, may rival ENSO in their climate and marine impacts. The NAO, in particular, involves an Atlantic-Pacific connection that may arise through fluctuations in the polar vortex, an aspect which may also characterize previous climates. In our discussion, we speculate on what might be learned from the instrumental record regarding possible characteristics of ancient climates, especially regarding the possibility that ENSO may have been considerably different or even absent in the mid-Holocene.
Enfield, D.B., A.M. Mestas-Nunez, and P.J. Trimble. The Atlantic multidecadal oscillation and its relation to rainfall and river flows in the continental U.S. Geophysical Research Letters, 28(10):2077-2080 (2001).
North Atlantic sea surface temperatures for 1856-1999 contain a 65-80 year cycle with a 0.4°C range, referred to as the Atlantic Multidecadal Oscillation (AMO) by Kerr (2000). AMO warm phases occurred during 1860-1880 and 1940-1960, and cool phases during 1905-1925 and 1970-1990. The signal is global in scope, with a positively correlated co-oscillation in parts of the North Pacific, but it is most intense in the North Atlantic and covers the entire basin there. During AMO warmings most of the United States sees less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Between AMO warm and cool phases, Mississippi River outflow varies by 10% while the inflow to Lake Okeechobee, Florida varies by 40%. The geographical pattern of variability is influenced mainly by changes in summer rainfall. The winter patterns of interannual rainfall variability associated with El Niño-Southern Oscillation are also significantly changed between AMO phases.
Goldenberg, S.B., C.W. Landsea, A.M. Mestas-Nunez, and W.M. Gray. The recent increase in Atlantic hurricane activity. Causes and implications. Science, 293:474-479 (2001).
The years 1995 to 2000 experienced the highest level of North Atlantic hurricane activity in the reliable record. Compared with the generally low activity of the previous 24 years (1971 to 1994), the last six years have seen a doubling of overall activity for the whole basin, a 2.5-fold increase in major hurricanes (>50 m/s), and a fivefold increase in hurricanes affecting the Caribbean. The greater activity is caused by simultaneous increases in North Atlantic sea-surface temperatures and decreases in vertical wind shear, both of which are known to favor hurricane formation. Because these changes exhibit a multidecadal time scale, the present high level of hurricane activity is likely to persist for an additional 10 to 40 years. The shift in climate calls for a reevaluation of preparedness and mitigation strategies.
Goni, G.J., and W.E. Johns. A census of North Brazil Current rings observed from TOPEX/POSEIDON altimetry: 1992-1998. Geophysical Research Letters, 28(1):1-4 (2001).
Six years of TOPEX/POSEIDON altimeter data are used to investigate the formation of rings and eddies shed by the North Brazil Current. Upper layer thickness maps were used to identify 34 of these features formed in the North Brazil Current retroflection region, an average of more than five rings and eddies per year. The ensemble of ring trajectories closely parallels the 500 m isobath, and one out of six rings penetrate into the Caribbean Sea through the southern Lesser Antilles. The rest of the rings and eddies follow a northern trajectory past Barbados once they reach 58°W. Their estimated mean translation speed is 14 km/day and their mean length scale is approximately 100 km. Our results suggest that the formation rate of NBC rings and eddies is nearly twice that previously thought, and that they may account for more than one-third of the interhemispheric transport within the Atlantic meridional overturning cell.
Hood, E.M., R.H. Wanninkhof, and L. Merlivat. Short time scale variations of fCO2 in a North Atlantic warm-core eddy: Results from the GASEX-98 carbon interface ocean atmosphere (CARIOCA) buoy data. Journal of Geophysical Research, 106(C2):2561-2572 (2001).
During a Lagrangian deliberate tracer study in the North Atlantic, the 1998 Gas Exchange Experiment, hourly measurements of wind speed, sea surface temperature, fCO2, and fluorescence were made from two carbon interface ocean atmosphere (CARIOCA) drifting buoys in a warm-core eddy near 46°N and 21.5°W over a period of approximately 20 days. Shipboard measurements of fCO2 near the buoys were used to verify the buoy operation, calibrate the buoy measurements, and assess the performance of the fCO2 sensor. The strong air-sea fCO2 gradient in the eddy and intense atmospheric forcing during the experiment provided ideal conditions for demonstrating the potential of autonomous drift buoy measurements for studies of surface ocean biogeochemistry, where changes of fCO2 were rapid and large. During the experiment, a storm occurred with wind speeds reaching as high as 16-17 m s-1, leading to a sharp decrease in sea surface temperature and an increase in fCO2 of ~30 µatm. The magnitude of this sudden change in fCO2 is equal to approximately half of the annual range of fCO2 in this area. The air-sea flux estimate for the ~20 day experiment using the Wanninkhof (1992) gas transfer velocity formulation was -0.012 mol m-2 d-1 and using the Liss and Merlivat (1986) formulation was -0.007 mol m-2 d-1. The storm event, lasting three to four days, accounted for ~38% of the flux over this period. Approximately 16 hours after the onset of the storm, there was an increase in surface fluorescence coincident with the initial increase in fCO2. Nitrate measurements made from the ship in the eddy show a sharp peak in surface concentrations ~24 hours after the increase in winds and ~6-8 hours after the increase in surface fluorescence. After the upwelling of the NO3 the fluorescence increases more sharply while the fCO2 decreases, consistent with biological productivity. The surface fluorescence measurements remain higher than prestorm conditions for ~5 days after the NO3 has disappeared.
Kaplan, J., and M. DeMaria. On the decay of tropical winds after landfall in the New England area. Journal of Applied Meteorology, 40(2):280-286 (2001).
A version of the Kaplan and DeMaria empirical model for predicting the decay of tropical cyclone 1-min maximum sustained surface winds after landfall is developed for the New England region. The original model was developed from the National Hurricane Center (NHC) best-track wind estimates for storms that made landfall in the United States south of 37°N from 1967 to 1993. In this note, a similar model is developed for U.S. storms north of 37°N, which primarily made landfall in New York or Rhode Island and then moved across New England. Because of the less frequent occurrence of New England tropical cyclones, it was necessary to include cases back to 1938 to obtain a reasonable sample size. In addition, because of the faster translational speed and the fairly rapid extratropical transition of the higher-latitude cases, it was necessary to estimate the wind speeds at 2-h intervals after landfall, rather than every 6 h, as in the NHC best track. For the model development, the estimates of the maximum sustained surface winds of nine landfalling storms (seven hurricanes and two tropical storms) at 2-h intervals were determined by an analysis of all available surface data. The wind observations were adjusted to account for variations in anemometer heights, averaging times, and exposures. Results show that the winds in the northern model decayed more (less) rapidly than those of the southern model, when the winds just after landfall are greater (less) than 33 knots. It is hypothesized that this faster rate of decay is due to the higher terrain near the coast for the northern sample and to the more hostile environmental conditions (e.g., higher vertical wind shear). The slower decay rate when the winds fall below 33 knots in the northern model might be due to the availability of a baroclinic energy source as the storms undergo extratropical transition.
Katsaros, K.B., E.B. Forde, P. Chang, W.T. Liu. QuikSCAT facilitates early identification of tropical depressions in 1999 hurricane season. Geophysical Research Letters, 28(6):1043-1046 (2001).
Far from land and surface ship observations, most tropical depressions are identified by examining images from geostationary satellites for the presence of rotation of the convective cloud masses. During the 1999 hurricane season, surface wind maps obtained by the SeaWinds scatterometer for the tropical Atlantic and Caribbean Sea were examined to test the hypotheses that tropical depressions (TDs) could be observed with this satellite sensor, before identification by the traditional means. SeaWinds was able to detect the presence of tropical depressions by early observations of a closed circulation in the surface winds. The satellite's unprecedented large swath width of 1800 km allows twice a day observation of most of the tropical oceans.
Katzberg, S.J., R.A. Walker, J.H. Roles, T. Lynch, and P.G. Black. First GPS signals reflected from the interior of a tropical storm: Preliminary reults from Hurricane Michael. Geophysical Research Letters, 28(10):1981-1984 (2001).
Using GPS signals reflected from the ocean surface is developing into a simple technique for measuring sea-state and inferring surface wind speeds. Theoretical models have been developed which are considered valid to approximately 24 meters per second. The GPS reflection technique has an obvious extension to extremely high sea states, cyclones, and extra-tropical storms. In October 2000, a GPS system mounted in a NOAA Hurricane Hunter research aircraft was flown into Hurricane Michael off the South Carolina coast. The first acquisition of GPS signals reflected from the sea surface inside tropical cyclones was accomplished. This paper presents some examples of the data sets, as well as early wind speed retrieval results using direct extensions of current models. Data from the GPS wind speed retrievals, as well as from direct aircraft measurements, are compared and discussed.
Liu, W.T., and K.B. Katsaros. Air-sea fluxes from satellite data. In Ocean Circulation and Climate: Observing and Modeling the Global Ocean, G. Siedler, J. Church, and J. Gould (eds.). Academic Press, 173-180 (2001).
No abstract.
Mestas-Nunez, A.M., and D.B. Enfield. Eastern equatorial Pacific SST variability: ENSO and non-ENSO components and their climatic associations. Journal of Climate, 14(3):391-402 (2001).
Using an updated Kaplan et al. global SST anomaly (SSTA) dataset (1870-1999), we construct a canonical representation of El Niño-Southern Oscillation (ENSO). When this canonical ENSO is subtracted from the data, we are left with a residual (non-ENSO) dataset for SSTA that includes inter-seasonal to multi-decadal variability. Over the eastern equatorial Pacific (NINO3) the canonical ENSO accounts for about 79% of the total SSTA variability, while the residual, dominated by decadal time scales, accounts for the rest. In particular, about 40-50% of the amplitudes of the strong 1982-83 and 1997-98 El Niño events were accounted for by the residual variability. The non-ENSO variability is characterized by the known shift from cold to warm eastern tropical Pacific in the mid-late 1970s as well as by a non-stationary interannual variance increase during the 1980s and 1990s. Composite maps of surface (SST, sea level pressure and winds) and tropospheric (divergent winds, velocity potential, and vertical velocity) variables are used to compare the spatial patterns characterizing the canonical ENSO and the residual components of the NINO3 variability. We find that the residual composites only share large amplitude fluctuations of SST anomalies in the equatorial Pacific east of the dateline. When these composites are separated into decadal and interannual components, the decadal part resembles closely the structure of the Pacific Decadal Oscillation (PDO). The major patterns of tropospheric variability associated with the ENSO and decadal non-ENSO components are quite different. At low latitudes, they imply nearly opposite impacts on far-field regional climates, based on their respective warming (or cooling) phases within the NINO3 region. This unexpected result for low latitude climate associations runs contrary to the naive expectation (recently shown to be true for North America) that a decadally warm tropical east Pacific will reinforce the climate effects associated with ENSO alone. This indicates that in the tropics climate outlooks may be more accurate if based on separately analyzed relationships between these SSTA components and their associated climate fluctuations.
Mestas-Nunez, A.M., D.B. Chelton, and D.B. Enfield. North Pacific circulation variability from TOPEX/POSEIDON sea level observations. Proceedings, 5th Pacific Ocean Remote Sensing Conference (PORSEC), Goa, India, December 5-8, 2000. National Institute of Oceanography, 1:263-267 (2001).
We analyze seven years (October 1992-October 1999) of sea level observations from the TOPEX/POSEIDON (T/P) satellite altimeter data to investigate the large-scale ocean circulation variability of the North Pacific from seasonal to interannual time scales. We focus in the mid-latitude western regions and use the T/P observations to estimate the barotropic volume transport variability of the Kuroshio, Oyashio, and Kuroshio Extension currents. We base our transport variability estimates on altimetric sea level differences, and our results agree well with simple wind-driven Sverdrup theory and with a global numerical ocean model simulation.
Millero, F.J., W.T. Hiscock, F. Huang, M. Roche, and J.-Z. Zhang. Seasonal variation of the carbonate system in Florida Bay. Bulletin of Marine Science, 68(1):101-123 (2001).
The carbonate system has been studied in the Florida Bay from 1997 to 2000. Measurements of pH, total alkalinity (TA), and total inorganic carbon dioxide (TCO2) were made from 20 stations in the Bay and used to calculate the partial pressure of carbon dioxide (pCO2) and the saturation states of aragonite (OMEGAArg) and calcite (OMEGACal). The results were found to correlate with the salinity. The pH was low and the pCO2 was high for the freshwater input from the mangrove fringe due to the photochemical and biological oxidation of organic material. The TA and TCO2 for the freshwater input are higher than seawater due to the low values of pH and OMEGA. The pH was high and the pCO2 was low in November in regions where the chlorophyll is high due to biological production. During the summer when the salinity is the highest, the normalized values of TA and TCO2 were lower than average seawater, due to the inorganic precipitation of CaCO3 caused by the resuspension of sediments or the biological loss by macroalgae. A transect across the mangrove fringe near the outflow of Taylor Slough shows that PO4 and TA increases as the freshwater enters the Bay. This is thought to be due to the dissolution of CaCO3 in the low pH waters from the bacterial and photo oxidation of plant material.
Millero, F.J., F. Huang, X. Zhu, X. Liu, and J.-Z. Zhang. Adsorption and desorption of phosphate on the calcite and aragonite in seawater. Aquatic Geochemistry, 7(1):33-56 (2001).
The adsorption and desorption of phosphate on calcite and aragonite were investigated as a function of temperature (5-45°C) and salinity (0-40) in seawater pre-equilibrated with CaCO3. An increase in temperature increased the equilibrium adsorption; whereas an increase in salinity decreased the adsorption. Adsorption measurements made in NaCl were lower than the results in seawater. The higher values in seawater were due to the presence of Mg2+ and Ca2+ ions. The increase was five times greater for Ca2+ than Mg2+. The effects of Ca2+ and Mg2+ are diminished with the addition of SO42-, apparently due to the formation of MgSO4 and CaSO4 complexes in solution and/or SO42- adsorption on the surface of CaCO3. The adsorbed Ca2+ and Mg2+ on CaCO3 (at carbonate sites) may act as bridges to PO43- ions. The bridging effect of Ca2+ is greater than Mg2+, apparently due to the stronger interactions of Ca2+ with PO43-. The apparent effect of salinity on the adsorption of PO4 was largely due to changes in the concentration of HCO3- in the solutions. An increase in the concentration of HCO3- caused the adsorption of phosphate to decrease, especially at low salinities. The adsorption at the same level of HCO3- (2 mM) was nearly independent of salinity. All of the adsorption measurements were modeled empirically using a Langmuir-type adsorption isotherm [[PO4]ad = Km Cm [PO4]T /(1 + Km [PO4]T)], where [PO4]ad and [PO4]T are the adsorbed and total dissolved phosphate concentrations, respectively. The values of Cm (the maximum monolayer adsorption capacity, mol/g) and Km (the adsorption equilibrium constant, g/(mol)) over the entire temperature (t, °C) and salinity (S) range were fitted to [Cm = 17.067 + 0.1707t - 0.4693S + 0.0082S2 (sigma = 0.7)] [ln Km = -2.412 + 0.0165t - 0.0004St - 0.0008S2 (sigma = 0.1)]. These empirical equations reproduce all of our measurements of [PO4]ad up to 14 µmol/g and within ±0.7 µmol/g. The kinetic data showed that the phosphate uptake on carbonate minerals appears to be a multi-step process. Both the adsorption and desorption were quite fast in the first stage (less than 30 min) followed by a much slower process (lasting more than one week). Our results indicate that within 24 hours aragonite has a higher sorption capacity than calcite. The differences between calcite and aragonite become smaller with time. Consequently, the mineral composition of the sediments may affect the short-term phosphate adsorption and desorption on calcium carbonate. Up to 80% of the adsorbed phosphate is released from calcium carbonate over one day. The amount of PO4 left on the CaCO3 is close to the equilibrium adsorption. The release of PO4 from calcite is faster than from aragonite. Measurements with Florida Bay sediments produced results between those for calcite and aragonite. Our results indicate that the calcium carbonate can be both a sink and source of phosphate in natural waters.
Morisseau-Leroy, N., M.K. Solomon, and G.P. Momplaisir. Oracle 9i SQLI Programming. Osborne McGraw-Hill, 608 pp. (ISBN 0072190930) (2001).
No abstract.
Rogers, R.F., and J.M. Fritsch. Surface cyclogenesis from convectively-driven amplification of mid-level mesoscale convective vortices. Monthly Weather Review, 129(4):605-637 (2001).
Mesoscale convective vortices (MCVs) are mid-tropospheric warm-core cyclonic circulations that often develop in the stratiform region of mesoscale convective systems. Typically, divergent, anticyclonically-circulating, mesoscale cold anomalies appear both above and below the MCV. The upper level cold anomaly is usually found near the tropopause while the low-level anomaly is surface-based and exhibits locally higher pressure. One aspect of MCVs that has received much attention recently is the role that they may play in tropical cyclogenesis. Of special interest is how an MCV amplifies when deep convection redevelops within the borders of its mid-level cyclonic circulation and how the amplified MCV transforms the divergent surface-based cold pool with anomalously high surface pressure into a convergent cyclonic circulation with anomalously low pressure. The Pennsylvania State University/National Center for Atmospheric Research mesoscale model MM5 is used to simulate an MCV that was instrumental in initiating, within the borders of the mid-level vortex's circulation, several successive cycles of convective development and decay over a two-day period. After each cycle of convection, both the horizontal size of the cyclonic circulation and the magnitude of the potential vorticity associated with the vortex were observed to increase. The simulation reproduces the development and evolution of the MCV and associated convective cycles. Mesoscale features responsible for the initiation of convection within the circulation of the vortex and the impact of this convection on the structure and evolution of the vortex are investigated. A conceptual model is presented to explain how convective redevelopment within the MCV causes low-level heights to fall and cyclonic vorticity to grow downward to the surface. Applying this conceptual model to a tropical marine environment is also considered.
Sainz-Trapaga, S.M., G.J. Goni, and T. Sugimoto. Identification of the Kuroshio Extension, its bifurcation and northern branch from altimetry and hydrographic data during October 1992-August 1999: Spatial and temporal variability. Geophysical Research Letters, 28(9):1759-1762 (2001).
A methodology is proposed using altimeter-derived upper layer thickness and baroclinic transport to identify the Kuroshio Extension, the Bifurcation Point, and the Northern Branch, by combining TOPEX/POSEIDON altimeter and climatological data within a two-layer reduced gravity model. Results obtained from the Japanese coast to 175°W show that the location of the Bifurcation Point presents interannual variability that is related with upstream conditions. The longitude of the Bifurcation Point ranged from 147 to 160°E. Estimates of baroclinic transport at the Kuroshio Extension and its Northern Branch decrease steadily to the east trough, the region of study from 35 to 11 and from 10 to 3 Sv, respectively.
Schmid, C., R.L. Molinari, and S.L. Garzoli. New observations of the intermediate depth circulation in the tropical Atlantic. Journal of Marine Research, 59(2):281-312 (2001).
The intermediate depth (around 1000 m) circulation in the interior tropical Atlantic has been described as several narrow flow bands. Due to a lack of data, these currents have previously only been poorly resolved in space and time. Recent observations, obtained during the mid-1997 Seward Johnson cruise and from PALACE floats which cover the period summer 1997 to spring 2000, allow a more detailed description of the intermediate depth circulation in the tropical Atlantic. The PALACE trajectories display several well defined currents between the equator and 4°N at 800 to 1100 m. Two regimes separated by the eastern edge of the Mid-Atlantic Ridge seem to exist at these latitudes. Velocities in the eastern regime are lower than in the western regime and, at some latitudes, the zonal flow in the two regimes is going in opposite directions. Farther south, between 4°S and 2°S, westward velocities of the central South Equatorial Current dominate the circulation. The flow north of 4°N and south of 4°S is governed by up to several month-long periods of eastward or westward flow, with only weak preferences for either direction. The southern region is characterized by the (meandering) transition between the central South Equatorial Current and the South Equatorial Countercurrent. It has been proposed earlier that these two currents do not extend eastward beyond about 10°W, and that the intermediate water follows a cyclonic path east of 10°W between about 5°S and 25°S. This could be interpreted as an intermediate expression of the Angola Gyre. Such a circulation is not found in the present data set. It is also noted that no significant cross-equatorial flow is found in the PALACE data.
Wang, C. A unified oscillator model for the El Niño-Southern Oscillation. Journal of Climate, 14(1):98-115 (2001).
The delayed oscillator, the western Pacific oscillator, the recharge-discharge oscillator, and the advective-reflective oscillator have been proposed to interpret the oscillatory nature of the El Niño-Southern Oscillation (ENSO). All of these oscillator models assume a positive ocean-atmosphere feedback in the equatorial eastern and central Pacific. The delayed oscillator assumes that the western Pacific is an inactive region and wave reflection at the western boundary provides a negative feedback for the coupled system to oscillate. The western Pacific oscillator emphasizes an active role of the western Pacific in ENSO. The recharge-discharge oscillator argues that discharge and recharge of equatorial heat content cause the coupled system to oscillate. The advective-reflective oscillator emphasizes the importance of zonal advection associated with wave reflection at both the western and eastern boundaries. Motivated by the existence of these different oscillator models, a unified oscillator model is formulated and derived from the dynamics and thermodynamics of the coupled ocean-atmosphere system. Consistent with ENSO anomaly patterns observed in the tropical Pacific, this oscillator model considers sea surface temperature anomalies in the equatorial eastern Pacific, zonal wind stress anomalies in both the equatorial central Pacific and the equatorial western Pacific, and thermocline depth anomalies in the off-equatorial western Pacific. If the western Pacific wind-forced response is neglected, thermocline and zonal wind stress anomalies in the western Pacific are decoupled from the coupled system, and the unified oscillator reduces to the delayed oscillator. If wave reflection at the western boundary is neglected, the unified oscillator reduces to the western Pacific oscillator. The mathematical form of the recharge-discharge oscillator can also be derived from this unified oscillator. Most of the physics of the advective-reflective oscillator are implicitly included in the unified oscillator, and the negative feedback of wave reflection at the eastern boundary is added to the unified oscillator. With appropriate model parameters chosen to be consistent with those of previous oscillator models, the unified oscillator model oscillates on interannual time scales.
Wang, C., and D.B. Enfield. The tropical Western Hemisphere warm pool. Geophysical Research Letters, 28(8):1635-1638 (2001).
The Western Hemisphere warm pool (WHWP) of water warmer than 28.5°C extends from the eastern North Pacific to the Gulf of Mexico and the Caribbean, and at its peak, overlaps with the tropical North Atlantic. It has a large seasonal cycle and its interannual fluctuations of area and intensity are significant. Surface heat fluxes warm the WHWP through the boreal spring to an annual maximum of SST and areal extent in the later summer/early fall, associated with eastern North Pacific and Atlantic hurricane activities and rainfall from northern South America to the southern tier of the United States. SST and area anomalies occur at high temperatures where small changes can have a large impact on tropical convection. Observations suggest that a positive ocean-atmosphere feedback operating through longwave radiation and associated cloudiness is responsible for the WHWP SST anomalies. Associated with an increase in SST anomalies is a decrease in atmospheric sea level pressure anomalies and an anomalous increase in atmospheric convection and cloudiness. The increase in convective activity and cloudiness results in less longwave radiation loss from the surface, which then reinforces SST anomalies.
Zhang, J.-Z. Oxidation of hydrogen sulfide by various oxidants in natural waters. Trends in Geochemistry, 1(2000):53-68 (2001).
This article reviews the literature on the oxidation of H2S by various oxidants, including oxygen, hydrogen peroxide, iodate, chromate, ferrate, Fe(III) hydroxides, and Mn(IV) oxides, in natural waters. The rates of H2S oxidation increased with oxidants in a order of chromate, oxygen, hydrogen peroxide, iodate, Fe(III) hydroxides, Mn(IV) oxides, and ferrate. Effect of pH on the rates of oxidation by various oxidants indicated that HS- is a reactive species while H2S is less reactive or, in some cases, non-reactive. The oxidation by oxygen has been a subject of extensive studies and its rates have been measured over a wide range of environmental conditions such as pH, temperature, and salinity. Dissolved and particulate metals have a significant effect on the rates of oxidation and the product formation. The reaction conditions and resulting product formation (S, Sn2-, SO32-, S2O32- and SO42-) were examined to unravel the reaction pathway.
Zhang, J.-Z., R.H. Wanninkhof, and K. Lee. Enhanced new production observed from the diurnal cycle of nitrate in an oligotrophic anticyclonic eddy. Geophysical Research Letters, 28(8):1579-1582 (2001).
A diurnal study in an anticyclonic eddy provides the first evidence of nutrient dynamics consistent with the observed trends in solar radiation, oxygen concentration changes, and estimates of the eddy diffusive flux of nitrate from nitracline. A new production rate of 24 mmol C m-2 d-1 was determined from nitrate inventory changes at nM levels in the mixed layer using a liquid waveguide technique combined with eddy diffusion estimates across the base of the mixed layer from temporal changes in the vertical penetration of SF6. The new production supported by nitrate from deepening of the mixed layer after storm events is two times larger than that from the daily diffusive flux. Our results demonstrate that new production in the oligotrophic ocean can be enhanced by a supply of nitrate through the eddy turbulence-induced diffusive flux and entrainment during storms.
**2000**
Aberson, S.D. A tropical cyclone ensemble forecasting system for the North Atlantic Basin. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F585, NG12A-05 (2000).
A real-time, 41-member VICBAR orthonormalized bred-mode ensemble forecasting system has been run once per day during the 1998 and 1999 hurricane seasons, and twice per day during the 2000 hurricane season, in the North Atlantic basin. VICBAR is a movable, nested-mesh shallow-water model using the National Centers for Environmental Prediction Aviation and Medium-Range Forecast Models as both initial and time-dependent boundary conditions. The numerics are based on cubic b-splines so as to eliminate discontinuities on the mesh boundaries. The deterministic run has provided skillful forecasts competitive with other track forecast models since 1989. The 850-200 hPa mass-weighted flow is combined with a vortex representative of the tropical cyclone including an asymmetry for the initial motion. Within 1500 km of the storm center, the forecast is wholly barotropic; more than 2500 km away from the storm center, the forecast is entirely that of the global model, with a transition region between the two circles. Forecasts extend to 120 h. This is the first ensemble forecasting system available for tropical cyclone track prediction in the Atlantic. Global models are either unable to skillfully forecast tracks, or, in some ensemble forecasting systems, the tropical regions are not perturbed. The three-year sample will be evaluated to show the value of the ensemble forecasting system, whether the ensemble spans the reality of the track, whether the ensemble mean provides an improved forecast over individual ensemble members and the control forecast, and whether the system can provide probabilistic forecasts of events such as landfall. Further uses of the ensemble, such as providing information for operational hurricane targeting missions with the National Oceanic and Atmospheric Administration's Gulfstream-IV jet aircraft, and for ensemble-based data assimilation schemes, add to the potential value of the ensemble.
Aberson, S.D. Improvements to the ensemble of tropical cyclone track forecasting models in the North Atlantic basin. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A140-A146 (2000).
No abstract.
Aberson, S.D. The first three years of operational targeting with the NOAA Gulfstream-IV. Preprints, 4th Symposium on Integrated Observing Systems, Long Beach, CA, January 9-14, 2000. American Meteorological Society, Boston, 198-199 (2000).
No abstract.
Aberson, S.D. Three years of tropical cyclone synoptic surveillance in the Atlantic basin. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 108-109 (2000).
Since 1997, NOAA has performed more than 50 synoptic surveillance missions in the core and environments of tropical cyclones threatening the United States mainland, Puerto Rico, and the Virgin Islands with their G-IV and P3 aircraft. GPS dropwindsonde observations are taken approximately every 250 km along the flight tracks and sent to the National Centers for Environmental Prediction and the National Hurricane Center for incorporation in numerical guidance and for subjective evaluation. The impact of these data on both track and intensity forecasts will be presented. Since small differences in initial conditions are known to grow in the numerical models at different rates, targeting the fastest growing modes has been studied. Results of such targeting, including methods to find target locations and sampling strategies, will be presented.
Aberson, S.D. Woman and minorities in meteorology since 1950. Program of the 80th Annual Meeting and Exhibition, Long Beach, CA, January 9-14, 2000. American Meteorological Society, Boston, 70-71 (2000).
No abstract.
Aberson, S.D. Women's trends: The changing status of women in the profession/society. Preprints, 9th Symposium on Education, Long Beach, CA, January 9-14, 2000. American Meteorological Society, Boston, 70-71 (2000).
No abstract.
Aberson, S.D., and K. Bedka. The operational ensemble of tropical cyclone track guidance at the National Hurricane Center (1976-1998). Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 177-178 (2000).
A suite of operational track forecast models has been run at NHC in support of NHC s task to provide tropical cyclone track forecasts. Official NHC forecasts have improved at a rate faster than 1% during the 1990s, suggesting substantial improvements to the numerical guidance. This operational ensemble since 1976 has been analyzed as a set to mark the improvements of the guidance with time. The improvements in the ability of the guidance to span the actual track of tropical cyclones, the performance of the ensemble mean with time, and changes in individual model performance are to be presented.
Atlas, D., C.W. Ulbrich, F.D. Marks, R.A. Black, E. Amitai, P.T. Willis, and C.E. Samsury. Partitioning tropical oceanic convective and stratiform rains by draft strength. Journal of Geophysical Research, 105(D2):2259-2267 (2000).
The discrimination of convective from stratiform tropical oceanic rains by conventional radar-based textural methods is problematic because of the small size and modest horizontal reflectivity gradients of the oceanic convective cells. In this work, the vertical air motion measured by an aircraft gust probe is used as a discriminator which is independent of the textural methods. A threshold draft magnitude approximately equal to 1 m s-1 separates the two rain types. Simultaneous airborne in-situ observations of drop size distributions (DSD) made during the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) were used to compute Z, R, and other integral parameters. The data were quality controlled to minimize misclassifications. The convective and stratiform rains, observed just below the melting level but adjusted to surface air density, are characterized by power law Z-R relations (Z = 129R1.38 [convective]) and 224R1.28 [stratiform]). However, at R < 10 mm h-1, the convective population is essentially coincident with the small-drop size, small-Z portion of the stratiform population. Tokay and Short (1996) found a similar result when their algorithm did not separate the rain types unambiguously at R < 10 mm h-1. The physical reasons for the wide variability of the drop size spectra and Z-R points in stratiform rain and their overlap with that of convective rain are proposed. The subtle distinctions in the microphysical properties and the Z-R relations by rain type could not be found by Yuter and Houze using the same airborne DSD data set as that in this work and a radar-based textural classification algorithm.
Beal, L.M., R.L. Molinari, T.K. Chereskin, and P.E. Robbins. Reversing bottom circulation in the Somali Basin. Geophysical Research Letters, 27(16):2565-2568 (2000).
Two sets of direct velocity measurements were taken, concurrent with hydrographic data, in the bottom waters of the northern Somali Basin in June and September 1995. The velocities indicate a temporal flow reversal in the bottom circulation, which is consistent with the changing density structure between the sections. In June, there is evidence of a southward Deep Western Boundary Current with a transport of 5 Sv. By September, flow close to the boundary is northward, with a transport of 2.6 Sv. Furthermore, the deep density gradient across the interior of the Somali Basin also changes between occupations, implying a cyclonic circulation in June and anticyclonic flow in September. Rossby wave activity is high in this region during the southwest monsoon, yet there is also evidence of a strong barotropic component to the Great Whirl in September, which may cause the reversal in the abyssal circulation.
Bentamy, A., P. Flament, Y. Quilfen, K.B. Katsaros, and H. Roquet. Analysis of ocean surface winds derived from ERS-1, ERS-2, and NSCAT measurements. CERSAT News, Issue No. 11, 2 pp. (2000).
No abstract.
Black, M.L., and J.L. Franklin. GPS dropsonde observations of the wind structure in convective and non-convective regions of the hurricane eyewall. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 448-449 (2000).
GPS dropsonde observations in the inner core regions of tropical cyclones have shown remarkable vertical variation in the wind structure. Vertical profiles from sondes released in the convective portions of the hurricane eyewall frequently exhibit multiple low to mid-level wind maxima. These maxima may contain peak winds significantly higher than those measured at typical reconnaissance altitudes (3 km). Convective mixing is thought to be a mechanism that may bring this high momentum air to altitudes at or near the sea-surface. In non-convective regions, both outside and within the eyewall, however, the wind profiles typically do not have the large low-level wind maxima and the wind speed frequently decreases rapidly toward the surface in the boundary layer. Preliminary analyses of dropsonde wind profiles have suggested systematic differences in the shape of these soundings. An important result from these analyses is that the surface wind speed is a substantially higher fraction of the wind at altitude in convective regions than in non-convective or stratiform regions. We plan on classifying several hundred dropsonde observations according to the convective environment they fall through. The classifications will be based upon simultaneous radar observations from NOAA P-3 research flights into tropical cyclones in various stages of development. Individual profiles from convective and non-convective regions of the storms will be presented to highlight some of the observed differences in wind structure. A brief statistical analyses is planned to describe the variance in the mean structure derived from these classifications. A discussion of some of the possible physical mechanisms for the difference in the observed wind profiles will be discussed.
Black, M.L., A.B. Damiano, and S.R. White. Meteorological aspects of the first eye penetration by the NOAA G-IV aircraft. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A97 (2000).
No abstract.
Black, M.L., A.B. Damiano, and S.R. White. The first eyewall penetration by the NOAA G-IV aircraft. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 175-176 (2000).
On August 9, 1999, NOAA's Aircraft Operations Center (AOC) was tasked by the Tropical Prediction Center/National Hurricane Center and the Central Pacific Hurricane Center (CPHC) to deploy the NOAA Gulfstream G-IV jet aircraft and crew to Honolulu, Hawaii for synoptic surveillance missions around Hurricanes Eugene and Dora. Both of these storms had tracked westward across the eastern Pacific basin into the area of responsibility of CPHC (west of 140°W) and posed potential threats to Hawaii. After a successful G-IV mission around Hurricane Eugene on 12 August, a similar flight-track was designed to collect synoptic data from GPS dropsondes around Hurricane Dora on 14 August. At the time, Dora was steadily weakening from a peak intensity of 120 kts on 13 August with maximum sustained surface winds forecast to be 70 kts during the mission. Dora was a compact hurricane with a circular, well-defined eye and had only a couple of weak rainbands outside of the central dense overcast. A deviation from the proposed flight track was planned to fly the G-IV on a heading towards the eye during the closest approach to Hurricane Dora. The maneuver's purpose was to observe the structure of a hurricane at altitudes >40,000 feet with the aircraft's nose radar system. During the flight, the G-IV crew observed that Hurricane Dora was closer to the flight track than was forecast, so that when the aircraft turned toward the south side of the storm, the eyewall was approximately 80 nmi away. After a brief discussion of the structure of Dora and safety considerations, the flight director and aircraft commander decided to fly into the eye before heading back to the original track. This represented the first time that the G-IV would penetrate the eyewall of a hurricane, and would do so at an altitude of 45,000 feet (~145 mb). The aircraft flew through a thick cirrus cloud cover in the eyewall and that thinned while in the eye. Two GPS dropsondes were released while in (above) the eye of Hurricane Dora, and a third sonde was dropped just outside of the southwest eyewall while the G-IV was exiting the storm. Both of the eye drops drifted near or into the eyewall as they descended and one of them showed winds in excess of 80 kts at altitudes below 3000 ft. During the penetration, wind speeds at a flight level of 45,000 feet were approximately 5 kts and the wind direction showed anticyclonic flow.
Black, P.G., E.W. Uhlhorn, M.D. Powell, and J. Carswell. A new era in hurricane reconnaissance: Real-time measurement of surface wind structure and intensity via microwave remote sensing. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A122-A126 (2000).
No abstract.
Black, P.G., E.W. Uhlhorn, M.D. Powell, and J. Carswell. A new era in hurricane reconnaissance: Real-time measurement of surface wind structure and intensity via microwave remote sensing. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 199-200 (2000).
No abstract.
Black, P.G., E.W. Uhlhorn, J.J. Cione, G.J. Goni, L.K. Shay, S.D. Jacob, E.J. Walsh, and E.A. D'Asaro. Hurricane intensity change modulated by air-sea interaction effects based on unique airborne measurements during the 1998-1999 hurricane seasons. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J7-J8 (2000).
No abstract.
Boebel, O., S. Anderson-Fontana, C. Schmid, I. Ansorge, P. Lazarevich, J.R.E. Lutjeharms, M. Prater, T. Rossby, and W. Zenk. KAPEX RAFOS float data report, 1997-1999. Part A: The Agulhas and South Atlantic Current components. GSO Technical Report 2000-2/UCT Oceanography Report 2000-1, 194 pp. (2000).
No abstract.
Bosart, L.F., W.E. Bracken, J. Molinari, C.S. Velden, and P.G. Black. Environmental influences on the rapid intensification of Hurricane Opal (1995) over the Gulf of Mexico. Monthly Weather Review, 128(2):322-352 (2000).
Hurricane Opal intensified rapidly and unexpectedly over the Gulf of Mexico between 1800 UTC 3 October 1995 and 1000 UTC 4 October 1995. During this period, the storm central pressure decreased from 963 to 916 hPa and sustained winds reached 68 m s-1. Analyses that include high-resolution GOES-8 water vapor winds and European Centre for Medium-Range Weather Forecasts (ECMWF) and National Centers for Environmental Prediction (NCEP) gridded datasets are employed to examine the rapid intensification phase of Opal. Opal first reached tropical storm strength on 29V30 September 1995 as it interacted with a trough while situated over the Yucatan Peninsula. Opal deepened moderately (20 hPa) in the 24 h ending 1200 UTC 2 October as it achieved minimal hurricane strength and as it turned northeastward. The deepening occurred in conjunction with an environmental flow interaction as determined by an Eliassen balanced vortex outflow calculation. As Opal accelerated toward the Gulf coast by 1200 UTC 3 October, it approached the equatorward jet-entrance region of a progressive synoptic-scale trough. The trough tail extended southwestward toward the lower Texas coast. As the poleward portion of the trough moved eastward, the equatorward end of the trough lagged behind, stretched meridionally, and partially fractured as it encountered a deformation region over the northwest Gulf. Enhanced outflow and increased divergence in the upper troposphere poleward of Opal was associated with the deformation zone and the partially fractured trough tail. An analysis of the 300-200-hPa layer-averaged divergence and 6-h divergence change based on an analysis of the water vapor winds shows a significant increase in the magnitude and equatorward extension of the divergence core toward Opal that begins at 1200 UTC 3 October and is most apparent by 1800 UTC 3 October and 0000 UTC 4 October. This divergence increase is shown to precede convective growth in the eyewall and the onset of rapid intensification and is attributed to a jet-trough-hurricane interaction in a low-shear environment. Calculations of balanced vortex outflow based on the ECMWF and NCEP gridded datasets confirms this interpretation. A crucial finding of this work is that the jet-trough-hurricane interaction and explosive intensification of Opal begins near 0000 UTC 4 October when the storm is far from its maximum potential intensity (MPI), and the 850-200-hPa shear within 500 km of the center is weak (2-3 m s-1). In this first stage of rapid intensification, the winds increase by almost 15 m s-1 to 52 m s-1 prior to the storm reaching an oceanic warm-core eddy. The second stage of rapid intensification occurs between 0600 and 1000 UTC 4 October when Opal is over the warm-core eddy and sustained winds increase to 68 m s-1. During this second stage, conditions are still favorable for a jet-trough-hurricane interaction as demonstrated by the balanced vortex outflow calculation. Opal weakens rapidly after 1200 UTC 4 October when the storm is near its MPI, the shear is increasing, and the eye is leaving the warm-core eddy. This weakening occurs as Opal moves closer to the trough. It is suggested that an important factor in determining whether a storm-trough interaction is favorable or unfavorable for intensification is how far a storm is from its MPI. The results suggest that a favorable storm-trough interaction ("good trough") can occur when a storm is far from its MPI. It is suggested that although the ECMWF (and to lesser extent NCEP) analyses reveal the trough-jet-hurricane interaction through the balanced vortex outflow calculation, that the failure of the same models to predict the rapid intensification of Opal can be attributed to the inability of the model to resolve the eye and internal storm structure and the associated influence of the trough-jet-hurricane interaction on the diabatically driven storm secondary circulation. The analyses also indicate that the high spatial and temporal resolution of the GOES-8 water vapor winds reveal important mesoscale details of the trough-jet-hurricane interaction that would otherwise be hidden.
Campos, E., A. Busalacchi, S.L. Garzoli, J. Lutjeharms, R. Matano, P. Nobre, D.B. Olson, A. Piola, C. Tanajura, and I. Wainer. The South Atlantic and the climate. OCEANOBS99: International Conference on the Ocean Observing System for Climate, Saint Raphael, France, October 18-22, 1999. Centre National d'Etudes Spatiales, 16 pp. (2000).
As a contribution to the OCEANOBS99 objectives, we give a brief description of the present knowledge of the South Atlantic and identify some key processes and areas which need to be monitored in order to understand the role of that part of the ocean in the global climate. Included are suggestions of strategies for a first approximation towards an ocean climate monitoring system in the South Atlantic.
Chai, F., R. Dugdale, R.T. Baraber, M. Jiang, and T.-H. Peng. Ecosystem modeling in the equatorial Pacific upwelling region. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS29, OS11P-06 (2000).
The equatorial Pacific Ocean is the dominant oceanic source of carbon dioxide to the atmosphere, an annual net flux of 1.0 Pg carbon. This net sea-to-air flux of carbon is the result of a complex interplay between physical and biological processes in the region. A physical-biogeochemical model has been developed and used to investigate physical variations, ecosystem responses, and biogeochemical consequences. The ecosystem model, embedded into a three-dimensional circulation model, is capable of reproducing the low silicate, high nitrate, low chlorophyll (LSHNLC) conditions in the equatorial Pacific upwelling region. Linkage of the ecosystem components to the carbon system provides a model estimated sea-to-air flux of carbon which is comparable with the observations. The ecosystem responses to the tropical instability waves have been documented to exam the transition from a "balanced" to "bloom" state of phytoplankton production. The physical-biogeochemical model results show a consistent decrease of the sea-to-air CO2 flux during El Niño events.
Cione, J.J., P.G. Black, and S.H. Houston. Surface observations in the hurricane environment. Monthly Weather Review, 128(5):1550-1561 (2000).
Composite analyses of marine surface observations from 37 hurricanes between 1975 and 1998 show that the difference between the sea surface temperature and the surface air temperature significantly increases just outside the hurricane inner core. This increase in the sea-air contrast is primarily due to a reduction in surface air temperature and is more likely to occur when sea temperatures are at least 27°C. Results show that 90% of the observed cooling occurs 3.25°-1.25° latitude from the hurricane center, well outside the region of strongest surface winds. Since surface pressure only decreases 3 mb over this interval, the 2°C drop in air temperature is not a result of adiabatic expansion. For the subset of observations that contained moisture measurements, surface specific humidity decreased 1.2 g kg-1 4.5°-1.75° latitude from the storm center. This finding suggests that the observed reduction in surface air temperature is not simply a result of near-surface evaporation from sea spray or precipitation. An alternate explanation may be that outside the hurricane inner core, unsaturated convective downdrafts act to dry and evaporatively cool the near-surface environment. Between 3.25° and 1.25° radius, composite analyses show that low-level inflow is not isothermal, surface moisture is not constant, and the near-surface environment is not in thermodynamic equilibrium with the sea. Calculations based on these observations show that thetae decreases between 4.0° and 1.25° radius and then quickly rises near the inner core as surface pressures fall and specific humidity increases. Surface fluxes of heat and moisture are also observed to significantly increase near the inner core. The largest increase in surface sensible heat flux occurs radially inward of 1.5°, where surface winds are strong and sea-air temperature contrasts are greatest. As a result, the average Bowen ratio is 0.20°-0.5° radius from the composite storm center. This increase in sensible heat flux (in conjunction with near-saturated conditions at low to midlevels) may help explain why average surface air temperatures inside 1.25° radius remain relatively constant, despite the potential for additional cooling from evaporation and adiabatic expansion within the high wind inner core.
Cione, J.J., E.W. Uhlhorn, and P.G. Black. Atmospheric boundary layer and upper ocean structure observed in Hurricane Erika (1997). Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J70-J71 (2000).
No abstract.
Cione, J.J., P. Molina, J. Kaplan, and P.G. Black. SST time series directly under tropical cyclones: Observations and implications. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 1-2 (2000).
No abstract.
Cook, T.M., L.K. Shay, P.G. Black, G.J. Goni, M.M. Huber, S.D. Jacob, and J.J. Cione. Coupled air-sea interactions during Hurricane Bonnie. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J68-J69 (2000).
No abstract.
Cosca, C.E., R.A. Feely, R.H. Wanninkhof, J. Boutin, J. Etcheto, and M.J. McPhaden. Seasonal and interannual variations of the fCO2-SST relationships in the equatorial Pacific. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS28, OS11O-11 (2000).
In order to utilize satellite temperature data for determining high-resolution variations of CO2 distributions in the equatorial Pacific, we have developed seasonal and interannual fCO2-SST relationships from shipboard data. The data were gathered onboard the NOAA ships Baldridge, Discoverer, and Ka'imimoana from 1992 through 1998 as a companion project to the biannual deployment of the TAO moorings. The cruises during the 6-year period included 55 10°S to 10°N crossings of the equatorial Pacific between 95°W and 165°E, and spanned two major ENSO events (1992-1994 and 1997-1998). Data were collected during the warm boreal spring season (February through June) and during the cooler boreal fall season (July through December) of each year, making it possible to examine the interannual and seasonal variability of the fCO2-SST relationship. A linear fit through all 55 data sets yields an inverse correlation between SST and fCO2, with an R2 of 0.583 and an RMS of 28.4 µatm. When separated, there is a significant difference between the regression lines for El Niño versus non-El Niño data sets. During non-El Niño periods, we observed seasonal differences in the fCO2-SST relationship. The regression lines through the spring and fall data sets have higher R2 and lower RMS values than the composite non-El Niño regression line, and the slopes are significantly different at the 95% confidence level. The slope for the fall season is less negative than during spring, suggesting higher biological productivity occurred during the fall non-El Niño seasons. The regression line for the composite El Niño data, which shows no significant seasonal variability, has a slope very similar to the non-El Niño spring slope, indicating less influence by biological processes. These relationships have been combined with satellite-based temperature data to provide a composite time-space map of DELTA-fCO2 in the equatorial Pacific.
Cushman-Roisin, B., O.E. Esenkov, and B.J. Mathias. A particle-in-cell-method for the solution of two-layer shallow-water equations. International Journal of Numerical Methods in Fluids, 32:515-543 (2000).
A particle-in-cell (PIC) numerical method developed for the study of shallow-water dynamics, when the moving fluid layer is laterally confined by the intersection of its top and bottom surfaces, is described. The effect of ambient rotation is included for application to geophysical fluids, particularly open-ocean buoyant vortices in which the underlying density interface outcrops to the surface around the rim of the vortex. Extensions to include the dynamical effect of a second moving layer (baroclinicity) and the presence of a lateral rigid boundary (sidewall) are also described. Although the method was developed for oceanographic investigations, applications to other fluid mechanics problems would be straightforward.
D'Asaro, E.A., and P.G. Black. Turbulence in the ocean boundary layer below Hurricane Dennis. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J62-J63 (2000).
No abstract.
Dodge, P.P., S.M. Spratt, F.D. Marks, D.W. Sharp, and J.F. Gamache. Dual-Doppler analyses of mesovortices in a hurricane rainband. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 302-303 (2000).
The U.S. Weather Research Program identified landfalling tropical cyclones as a major focus for research in the coming years. In 1998, the Hurricane Research Division (HRD) of NOAA's Atlantic Oceanographic and Meteorological Laboratory coordinated experiments with other agencies and university groups in Hurricanes Bonnie, Earl, and Georges. On these flights, airborne Doppler radar data were collected to combine with WSR-88D radar data in three-dimensional analyses to document evolution of tropical cyclones as they make landfall, and to provide data for testing WSR-88D tropical cyclone algorithms. Hurricane Bonnie made landfall in near Wilmington, North Carolina as a Category 2 hurricane on 26 August. There were two HRD missions near the time of landfall. The first flight concentrated on examining the structure of the spiral rainbands and the second flight surveyed the hurricane as it interacted with the coast. During the flights, there was a vigourous rainband ~180 km northeast of the center with several mesocyclones (as identified on the Morehead City WSR-88D) that later produced confirmed tornadoes on land. Both NOAA aircraft had to deviate around strong cells in this band, between 1540 and 1830 UTC, and those deviations resulted in small Doppler analysis boxes enclosing some of the mesocyclones. A companion paper (Spratt et al.) uses dropsondes and adjacent radiosondes to describe the local environment in which the Bonnie mesocylones were embedded, and in this paper we will present windfield analyses, from combining WSR-88D and airborne Doppler radar data, that provide the three dimensional structure of the mesocyclones. The Doppler data are too coarse to resolve actual tornadoes, but the parent mesoscale circulations are clearly resolved.
Dunion, J.P., S.H. Houston, M.D. Powell, C.S. Velden, and P.G. Black. Using surface adjusted GOES low-level cloud-drift winds to improve the estimation of tropical cyclone outer wind radii. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 488-489 (2000).
No abstract.
Dye, J.E., E. Defer, A. Grainger, M. Poellot, H. Christian, M. Bateman, D. Mach, M. Stewart, P.T. Willis, and F. Merceret. Electric field and associated microphysical measurements in the anvil of a decaying Florida thunderstorm. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F91, A62D-09 (2000).
The ABFM 2000 (Airborne Field Mill Mission 2000) was conducted during June 2000 to investigate the decay time and spatial distribution of electric fields and microphysical and radar structure in anvils of dissipating storms near Kennedy Space Center (KSC). The University of North Dakota Citation jet aircraft was flown with six electric field meters to determine the 3-D electric field, an array of particle probes to characterize particle concentrations, sizes and types, and standard instruments for measuring state parameters. Ground-based instruments included the KSC Lightning Ranging and Detection System (LDAR), KSC field mill network, KSC cloud-to-ground lightning network, radar, and rawinsondes. In this paper we present measurements from the June 13 case in which the Citation investigated the temporal and spatial distribution of electric fields and microphysics of the anvil from before last lightning to 2 hours after the last flash. Numerous penetrations were made across the anvil early in the flight and later along the anvil axis. Although electric fields were in excess of 50 kV/m near the core, the fields decreased with distance from the core and became less than a few kV/m at distances of about 50-60 km from the storm core even while lightning was occurring. The stronger fields tended to be associated with reflectivities greater than 20 dBz and concentrations of particles larger than 1 mm size.
Enfield, D.B., and A.M. Mestas-Nunez. Global modes of ENSO and non-ENSO SST variability and their associations with climate. In: El Niño and the Southern Oscillation: Multiscale Variability and its Impacts on Natural Ecosystems and Society, H.F. Diaz and V. Markgraf (eds.). Cambridge University Press, 89-112 (ISBN 0521621380) (2000).
In this chapter we review much of the recent work by others regarding the nature of the global modes of sea surface temperature (SST) variability and the SST involvement in interannual to multidecadal climate variability. We also perform our own analysis of global SST so as to describe and separate the SST variability associated with El Niño-Southern Oscillation (ENSO) from the low-frequency modes not associated with ENSO (non-ENSO). ENSO is a global phenomenon with significant phase propagation between basins, which we preserve and describe using complex EOF (CEOF) analysis, and subsequently remove from the global SST data. A second CEOF analysis of the residuals reveals three non-ENSO modes of low-frequency variability that are identified with and related to signals described in the reviewed literature: (1) a secular trend representing the global warming signal with associated superimposed decadal variability; (2) an interdecadal mode with maximal realization in the extratropical North Pacific; and (3) a multidecadal mode with maximal realization in the extratropical North Atlantic. Regression- and SVD-based analyses of the relationships between the SST data and a high-quality precipitation data set demonstrate for the interannual-to-decadal time scales of the western hemisphere tropics that (a) tropical Atlantic SSTA is comparable to the Pacific ENSO in its relevance to regional rainfall and is not redundant with respect to ENSO; and (b) non-ENSO variability explains a significant fraction of the total covariance between the two variables. We are led to conclude that present operational climate predictions can be significantly improved by extending numerical SST predictions from the Pacific to the world ocean and by enabling these models to emulate the observed non-ENSO modes of global variability.
Enfield, D.B., and A.M. Mestas-Nunez. Tropospheric direct circulations associated with the climatic components of SST variability in the equatorial Pacific. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J49-J50 (2000).
No abstract.
Esenkov, O.E. A numerical study of the dynamics of the Somali Current system. Ph.D. Thesis, University of Miami/Rosenstiel School of Marine and Atmospheric Science, 140 pp. (2000).
The evolution of surface circulation, salinity budget, and processes at intermediate depth in the northwestern Indian Ocean were studied with the open boundary version of the Miami Isopycnic Coordinate Ocean Model (MICOM). Under climatological wind and thermodynamic forcing, the model develops solutions that are in good agreement with global MICOM results and with observations. When the observed winds (Legler et al., 1989) force the model, interannual variability of the surface fields increases significantly. However, coalescence of the two large eddies in the end of the summer monsoon, which was observed in some years, does not occur in the model. To identify what processes facilitate the merger, a series of experiments was performed with modified model parameters and forcing fields. The eddies coalesced when half-slip, rather than no-slip, boundary conditions were used. In this case, less positive vorticity was produced at the coast, resulting in reduced blocking effect on the propagation of the southern eddy. The Socotra Island, which is submerged in the standard model, hinders movement of the northern anticyclone, leading to stronger interaction between the eddies and their subsequent merging. A more realistic coalescence occurs in an experiment where winds are held constant after reaching the peak summer value. Freshwater fluxes from the east and south were previously considered important for the salinity budget in the Arabian Sea, where evaporation exceeds precipitation; however, the model demonstrated that only cross-equatorial transport of low-salinity water in the upper 400 m is essential. About 86% of this water is advected below the surface layer at the western boundary. The strongest interaction between the mixed layer and the oceanic interior occurs during the summer in the coastal upwelling regions off Somalia. Forty-three percent of all upwelled water comes from depths between 100 m and 200 m, thus signifying the importance of mid-depth circulation and water mass distribution for the surface processes. Both observations and model solutions demonstrate strong annual cycle and alongshore variability of coastal subsurface circulation. A cross-equatorial northward flow below the surface, which exists throughout the year, is disconnected from currents farther north. A southward undercurrent north of 5°N is present during the winter monsoon. Water for the current is supplied by flows from the north and northeast. The former originates in the Persian Gulf and carries higher-salinity water, while the latter contribution is mainly from the Gulf of Aden. Separation of the southward undercurrent near 4°N is not caused by its interaction with a topographical ridge, as was previously suggested. Agreement with the observations north of 5°N improves when the Socotra Island is present in the model.
Feely, R.A., C.E. Cosca, R.H. Wanninkhof, M.J. McPhaden, C.S. Meinen, J. Boutin, and J. Etcheto. The role of ENSO on the phasing of the CO2 signal in the equatorial Pacific. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS279, OS42J-02 (2000).
Recent modeling studies, based upon inversions of atmospheric CO2, delta13C, and O2/N2 records from Cape Grim, Tasmania by Rayner et al. (1999), have suggested a decrease in the equatorial Pacific Ocean source of CO2 to the atmosphere which precedes the SOI by about seven to ten months. In order to test this model result, we have utilized satellite temperature data to obtain high-resolution variations of fCO2 distributions in the eastern equatorial Pacific based on shipboard fCO2-SST relationships. The data were gathered onboard the NOAA ships Baldridge, Discoverer, and Ka'imimoana from 1992 through 1998 as a companion project to the biannual deployment of the TAO moorings. The results indicate rapid drops in surface water fCO2 at 110°W, 125°W and 140°W several months ahead of the peak SST anomalies associated with the 1986-1887, 1991-1992, and 1997-1998 warm ENSO events. These rapid changes in fCO2 are inversely correlated with the integrated volume of the warm water above the 20°C isotherm in the eastern equatorial Pacific. During the onset phase of warm ENSO events, the propagation of Kelvin waves from west to east along the equatorial waveguide results in a deepening of the thermocline and a rapid decrease in surface water fCO2. The phasing of the beginning of the decrease in fCO2 is approximately six to eight months ahead of the minimum in the SOI index. During strong El Niño events, such as the 1997-2998 ENSO event, seawater fCO2 values decrease by as much as 125 µatm over the course of a few weeks, indicating a rapid decrease in the outgassing of CO2 near the equator. These results help to explain the dramatic decrease in the growth rate of CO2 in the atmosphere that occurs at the beginning of each ENSO event.
Feely, R.A., C.L. Sabine, R.H. Wanninkhof, R.M. Key, G.C. Johnson, F.J. Millero, K. Lee, T.-H. Peng, J.L. Bullister, A. Kozyr, and M.F. Lamb. Synthesis of global ocean CO2 survey data. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F691, OS72E-01 (2000).
The synthesis of the global ocean CO2 survey data is proceeding by ocean basin. Between 1991 and 1998, investigators analyzed dissolved inorganic carbon (DIC) and one or more other carbon system parameters (TAlk, pCO2, or pH) on WOCE/JGOFS/OACES cruises in the Indian, Pacific, and Atlantic Oceans. The analysis of the Indian Ocean data is published in Sabine et al., GBC, 13, 179-198, 1999) and can be obtained at: http://cdiac.esd.ornl.gov/oceans/glodap/index.html. DIC and TAlk were measured on all cruises, with an estimated overall accuracy of 2-4 µmol kg-1, respectively. For the Pacific Ocean, investigators from 15 different laboratories and four countries analyzed at least two of the four measurable ocean carbon parameters. Several different lines of evidence were used to examine the consistency among data sets and recommend adjustments. The analysis included comparison of calibration techniques, results from certified reference material analyses, precision of at-sea replicate analyses, agreement between shipboard analyses and replicate shore-based analyses, comparison of deep water values at locations where two or more cruises overlapped or crossed, consistency with other hydrographic parameters, and internal consistency with multiple carbon parameter measurements. With the adjustments recommended here, the data can be combined to generate a Pacific Ocean data set with over 36,000 unique sample locations. The best data coverage was for DIC, which has an estimated overall accuracy of ~3 µmol kg-1 after the recommended adjustments. TAlk, the second most common carbon parameter, has an estimated overall accuracy of ~5 µmol kg-1. The data have been integrated into a unified, internally-consistent data set and the physical and chemical controls of the basinwide distributions of DIC and TAlk will be discussed. The synthesis of the Atlantic data is just getting underway and will be conducted in association with the European Carbon Dioxide in the North Atlantic Ocean (CARINA) Project, with a projected completion date of mid-2002.
Feuer, S.E., M.L. Black, and J.L. Franklin. The asymmetric wind structure of tropical cyclones in various shear environments. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 450-451 (2000).
The Hurricane Research Division (HRD) of NOAA's Atlantic Oceanographic and Meteorological Laboratory conducts an annual field program involving research flights into tropical cyclones with NOAA WP-3D aircraft. As part of this program, dropwindsondes are launched from the aircraft during a variety of airborne experiments. Since 1996, dropsondes based on satellite navigation from built-in Global Positioning System (GPS) modules have been deployed in and around the tropical cyclones. These GPS sondes demonstrate a remarkable ability to accurately measure kinematic and thermodynamic quantities, including winds to an accuracy of 0.5-2.0 m s-1 at approximately 5 m resolution, as they descend from flight level to the surface. This study focuses on documenting the vortex-scale wind structure in the middle and lower troposphere of three hurricanes: Bonnie (1998), Guillermo (1997), and Bret (1999), which had experienced high, moderate, and low 200-850 mb environmental shear, respectively. These hurricanes are all well sampled by GPS sondes released within 300 km of the center during HRD's Vortex Motion and Evolution (VME) and modified Air-Sea Interaction experiments. Objective analyses of the dropsonde data are performed to resolve significant wind features approximately 50-300 km from the center and filter out smaller scales. Using the analyzed field, the distribution of kinematic asymmetries is contrasted among the storms and is related to the shear and reflectivity fields simultaneously collected from airborne radar systems. Variations in the height of analyzed wind features are also described.
Ffield, A., K. Vranes, A.L. Gordon, R.D. Susanto, and S.L. Garzoli. Temperature variability within Makassar Strait. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS17, OS11I-05 (2000).
The Indonesian throughflow impacts the global climate system by carrying warm Pacific water from about 5°N, through the Indonesian Seas, into the Indian Ocean at 12°S. As part of the U.S./Indonesian Arlindo program, recent mooring observations of ocean temperature provide the first high-resolution, long-term record of temperature variability in the Makassar Strait of the Indonesian Seas. The mooring observations span the entire cycle of the strong 1997/1998 El Niño, and they reveal the complexity of the Makassar Strait thermocline with significant short and long period temperature variations as a function of both depth and time. A high correspondence (r = 0.67) is found between variability in the average thermocline temperature, to variability in the southward Makassar volume transport: during high (low) volume transport, the average temperature of the thermocline is also high (low). In addition, during the measurement period, the Makassar thermocline temperature corresponds strongly (r = -0.87) to NINO3. This implies that the Makassar temperature field, when coupled with the throughflow, transmitted the equatorial Pacific El Niño and La Niña temperature fluctuations into the Indian Ocean with potential consequences to the climate system. The Makassar mooring temperature observations are related to 15 years of regional XBT data to better estimate the semi-annual, annual (monsoonal), and interannual (ENSO) characteristics of the mooring temperature observations, and of the Makassar Strait thermocline in general. The potential of Makassar XBT measurements to efficiently monitor the Makassar throughflow as part of the developing global monitoring system is assessed.
Ffield, A., K. Vranes, A.L. Gordon, R.D. Susanto, and S.L. Garzoli. Temperature variability within the Makassar Strait. Geophysical Research Letters, 27(2):237-240 (2000).
Recent mooring observations of ocean temperature provide the first high-resolution, long-term record of temperature variability in the Makassar Strait of the Indonesian Seas. The mooring observation span the entire cycle of the strong 1997/1998 El Niño. A high correlation (r = 0.67) is found between variability in the average thermocline temperature, to variability in the southward Makassar volume transport: during high (low) volume transport, the average temperature of the thermocline is also high (low). In addition, from nearly 15 years of XBT data, the Makassar thermocline temperature is shown to be highly correlated (r = 0.77) to SOI. This reveals that the Makassar temperature field, when coupled with the throughflow, transmits the equatorial Pacific El Niño and La Niña temperature fluctuations into the Indian Ocean. The ENSO variability in the internal energy transport is calculated: 0.63 PW during the La Niña months of December 1996 through February 1997, and 0.39 PW during the El Niño months of December 1997 through February 1998.
Fine, R.A., L. Merlivat, W. Roether, W.M. Smethie, and R.H. Wanninkhof. Observing tracers and the carbon cycle. OCEANOBS99: International Conference on the Ocean Observing System for Climate, Saint Raphael, France, October 18-22, 1999. Centre National d'Etudes Spatiales, 14 pp. (2000).
A program for repeated sampling of tracers and variables essential for quantitative understanding of the carbon cycle is recommended within CLIVAR/GOOS. The program is critical to our monitoring and understanding of climate change, both natural and anthropogenic. The objectives are: quantification of changes in the rates and spatial patterns of oceanic carbon uptake, fluxes, and storage of anthropogenic CO2; detection and possible quantification of changes in water mass renewal and mixing rates; and provision of a stringent test of the time integration of models' natural and anthropogenic climate variability. The strategy is to put in place a global observing network for tracers and CO2 to document the continuing large-scale evolution of these fields. Hydrographic lines are advocated, although it is realized that there has to be a limit on these observations due to logistical and resource constraints. Thus, there is the need to supplement these observations with time series and autonomous measurements to provide detail in the temporal evolution of the fields.
Fleurant, C.I., W.D. Wilson, W. Johns, S.L. Garzoli, R.H. Smith, D. Fratantoni, P. Richardson, and G.J. Goni. CTD/O2, LADCP, and XBT measurements collected aboard the R/V Seward Johnson, February-March 1999: North Brazil Current Rings Experiment, cruise 2 (NBC-2). NOAA Data Report, OAR-AOML-37, 291 pp. (2000).
Summaries of conductivity-temperature-depth (CTD/O2), lowered acoustic Doppler current profiler (LADCP), and expendable bathythermograph (XBT) measurements and hydrographic data acquired on an oceanographic research cruise during the winter of 1999 aboard the Harbor Branch Oceanographic Institution ship R/V Seward Johnson are presented. Data acquisition and processing systems are described, and calibration procedures are documented. Station location, CTD/O2, LADCP, XBT summary data listings, and profiles are included for each station.
Fleurant, C.I., W.D. Wilson, W. Johns, S.L. Garzoli, R.H. Smith, D. Fratantoni, P. Richardson, and G.J. Goni. CTD/O2, LADCP, and XBT measurements collected aboard the R/V Seward Johnson, February-March 2000: North Brazil Current Rings Experiment, cruise 3 (NBC-3). NOAA Data Report, OAR-AOML-38, 251 pp. (2000).
Summaries of conductivity-temperature-depth (CTD)/O2, lowered acoustic Doppler current profiler (LADCP) measurements, and hydrographic data acquired on an oceanographic research cruise during the winter of 2000 aboard the Harbor Branch Oceanographic Institution ship R/V Seward Johnson are presented. Data acquisition and processing systems are described, and calibration procedures are documented. Station location, CTD/O2, LADCP summary data listings, and profiles are included for each station.
Fleurant, C.I., W.D. Wilson, W. Johns, S.L. Garzoli, R.H. Smith, D. Fratantoni, P. Richardson, and G.J. Goni. CTD/O2, LADCP, and XBT measurements collected aboard the R/V Seward Johnson, November-December 1998: North Brazil Current Rings Experiment, cruise 1 (NBC-1). NOAA Data Report, OAR-AOML 39, 274 pp. (2000).
Summaries of conductivity-temperature-depth (CTD/O2), lowered acoustic Doppler current profiler (LADCP), expendable bathythermograph (XBT) measurements, and hydrographic data acquired on an oceanographic research cruise during the fall of 1998 aboard the Harbor Branch Oceanographic Institution ship R/V Seaward Johnson are presented. Data acquisition and processing systems are described, and calibration procedures are documented. Station location, CTD/O2, LADCP, XBT summary data listings, and profiles are included for each station.
Franklin, J.L., M.L. Black, and K. Valde. Eyewall wind profiles in hurricanes determined by GPS dropwindsondes. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 446-447 (2000).
No abstract.
Friedman, H.A., F. Horsfall, and E. Van Coverden. Pipeline: What does the future hold for the society and the profession as we access those in the educational pipeline. Preprints, 9th Symposium on Education, Long Beach, CA, January 9-14, 2000. American Meteorological Society, Boston, 75 (2000).
The composition of students in the educational pipeline is examined with respect to the number of women and minorities enrolled in colleges and universities that offer degree programs in atmospheric, oceanographic, and hydrologic sciences. Data from recent AMS surveys of its members and from information supplied by colleges and universities are examined to ascertain if some change has taken place, especially with respect to women and minorities in science fields. Barriers to a more diverse composition in the profession are discussed.
Gamache, J.F., M.L. Black, and H.E. Willoughby. Radial variation of azimuthally averaged flow across the hurricane core as observed with airborne Doppler radar. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 416-417 (2000).
Examination of the variation of azimuthally averaged zonal and meridional winds in the cores of Hurricanes Olivia and Jimena indicate that the vertical shear increased with increasing radius. Divergent wind fields computed for the hurricane core have azimuthally averaged flow that tends to oppose the overall wind shear, which is in agreement with one of the model results shown by Jones. Additionally, in the core, winds at smaller radii imply a more vertically aligned storm center than do winds at larger radii. These results will be documented in several hurricanes, including Olivia and Jimena.
Garraffo, Z.D., W.E. Johns, E.P. Chassignet, and G.J. Goni. Impact of North Brazil Current rings on the eastern Caribbean. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS69, OS12P-04 (2000).
The influence of North Brazil Current (NBC) rings on the eastern Caribbean is investigated using new results from a high-resolution North Atlantic model simulation, ship surveys, drifters, and Topex/Poseidon (T/P) altimetry. North Brazil Current rings are large (~400-km diameter) anticyclonic eddies that periodically pinch off from the North Brazil Current Retroflection and propagate northwestward toward the Lesser Antilles, carrying with them water masses and biogenic materials from the equator and Amazon regions. Results from the high-resolution MICOM North Atlantic model and from five years of T/P altimetry now suggest that approximately five NBC rings are formed each year, nearly twice what had been previously documented. New shipboard surveys obtained as part of an intensive 1998-2000 in-situ study of NBC rings have shown that these rings can have highly varying vertical structures, ranging from shallow (<200 m) to deep (>1000 m) features, and even subsurface intensified rings with maximum swirl velocities in the thermocline. A similar range of features is produced in the MICOM-simulated rings. The model results and altimetry suggest that the strongest and deepest reaching NBC rings are the ones most likely to travel well northward along the Lesser Antilles arc before breaking up and dispersing their waters. The passage of the rings along the island arc and their interaction with the island topography strongly influences flow and transport variations through the Lesser Antilles passages.
Garzoli, S.L., and G.J. Goni. Combining altimeter observations and oceanographic data for ocean circulation and climate studies. In Satellites, Oceanography, and Society, D. Halpern (ed.). Elsevier Oceanographic Series, 63:79-95 (2000).
Calibrating Topography Experiment (TOPEX)/Poseidon (T/P) altimeter data to inverted echo sounder measurements is one of the methodologies developed to advance the study of the South Atlantic Ocean. The mass transport of the main boundary currents can be monitored using dynamic height time series obtained from altimeter-derived sea surface height anomalies. A two-layer model yields upper-layer thickness and surface dynamic height of the ocean in areas of strong vertical stratification to identify and track anticyclonic rings, such as those shed from the Agulhas retroflection, which play an important role in the interocean exchange of heat and mass. Interannual variability of boundary currents, derived from analysis of the first five years of T/P data, is discussed. A combination of T/P data and in-situ observations provides significant contributions to the study of ocean dynamics for climate applications.
Garzoli, S.L., D.B. Enfield, G. Reverdin, G. Mitchum, R.H. Weisberg, P. Chang, and J. Carton. COSTA: A Climate Observing System for the Tropical Atlantic. OCEANOBS99: International Conference on the Ocean Observing System for Climate, Saint Raphael, France, October 18-22, 1999. Centre National d'Etudes Spatiales, 19 pp. (2000).
This paper summarizes the discussions that took place during the COSTA (Climate Observing System for the Tropical Atlantic) workshop held in Miami, Florida during May 1999. The main objective of the workshop was to coordinate the present efforts in the region and to set the scientific basis for an extended and more permanent observing system. The intent of the COSTA workshop, based in the CLIVAR (global) and ACVE (basin) experience, was to formulate the basis for an extended and more permanent (regional) tropical Atlantic observing system, building on the present existing monitoring programs and process studies, and the current scientific underlayment. The first part of this paper establishes the importance and the role of the tropical Atlantic in climate fluctuations and their impact in society. This is followed by a description of the climate variability in the Atlantic sector, its relationship to tropical Atlantic variability, especially sea surface temperature (SST), and to the North Atlantic Oscillation and meridional overturning circulation. The possible mechanisms behind tropical Atlantic SST fluctuations and their relation to climate is also discussed, highlighting, in particular, the role of surface fluxes in the off-equatorial regions, the equatorial ocean-atmosphere interactions, and their relationships to movements of the Inter-Tropical Convergence Zone. The second part of this paper summarizes the scientific discussions and recommendations from the working groups who centered their discussions in the following themes: (1) SST and surface fluxes; (2) sea level and subsurface structure; (3) circulation; and (4) modeling and data assimilation. Finally, the present status of the observing system and a summary of recommendations is presented.
Goldenberg, S.B. Intraseasonal predictability of Atlantic basin hurricane activity. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 59-60 (2000).
The Atlantic basin hurricane season officially lasts from 1 June through 30 November. The vast majority of the activity (>95% of the major hurricane activity) occurs during the peak months August, September, and October. Previous analyses have demonstrated that early season (June-July) overall tropical cyclone activity has no relationship to the activity during the remainder of the season. Results will be presented that demonstrate that if the June-July activity is stratified properly, it can yield a strong predictive signal for the activity during the rest of the season. The occurrence of a certain type of activity in June or July is, in fact, a sufficient (but not necessary) condition for a year with above-average activity. Results will also be discussed showing how just as the June-July activity contains a signal to help predict the activity for the coming months, June-September (or simply August-September) activity can give a clear indication of what is to come during the final peak month of October.
Goldenberg, S.B., C.W. Landsea, and G.D. Bell. Summary of the 1999 Atlantic hurricane season: A climatic perspective. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A251-A256 (2000).
The tropical cyclone activity from the 1999 Atlantic hurricane season will be related to observed fluctuations in various climatic factors such as ENSO, Atlantic SSTs, and vertical shear. The character of the season's activity will also be discussed with respect to different time scales: multi-decadal, interannual, and intraseasonal. Implications for Atlantic activity in the coming season (2000) and decade will also be addressed. For the last two seasons, NOAA has issued forecasts of the Atlantic basin hurricane activity as a collaboration between scientists at NOAA's Climate Prediction Center, Hurricane Research Division, and National Hurricane Center. Verifications of the forecasts for the 1998 and 1999 seasons will be discussed.
Goldenberg, S.B., C.W. Landsea, and G.D. Bell. Summary of the 1999 Atlantic hurricane season: A climatic perspective. Proceedings, 24th Annual Climate Diagnostics and Prediction Workshop, Tucson, AZ, November 1-5, 1999. National Weather Service, 1-4 (2000).
No abstract.
Goni, G.J., S.M. Sainz-Trapaga, and T. Sugimoto. Transport estimates and variability of the Kuroshio Extension Current from satellite altimetry data. AGU 2000 Western Pacific Geophysics Meeting, Tokyo, Japan, June 27-30, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(22):WP77-WP78, OS32B-06 (2000).
Satellite altimetry observations of sea level in combination with historical vertical profiles of ocean density and dynamical modeling provide an excellent tool to understand the global meso- and large-scale ocean circulation. A two-layer dynamical model is used in conjunction with six years of TOPEX/POSEIDON (T/P) altimeter-derived sea height anomaly to monitor the upper ocean transport in a region east of Japan from 1993 to 1998. The key objective of this work is to estimate the upper layer thickness and investigate the baroclinic transport variability along a selected T/P groundtrack, in which a two-year time series of the 14°C isotherm derived from inverted echo sounders is available. The upper layer thickness field is used to monitor the Kuroshio Extension front, which is found to fluctuate between 33.7°N and 36.5°N. The across-track upper layer velocity and baroclinic transports are used to monitor the Kuroshio Extension axis. Estimates in this work reveal that the axis fluctuates between 32.1°N and 35.9°N. Two events are identified, one in 1996 and another in 1997, with unusual southern paths of the Kuroshio Extension axis, and related to large variations in baroclinic transport values. It is speculated that these extreme southern excursions of the axis may be compensating for large changes in relative vorticity and upper layer thickness.
Goni, G.J., L.K. Shay, P.G. Black, S.D. Jacob, T.M. Cook, J.J. Cione, and E.W. Uhlhorn. Role of the upper ocean structure on the intensification of Hurricane Bret from satellite altimetry. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J5-J6 (2000).
No abstract.
Hendee, J.C. A data-driven soft real-time expert system for producing coral bleaching alerts. Ph.D. Thesis, Nova Southeastern University, 131 pp. (2000).
In the Florida Keys there are many physical, chemical, and biological events of interest and concern to personnel of the Florida Keys National Marine Sanctuary, marine biologists, oceanographers, fishermen, and divers. Large volumes of continuously-generated meteorological and oceanographic data from instruments in the SEAKEYS (Sustained Ecological Research Related to Management of the Florida Keys Seascape) network help to understand these events. However, since no one has the time to look at every printout of data from every station, every day, seven days a week, it is highly desirable to have an automated system that can monitor parameters of interest and produce specialized alerts of specific events, as indicated by prescribed or abnormal ranges, or combinations of parameters. A soft real-time expert system was developed to produce such alerts based on data input from the SEAKEYS network. The prototype system collected data from the Sombrero Reef station in the network and produced automated e-mail and World-Wide Web alerts when conditions were thought to be conducive to, or predictive of, coral bleaching, which occurs under environmental conditions stressful to corals. Configuration of the system included a point system for three coral bleaching models (high sea temperature only, high sea temperature plus low winds, high sea temperature plus low winds plus low tide). The approach is an important development in the use of knowledge-based systems to solve environmental problems, as it provides for knowledge synthesis (in the form of data summaries) from any environmental ASCII data stream or table, be it real-time or not.
Hendee, J.C. An environmental information synthesizer for expert systems: A framework for use in near real-time detection of harmful algal blooms. Proceedings, 17th International Conference of The Coastal Society: Coasts at the Millennium, Portland, OR, July 9-12, 2000. The Coastal Society, 233-241 (2000).
As an enhancement to the SEAKEYS environmental monitoring network in the Florida Keys National Marine Sanctuary, software called the Environmental Information Synthesizer for Expert Systems (EISES) has been utilized together with a specially developed expert system to model and report the near real-time sensing of environmental conditions conducive to the onset of a harmful algal bloom (HAB, e.g., "red tide"). Actual near real-time in-situ fluorometry data was matched with wind speeds and photosynthetically active radiation at the Long Key SEAKEYS station in Florida Bay to simulate the onset of an HAB. These incidences were e-mailed to the knowledge engineer as they occurred, and could in the future be e-mailed to regulatory agencies, or posted to a Web site, as is done with a similarly developed expert system for coral bleaching. This approach shows promise with the future remote detection of HAB pigment data via in-situ or satellite sensors.
Houston, S.H., P.P. Dodge, M.D. Powell, M.L. Black, G.M. Barnes, and P.S. Chu. Surface winds in hurricanes from GPS-sondes: Comparisons with observations. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 339 (2000).
The Hurricane Research Division (HRD) of NOAA began dropping NCAR Global Positioning System (GPS) sondes in the vicinity of tropical cyclones (TC) on an experimental basis in 1996. High-resolution vertical profiles of wind speed and direction, temperature, dew point, and pressure were collected from flight-level to the surface. The boundary layer and near surface winds measured by sondes are considered particularly important, since few surface wind instruments operate in sustained wind speeds greater than 50 m/s. There have been some uncertainties about whether the profiles of boundary layer (especially near the surface) winds and thermodynamic measurements made by sondes in TC convective eyewalls were representative of conditions observed at the surface. In addition, the averaging times of sonde winds relative to fixed earth measurements from standard anemometers have been uncertain. Based on the preliminary results from data in relatively high winds from three hurricanes in 1998, the sondes appeared to be recording very accurate and representative wind speeds when compared to in-situ measurements from marine platforms. There appeared to be a slight negative bias in the sondes' reported surface wind speeds, while there was hardly any bias in the wind speeds adjusted to 10 m using the mean boundary layer winds averaged over the lowest 500 m layer. The pressure and temperature observations also showed good agreement between the sondes and surface platforms. Although these results are very preliminary, it appeared that the sondes provided accurate measurements in the boundary layer and near surface observations which are extremely beneficial for operational and research purposes. The sample size has been increased during the 1999 hurricane season. Therefore, more definitive statistics for sondes and surface platform comparisons that were available during the 1996-1999 hurricane seasons will be presented at the conference.
Jacob, S.D., L.K. Shay, P.G. Black, and S.H. Houston. Upper ocean response to hurricane wind asymmetries. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J66-J67 (2000).
No abstract.
Jacobs, S.D., L.K. Shay, A.J. Mariano, and P.G. Black. The 3D oceanic mixed layer response to Hurricane Gilbert. Journal of Physical Oceanography, 30(6):1407-1429 (2000).
Upper-ocean heat and mass budgets are examined from three snapshots of data acquired during and after the passage of Hurricane Gilbert in the western Gulf of Mexico. Measurements prior to storm passage indicated a warm core eddy in the region with velocities of O(1) m s-1. Based upon conservation of heat and mass, the three-dimensional mixed layer processes are quantified from the data. During and subsequent to hurricane passage, horizontal advection due to geostrophic velocities is significant in the eddy regime, suggesting that prestorm oceanic variability is important when background flows have the same magnitude as the mixed layer current response. Storm-induced near-inertial currents lead to large vertical advection magnitudes as they diverge from and converge toward the storm track. Surface fluxes, estimated by reducing flight-level winds to 10 m, indicate a maximum wind stress of 4.2 N m-2 and a heat flux of 1200 W m-2 in the directly forced region. The upward heat flux after the passage of the storm has a maximum of 200 W m-2 corresponding to a less than 7 m s-1 wind speed. Entrainment mixing across the mixed layer base is estimated using three bulk entrainment closure schemes that differ in their physical basis of parameterization. Entrainment remains the dominant mechanism in controlling the heat and mass budgets irrespective of the scheme. Depending on the magnitudes of friction velocity, surface fluxes and/or shear across the mixed layer base, the pattern and location of maximum entrainment rates differ in the directly forced region. While the general area of maximum entrainment is in the right-rear quadrant of the storm, the shear-induced entrainment scheme predicts a narrow region of cooling compared to the stress-induced mixing scheme and observed SST decreases. After storm passage, the maximum contribution to the mixed layer dynamics is associated with shear-induced entrainment mixing forced by near-inertial motions up to the third day as indicated by bulk Richardson numbers that remained below criticality. Thus, entrainment based on a combination of surface fluxes, friction velocity, and shear across the entrainment zone may be more relevant for three-dimensional ocean response studies.
Jiang, M., F. Chai, R.C. Dugdale, R.T. Barber, T.-H. Peng, Y. Chao, and F.P. Wilkerson. Physical-biogeochemical modeling: Modulation of decadal variability on ENSO events in the equatorial Pacific. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F702, OS11B-18 (2000).
Although decadal scale physical changes have been observed at several locations in the Pacific Ocean, how these subtle but pervasive variations have altered ecosystem processes and biogeochemical fluxes remains largely unclear. To improve our understanding of physical variability and the ecosystem response in the Pacific Ocean, a coupled physical-biogeochemical model has been developed. A 10-component biogeochemical model has been embedded in a Modular Ocean Model (MOM) with modifications and configurations for the Pacific Ocean by Chao et al. at the JPL. The model is used to simulate both physical and biogeochemical conditions between 1955-1993. Based on this long-term model simulation, we present the results focused on the role of decadal variations on the ENSO events occurring before/after the climatic regime shift in 1976/1977. It is generally agreed that the signals of Pacific Decadal Oscillation (PDO) primarily originate from the northwest Pacific and affect the equatorial Pacific through intergyre exchanges or atmospheric teleconnections. The detailed nature of ENSO events may be modulated by these persistent processes. As a consequence, the ecosystem behaviors in the equatorial Pacific should be affected by the modulated ENSO, primarily through the depth of nutricline and upwelling variability. With preliminary modeled results, we examine the possible decadal trends of macro-nutrients (nitrate and silicate), which are regulating the primary production, and the evolution of nutrient concentrations during ENSO before and after climatic shifts. The phytoplankton responses to different levels of available macro-nutrients are studied as well.
Jones, R.W., and H.E. Willoughby. Linear motion of a two-layer baroclinic hurricane in shear. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 83-84 (2000).
No abstract.
Kang, W.-J., J.H. Trefy, T.A. Nelsen, H.R. Wanless. Direct atmospheric inputs versus runoff fluxes of mercury to the lower Everglades and Florida Bay. Environmental Science and Technology, 34(19):4058-4063 (2000).
Age-dated sediments from the lower Everglades and Florida Bay provide a record of inputs of excess Hg from direct atmospheric input versus runoff. Direct atmospheric fluxes of excess Hg to sediments in the lower Everglades and Florida Bay, calculated using a mass balance model for excess 210Pb, currently average 24 ± 9 µg m-2 yr-1 and are comparable with recent results from bulk atmospheric deposition. In contrast, present-day runoff fluxes of excess Hg to area sediments are variable, ranging from about 4-160 µg m-2 yr-1. The runoff flux now carries 60-80% of the total flux of excess Hg to the sediments in areas near river sloughs but less than 20% of the total flux of excess Hg in more remote areas of Florida Bay. These results show the greater importance of runoff relative to direct atmospheric deposition for Hg inputs to many areas of the lower Everglades and immediately adjacent Florida Bay. Thus, the choice of future water management strategies can play an important role in controlling Hg inputs to the lower Everglades and portions of Florida Bay.
Kaplan, J., and M. DeMaria. Large-scale characteristics of rapidly intensifying tropical cyclones in the North Atlantic basin. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 232-233 (2000).
An analysis of recent operational Atlantic basin tropical cyclone forecasts issued by the National Hurricane Center indicates that tropical cyclone intensity forecasting has proven to be less skillful than has tropical cyclone track prediction. Moreover, the forecasting of rapid intensity change has proven to be especially difficult, as was underscored by the failure of operational models to adequately predict the rapid intensification of Hurricanes Opal (1995) and Bret (1999). In this study, data obtained from the SHIPS database for the period from 1989-1999 will be utilized to identify the large-scale conditions that appear to be conducive to rapid intensification. This will be accomplished by evaluating the magnitude of various synoptic variables (e.g., vertical shear, relative-eddy angular momentum fluxes) that were present at the start of each period of rapid intensification to determine if these conditions were significantly different from those associated with storms whose rates of intensification were much less rapid. In addition, data collected by the Hurricane Research Division during the 1999 hurricane season may also be employed to determine if the statistical results obtained by analyzing the SHIPS database can be confirmed by more detailed case studies.
Katsaros, K.B. Millennium perspectives. Bulletin of the American Meteorological Society, 81(4):837-838 (2000).
No abstract.
Katsaros, K.B., and R.T. Pinker. Algorithm improvement for novel applications in earth science research. Proceedings, First Meteosat Second Generation Research Announcement of Opportunity Workshop, Bologna, Italy, May 17-19, 2000. European Space Agency, ESA SP-452, 103-106 (2000).
No abstract.
Katsaros, K.B., P. Vachon, P.G. Black, P.P. Dodge, and E.W. Uhlhorn. Wind fields from SAR: Could they improve our understanding of storm dynamics? John Hopkins APL Technical Digest, 21(1):86-93 (2000).
Four hurricane images obtained by RADARSAT are examined for what they reveal about the storms. Features seen include strong variations in backscatter from the surface in and around convective cells associated with rain cells and rainbands, coupled with increased backscatter in regions of high wind outflow. Long linear features of scale 3-6 km are observed in three of the four hurricanes, probably from secondary circulations in the atmospheric boundary layer (roll vortices). They occur between convective rainbands, where the descending motion could produce a well-defined boundary layer. Although the origins of and the mechanisms producing the features are still not clear, the high resolution, wide-swath coverage modes of synthetic aperture radar provide new observations and present important questions for further research.
Kelly, P.S., K.M.M. Lwiza, R.K. Cowen, and G.J. Goni. Low-salinity pools at Barbados, West Indies: Their origin, frequency, and variability. Journal of Geophysical Research, 105(C8):19,699-19,708 (2000).
A vertical array of conductivity-temperature sensors moored off the west coast of Barbados, West Indies, from May 1996 to November 1997 revealed a heterogeneous and variable salinity pattern punctuated by six intrusions of low-salinity water (<34.5 psu) into the region. A typical intrusion extended to 30 m depth and lasted ~25 days, although one intrusion extended to 47 m and lasted 94 days. Water samples taken during an intrusion in May 1997 have Radium 228/226 activity ratios of approximately 1, consistent with previous measurements in Barbados of water that originated in the Amazon River mixing zone. The Amazon water likely was translated to Barbados in rings spawned from the North Brazil Current. Analysis of sea height anomaly derived from the TOPEX/Poseidon satellite supports this conclusion and reveals that, contrary to previous studies, rings are shed throughout the year, mostly during spring. The intrusions of low-salinity water and their associated velocities dramatically changed the already variable flow in our study area. We believe the complex salinity and flow we observed represented the disorganized remnants of rings that were at or near the ends of their lives. The changes we observed in the velocity and water structure are interesting in their own right as evidence of the Barbados region as a mixing zone and for their influence on recruitment of larval fishes to the reef along the island's west coast.
Kiesling, T.L., J. Fell, and P.B. Ortner. Rapid molecular identification of copepods froma plankton tow. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS234, OS41F-04 (2000).
Florida Bay is a 1000 square mile subtropical lagoon located between the Florida Keys and the Florida mainland. Like other estuarine systems, Florida Bay serves as a nursery ground for commercially and recreationally important species of fish. Despite the fact that the primary source of food for many first-feeding larval fish is copepod nauplii, the trophodynamic role of the zooplankton community in Florida Bay has historically been ignored. There is currently a multi-agency effort underway to describe the Florida Bay zooplankton community. Along with traditional sorting methods, molecular methods are being designed to identify and quantify juvenile stages of copepods so that their trophodynamic role can be more accurately defined. We have developed a microtiter plate based hybridization assay to identify copepod species in a mixed sample. With this method, species-specific probes based on DNA sequence are used to identify the copepod species. This method is superior to other PCR-based identification procedures, which require several PCR reactions using several species-specific primers to determine the identity of the DNA. Our technique requires one PCR reaction, which creates an amplicon using universal primers that target a region containing the probe sequences. This amplicon can be tested with a macroarray of several different probes on a single plate. This is especially important when dealing with the limited amounts of DNA that are extracted from these small metazoans. We isolated eight of the most common species of copepods found in Florida Bay, extracted their DNA and sequenced the large subunit of ribosomal DNA for each species. The rDNA sequences were compared and species-specific probes were designed based on base pair differences. Each probe was immobilized to the wells of a microtiter plate. The plates were hybridized with amplified and labeled target DNA from a mixed sample of copepods. If the DNA from the species in question was present in the DNA mix, it would bind to the species-specific probe. The labeled target DNA, once bound to the probe, can be detected via a colorimetric assay. With this method, We were able to identify each of six species of copepods from mixed samples. Testing is now proceeding with the juvenile forms of the copepods. Efforts are also underway to make the method quantitative.
King, D.B., J.H. Butler, S.A. Montzka, S.A. Yvon-Lewis, and J.W. Elkins. Implications of methyl bromide supersaturations in the temperate North Atlantic Ocean. Journal of Geophysical Research, 105(D15):19,763-19,769 (2000).
Methyl bromide saturation anomalies measured in the springtime North Atlantic and summertime North Pacific Oceans during 1998 revealed persistent supersaturations in the temperate waters of the northeastern Atlantic but undersaturtions in tropical waters of both oceans. A comparison of data from this study with those from a previous cruise to the northeastern Atlantic suggests that methyl bromide is cycled seasonally in these waters and perhaps in all temperate open-ocean waters. This means that the calculated net flux of methyl bromide into the oceans is slightly less negative than previously reported. With these new insights we estimate that the global air-sea flux of methyl bromide ranges from -11 to -20 Gg yr-1. Data combined from this and three previous cruises support a flux dependence upon sea surface temperature, as reported recently by Groszko and Moore (1998). Whereas sea surface temperature can account for 40-70% of the observed variability in methyl bromide globally, it is able to reproduce only a small fraction of the observed seasonal cycle in the temperate northeastern Atlantic. The development of reliable predictions of air-sea fluxes of methyl bromide will require information on additional variables as well.
King, D.B., J.H. Butler, S.A. Montzka, S.A. Yvon-Lewis, and J.W. Elkins. Correction to "Implications of methyl bromide supersaturations in the temperate North Atlantic Ocean." Journal of Geophysical Research, 105(D20):24,713-24,714 (2000).
No abstract.
King, D.B., J.H. Butler, S.A. Yvon-Lewis, S.A. Montzka, and J.W. Elkins. Measurements of climatically important halocarbons in the North Pacific Ocean. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F277, B22A-01 (2000).
Atmospheric halocarbons are significant contributors to stratospheric ozone depletion and radiative heating of the atmosphere. Although we have a reasonable understanding of the budgets of those species that are solely anthropogenic, the calculated budgets of many naturally produced halocarbons are not in balance. The oceanic contribution to these budgets can be complex, is often large, and currently is not that well understood. Future changes in global climate likely will alter the concentrations of natural halocarbons in the air and seawater, and, consequently, their air-sea fluxes. Field measurements identify gross sensitivities that models can then use to assess the potential effects of such changes in global climate. NOAA/CMDL has measured the saturations of about 20 halocarbons during five separate research cruises, dating back to 1994. These field missions have encompassed a number of oceanic regions over different seasons. The results provide clues as to the overall behavior of these gases in the surface ocean and lower atmosphere. Here we present data from our most recent field project to the North Pacific Ocean (10°N-58°N) during September and October of 1999. CH3Br was generally undersaturated, with supersaturations observed in some coastal waters. CH3Cl was supersaturated south of 48°N, yet undersaturated in the Gulf of Alaska. CH3I was supersaturated everywhere. Other brominated compounds, such as CH2Br2 and CHBr3, were generally supersaturated with higher values occurring in the subtropics. A correlation between CH2Br2 and CHBr3 seawater partial pressures suggests that these compounds have similar oceanic sources and/or sinks. Nucleophilic substitution can account for only some of the production of these compounds, implying that production from unidentified processes, such as photolysis or biology, is important. Relationships between the methyl halides and sea surface temperature can be useful in developing predictive models of organic halide concentrations and fluxes to the atmosphere. Correlations with other physical properties, such as chlorophyll, wind speed, and solar irradiance, are also investigated.
Lamb, M.F., C.L. Sabine, R.M. Key, J.L. Bullister, F.J. Millero, R.H. Wanninkhof, T.-H. Peng, A. Kozyr, and R.A. Feely. Dissolved inorganic carbon crossover points in the Pacific Ocean. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS122, OS22F-03 (2000).
Between 1991 and 1996, carbon measurements were made on 25 U.S. WOCE, U.S. JGOFS, and NOAA OACES cruises in the Pacific Ocean. These cruises were co-sponsored by the National Science Foundation, the U.S. Department of Energy, and NOAA's Climate and Global Change Program. Although at least two carbon parameters were measured on all of the cruises, dissolved inorganic carbon (DIC) was the only parameter common to all of the cruises. The measurements were collected over six years by ten different laboratories. Together, these data comprise the most comprehensive high-precision survey of carbon distributions in the Pacific Ocean with a greater than ten-fold increase in the number of samples analyzed than for the GEOSECS expedition of the early 1970s. As a part of the JGOFS Synthesis and Modeling Project, we have been working to combine these data into an internally consistent, unified data set. Additional DIC data collected by international investigators have also been included, where possible, to fill in holes in the U.S. survey program. In an effort to ensure the accuracy and internal consistency of these data, we have compared the deep water (>2000 m) DIC values measured on different cruises in areas where two or more cruises overlapped or crossed (within ~100 km). Data from each of the comparison stations were plotted against the density anomaly referenced to 3000 dbar (sigma 3). Polynomial fits of the data from each cruise were evaluated at evenly-spaced intervals over the density range common to both sets of stations. These results, together with information on the calibration procedures, analyses of Certified Reference Materials (CRMs), the quality of duplicate analyses, internal consistency with other carbon parameters, and with large-scale correlations with hydrographic parameters, were used to suggest minor adjustments to some of the cruises to optimize the internal consistency of the data. Our results show that a unified Pacific data set of over 30,000 samples can be achieved with an estimated precision and accuracy of ±2 µmol/kg.
Lamb, M.F., C.L. Sabine, R.A. Feely, F.J. Millero, R.H. Wanninkhof, R.M. Key, G.C. Johnson, K. Lee, T.-H. Peng, A. Kozyr, J.L. Bullister, and D. Greeley. Consistency and proposed adjustments of Pacific Ocean CO2 survey data. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F700, OS11B-10 (2000).
Between 1991 and 1996, carbon measurements were made on 24 WOCE/JGOFS/OACES survey cruises in the Pacific Ocean. This combined database will be used to determine the distribution and inventory of carbon parameters in the Pacific Ocean, and will enhance our understanding of the ocean carbon cycle, including estimates of the anthropogenic CO2 uptake by the oceans. Of the four measurable carbon parameters, (dissolved inorganic carbon (DIC), total alkalinity (TAlk), fugacity of CO2 (fCO2), and pH), DIC was measured on all the cruises, and TAlk was the second most measured. We examined the data where cruises overlapped using several independent techniques, and have proposed adjustments that will result in a consistent, unified data set. Based on our results, we recommend DIC adjustments for P16N, P17N, and P2, and TAlk adjustments for P8S, P17C, P17N, P2 and P31. Details of our proposed adjustments are posted at http://cdiac.esd.ornl.gov/oceans/glodap/index.html. This CO2 data set represents the most comprehensive high-precision survey of carbon distributions in the Pacific Ocean since the GEOSECS expedition, and provides an order of magnitude improvement in the quality and quantity of Pacific DIC and Talk data. With the proposed adjustments, DIC and TAlk have an estimated overall accuracy of ~3 and 5 µmol kg-1 respectively.
Landsea, C.W. Climate variability of tropical cyclones: Past, present, and future. In Storms (Volume 1), R.A. Peilke, Sr. and R.A. Peikle, Jr. (eds.). Routledge, New York (ISBN 041517239X), 220-241 (2000).
No abstract.
Landsea, C.W., and J.A. Knaff. Application of the El Niño-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 9(1):32-34 (2000).
No abstract.
Landsea, C.W., and J.A. Knaff. Application of the El Niño-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 9(2):31-33 (2000).
No abstract.
Landsea, C.W., and J.A. Knaff. How much "skill" is there in forecasting El Ni Niño? Weatherzine, 23:2-4 (2000).
No abstract.
Landsea C.W., and J.A. Knaff. How much skill was there in forecasting the very strong 1997-1998 El Niño? Bulletin of the American Meteorological Society, 81(9):2107-2120 (2000).
The very strong 1997-1998 El Niño was the first major event in which numerous forecasting groups participated in its real-time prediction. A previously developed simple statistical tool, the El Niño-Southern Oscillation Climatology and Persistence (ENSO-CLIPER) model, is utilized as a baseline for determination of skill in forecasting this event. Twelve statistical and dynamical models were available in real time for evaluation. Some of the models were able to outperform ENSO-CLIPER in predicting either the onset or the decay of the 1997-1998 El Niño, but none were successful at both for a medium-range two season (6-8 months) lead time. There were no models, including ENSO-CLIPER, able to anticipate even one-half of the actual amplitude of the El Niño's peak at medium-range (6-11 months) lead. In addition, none of the models showed skill (i.e., lower root-mean-square error than ENSO-CLIPER) at the zero season (0-2 months) through the two season (6-8 months) lead times. No dynamical model and only two of the statistical models (the canonical correlation analysis [CCA] and the constructed analog [ANALOG]) outperformed ENSO-CLIPER by more than 5% of the root-mean-square error at the three season (9-11 months) and four season (12-14 months) lead time. El Niño impacts were correctly anticipated by national meteorological centers one-half year in advance, because of the tendency for El Niño events to persist into and peak during the boreal winter. Despite this, the zero to two season (0-8 month) forecasts of the El Niño event itself were no better than ENSO-CLIPER and were in that sense, not skillful, a conclusion that remains unclear to the general meteorological and oceanographic communities.
Landsea, C.W., and J.A. Knaff. How much skill was there in forecasting the very strong 1997-1998 El Niño? Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J46 (2000).
No abstract.
Landsea, C.W., C.A. Anderson, G. Clark, P. Hungerford, C. Neumann, M. Zimmer, and J. Fernandez-Partagas. The Atlantic hurricane database re-analysis project: Results for 1851-1885. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A230-A231 (2000).
No abstract.
Landsea, C.W., C. Anderson, N. Charles, G. Clark, J. Fernandez-Partagas, P. Hungerford, C. Neumann, and M. Zimmer. The Atlantic hurricane database re-analysis project: Results for 1851-1885. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 542-543 (2000).
No abstract.
Lawrence, J.R., S.D. Gedzelman, and J.F. Gamache. Tropical cyclogenesis and stable isotope ratios of water. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 260-261 (2000).
No abstract.
Leaman, K.D., W.D. Wilson, and Z.D. Garraffo. Physical variability of surface currents in the the Panama-Colombia Gyre: Nature, causes, and comparisons with a high-resolution numerical model. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS33, OS11R-09 (2000).
As part of the National Oceanographic Partnership Program Year of the Ocean (YOTO) contribution, a total of 32 WOCE surface drifters have to date been launched in the southwestern Caribbean Sea using vessels of the Colombian Navy. These deployments consist of groups of eight surface drifters launched nominally every three to four months on a line between Cartagena and San Andres Island. All drifters have been drogued at a depth of 15 m and are designed to report surface positions and temperatures. This launch program is planned to continue through at least the next year with launches of six floats roughly every three months. These drifter tracks can be found at Web pages for the NOPP drifters (www.drifters.doe.gov), the IAS oceanography page (IASlinks.org), or the Intra-Americas Sea Initiative page (www.rsmas.miami.edu/groups/IASI/IASIhome.htm). The purpose of these deployments is to explore the structure and variability of a prominent circulation feature in the southwestern Caribbean known as the Panama-Colombia Gyre (PCG). This cyclonic gyre has been revealed by the drifter tracks obtained so far to be a permanent feature of the circulation but one that shows considerable seasonal and shorter-term variability as well. Retention times for drifters launched in the PCG are order several months. Very few drifters from the open Caribbean find their way into the PCG; however, a large number of PCG drifters exit the PCG at various locations and times, and a significant number of these become trapped in shelf waters south of Cuba. This latter fact has implications for biological problems of larval transport and interconnectivity of coastal habitats. Observed drifter tracks are compared to numerical surface drifters "deployed" in a high-resolution isopycnic-coordinate numerical model. Similar seasonal variability is observed in both real and numerical drifter trajectories; in particular, a deformation of the flow field in late summer has been observed in the model, as well as in two sequential years of drifter observations. Over longer periods, numerical drifter concentrations in the PCG decrease until a balance is achieved between northward Ekman advection and diffusion of drifters from the interior.
Lee, K., J.-Z. Zhang, and R. Wanninkhof. Carbon export in nitrate-depleted tropical and subtropical oceans: Implication of nitrogen fixation. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F693, OS72E-12 (2000).
The export of carbon from surface waters to the interior of the ocean is a central mechanism controlling the net uptake of carbon dioxide from the atmosphere. Existing estimates of the vertical carbon export vary greatly in regional and global comparisons. We estimate the biologically-mediated vertical carbon export, referred to as "new production," from the mean annual cycle of total inorganic carbon concentration normalized to salinity (NDIC = DIC × 35/S) in the mixed layer. It is assumed that the decrease in NCT from early spring to fall is solely caused by biological uptake and subsequent transport out of the upper oceans. Seasonal drawdown of NDIC in the mixed layer is quantified from regional algorithms relating NDIC to sea surface temperature (SST) and nitrate (NO3-) combined with seasonal changes in climatological SST and NO3- fields, and separately from the surface partial pressure of CO2 and alkalinity fields using thermodynamic models. The two independent methods show similar regional trends and yield global new production values of 7.5 GtC/yr and 8.6 GtC/yr, respectively. A significant fraction of the global total, 0.8-1.1 GtC/yr, is exported in the absence of measurable nitrate levels in the oligotrophic tropical and subtropical oceans. This estimate is a direct indication of carbon export supported by nitrogen fixation. The value constitutes a significant fraction (30-50%) of the total new production in the oligotrophic oceans.
Lee, K., F.J. Millero, R.H. Byrne, R.A. Feely, and R. Wanninkhof. The recommended dissociation constants for carbonic acid seawater. Geophysical Research Letters, 27(2):229-232 (2000).
A coherent representation of carbonate dissociation constants and measured inorganic carbon species is essential for a wide range of environmentally important issues such as oceanic uptake of anthropogenic CO2 and carbon cycle depictions in ocean circulation models. Previous studies have shown varying degrees of discordance between calculated and measured CO2-system parameters. It is unclear if this is due to errors in thermodynamic models or in measurements. In this work, we address this issue using a large field data set (15,300 water samples) covering all ocean basins. Our field data, obtained using laboratory-calibrated measurement protocols, are most consistent with calculated parameters using the dissociation constants of Mehrbach et al. (1973) as refit by Dickson and Millero (1987). Thus, these constants are recommended for use in the synthesis of the inorganic carbon data collected during the global CO2 survey during the 1990s and for characterization of the carbonate system in seawater.
Lee, K., R.H. Wanninkhof, R.A. Feely, F.J. Millero, and T.-H. Peng. Global relationships of total inorganic carbon with temperature and nitrate in surface seawater. Global Biogeochemical Cycles, 14(3):979-994 (2000).
High quality total inorganic carbon (CT) measurements made in the major ocean basins as part of the Joint Global Ocean Flux Study (JGOFS), the National Oceanic and Atmospheric Administration/Ocean Atmosphere Carbon Exchange Study (NOAA/OACES), and the Department of Energy/World Ocean Circulation Experiment (DOE/WOCE) programs are related to sea surface temperature (SST) and nitrate (NO3-). A simple two-parameter function with SST and NO3- of the form NCT = a + b SST + c SST2 + d NO3 - fits salinity (S)-normalized surface CT (NCT = CT × 35/S) data for different parts of the oceans within an area-weighted error of ±7 µmol kg-1 (1 sigma). Estimated values of NCT using the derived algorithms with NO3- and SST are compared with values calculated from the surface partial pressure of CO2 (pCO2SW) (Takahashi et al., 1997) and total alkalinity (AT) (Millero et al., 1998) fields using thermodynamic models. Comparisons of the estimated values of NCT with measurements not used to derive the same algorithms, and comparisons with the values calculated from global AT and pCO2SW fields, give a realistic uncertainty of ±15 µmol kg-1 in estimated CT. The derived correlations of NCT with SST and NO3- presented here make it possible to estimate surface CT over the ocean from climatological SST, S, and NO3- fields.
Lee, W.-C., and F.D. Marks. An objective method to determine tropical cyclone center near landfall from WSR-88D data: The GBVTD-simplex algorithm. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 310-311 (2000).
No abstract.
Lee, W.-C., and F.D. Marks. Tropical cyclone kinematic structure retrieved from single Doppler radar observations, Part II: The GBVTD-simplex center finding algorithm. Monthly Weather Review, 128(6):1925-1936 (2000).
This paper is the second of a series and focuses on developing an algorithm to objectively identify tropical cyclone (TC) vorticity centers using single-Doppler radar data. The first paper dealt with the formulation of a single-Doppler radar TC wind retrieval technique, the ground-based velocity-track-display (GBVTD), and the results are verified using analytical TCs. It has been acknowledged that the quality of the GBVTD-retrieved TC circulation strongly depends on accurately knowing its center position. However, existing single-Doppler radar center finding algorithms are limited to estimate centers for axisymmetric TCs. The proposed algorithm uses a simplex method to objectively estimate the TC vorticity center by maximizing GBVTD-retrieved mean tangential wind. When tested with a number of axisymmetric and asymmetric analytical TCs, the accuracy of the TC centers estimated by the GBVTD-simplex algorithm is approximately equal to 340 m from the true center. When adding 5 m s-1 random noise to the Doppler velocities, the accuracy of the TC centers is nearly unchanged at 350 m. When applying the GBVTD-simplex algorithm to Typhoon Alex (1987), the estimated uncertainty varies between 0.1 and 2 km. When the overall velocity gradient is weak, the uncertainties in the retrieved TC centers are usually large. The GBVTD-simplex algorithm sometimes has problems finding a solution when a large sector of Doppler radar data is missing in conjunction with weak velocity gradients. The GBVTD-simplex algorithm significantly reduces the uncertainties in estimating TC center position compared with existing methods and improves the quality of the GBVTD-retrieved TC circulation. The GBVTD-simplex algorithm is computationally efficient and can be easily adapted for real-time applications.
Lee, W.-C., B. J.-D. Jou, P.-L. Chang, and F.D. Marks. Tropical cyclone kinematic structure retrieved from single-Doppler radar observations. Part III: Evolution and structures of Typhoon Alex (1987). Monthly Weather Review, 128(12):3982-4001 (2000).
This paper is the third of a series that focuses on the applications of the ground-based velocity track display (GBVTD) technique and the GBVTD-simplex center finding algorithm developed in the previous two papers to a real tropical cyclone (TC). The evolution and structure of Typhoon Alex (1987), including full tangential winds, mean radial winds, one component of the mean flow, and their derived axisymmetric angular momentum and perturbation pressure fields are reconstructed from 16 volume scans (6.5 h of data with a 2-h gap) from the Civil Aeronautic Administration (CAA) Doppler radar while Typhoon Alex moved across the mountainous area in northern Taiwan. This analysis retrieves a plausible and physically consistent three-dimensional primary circulation of a landfalling TC using a single ground-based Doppler radar. Highly asymmetric wind structures were resolved by the GBVTD technique where the maximum relative tangential wind at z = 2 km evolved from 52 m s-1 (before landfall), to less than 40 m s-1 (after landfall), to less than 35 m s-1 (entering the East China Sea). Alex's eye began to fill with precipitation while its intensity decreased rapidly after landfall, a characteristic of circulations disrupted by terrain. The mean radial wind field revealed a layer of low-level inflow in agreement with past TC observations. The outward slope of the eyewall reflectivity maximum was consistent with the constant angular momentum contours within the eyewall. After Alex entered the East China Sea, its circulation became more axisymmetric. The axisymmetric perturbation pressure field was retrieved using the gradient wind approximation, which, when used in conjunction with one or more surface pressure measurements within the analysis domain, can estimate the central pressure. The retrieved perturbation pressure fields at two time periods were compared with surface pressures reported in northern Taiwan. Considering the assumptions involved and the influence of terrain, good agreement (only 1V2-mb deviation) was found between them. This agreement indicates the relative quality of the GBVTD-retrieved axisymmetric circulation and suggests GBVTD-retrieved quantities can be useful in operational and research applications.
Lonfat, M., F.D. Marks, and S. Chen. A study of the rain distribution in tropical cyclones using TRMM/TMI. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 480-481 (2000).
No abstract.
Lonfat, M., F.D. Marks, and S. Chen. Characterization of the rain distribution in tropical cyclones using TRMM/TMI-PR. AGU 2000 Spring Meeting, Washington, D.C., May 30-June 3, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(19):S237-S238, H42B-16 (2000).
The goals of this study are (1) to improve our understanding of tropical cyclone (TC) precipitation fields by developing a climatology of rainfall distribution and vertical profiles of hydrometeors and heating in TCs around the globe, and (2) to develop methodologies to validate operational and research model forecasts of TC rainfall distribution and structure. Surface rain estimates from the NASA Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR) were used to study the global TC rainfall distribution. From November 1997 to December 1998, 87 storms were observed, providing approximately 1200 events, ranging from tropical storm intensity to category 4 hurricanes. At the time of the satellite measurement, approximately 70% of the events were tropical storms, 25% were category 1-2 hurricanes, and 5% were category 3 or higher. Although the sample size for major hurricanes is smaller than other categories, we have more than 50 observations, which is an order of magnitude larger than previous studies. TMI was used to develop the climatology, as the instrument swath allows a more extended coverage of the storms than PR. For each event, we derive mean rain rates in 10-km rings around the TC center. Averaging these distributions produces rates up to 5 mm h-1 close to the center. Rain rates decrease rapidly below 1 mm h-1 by 200 km radius. We examine the rain rate distribution as a function of the storm intensity and geographical location. Close to the storm center, the mean rates are greater than 15 mm h-1 for category 3 and higher hurricanes, and about 3 mm h-1 for tropical storms. Rain distributions show strong asymmetries in the rain patterns between the different basins. PR data were used on several individual 1999 storm cases (Floyd and Bret) and compared to TMI distributions. This comparison pointed out a problem in version 4 of the TMI surface rain algorithm. We are also in the process of comparing our TC rain rate distributions with a high-resolution model simulation. Our study provides a broad description of hurricane precipitation distributions, which is of fundamental use as a climatological basis, notably for simulation purpose, and gives a feedback for TRMM/TMI algorithm improvement as well.
Lonfat, M., F.D. Marks, and S.S. Chen. Comparison of TRMM/TMI-PR and airborne radar rainfall distributions in severe Atlantic hurricanes. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F158, A21G-08 (2000).
The goals of this study are to improve our understanding of tropical cyclone (TC) precipitation fields by constructing rainfall distributions in severe hurricanes, and to validate Tropical Rainfall Measuring Mission (TRMM) results by comparing distributions with aircraft radar observations. Surface rain estimates from the NASA TRMM Microwave Imager (TMI) and Precipitation Radar (PR) are used to determine rainfall distributions for five major 1998-1999 Atlantic hurricanes (category 3 or higher). Only TRMM orbits which fully observe TC cores are considered, in order to improve comparisons with aircraft data. Airborne radar data aboard the NOAA WP-3D aircrafts are examined for individual cases such as Floyd. For each event, we derive mean rain rates in 10 km rings around the TC center. Averaging distributions for TRMM/TMI produces rates up to 8 mm h-1 close to the center, within about 70 km. Rates are below 1 mm h-1 by 250 km. Rain rates from TRMM/PR are similar in magnitude close to the center, but decrease more sharply with radial distance than TMI rates. Probability density functions (PDF) are constructed as well. Both TMI and PR PDF resemble normal distributions. The TMI distribution is narrower and shifted to larger rain rates than the PR curve. Peaks are located at about 8 and 5 mm h-1 respectively. TRMM/PR results seem to match better with airborne radar distributions than TMI does.
Luo, J., P.B. Ortner, D. Forcucci, and S.R. Cummings. Diel vertical migration of zooplankton and mesopelagic fish in the Arabian Sea. Deep-Sea Research, II, 47(7-8):1451-1473 (2000).
Acoustic (153 kHz ADCP and 12 kHz hull-mounted transducers) data and MOCNESS (MOC01 and MOC10) net tow samples collected in the Arabian Sea during the Spring Intermonsoon (April/May) and Southwest Monsoon (August) in 1995 documented substantial diel migrations of fish and zooplankton despite the year-round presence of an oxygen minimum (<0.2 ml l-1 at 125-150 m). Fish and zooplankton layers were distinguished by comparing 12 kHz sonar and 153 kHz ADCP backscatter data, which indicated that the strongly migrating layers were predominantly composed of fishes. Fish vertical migration speeds were independently estimated from the slopes of the volume scattering layers and from the vertical velocity components of the ADCP, yielding average speeds of 4 and 3 cm s-1 and maximum speeds of 13 and 10 cm s-1, respectively. A few migrating zooplankton layers were identified with an average speed of about 2 cm s-1 and maximum speeds as high as 8 cm s-1. Migration depths for both zooplankton and fish differed somewhat amongst stations and appeared to be related to local hydrographic conditions (principally the vertical gradients in DO and water temperature). Zooplankton displacement volumes at individual sites suggested that zooplankton biomass during the Southwest Monsoon could be as much as fivefold greater than during the Spring Intermonsoon. This observation was confirmed for the region in general by first deriving a relationship between ADCP backscatter intensity and daytime zooplankton biomass and then comparing the latter between cruises using daytime ADCP data taken along a 1500 km transect that extended from the coast of Somalia to the center of the northern basin.
Marks, F.D., M.L. Black, and H.A. Friedman. 2000 Hurricane Field Program Plan. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, FL (published for limited distribution), 97 pp. (2000).
No abstract.
Marks, F.D., L. Selevan, and J.F. Gamache. WSR-88D derived rainfall distributions in Hurricane Danny (1997). Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 298-299 (2000).
A tropical cyclone (TC) poses a significant quantitative precipitation forecast (QPF) problem as evidenced by the recent tragic loss of life and property from rainfall during Hurricanes Mitch (1998) and Floyd (1999). Improved QPF is one of the primary objectives of the U. S. Weather Research Program (USWRP), and a specific goal of the Hurricane at Landfall effort under USWRP. Estimates of rainfall based on radar and other remote sensors offer promising avenues for improvement. The current level of QPF skill for TCs in the United States is to predict the peak storm rainfall amount using the "rule of thumb" first proposed by Kraft in the late 1950s, which states that the maximum storm rainfall amount will be 100 inches divided by the storm forward motion in knots. While this "rule of thumb" provides a reasonable estimate of the peak storm total rain, it provides no information about the distribution of rain in space or time. There is also no adjustment in the rule for storm intensity, topography, or other dynamical or microphysical parameters. A major stumbling block to improving over this simple "rule of thumb" is a lack of a comprehensive climatology of TC precipitation, i.e., a description of the distribution of rain in space and time. This study focuses on the distribution of WSR-88D radar derived rain in space and time during Hurricane Danny from 17-21 September 1997. The WSR 88D radars provides 1-h mean rain estimates (R) over a domain extending to 230 km range from the radar with a 4 × 4 km resolution (Digital Precipitation Array, DPA). Over the four days, Danny, a category 1 hurricane, was visible from four different WSR-88D radars as it tracked slowly east-northeastward along the Gulf coast. The rain estimates from the four radars provide an excellent opportunity to estimate the TC precipitation distribution in space and time as the storm passed along the Louisiana, Mississippi, and Alabama coasts. The radial distribution of the mean R is calculated in 10 km radial bands out to 300 km from the storm center for each hour and for the total four-day period. The probability distribution of R is also computed for each 10 km radial band in 1 dBR (10log10R) steps from 0.3-300 mm h-1 (-5 to 25 dBR) for each hour and the total four-day period. These distributions in range and intensity are compared to results from earlier studies done using rain gage estimates.
Mayer, D.A., M.O. Baringer, R.L. Molinari, G.J. Goni. Comparison of hydrographic and altimetric estimates of sea level height variability in the Atlantic Ocean. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F740, OS21D-13 (2000).
Using an ensemble of expendable bathythermograph (XBT) profiles and TOPEX/Poseidon (T/P) altimeter data, we have considered how much can be inferred about the internal field of mass from sea level changes for the period 1993 through 1997. Sea height anomalies (SHA) derived from T/P data are compared to temperature anomalies (TA) and to dynamic height anomalies (DHA) from 10°S to 40°N along two well sampled XBT sections on the western and eastern sides of the Atlantic Ocean. XBT profiles were matched (time/location) to SHA, converted into DHA using TS relationships and then binned monthly into 2° of latitude by 4° of longitude boxes. The vertical mass distribution cannot always be inferred from SHA alone. Specifically, the relationships between SHA and both TA and DHA can be problematic if SHA are small. This occurs in the transition regions between the tropics (where temperature variability is largest in the thermocline due to wind-driven ocean dynamics), and in the subtropics (where variability is largest near the surface due to surface fluxes). Transition regions are characterized by competing influences between surface and thermocline variability that act in opposition; hence, SHA are not particularly well suited in drawing inferences about the temperature of the upper ocean. Generally, the relationships between SHA and DHA for residual signals (obtained by removing the annual cycle) are poor. The exceptions are in two areas of large sea height variability in the western basin where there is significant interannual variability. The first is in the tropics in the vicinity of the tropical gyre trough, and the second is in the Gulf Stream near 70°W, 38°N. An analysis of Panulirus data at (32.2°N, 64.5°W) suggests that in-situ data may be needed down to at least 1000 m where interannual variability accounts for about 40% of the SHA variance.
McAdie, C.J., and P.P. Dodge. Maximum sustained winds in Hurricane Irene as measured by the Miami WSR-88D. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 212-213 (2000).
No abstract.
McArthur, C., R. Ferry, and J.R. Proni. Amenities monitoring for dredged material disposal management. Proceedings, 17th Conference of the Coastal Society: Coasts at the Millennium, Portland OR, July 9-12, 2000. The Coastal Society, 6 pp. (2000).
Valuable amenities are present throughout U.S. coastal waters, from coral reefs, to oyster beds, to coastal fisheries. In essentially every case in which navigation and/or maintenance dredging is contemplated, the issues of potential impact of dredging activities on nearby amenities arise. In order to evaluate that potential impact, long-term monitoring of amenities is required. Key management issues related to amenities include: (1) reduction or elimination of dredging impacts; (2) scheduling ("windows") for dredging and dredged material disposals; (3) monitoring of transport to, and effects upon amenities; and (4) compliance with defined procedures for dredging activities. While the data needed for management decisions may vary from location to location, certain basic measurement needs appear almost universally: (1) characterization and quantification of dredged sediments arriving at amenities sites; (2) determination of "natural" sediment ranges at amenities sites; (3) photosynthetic light reductions; (4) sediment resuspension and transport; and (5) other sources of materials of potential impact to amenities sites. Dredging and disposal must also be considered in the context of temporal "windows." In the Miami Offshore Disposal Site project, data for management of dredging activities is coordinated between the disposal and amenities (coral reef) sites where dumping windows are determined by realtime current meter data, indicating potential transport to the reef site. In the Pacific Northwest, "curtains" of dredge-related sediment may inhibit upstream spawning activities of valued fisheries resources and thus they are subject to similar temporal windows.
Mestas-Nunez, A.M. Orthogonality properties of rotated empirical modes. International Journal of Climatology, 20(12):1509-1516 (2000).
The properties (spatial orthogonality and temporal uncorrelatedness) of orthogonally-rotated empirical modes depend on the normalization of the modes, prior to rotation. It is shown here that these properties also depend on how the empirical modes are formulated. The preferred convention is one that allows us to reconstruct the data from the unrotated or rotated modes. When the empirical modes are normalized so that the spatial eigenvectors are unit length (i.e., EOFs), the rotated modes preserve spatial orthogonality but are no longer temporally uncorrelated. Relaxing the temporal orthogonality in this way does not prejudice conclusions that can be inferred regarding the temporal couplings of the rotated modes.
Mestas-Nunez, A.M., and D.B. Enfield. El Niño-Southern Oscillation: Canonical and non-canonical aspects. Proceedings, 24th Annual Climate Diagnostics and Prediction Workshop, Tucson, AZ, November 1-5, 1999. National Weather Service, 111-114 (2000).
The main goal of this paper is to investigate and compare the atmospheric signatures associated with the canonical ENSO and residual components of the SST anomaly variability in the eastern tropical Pacific. An expanded version of this paper will appear in the Journal of Climate (Mestas-Nuñez and Enfield, 2001).
Molinari, R.L., and J.F. Festa. Effect of subjective choices on the objective analysis of sea surface temperature data in the tropical Atlantic and Pacific Oceans. Oceanologica Acta, 23(1):3-14 (2000).
Many subjective choices are required to perform an objective interpolation (OI) analysis of environmental variables. Herein, we consider the effects on the statistical analysis of sea surface temperature (SST) using (1) a structure function or covariance analysis, (2) different analytical expressions to represent the statistics of the raw data, and (3) different historical SST data sets. The historical data sets are the well-sampled Comprehensive OceanAtmospheric Data Set (COADS) and the poorly sampled historical expendable bathythermograph (XBT) data set. Results from these analyses are used to generate error maps for a poorly-sampled, two month XBT array and a proposed well-sampled profiling float array. For the relatively data-rich COADS analysis, decorrelation scales are the same using either the structure function or covariance analyses. Results differ for the data-poor XBT analysis. Representative decorrelation scales in the Pacific (Atlantic) are about 11-14 (6-10) degrees in the zonal direction and 4-7 (3-6) degrees in the meridional direction. As COADS SST data are less precise than XBT SST data, error and signal variances are greater for the former. The choice of analytical fit to the raw data (needed to generate error maps) has a dramatic effect on the resulting uncertainty fields. Gaussian fits, because of their parabolic shape near the origin, result in smaller errors than exponential fits for the same observing array. Finally, the proposed float array can achieve the accuracies needed to resolve satisfactory upper layer heat content changes over larger areas than the present XBT network.
Morisseau-Leroy, N., M.K. Solomon, and J. Basu. Oracle 8i: Java Component Programming. Osborne McGraw-Hill (ISBN 0072127376), 697 pp. (2000).
No abstract.
Murillo, S.T., W.-C. Lee, and F.D. Marks. Evaluating the GBVTD-tropical center finding simplex algorithm. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 312-313 (2000).
The GBVTD simplex algorithm has been tested using axisymmetric and asymmetric analytic tropical cyclones by Lee et al. (1999). The algorithm objectively identifies the tropical cyclone center by maximizing the GBVTD-derived mean tangential wind field. Lee and Marks (1999) applied the GBVTD simplex algorithm to Typhoon Alex (1987). However, a true center was not available to verify the accuracy of the algorithm. This study applies the GBVTD simplex algorithm to Hurricane Danny (1997). The estimated storm track derived by the algorithm is compared to radar and aircraft storm fixes. The derived track is in good agreement with the true storm track within 2 km. Results will be presented that show how the GBVTD simplex algorithm improves the quality of the GBVTD retrieved wind analysis.
Nelsen, T.A., S.J. Stamates, B.J. Elkind, W.P. Dammann, and J.R. Proni. Field evaluation of the temporal and spatial variations in total suspended matter and current fields at Chesapeake Bay Site 104 and contiguous areas. Final Report, U.S. Army Corps of Engineers, MIPR No. W81W3@00604995, 47 pp. (2000).
No abstract.
Nolan, D.S., M.T. Montgomery, and P.D. Reasor. Studies of the wavenumber one instability in hurricane-like vortices. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 29-30 (2000).
No abstract.
Ooyama, K.V. A dynamic and thermodynamic foundation for modeling the moist atmosphere with classical thermodynamics and parameterized microphysics. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 561-562 (2000).
No abstract.
Otero, S., N. Morisseau-Leroy, N. Carrasco, and M.D. Powell. A distributed real-time hurricane wind analysis system. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 197-198 (2000).
No abstract.
Parrish, J.R., M.L. Black, S.H. Houston, P.P. Dodge, and J.J. Cione. The structure of Hurricane Irene over South Florida. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 456-457 (2000).
On October 15, 1999, Hurricane Irene made landfall on the southwest coast of Florida and tracked to the northeast across the peninsula before emerging into the Atlantic Ocean north of Palm Beach. Irene was a Category 1 hurricane at landfall with maximum sustained surface winds estimated at 65 kts and a central pressure of ~982 mb. A NOAA WP-3D aircraft conducted a landfall research mission during the time Irene was crossing Florida. The aircraft, operated by the Aircraft Operations Center (AOC) and staffed by scientists from HRD, flew at an altitude of 8,000 feet and completed a flight track that provided coverage over the South Florida Peninsula and adjacent coastal waters in the Gulf of Mexico, Florida Bay, and Atlantic Ocean. In addition to the in-situ wind and thermodynamic measurements at flight-level, observations from the airborne Doppler tail radar, lower-fuselage radar, GPS dropsondes, and step-frequency microwave radiometer (SFMR, surface wind speeds) were collected by the AOC and HRD crew. A detailed description of the wind and thermodynamic structure of Irene while over South Florida will be presented. Of particular interest is comparisons of flight-level wind measurements with surface observations from regular observing sites over land and from C-MAN and buoy measurements, and those from the GPS dropwindsondes and the SFMR. Satellite imagery showed that intense, deep convection was occurring over the center of Irene, obscuring the eye and eyewall that was visible on radar displays beneath the high clouds. An unusual aspect of Irene was the extremely dry air that was entraining into the west side of the storm and that may have contributed to some of the observed asymmetries and to the clear-air turbulence encountered by the P-3 aircraft.
Peng, T.-H., and F. Chai. Modeling the carbon cycle in the equatorial Pacific Ocean. Proceedings, Marine Environment: The Past, Present, and Future, Kaohsiung, Taiwan, January 26-28, 1999. Sueichan Press, 240-255 (2000).
An ocean ecosystem model of the equatorial Pacific Ocean has been developed with new and export productivity regulated by Si and Fe to synthesize and analyze data collected during the JGOFS process-study-oriented survey cruises in 1992. The data also include those obtained by NOAA/OACES cruises in concert with the JGOFS EqPac process study. The circulation model is based on the Modular Ocean Model of the NOAA/GFDL ocean general circulation model. The ecosystem model is originally formulated by Chai et al. (1996), and is now expanded to consist of nine components describing two sizes of phytoplankton, two sizes of zooplankton, two detritus pools, and three dissolved nutrients: silicate, nitrate, and ammonium. The carbonate chemistry is parameterized in the model to evaluate the variations of pCO2 and, hence, the CO2 flux across the air-sea interface. At this initial stage, a test case by using a 1D model is performed to simulate low-silicate, high-nitrate, and low-chlorophyll conditions in the equatorial Pacific, and to investigate how the carbon system behaves in this ecosystem structure. The model includes the vertical upwelling and diffusion processes. The modeled upwelling rate and vertical diffusivity, from a 3D circulation model, were initially averaged for the region with latitudes 5°S to 5°N, and longitude 180° to 90°W, the "cold tongue" of the equatorial Pacific. Temperature is used to calibrate model upwelling and vertical diffusion rates. Comparison of model results with the observations made during the NOAA/OACES EqPac 1992 expeditions indicates that the vertical profiles of DIC, NO3, and Si(OH)4 are consistent with the measurements made in the fall season when the ocean was in a normal non-El Niño condition. A tight fit of profiles between model and observation is not possible because of spatial variations of the observed values. A 3D simulation is required, which is in progress. The 1D model CO2 evasion rate is estimated to be 2.9 mol/m2/yr, which is consistent with the range of estimates from measurements made during non-El Niño conditions.
Powell, M.D. Performance of the HRD real-time Hurricane Wind Analysis System in 1999. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A232-A237 (2000).
No abstract.
Powell, M.D. Tropical cyclones during and after landfall. In Storms (Volume 1), R. Peilke, Sr. and R. Peikle, Jr. (eds.). Routledge, New York (ISBN 041517239X), 196-219 (2000).
No abstract.
Powell, M.D., and S.D. Aberson. Accuracy of U.S. hurricane landfall forecasts in the Atlantic basin (1976-1998). Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A138-A139 (2000).
No abstract.
Powell, M.D., and S.D. Aberson. Accuracy of U.S. hurricane landfall forecasts in the Atlantic basin (1976-1998). Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 326 (2000).
No abstract.
Powell, M.D., A. Lazar-Viront, and D. Bowman. Documentation of automatic weather station wind exposure in tropical cyclone areas. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A260-A264 (2000).
No abstract.
Powell, M.D., T.A. Reinhold, and R.D. Marshall. Tropical cyclone boundary layer wind variability. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J57 (2000).
No abstract.
Proni, J.R. Using acoustical methods to study and monitor the discharge of sewage and dredged-material in the coastal ocean. Proceedings, Fifth European Conference on Underwater Acoustics (ECUA 2000), Lyon, France, July 10-13, 2000. European Acoustics Association, Volume 1, 755-760 (2000).
Acoustical backscatter has been shown to be very effective in the study and monitoring of sewage efffluent and dredged material released into the coastal waters. Acoustical detection of a detrainment phenomenon in discharge plumes shows the extreme sensitivity of effluent distributions to small water column density changes. Acoustic measurements, as part of an ensemble of sensor systems, reveal turbidity changes occurring at environmentally valuable biological communities such as coral reefs and oyster beds. Examples of acoustic observations are presented.
Quilfen Y., A. Bentamy, P. Delecluse, K.B. Katsaros, and N. Grima. Prediction of sea level anomalies using ocean circulation model forced by scatterometer wind and validation using TOPEX/Poseidon data. IEEE Transactions on Geoscience and Remote Sensing, 38(4):1871-1884 (2000).
Uncertainties in the surface wind field have long been recognized as a major limitation in the interpretation of results obtained by oceanic circulation models. It is especially true in the tropical oceans, where the response to wind forcing is very strong on short time scales. The purpose of this paper is to show that these uncertainties can be greatly reduced by using spaceborne wind sensors that provide accurate measurements on a global basis. Surface winds over the global oceans have been measured by scatterometry since the launch of the European Remote Sensing Satellite (ERS-1) in August 1991 by the European Space Agency, Noordwijk, The Netherlands, and is currently provided by ERS-2, launched in April 1995. The ground-track wind vectors are processed to compute mean weekly surface winds onto a 1° square grid at the Institut Francais de Recherche pour l'Exploitation de la Mer (IFREMER), Plouzane, France. These winds are validated by comparison with the buoy array in the tropical Pacific Ocean, showing good agreement. In order to further evaluate this wind field, the three-dimensional ocean model OPA7 developed at Laboratoire d'Océanographie Dynamique et de Climatologie, Paris, France, is forced over the tropical oceans by the ERS-derived wind stress fields and by fields from the atmospheric model "Arpege/Climat." Selected ocean parameters are defined in order to validate the ocean model results with measurements of the tropical ocean and global atmosphere (TOGA) buoys in the Pacific Ocean. The ability of the model to describe the short scale (a few weeks to a few years) oceanic variability is greatly enhanced when the satellite-derived surface forcing is used. In this paper, we present further comparison of the ocean model results with the TOPEX-Poseidon altimeter measurements. Simulated and measured sea level variability are described over the three tropical oceans. The annual and semi-annual signals, as well as the interannual variability, partly linked to the El Niño-Southern Oscillation (ENSO) phenomenon, are well simulated by the OPA7 model when the satellite winds are used. Furthermore, it shows that the objective method, kriging technique, used to interpolate the mean ERS wind fields, dramatically reduces the effects of the satellite bandlike sampling. In the last part of this paper, we focus on the relationship between the wind stress anomalies and the sea level anomalies in the case of the 1997-1998 El Niño event. It clearly shows that sea level anomalies in the eastern and western parts of the Pacific are strongly linked to wind stress anomalies in the central Pacific. The forthcoming scatterometers aboard the METOP and ADEOS satellites will provide a much better coverage. It will enable the wind variability spatial and temporal scales to be resolved better, in order that wind uncertainties no longer blur the interpretation of ocean circulation numerical model results.
Reasor, P.D., and M.T. Montgomery. 3D alignment and co-rotation of weak, TC-like vortices via linear vortex Rossby waves. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 268-269 (2000).
No abstract.
Reasor, P.D., M.T. Montgomery, F.D. Marks, and J.F. Gamache. Low-wavenumber structure and evolution of the hurricane inner core observed by airborne dual-Doppler radar. Monthly Weather Review, 128(6):1653-1680 (2000).
The asymmetric dynamics of the hurricane inner-core region is examined through a novel analysis of high temporal resolution, three-dimensional wind fields derived from airborne dual-Doppler radar. Seven consecutive composites of Hurricane Olivia's (1994) wind field with 30-min time resolution depict a weakening storm undergoing substantial structural changes. The symmetric and asymmetric mechanisms involved in this transformation are considered separately. To zeroth order the weakening of the primary circulation is consistent with the axisymmetric vortex spindown theory of Eliassen and Lystad for a neutrally-stratified atmosphere. Vertical shear, however, increased dramatically during the observation period, leading to a strong projection of the convection onto an azimuthal wavenumber 1 pattern oriented along the maximum vertical shear vector. Recent theoretical ideas elucidating the dynamics of vortices in vertical shear are used to help explain this asymmetry. The role of asymmetric vorticity dynamics in explaining some of the physics of hurricane intensity change motivates a special focus on Olivia's vorticity structure. It is found that an azimuthal wavenumber 2 feature dominates the asymmetry in relative vorticity below 3-km height. The characteristics of this asymmetry deduced from reflectivity and wind composites during a portion of the observation period show some consistency with a wavenumber 2 discrete vortex Rossby edge wave. Barotropic instability is suggested as a source for the wavenumber 2 asymmetry through a series of barotropic numerical simulations. Trailing bands of vorticity with radial wavelengths of 5-10 km are observed in the inner core approximately 20 km from the storm center, and may be symmetrizing vortex Rossby waves. Elevated reflectivity bands with radial scales comparable to those of the vorticity bands, also near 20-25-km radius, may be associated with these vorticity features.
Roemmich, D., O. Boebel, Y. Desaubies, H. Freeland, B. King, P.-Y. Letraon, R.L. Molinari, W.B. Owens, S. Riser, U. Send, K. Takeuchi, and S. Wijffels. Argo: The global array of profiling floats. OCEANOBS99: International Conference on the Ocean Observing System for Climate, Saint Raphael, France, October 18-22, 1999. Centre National d'Etudes Spatiales, 12 pp. (2000).
A broad-scale global array of temperature/salinity (T/S) profiling floats, known as Argo, is planned as a major component of the ocean observing system, with deployment scheduled to begin in 2000. Conceptually, Argo builds on the existing upper-ocean thermal networks, extending their spatial and temporal coverage, depth range and accuracy, and enhancing them through addition of salinity and velocity measurements. The name Argo is chosen to emphasize the strong complementary relationship of the global float array with the Jason altimeter mission. For the first time, the physical state of the upper ocean will be systematically measured and assimilated in near real time. Objectives of Argo fall into several categories. Argo will provide a quantitative description of the evolving state of the upper ocean and the patterns of ocean climate variability, including heat and freshwater storage and transport. The data will enhance the value of the Jason altimeter through measurement of subsurface vertical structure (T(z), S(z)) and reference velocity, with sufficient coverage and resolution for interpretation of altimetric sea surface height variability. Argo data will be used for initialization of ocean and coupled forecast models, data assimilation, and dynamical model testing. A primary focus of Argo is seasonal to decadal climate variability and predictability, but a wide range of applications for high-quality global ocean analyses is anticipated. The initial design of the ARGO network is based on experience from the present observing system, on newly gained knowledge of variability from the TOPEX/Poseidon altimeter, and on estimated requirements for climate and high-resolution ocean models. Argo will provide 100,000 T/S profiles and reference velocity measurements per year from about 3000 floats distributed over the global oceans at 3-degree spacing. Floats will cycle to 2000 m depth every 10 days, with a 4-5 year lifetime for individual instruments. All Argo data will be publicly available in near real-time via the GTS, and in scientifically quality-controlled form with a few months delay. Global coverage should be achieved during the Global Ocean Data Assimilation Experiment, which together with CLIVAR and GCOS/GOOS, provide the major scientific and operational impetus for Argo. The design emphasizes the need to integrate Argo within the overall framework of the global ocean observing system. International planning for Argo, including sampling and technical issues, is coordinated by the Argo Science Team. Nations presently having Argo plans that include float procurement or production include Australia, Canada, France, Germany, Japan, the U.K., and the U.S.A., plus a European Union proposal. Combined deployments from these nations may exceed 700 floats per year as early as 2001. Broad participation in Argo by many nations is anticipated and encouraged either through float procurement, logistical support for float deployment, or through analysis and assimilation of Argo data.
Rogers, R.F. Surface-based modification of convectively-generated mesovortices and its implications for tropical cyclogenesis. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 151-152 (2000).
Numerical simulations have been performed on a long-lived midlevel mesovortex over the continental United States that was instrumental in initiating and organizing multiple cycles of deep convection. These simulations showed how the cycles of convective redevelopment amplify the mid- to upper-level warm core of the vortex, causing the cyclonic vorticity to strengthen in the midlevels and penetrate down into the lower troposphere, briefly reaching the surface. However, low-level cooling caused by convective and mesoscale downdrafts and adiabatic ascent offsets the impact of the mid- to upper-level warming, limiting the extent to which the cyclonic vorticity penetrates to the surface. In this study the impact of weakening the surface-based cold pool on the structure of the simulated mesovortex is investigated. Methods for weakening the cold pool in the simulations include: eliminating the convective (subgrid-scale) and mesoscale (resolvable-scale) downdrafts and replacing the lower land boundary with a water surface of varying temperatures. The resultant structures of the mesovortex for these different conditions are compared to explain how a mesovortex, with cyclonic vorticity initially confined to the midlevels, can grow downward to the surface, marking a key step in the tropical cyclogenesis process.
Rogers, R.F., J.M. Fritsch, and W.C. Lambert. A simple technique for using radar data in the dynamic initialization of a mesoscale model. Monthly Weather Review, 128(7):2560-2574 (2000).
A simple technique for using radar reflectivity to improve model initialization is presented. Unlike previous techniques, the scheme described here does not infer rain rates and heating profiles from assumed relationships between remotely-sensed variables and precipitation rates. Rather, the radar data are only used to tell the model when and where deep moist convection is occurring. This information is then used to activate the model's convective parameterization scheme in the grid elements where convection is observed. This approach has the advantage that the convective precipitation rates and heating profiles generated by the convective parameterization are compatible with the local (grid element) environment. The premise is that if convection is forced to develop when and where it is observed during a data assimilation period, convectively-forced modifications to the environment will be in the correct locations at the model initial forecast time and the resulting forecast will be more accurate. Three experiments illustrating how the technique is applied in the simulation of deep convection in a warm-season environment are presented: a control run in which no radar data are assimilated, and two additional runs where radar data are assimilated for 12 h in one run and 24 h in the other. The results indicate that assimilating radar data can improve a model's description of the mesoscale environment during the pre-forecast time period, thereby resulting in an improved forecast of precipitation and the mesoscale environment.
Rogers, R.F., S.S. Chen, J.E. Tenerelli, and M. Lonfat. A numerical study of the distribution of precipitation in Hurricane Bonnie (1998). Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 408-409 (2000).
As the damage that accompanied the floods from Hurricanes Georges and Mitch of 1998 and Floyd and Irene of 1999 dramatically highlighted, rainfall is one of the most significant impacts that accompanies a landfalling tropical cyclone. However, quantitative precipitation forecasting (QPF) is one of the most difficult problems in tropical cyclone forecasting. Rainfall measured at a particular location during the landfall of a tropical cyclone depends on many factors, such as the location with respect to the storm's track, the intensity and distribution of rainfall around the storm, the translational speed of the storm, and local effects such as topography and orientation of the coast. Understanding how these and other factors influence the precipitation distribution of landfalling hurricanes is an important step in improving hurricane QPFs. In this study, the distribution of precipitation from Hurricane Bonnie (1998) is explored by performing a numerical simulation using the primitive-equation, nonhydrostatic mesoscale model MM5. A six-day simulation is performed, and precipitation fields from the innermost domain (5-km grid length) are compared against observations. The wealth of observational information that accompanied the third phase of the NASA Convection and Moisture Experiment (CAMEX-3) field program, including the NASA TRMM satellite and various airborne observations from the NOAA P-3's and G-IV and the NASA DC-8 and ER-2, are used to validate the simulation. Statistics related to precipitation distribution, such as radial profiles of rainfall, radial-height profiles of hydrometeors, and probability distributions of various rainfall thresholds, are presented for the simulation and the observations from the TRMM satellite. Validation of these parameters will lend confidence in the skill of the model in capturing the precipitation distribution and enable an investigation of the physical processes governing the distribution to be performed in a later study.
Rogers, R.F., S.D. Aberson, J. Kaplan, S.B. Goldenberg, B. Damiano, R. McNamara, and J. Parrish. Pronounced upper-tropospheric temperature anomalies encountered by the Gulfstream-IV in the vicinity of deep convection. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 15-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., 275-279 (2000).
In several instances during the 1999 hurricane season, temperature sensors aboard the NOAA Gulfstream-IV (G-IV) aircraft measured significant temperature increases (some as large as 40°C) while flying between 41,000 and 45,000 feet in the vicinity of deep convection. Similar temperature anomalies have been encountered by commercial aircraft flying at similar altitudes and balloon measurements taken at high temporal frequency in the proximity of deep convection. In this presentation, the observations gathered from the G-IV are summarized and compared to observations taken previously. While it is still not certain whether or not the anomalies measured by the sensors aboard the G-IV last year owed their existence to real meteorological phenomena or to instrument deficiencies, it is important to document this occurrence, since the response of the aircraft's autopilot is to change altitude and airspeed. Suggestions for how to avoid this from happening again are also offered.
Sabine, C.L., R.H. Wanninkhof, R.M. Key, C. Goyet, and F.J. Millero. Seasonal CO2 fluxes in the tropical and subtropical Indian Ocean. Marine Chemistry, 72(1):33-53 (2000).
Improved estimates of the variability in air-sea CO2 fluxes on seasonal and interannual time scales are necessary to help constrain the net partitioning of CO2 between the atmosphere, oceans, and terrestrial biosphere. Few direct measurements of the carbon system have been made in the main Indian Ocean basin. In the mid 1990s, several global carbon measurement programs focused on the Indian Ocean, greatly increasing the existing carbon database for this basin. This study examines the combined surface CO2 measurements from three major U.S. programs in the Indian Ocean: the global carbon survey cruises, conducted in conjunction with the World Ocean Circulation Experiment (WOCE); the NOAA Ocean-Atmosphere Carbon Exchange Study (OACES) Indian Ocean survey; and the Joint Global Ocean Flux Study (JGOFS) Arabian Sea Process Study. These data are fit with multiparameter linear regressions as a function of commonly-measured hydrographic parameters. These fits are then used with NCEP/NCAR reanalysis and Levitus 94 gridded values to evaluate the seasonal variability of surface seawater CO2 in the tropical and subtropical Indian Ocean and to estimate the magnitude of the Indian Ocean as a net sink for atmospheric CO2. The net annual flux for the Indian Ocean (north of 36°S) was -12.4 ± 0.5 × 1012 mol of carbon (equivalent to -0.15 Pg C) in 1995. The relatively small net flux results from the very different surface water pCO2 distributions and seasonal variations in the northern and southern Indian Ocean. The equatorial and northern hemisphere regions have values that are generally above atmospheric values. During the southwest monsoon, pCO2 values in the Arabian Sea coastal upwelling region are among the highest observed in the oceans. The upwelling is seasonal in nature, however, and only affects a relatively small area. The Indian Ocean equatorial region generally has values slightly above atmospheric. Unlike the Pacific and Atlantic Oceans, however, no clear equatorial upwelling signature was observed in 1995. The Southern Hemisphere Indian Ocean, which represents the largest region by area, generally has values below atmospheric. The strongest undersaturations are observed in the austral winter, with summer values reaching near or slightly above atmospheric.
Sabine, C.L., R.A. Feely, R.M. Key, F.J. Millero, R.H. Wanninkhof, T.-H. Peng, A. Kozyr, J.L. Bullister, K. Lee, and M.F. Lamb. Anthropogenic CO2 distributions in the Pacific. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F692, OS72E-02 (2000).
As a part of the JGOFS synthesis and modeling project, researchers have been working to synthesize the WOCE/JGOFS/NOAA global carbon survey data to better understand carbon cycling in the oceans. Working with international investigators, we have compiled a Pacific Ocean data set with over 36,000 unique sample locations analyzed for at least two carbon parameters. These data are being used to estimate the distribution of anthropogenic CO2 in the Pacific using the delta-C technique. The physical and geochemical makeup of the Pacific waters, however, poses a particular challenge for the anthropogenic calculations. This measurement-based approach requires a number of assumptions that will be examined with respect to the Pacific. Preliminary estimates of the anthropogenic CO2 distribution indicate that the largest inventories are in the subtropical South and North Pacific. These distributions will be discussed and compared with three-dimensional global carbon model estimates.
Sabine, C.L., M.F. Lamb, J.L. Bullister, R.A. Feely, G.L. Johnson, R.M. Key, A. Kozyr, K. Lee, F.J. Millero, T.-H. Peng, and R.H. Wanninkhof. U.S. JGOFS team examines Pacific Ocean CO2 data quality. International WOCE Newsletter, 38:10-14 (2000).
No abstract.
Sainz-Trapaga, S.M., G.J. Goni, and T. Sugimoto. Identification and variability of the Kuroshio Extension and its northern branch from altimeter and hydrographic data during October 1992-August 1999. AGU 2000 Western Pacific Geophysics Meeting, Tokyo, Japan, June 27-30, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(22):WP80, OS41A-08 (2000).
The Kuroshio Extension to the east of Japan is an eastward-flowing, meandering jet with current velocities at its core over 100 cm s-1. This jet presents two quasi-stationary meanders with crests at 144°E and 150°E, and becomes wider and weaker to the east. These and other hydrodynamic modifications along its course can be related to the Shatsky Rise and the Emperor Sea Mounts, the main bathymetric features encountered by the Kuroshio Extension while flowing to the east. The Kuroshio Extension usually bifurcates between 150°E and 165°E, where its northern branch deviates northeastward along the Shatsky Rise approaching the subarctic front. Due to the lack of a long-term and continuous monitoring system, several aspects of the variability at the different regions of the Kuroshio Extension remains unclear. In this work, altimeter-derived sea height anomaly data from November 1992 to August 1999 is combined with climatological hydrographic data within a two-layer reduced gravity ocean model to identify the Kuroshio Extension and its northern branch, to estimate their baroclinic transports, and to study their variabilities, from the Japanese coast to 175°W. Results reveal different patterns of variability to the east and west of 155°E. East of 155°E, the Kuroshio Extension and its northern branch show a clear seasonal cycle. The location of the Kuroshio Extension and its northern branch have both maximum standard deviations from the mean between 150°E and 170°E. This area is characterized by the separation of the northern branch from the Kuroshio Extension. Moreover, the northern branch deviates to the northeast while the main path to the southeast, showing here its lower mean axis position. The location of the Bifurcation Point, partly determined by the bottom topography, correlates also with the Kuroshio Extension axis location and its transport.
Sandrik, A., C.W. Landsea, and B. Jarvinen. The North Florida hurricane of 29 September 1896: A historical case of extreme inland high winds. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 547-548 (2000).
No abstract.
Schmid, C., S.L. Garzoli, and R.L. Molinari. The intermediate depth circulation in the tropical Atlantic. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union,80(49):OS44, OS12D-18 (2000).
The intermediate circulation in the interior tropical Atlantic consists, according to the current knowledge, of several narrow zonal currents. Especially south of the equator, many changes of direction have been reported. Due to a lack of data, this flow pattern is only poorly resolved in space and time. Recent observations, both during the mid-1997 Seward Johnson cruise and from PALACE trajectories which extend from mid-1997 to today, allow a more detailed description of the intermediate depth circulation in the tropical Atlantic. The PALACE floats indicate that the intermediate layer flow between the equator and about 4°N consists of two different regimes which are separated by the eastern edge of the Mid-Atlantic Ridge. Velocities in the eastern regime are lower. The zonal flow in the two regimes is going in opposite directions at certain latitudes. We will discuss how the different regimes are related to the water masses and the interbasin exchange. Further south, between 4° and 2°S, westward velocities are clearly dominating the circulation. This latitude range is often occupied by the central South Equatorial Current. The flow between 8° and 4°S is governed by short periods (up to several months) of flow towards the east or west with only weak preferences of either one of the directions. This region is characterized by the (meandering) transition between the central South Equatorial Current and the South Equatorial Countercurrent. It has been proposed earlier that these two currents do not extend beyond about 8°W and that the intermediate water follows a cyclonic path east of 10°W between about 5° and 25°S. This could be seen as an intermediate expression of the Angola Gyre. Such a circulation is not visible in the PALACE trajectories to date.
Schmid, C., G. Siedler, and W. Zenk. Dynamics of intermediate water circulation in the subtropical South Atlantic. Journal of Physical Oceanography, 30(12):3191-3211 (2000).
The circulation of the low-salinity Antarctic Intermediate Water in the South Atlantic and the associated dynamical processes are studied, using recent and historical hydrographic profiles, Lagrangian and Eulerian current measurements as well as wind stress observations. The circulation pattern inferred for the Antarctic Intermediate Water supports the hypothesis of an anticyclonic basin-wide recirculation of the intermediate water in the subtropics. The eastward current of the intermediate anticyclone is fed mainly by water recirculated in the Brazil Current and by the Malvinas Current. An additional source region is the Polar Frontal Zone of the South Atlantic. The transport in the meandering eastward current ranges from 6 Sv to 26 Sv (1 Sv = 106 m3 s-1). The transport of the comparably uniform westward flow of the gyre varies between 10 Sv and 30 Sv. Both transports vary with longitude. At the western boundary near 28°S, in the Santos Bifurcation, the westward current splits into two branches. About three quarters of the 19 Sv at 40°W go south as an intermediate western boundary current. The remaining quarter flows northward along the western boundary. Simulations with a simple model of the ventilated thermocline reveal that the wind-driven subtropical gyre has a vertical extent of over 1200 m. The transports derived from the simulations suggest that about 90% of the transport in the westward branch of the intermediate gyre and about 50% of the transport in the eastward branch can be attributed to the wind-driven circulation. The structure of the simulated gyre deviates from observations to some extent. The discrepancies between the simulations and the observations are most likely caused by the interoceanic exchange south of Africa, the dynamics of the boundary currents, the nonlinearity, and the seasonal variability of the wind field. A simulation with an inflow/outflow condition for the eastern boundary reduces the transport deviations in the eastward current to about 20%. The results support the hypothesis that the wind field is of major importance for the subtropical circulation of Antarctic Intermediate Water followed by the interoceanic exchange. The simulations suggest that the westward transport in the subtropical gyre undergoes seasonal variations. The transports and the structure of the intermediate subtropical gyre from the Parallel Ocean Climate Model (Semtner/Chervin model) agree better with observations.
Schubert, W.H., S.A. Hausman, M. Garcia, K.V. Ooyama, and H.-C. Kuo. Potential vorticity in a moist atmosphere. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 563-564 (2000).
No abstract.
Shay, L., G.J. Goni, and P.G. Black. Effects of a warm oceanic feature on Hurricane Opal. Monthly Weather Review, 128(5):1366-1383 (2000).
On 4 October 1995, Hurricane Opal deepened from 965 to 916 hPa in the Gulf of Mexico over a 14-h period upon encountering a warm core ring (WCR) in the ocean shed by the Loop Current during an upper-level atmospheric trough interaction. Based on historical hydrographic measurements placed within the context of a two-layer model and surface height anomalies (SHA) from the radar altimeter on the TOPEX mission, upper-layer thickness fields indicated the presence of two warm core rings during September and October 1995. As Hurricane Opal passed directly over one of these WCRs, the 1-min surface winds increased from 35 to more than 60 m s-1, and the radius of maximum wind decreased from 40 to 25 km. Pre-Opal SHAs in the WCR exceeded 30 cm where the estimated depth of the 20°C isotherm was located between 175 and 200 m. Subsequent to Opal's passage, this depth decreased approximately 50 m, which suggests upwelling underneath the storm track due to Ekman divergence. The maximum heat loss of approximately 24 Kcal cm-2 relative to depth of the 26°C isotherm was a factor of 6 times the threshold value required to sustain a hurricane. Since most of this loss occurred over a period of 14 h, the heat content loss of 24 Kcal cm-2 equates to approximately 20 kW m-2. Previous observational findings suggest that about 10%-15% of upper-ocean cooling is due to surface heat fluxes. Estimated surface heat fluxes based upon heat content changes range from 2000 to 3000 W m-2 in accord with numerically simulated surface heat fluxes during Opal's encounter with the WCR. Composited AVHRR-derived SSTs indicated a 2°-3°C cooling associated with vertical mixing in the along-track direction of Opal except over the WCR where AVHRR-derived and buoy-derived SSTs decreased only by about 0.5°-1°C. Thus, the WCR's effect was to provide a regime of positive feedback to the hurricane rather than negative feedback induced by cooler waters due to upwelling and vertical mixing as observed over the Bay of Campeche and north of the WCR.
Shay, L.K., G.J. Goni, P.G. Black, S.D. Jacob, J.J. Cione, and E.W. Uhlhorn. Global analogues of deep warm upper ocean layers: Hurricane heat potential estimates. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J3-J4 (2000).
No abstract.
Smith, N.R., D.E. Harrison, R. Bailey, O. Alves, T. Delcroix, K. Hanawa, B. Keeley, G. Meyers, R.L. Molinari, and D. Roemmich. The role of XBT sampling in the ocean thermal network. OCEANOBS99: International Conference on the Ocean Observing System for Climate, Saint Raphael, France, October 18-22, 1999. Centre National d'Etudes Spatiales, 26 pp. (2000).
This paper evaluates the present role of the XBT program and proposes a strategy for the future under the assumption that there are other direct and indirect contributions to sampling the temperature and salinity of the ocean. Since the focus is on XBT sampling, the paper restricts its scope to the upper ocean, mostly above 1000 m. The conclusions of the paper are based on a study and workshop that were convened specifically to look at the design of the ship-of-opportunity network and to look at options for its implementation in the future under the assumption that Argo happens. The paper also addresses issues related to data distribution and management. The primary conclusion is that the network of the future should place greatest emphasis on line sampling, at intermediate to high densities, and assume that a proposed profiling float array, Argo, will largely take over the role formerly occupied by area (broadcast) sampling. It is argued that line sampling exclusively addresses several needs of the ocean observing system that cannot easily be addressed by other forms of sampling. Further, it is argued that such a mode complements other in-situ components such as moorings and floats, as well as remotely-sensed surface topography. A new network is outlined with a strategy for implementation that ensures continuity between existing and planned networks. We conclude the data management system that was established around the SOOP program requires substantial renovation if it is to adequately address the needs of the data gatherers and suppliers, and the data users (modelers, scientists, operational applications).
Spratt, S.M., F.D. Marks, P.P. Dodge, and D.W. Sharp. Examining the pre-landfall environment of mesovortices within a Hurricane Bonnie (1998) outer rainband. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 300-301 (2000).
No abstract.
Tenerelli, J.E., S.S. Chen, M. Lonfat, R. Foster, and R.F. Rogers. Surface winds in Hurricane Floyd: A comparison between numerical simulations, aircraft data, and QuikScat satellite data. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 418-419 (2000).
A principal benefit of numerical simulations of hurricanes is that they provide detailed, high-resolution information on the structure and evolution of the atmosphere that cannot be obtained through current observational techniques. However, simulations can be strongly dependent on the initial and boundary data, as well as on the physical parameterizations in the numerical model, and so it is necessary to compare simulation results with observational data when available. The objectives of this study are to: (1) validate model simulations of Hurricane Floyd with all available observations, including in-situ and remote sensing data sets; and (2) explore the impact of the observations on high-resolution model simulations. One important aspect of the model simulations is the surface wind field. The surface wind has a substantial impact on the fluxes of heat and moisture at the surface, which in turn have a large influence on the storm intensity and structure. Yet, near the surface, the model results are influenced greatly by the parameterization of boundary layer and surface processes. Hurricane Floyd presents an excellent opportunity for model-observation intercomparison of winds near the surface. Several swaths of data from NASA's QuikScat satellite were obtained while Floyd was over water. Additionally, surface winds derived from NOAA/HRD aircraft observations were obtained at several times during the life of the storm. In this study, we conduct a four-day long simulation of Floyd using the PSU/NCAR nonhydrostatic mesoscale model (MM5) with one fixed mesh and two levels of moving nested grid. We compare surface winds derived from QuikScat and aircraft data to the surface winds in our numerical simulation of Floyd. Additionally, we compare vertical profiles of reflectivity and hydrometeors from the simulations with those derived from the TMI and PR instruments on NASA's TRMM satellite. Although the TRMM swaths, the QuikScat swaths, and HRD data are not coincident in time, the MM5 simulations' continuity in time allows a comparison with all observational data sources. The MM5 can be used as a cross-validation platform. This model-observation comparison is the first step towards the goal of assimilating observed surface winds into the MM5.
Uhlhorn, E.W., K.B. Katsaros, and M.D. Powell. Assimilation of scatterometer-derived winds into real-time tropical cyclone surface wind analyses. Preprints, 10th Conference on Satellite Meteorology and Oceanography, Long Beach, CA, January 9-14, 2000. American Meteorological Society, Boston, 214-215 (2000).
No abstract.
Uhlhorn, E.W., P.G. Black, L.K. Shay, J.J. Cione, S.D. Jacob, and G.J. Goni. Warm core ocean features in the central and eastern Gulf of Mexico. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 147-148 (2000).
No abstract.
Wainer, I., P. Gent, and G.J. Goni. Annual cycle of the Brazil-Malvinas confluence region in the National Center for Atmospheric Research climate system model. Journal of Geophysical Research, 105(C11):26,167-26,177 (2000).
The objective of this study is to compare the mean and seasonal variability of the circulation in the southwest Atlantic with observations. The results used in the comparison are from the last 200 years of a 300-year control integration of the Climate System Model (CSM). The area of study includes the confluence region between the subtropical and subpolar waters represented by the Brazil and Malvinas Currents. The seasonal variation of transport and its relationship to changes in the wind stress forcing and in the sea surface temperature are examined and compared to available oceanographic observations. This study shows that a coarse resolution climate model, such as the CSM, can successfully reproduce major characteristics of the Brazil-Malvinas confluence seasonality, although the mesoscale features involving recirculation and meander dynamics are not resolved. The CSM transport values in the region of 38°S are consistent with hydrographically-derived values. The transport of the CSM Brazil Current is higher during austral summer and smaller during austral winter. Conversely, the Malvinas Current transport is weaker during austral summer and stronger during austral winter. This is also consistent with observations. The CSM seasonal cycle in transport associated with both the Brazil and Malvinas Currents and its meridional displacement is closely linked to the seasonal variations in the local wind stress curl. However, the displacement is much smaller in the model than in observations. The CSM results show that the latitudinal displacement of the 24°C and 17°C at the South American coast between austral summer and winter is 20° and 12°, respectively. This is very similar to the displacement seen in observations.
Walsh, E.J., C.W. Wright, D.C. Vandemark, W.B. Krabill, A.W. Garcia, S.H. Houston, M.D. Powell, P.G. Black, and F.D. Marks. Hurricane directional wave spectrum spatial variation in the open ocean and at landfall. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A116-A121 (2000).
The sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane in open water using the NASA/GSFC airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane research aircraft at 1.5 km height. The data were acquired on 24 August 1998 when Hurricane Bonnie was east of the Bahamas and moving slowly to the north. Two days later, the SRA documented the directional wave spectrum spatial variation again as Bonnie made landfall near Wilmington, North Carolina.
Walsh, E.J., C.W. Wright, D.C. Vandemark, W.B. Krabill, A.W. Garcia, S.H. Houston, M.D. Powell, P.G. Black, and F.D. Marks. Hurricane directional wave spectrum spatial variation at landfall. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 327-328 (2000).
No abstract.
Wang, C. A unified theory for the El Niño-Southern Oscillation. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, Florida, May 29-June 2, 2000. American Meteorological Society, Boston, J42-J43 (2000).
No abstract.
Wang, C. On the atmospheric responses to tropical Pacific heating during the mature phase of El Niño. Journal of Atmospheric Sciences, 57(22):3767-3781 (2000).
The atmospheric heating and sea surface temperature (SST) anomalies during the mature phase of El Niño are observed to show both eastern and western Pacific anomaly patterns, with positive anomalies in the equatorial eastern/central Pacific and negative anomalies in the off-equatorial western Pacific. The detailed spatial patterns of the heating anomalies differ from the SST anomalies. The heating anomalies are more equatorially confined than the SST anomalies, and maxima of positive and negative heating anomalies are located farther to the west than the SST anomalies. The Gill/Zebiak atmospheric model assumes that the atmospheric initial heating has the same spatial patterns as the SST anomalies. This assumption results in some unrealistic model simulations for El Niño. When the model heating anomaly forcing is modified to resemble the observed heating anomalies during the mature phase of El Niño, the model simulations have been improved to: (1) successfully simulate equatorial easterly wind anomalies in the western Pacific; (2) correctly simulate the position of maximum westerly wind anomalies; and (3) reduce unrealistic easterly wind anomalies in the off-equatorial eastern Pacific. This paper shows that off-equatorial western Pacific negative atmospheric heating (or cold SST) anomalies are important in producing equatorial easterly wind anomalies in the western Pacific. These off-equatorial cold SST anomalies in the western Pacific also contribute to equatorial westerly wind anomalies observed in the central Pacific during the mature phase of El Niño. Although off-equatorial cold SST anomalies in the western Pacific are smaller than equatorial positive SST anomalies in the eastern Pacific, they are enough to produce atmospheric responses of comparable magnitude to the equatorial eastern Pacific. This is because the atmospheric mean state is convergent in the western Pacific and divergent in the equatorial eastern Pacific. By either removing the atmospheric mean convergence or removing off-equatorial cold SST anomalies in the western Pacific, the atmospheric responses show no equatorial easterly wind anomalies in the western Pacific. In the Gill/Zebiak model, the mean wind divergence field is an important background state, whereas the mean SST is secondary.
Wang, C. The El Niño-Southern Oscillation. Proceedings, International Conference on Climate and Environment Variability and Predictability, Shanghai, China, August 7-11, 2000. International Commission on Dynamic Meteorology/International Association of Meteorology and Atmospheric Sciences, 126 (2000).
No abstract.
Wang, C., and R.H. Weisberg. The 1997-1998 El Niño evolution relative to previous Niño events. Journal of Climate, 13(2):488-501 (2000).
The evolution of the 1997-1998 El Niño is described using NCEP sea surface temperature (SST) and outgoing longwave radiation (OLR) data, NCEP-NCAR reanalysis sea level pressure (SLP) fields, and FSU surface wind data. From November 1996 to January 1997, the eastern Pacific is characterized by equatorial cold SST and high SLP anomalies, while the western Pacific is marked by off-equatorial warm SST anomalies and off-equatorial anomalous cyclones. Corresponding to this distribution are high OLR anomalies in the equatorial central Pacific and low OLR anomalies in the off-equatorial far western Pacific. The off-equatorial anomalous cyclones in the western Pacific are associated with a switch in the equatorial wind anomalies over the western Pacific from easterly to westerly. These equatorial westerly anomalies then appear to initiate early SST warmings around the date line in January/February 1997 and around the far eastern Pacific in March 1997. Subsequently, both the westerly wind and warm SST anomalies, along with the low OLR anomalies, grow and progress eastward. The eastward propagating warm SST anomalies merge with the slower westward spreading warm SST anomalies from the far eastern Pacific to form large-scale warming in the equatorial eastern and central Pacific. The anomaly patterns in the eastern and central Pacific continue to develop, reaching their peak values around December 1997. In the western Pacific, the off-equatorial SST anomalies reverse sign from warm to cold. Correspondingly, the off-equatorial SLP anomalies in the western Pacific also switch sign from low to high. These off-equatorial high SLP anomalies initiate equatorial easterly wind anomalies over the far western Pacific. Like the equatorial westerly wind anomalies that initiate the early warming, the equatorial easterly wind anomalies over the far western Pacific appear to have a cooling effect in the east and, hence, help facilitate the 1997-1998 El Niño decay. The paper also compares the 1997-1998 El Niño with previous warm events, and discusses different ENSO mechanisms relevant to the 1997-1998 El Niño.
Wilkerson, J.C., and J.R. Proni. Monitoring tropical and subtropical rainfall over the ocean using underwater acoustic techniques. Proceedings, Fifth European Conference on Underwater Acoustics (ECUA 2000), Lyon, France, July 10-13, 2000. European Acoustics Association, Volume 1, 741-746 (2000).
Measurements of underwater sound produced by rain were made at three U.S. coastal sites to determine feasibility and limitations of acoustic detection and classification of rainfall over water. In the study, concurrent radar observations were used to identify convective and stratiform regions of the precipitating clouds overhead. Acoustic-derived classifications of rain type, based on information in the 4-30 kHz frequency band, were in general agreement with radar-derived classifications. A correlation of 0.9 was found to exist between sound spectrum levels (in decibels) in the 4-10 kHz frequency band and rain rate, suggesting the use of acoustical methods for rainfall estimation. Testing of the acoustic technique in deep water is currently underway at the U.S. Navy Atlantic Undersea Test and Evaluation Center, Bahamas. Examples of acoustic spectra are presented.
Willoughby, H.E. Costs and benefits of hurricane forecasting. Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 557 (2000).
No abstract.
Willoughby, H.E. The proposed upgrade of NOAA's Gulfstream-IV for tropical cyclone reconnaissance. Minutes, 54th Interdepartmental Hurricane Conference, Houston, TX, February 14-18, 2000. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A239-A241 (2000).
No abstract.
Willoughby, H.E. and R.W. Jones. Are the beta gyres really normal modes? Preprints, 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, 187-188 (2000).
No abstract.
Wilson, W.D., and K.D. Leaman. The NOPP Year of the Ocean drifter program: A new Lagrangian perspective on IAS circulation. AGU 2000 Ocean Sciences Meeting, San Antonio, TX, January 24-28, 2000. Supplement to EOS, Transactions, American Geophysical Union, 80(49):OS234, OS41E-24 (2000).
Since March of 1998, 130 "WOCE-type" drifting buoys, drogued at 15 m, have been launched in the Gulf of Mexico and the Caribbean Sea and its approaches, providing in excess of 15,000 "drifter days" of data to date. Buoys were provided by the U.S. National Ocean Partnership Program (NOPP); launch coordination was provided by scientists at NOAA/AOML and UM/RSMAS; and logistical and data processing support was provided by the NOAA/AOML Global Drifter and Data Assembly Centers. Buoys were launched with the cooperation of commercial ships, the Colombian Navy, the U.S. Coast Guard, and research vessels working in the region. Drifter track figures and data have been made available in real time via the World-Wide Web at www.IASlinks.org and www.drifters.doe.gov. Repeated launches were concentrated in three areas: The Panama-Colombia gyre in the southwest Caribbean; the island passages in the eastern Caribbean; and in the North Brazil Current rings, a primary source of mesoscale variability upstream of the Caribbean. This strategy was designed to maintain maximum coverage within the IAS, as well as study propagation of variability through the region, the formation and intensification of the Caribbean Current, and the structure and permanence of the circulation within the Panama-Colombia gyre. Individual drifter tracks are shown which illustrate pathways and time scales of connectivity within the region. There is also sufficient data coverage to estimate fields of mean velocity, velocity variability, and several different indicators of dispersal. Drifter-derived fields are compared to existing estimates of mean velocity (ship drift, climatological, geostrophic, and Ekman estimates) and variability (ship drift, altimetry). Discussion will focus on the usefulness of Lagrangian measurements for larval and other transport studies, and diagnostics of the large-scale IAS circulation field. A companion presentation by Leaman and Wilson will focus on drifters in the Panama-Colombia Gyre and comparison with the high-resolution MICOM model. The merits of a cooperative plan for maintaining long-term drifter coverage of the IAS will be considered.
Wilson, W.D., and K.D. Leaman. Transport pathways through the Caribbean: The tropical origins of the Gulf Stream. Current, 16(1):14-18 (2000).
No abstract.
Wright, C.W., E.J. Walsh, D.C. Vandemark, W.B. Krabill, A.W. Garcia, S.H. Houston, M.D. Powell, P.G. Black, and F.D. Marks. Hurricane directional wave spectrum spatial variation in the open ocean. Proceedings, 10th Conference on Interaction of the Sea and Atmosphere, Ft. Lauderdale, FL, May 29-June 2, 2000. American Meteorological Society, Boston, J1-J2 (2000).
No abstract.
Yvon-Lewis, S.A. Methyl bromide in the atmosphere and ocean. IGACtivities Newsletter, 19:9-12 (2000).
No abstract.
Zhang, J.-Z. Shipboard automated determination of trace concentrations of nitrite and nitrate in oligotrophic water by gas-segmented continuous flow analysis with a liquid waveguide capillary flow cell. Deep-Sea Research, Part I, 47(6):1157-1171 (2000).
Incorporation of a liquid waveguide capillary flow cell to a gas-segmented continuous flow auto-analyzer significantly enhances the sensitivity of automated colorimetric analysis. Nanomolar concentrations of nitrite and nitrate in oligotrophic surface seawater can be accurately determined. The advantages of this technique are low detection limit, high precision, and automation for rapid analysis of a large number of samples. This technique has been successfully used on shipboard measurements of about 1000 seawater samples during a one-month cruise in North Atlantic.
Zhang, J.-Z. The use of pH and buffer intensity to quantify the carbon cycle in the ocean. Marine Chemistry, 70(1-3):121-131 (2000).
The pH of seawater is governed by the content of total carbon dioxide and ionic equilibra between hydrogen ions and various inorganic carbon species in seawater. Buffer intensity is defined as a measure of the ability of seawater to accommodate the addition of acid or base without appreciable pH change. It can be calculated from pH and total carbon dioxide of seawater. pH data in conjunction with buffer intensity can be used to quantify the carbon cycle in the ocean. The total amount of acid that has been released or consumed by any biogeochemical processes can be calculated from the change in pH multiplied by buffer intensity of seawater, dCH = d(beta-pH). This approach has been used to quantify the remineralization process in the Antarctic Intermediate Water in the South Pacific. Based on the observational data (pH, total carbon dioxide, O2, and nutrient measurements on P18 cruise), calculated elemental remineralization ratios are 173, 107, and 14.3 for O/P, C/P and N/P, respectively. The dissolution of calcium carbonate accounts for 21.5% of carbon increased from the remineralization in the Antarctic Intermediate Water.
Zhang, J.-Z., and C.R. Kelble. Gas-segmented continuous flow analysis of iron in water with a long liquid waveguide capillary flow cell. Proceedings, 8th International Conference on Flow Analysis, Warsaw, Poland, June 25-29, 2000. International Union of Pure and Applied Chemistry, 107 (2000).
A long liquid waveguide capillary flow cell has been successfully adapted into a gas-segmented continuous flow auto-analyzer for trace analysis of iron. The flow cell was made of a new material, Teflon AF-2400, that has a refractive index (1.29) lower than water (1.33). Total reflection of light can be achieved when the light beams intersect the water/AF-2400 Teflon tubing interfaces at greater than critical angle. Teflon AF-2400 is superior to currently used materials in both refractivity and mechanical stability. This allows the construction of a long liquid waveguide capillary flow cell in helical, rather than linear shape, with compact dimension. Small sample volumes are required since the internal volume of a 2 m-long liquid waveguide capillary flow cell with 550 µm ID is only approximately 0.5 cm3. According to the Lambert-Beer law, the absorbance of a sample in spectrophotometry is proportional to the light path length in the flow cell. Utilization of this long flow cell significantly enhances the sensitivity of automated colorimetric analysis of iron by the ferrozine method. Nanomolar concentrations of iron in natural water can be accurately determined. The advantages of this technique are low detection limit, small sample volume, high precision, and automation for rapid analysis of a large number of samples. This technique has potential application in many spectrophotometric detections to augment the capability of gas-segmented continuous flow analysis and flow injection analysis.
Zhang, J.-Z., C.J. Fischer, and P.B. Ortner. Comparison of open tubular cadmium reactors and packed cadmium columns in automated gas-segmented continuous flow nitrate analysis. International Journal of Environmental Analytical Chemistry, 76(2):99-113 (2000).
Detailed procedures are provided for preparing packed cadmium columns to reduce nitrate to nitrite. Experiments demonstrated the importance of conditioning both open tubular cadmium reactor (OTCR) and packed copper-coated cadmium columns to achieve 100% reduction efficiency. The effects of segmentation bubbles in the OTCR upon reduction efficiency and baseline noise in nitrate analysis are investigated using an auto-analyzer. Metal particles derived from segmentation bubbles in OTCR result in i nterference with continuous flow analyses. Therefore, packed columns are recommended for determination of low level nitrate in natural waters.
Zhang, J.-Z., R.H. Wanninkhof, and K. Lee. New production in oligotrophic waters: Estimation based on diel cycle of nitrate. Proceedings, Joint Global Ocean Flux Study (JGOFS) Open Science Conference, Bergen, Norway, April 13-17, 2000. JGOFS International Project Office, 76-77 (2000).
New production can be estimated from accurate measurements of inventory change in nitrate at nM levels in the photic zone. A strong diel cycle was observed in nitrate concentrations in response to photosynthesis in the eastern North Atlantic during the GASEX-98 cruise. During a diel study, nitrate concentration was 92 nM in the morning and decreased to 12 nM by 6 p.m. It increased after dark, presumably due to the diffusive flux from the nitracline. Oxygen showed a similar diel cycle with a change in concentration of about 2 µM. The vertical eddy diffusivity was derived from temporal changes in concentrations of a deliberate tracer, SF6, below the mixed layer. Together with vertical nitrate distributions, the nitrate flux from nitracline throughout the nighttime can account for a nitrate concentration of 102 nM by morning, which is in good agreement with measured nitrate of 92 nM at 6 a.m. The new production estimated from changes of nitrate inventory in the photic zone during the day was 28 mmole C/m2 d. Increases in the mixed layer nitrate were observed during storm events that deepened the mixed layer and brought the nitrate to the surface. The storm-induced nitrate disappeared within two days, indicating a rapid uptake by phytoplankton. The relative importance of sporadic storm events versus daily diffusive flux in supply nitrate to new production can be estimated based on nitrate inventory changes in the photic zone.
Zhang, J.-Z., C.W. Mordy, L.I. Gordon, A. Ross, and H.E. Garcia. Temporal trends in deep ocean Redfield ratios. Science, 289:1839 (2000).
No abstract.
**1999**
Aberson, S.D. Ensemble-based products to improve tropical cyclone forecasting. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 843-844 (1999).
No abstract.
Aberson, S.D. Targeting and sampling strategies to improve hurricane forecasts. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 105-107 (1999).
No abstract.
Aberson, S.D., and J.L. Franklin. Impact on hurricane track and intensity forecasts of GPS dropwindsonde observations from the first-season flights of the NOAA Gulfstream-IV jet aircraft. Bulletin of the American Meteorological Society, 80(3):421-428 (1999).
In 1997, the Tropical Prediction Center (TPC) began operational Gulfstream-IV jet aircraft missions to improve the numerical guidance for hurricanes threatening the continental United States, Puerto Rico, and the Virgin Islands. During these missions, the new generation of Global Positioning System dropwindsondes were released from the aircraft at 150-200-km intervals along the flight track in the environment of the tropical cyclone to obtain profiles of wind, temperature, and humidity from flight level to the surface. The observations were ingested into the global model at the National Centers for Environmental Prediction, which subsequently served as initial and boundary conditions to other numerical tropical cyclone models. Because of a lack of tropical cyclone activity in the Atlantic basin, only five such missions were conducted during the inaugural 1997 hurricane season. Due to logistical constraints, sampling in all quadrants of the storm environment was accomplished in only one of the five cases during 1997. Nonetheless, the dropwindsonde observations improved mean track forecasts from the Geophysical Fluid Dynamics Laboratory hurricane model by as much as 32%, and the intensity forecasts by as much as 20% during the hurricane watch period (within 48 h of projected landfall). Forecasts from another dynamical tropical cyclone model (VICBAR) also showed modest improvements with the dropwindsonde observations. These improvements, if confirmed by a larger sample, represent a large step toward the forecast accuracy goals of TPC. The forecast track improvements are as large as those accumulated over the past 20-25 years, and those for forecast intensity provide further evidence that better synoptic-scale data can lead to more skillful dynamical tropical cyclone intensity forecasts.
Albrecht, B., T. Faber, A. Savtchenko, D. Churchill, F.D. Marks, and P.G. Black. Surface-based remote sensing of a landfalling tropical storm. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 489-492 (1999).
No abstract.
Atlas, D., C.W. Ulbrich, F.D. Marks, E. Amitai, and C.R. Williams. Systematic variation of drop size and radar-rainfall relations. Journal of Geophysical Research, 104(D6):6155-6169 (1999).
Time histories of the characteristics of the drop size distribution of surface disdrometer measurements collected at Kapingamarangi Atoll were partitioned for several storms using rain rate, R, reflectivity factor Z, and median diameter of the distribution of water content D0. This partitioning produced physically based systematic variations of the drop size distribution (DSD) and Z-R relations in accord with the precipitation types viewed simultaneously by a collocated radar wind profiler. These variations encompass the complete range of scatter around the mean Z-R relations previously reported by Tokay and Short (1996) for convective and stratiform rain and demonstrate that the scatter is not random. The systematic time or space variations are also consistent with the structure of mesoscale convective complexes with a sequence of convective, transition, and stratiform rain described by various authors. There is a distinct inverse relation between the coefficient A and the exponent of the Z-R relations which has been obscured in prior work because of the lack of proper discrimination of the rain types. Contrary to previous practice, it is evident that there is also a distinct difference in the DSD and the Z-R relations between the initial convective and the trailing transition zones. The previously reported Z-R relation for convective rain is primarily representative of the transition rain that was included in the convective class. The failure of present algorithms to distinguish between the initial convective and the trailing transition rains causes an erroneous apportionment of the diabatic heating and cooling and defeats the primary intent of discriminating stratiform from convective rains.
Alvarez-Zarikian, C., P.L. Blackwelder, T. Hood, T.A. Nelsen, and C.M. Featherstone. A century of hydrological variability in the lower Everglades National Park as interpreted from stable isotopes on ostracods and foraminifers. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 198 (1999).
Stable isotopic analysis of selected ostracods and foraminifers were carried out from high-resolution sediment cores collected from Oyster and Florida Bays. The core localities provide distinctive environmental conditions in which the effects of freshwater runoff, rainfall, and, consequently, salinity, can be assessed. Oyster Bay lies at the end of the Shark River Slough and is an area that experiences extreme salinity fluctuations due to the interaction between freshwater runoff and marine water input from the Gulf of Mexico due to tidal flow. A second core, collected near Jimmy Key, in the center of Florida Bay, provides a contrasting salinity history in which salinity has remained close to marine during this century. Stable isotope (13C, 18O) trends of ostracods and foraminifers at Oyster Bay and Jimmy Key suggest a general transition to more saline conditions over this time period. Relative abundance of salinity-sensitive species confirmed this observations. Moreover, stable isotopes indicate an increase in salinity variability over time, which is represented in the microfaunal assemblage by survivor-mode dominance by highly-tolerant species, both in foraminifers and ostracods, that occurred during a period of drought or highly evaporative conditions during the mid to late 1980s that also lead to reduced flow from Shark River Slough. Fluctuations on stable isotope values appeared to be more a direct response to regional rainfall than freshwater runoff; however, distinct patterns can be temporally correlated to freshwater management strategies by the South Florida Water Management District.
Alvarez-Zarikian, C., T. Hood, P. Blackwelder, T.A. Nelsen, P. Swart, H. Wanless, J. Trefry, and W.-J. Kang. Paleoecological significance of temporal fluctuations in assemblages and isotopic composition of ostracoda and foraminifera from Florida Bay. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. EOS, Transactions, American Geophysical Union, 80(17):S178, OS31A-17 (1999).
Microfaunal populations and stable isotopic analysis of selected ostracods and benthic foraminifers were examined from high-resolution sediment cores in the lower Everglades/Florida Bay ecosystem. Microfaunal characteristics and population fluctuations can be temporarily related to forces of natural (hurricanes, precipitation) and anthropogenic (historic practices from the South Florida Water Management District [SFWMD]) origin since the turn of the century. Dramatic shifts in community structure are observed in both microfaunal groups and are represented by major swings in species diversity and dominance, and total loss of numerous species. Before the 1960s, significant crashes in the community structure of both groups were temporally correlated with major hurricanes, but fairly rapid recoveries indicate a relatively resilient community. Community changes during the 1970s were most systematic, and temporally correlate with changes in SFWMD policy. In Oyster Bay, the 1970s Monthly Water Allocation Plan corresponds to a boom period for ostracods and benthic foraminfers possibly due to a more efficient water flow and exchange. This is followed by a dramatic crash in both groups corresponding to the start of the SFWMD's Rainfall Plan and the closing of the Buttonwood Canal in the early 1980s, from which neither community has recovered. Sediment cores from Oyster Bay and near Jimmy Key in Florida Bay show a reduction in the number of species and a pronounced dominance of survivor-type species since that time. delta-180 data from ostracods and foraminifers shift to heavier values during this period, indicating drought conditions. Microfaunal and isotopic data from this study complemented with an analysis of historical rainfall, gauged freshwater flow, and limited near-shore salinity data show a significant increase in the magnitude and range of seasonal salinity variability due to fluctuations in regional rainfall and the current water management plan, resulting in significantly drier conditions in the lower portion of Shark River Slough.
Amat, L.R., M.D. Powell, and S.H. Houston. A real-time, Internet-based application for the archival, quality control, and analysis of hurricane surface wind observations. Preprints, 15 International Conference on Interactive Information and Processing Systems for Meteorology, Oceanography, and Hydrology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 573-576 (1999).
No abstract.
Atakturk, S.S., and K.B. Katsaros. Wind stress and surface waves observed on Lake Washington. Journal of Physical Oceanography, 29(4):633-650 (1999).
New results from turbulent flux measurements made over Lake Washington include the following:

(1) The only direct measure of the vertical transport of the horizontal momentum, heat, and matter in the surface boundary layer is the so-called eddy correlation method. However, even if the measurement errors are negligible, the results obtained from point observations may show large scatter due to lack of stationarity and horizontal homogeneity in the turbulent field and to the sampling variability. Scatter may be greatly reduced by spatial averaging. In this study, such an effect is achieved by determining the surface roughness length; hence, the neutral drag coefficient from the measured wave height spectrum, which reflects the atmospheric input integrated over the fetch. Applicability and usefulness of the approach for general field measurements and remote sensing is discussed.

(2) The evolution of the wave field observed on Lake Washington agrees in peak frequency and the slope of the equilibrium range parameter as a function of "wind forcing" with other observations, while the magnitude is significantly smaller (by a factor of 2.1) than the values obtained from larger bodies of water. Based on the results obtained from a wave model, we attribute this observed difference to the narrower width of the water body on Lake Washington. These findings indicate that the state-of-the-art spectral parameterization of surface waves has limitations in describing the observations from a natural but small body of water.

Baringer, M.O., and R.L. Molinari. Atlantic Ocean baroclinic heat flux at 24-26°N. Geophysical Research Letters, 26(3):353-356 (1999).
The spatially varying, interior geostrophic baroclinic heat flux component of the total meridional oceanic heat flux near 24°N in the Atlantic Ocean is examined using four transatlantic hydrographic sections including the October 1957 Discovery II IGY section, the September 1981 Atlantis section, the August 1992 Hesperides section, t he February 1998 Ronald H. Brown section and the 1982 Levitus and the Lozier, Owens, Curry climatologies. The 1992 section is complemented by shorter western boundary sections obtained concurrently during the Trident cruise. We find an average southward baroclinic heat flux of 0.9 0.3 PW with an annual cycle amplitude of 0.3 PW. More than 90% of the annual cycle is captured within 30° of the western boundary.
Baringer, M.O., and J.F. Price. A review of the physical oceanography of the Mediterranean Outflow. Marine Geology, 155(1-2):63-82 (1999).
The physical oceanography of the Mediterranean Sea is reviewed with particular emphasis on the Mediterranean outflow in the Gulf of Cadiz. In this region the dense Mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor. The major energy source for the plume comes from the release of potential energy as the plume descends the continental slope, and the major energy sink is work against bottom stress, which is as large as 4 Pa where the plume begins to descend the continental slope. In this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography. The Mediterranean plume entrains the overlying North Atlantic Central Water and thereby loses much of its density anomaly. The mixed Mediterranean water becomes neutrally buoyant in the lower portion of the North Atlantic thermocline near Cape St. Vincent. There are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open North Atlantic. The temperature, salinity and volume of the Mediterranean water in the Strait of Gibraltar and in the Gulf of Cadiz appear to be roughly constant since modern measurements have been made. The estimated westward transport of Mediterranean water has gone down considerably as direct measurement techniques have been applied. A recent estimate is that the westward transport of pure Mediterranean water is only about a half a Sv (1 Sv = 106 m3/s); the transport of mixed Mediterranean water in the western Gulf of Cadiz is larger by about a factor of three or four because of the entrainment of North Atlantic water.
Bentamy, A.P., P. Queffeulou, Y. Quilfen, and K.B. Katsaros. Ocean surface wind fields estimated from satellite active and passive microwave instruments. IEEE Transactions on Geoscience and Remote Sensing, 37(5):2469-2486 (1999).
This study examines the consistency of surface wind speeds estimated from the European Remote Sensing Satellite (ERS-1) scatterometer, ERS-1 altimeter, and the special sensor microwave/imager (SSM/I). The goal is to combine these wind estimates to produce surface wind fields. With this in mind, a comparison with buoy wind measurements and comparison among the three sensors is performed. According to the in-situ data, the rms errors of the three wind estimates are all within 2 m/s. The differences between the remotely-sensed and buoy wind speeds are studied according to atmospheric and oceanic variables, and their impact is shown. A large data base is obtained from the comparisons among the three sensor winds. The rms values of the differences between the scatterometer and the altimeter and between the scatterometer and the SSM/I are 1.67 and 1.45 m/s, respectively. There is no global bias between the scatterometer and the SSM/I, but between the scatterometer and the altimeter wind speeds, the bias is about 0.3 m/s. Furthermore, it is shown that the difference between the scatterometer and the altimeter wind estimates is dependent on the significant wave height, while the difference between the scatterometer and the SSM/I winds is dependent on the integrated water vapor content. The comparison enables some corrections to be made for consistency and combining products. The use of combining scatterometer, altimeter, and SSM/I wind estimates is illustrated by two examples.
Berberian, G.A., and A.Y. Cantillo. Oceanographic conditions in the Gulf of Mexico and Straits of Florida: Fall 1976. NOAA Data Report, OAR AOML-36 (PB2000-106209), 64 pp. (1999).
NOAA conducted an investigation in the Gulf of Mexico and the Straits of Florida of oceanographic conditions and nutrients and trace metal levels in seawater during September and October 1976 aboard the NOAA Ship Researcher. This report lists the chemical data obtained from 118 stations. Collection and analyses methodologies, as well as results, are described.
Bishop, C.H., S. Majumdar, I. Szunyogh, Z. Toth, and S.D. Aberson. Using ensembles to simulate the impact of targeted observations. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 117-118 (1999).
No abstract.
Black, M.L. Recent observations of the hurricane eyewall: Unusual and complex structure. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 313-316 (1999).
No abstract.
Black, M.L., and J.L. Franklin. Recent observations of the convective structure associated with low-level wind maxima in the hurricane eyewall. Preprints, 29th International Conference on Radar Meteorology, Montreal, Quebec, Canada, July 12-16, 1999. American Meteorological Society, Boston, 370-373 (1999).
No abstract.
Black, R.A., and J. Hallett. Electrification of the hurricane. Journal of the Atmospheric Sciences, 56(12):2004-2028 (1999).
A survey of reports of electrical activity in hurricanes and typhoons from flight notes and personal experience (18 years, >230 eyewall penetrations for R. A. Black; ~20 years for J. Hallett, plus that of others at the Hurricane Research Division), and perusal of flight notes dating from 1980, show that lightning in and within 100 km or so of the eyewall is usually sparse. However, occasionally, significant electrical activity (>one flash per minute) occurs in or near the eyewall. National Oceanic and Atmospheric Administration WP-3D aircraft penetrations through a number of storms relate the lightning occurrence to strong vertical velocity (>10 m s-1) and the presence of supercooled liquid cloud droplets extending to temperatures below 20°C. Specific measurements of cloud properties during eyewall penetrations show that the supercooled cloud water content increases with upward velocities > ~5.0 m s-1, as does the presence of large (>2 mm) supercooled drops. Measurements at temperatures >-13°C show that the transition of supercooled cloud water to ice along an outward radial in all systems is associated with local electric fields (occasionally >20 kV m-1) and negative charge above positive charge. In systems with stronger vertical velocity there is a larger region of supercooled cloud extending to lower temperatures where charge separation may occur, as judged by the presence of regions containing graupel, small ice, and cloud droplets. The ratio of ice to supercooled water increases radially outward from the eyewall and depends upon altitude (temperature). The spatial distribution of charge is further influenced by the relation of vertical velocity to the radial flow, with the upper charge regions tending to be advected outward. In symmetrical, mature hurricanes, supercooled water usually occurs only in regions at temperatures above about -5°C. The upward transport of supercooled cloud water is limited by a balance between water condensed in the eyewall updraft and its erosion by ice in downdrafts descending in the outward regions of the eyewall. This ice originates from both primary and secondary ice nucleation in the updraft. This is consistent with an exponential increase in ice concentration, as the rate at which the ice particle concentrations increase depends on the production of secondary particles by preexisting graupel, some of which ultimately grow into new graupel, and its outward transport in the anvil flow aloft. Penetrations at temperatures as low as -15°C show the presence of electric fields consistent with specific laboratory-derived criteria for charge separated during ice-graupel collisions, given that a liquid water-dependent sign reversal temperature may occur. Such a reversal may result from either a changing temperature in the vertical, a changing cloud liquid water content in the horizontal, or a combination of the two. Since cloud-to-ground (CG) lightning can be observed with remote detection networks that provide the polarity and frequency of CG lightning, there is potential that hurricane evolution may be detected remotely and that lightning may be usable as an indicator of a change in the storm intensity and/or track.
Blackwelder, P.L., T. Hood, C. Alvarez-Zarikian, P. Swart, C.M. Featherstone, and T.A. Nelsen. Historical salinity effects on microfauna in the lower Everglades and Florida Bay. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 181 (1999).
A multi-faceted approach examines the relationship between microfauna (ostracods and foraminifers) and salinity in Florida Bay and its environs. Several "levels" of microfaunal population variability were examined, which range from overall population characteristics to species- and individual-specific isotopic composition and morphological differences. These levels include documentation of changes in population abundance and diversity over time with variability in salinity and individual species-specific responses, which produce decipherable salinity-related records. Isotopic composition of stained individuals living in the surface sediment in each environment, as well as documentation of salinity related ostracod valve morphological change are studied. Attention is focused on those species capable of withstanding the greatest salinity fluctuations. Core and surface microfaunal populations at Oyster Bay, Jimmy Key, and First National Bank are compared and contrasted. These three sites comprise distinct environmental regimes with well-documented salinity records. Oyster Bay has experienced the greatest salinity variability of the three sites, as well as freshest overall conditions over the last 100 years. The Jimmy Key site, in the center of the Bay, has experienced higher average salinity with less variability over this period. Taphonomic microfaunal studies routinely utilize population characteristics as a tool for paleoenvironmental reconstruction. This study extends population work to include species and individual-specific characteristics, which may record salinity variability. In addition to the field and core collections, we are culturing ostracods to examine isotopic and morphological relationships under controlled conditions. This multi-faceted approach extends our population characterization work to include documentation of physiological response of individuals within the microfaunal populations to documented changes in salinity. This data will extend the use of microfauna as indicators of modern and paleo-salinity change.
Boebel, O., C. Schmid, and W. Zenk. Kinematic elements of Antarctic Intermediate Water in the western South Atlantic. Deep Sea Research, Part II, 46(1-2):355-392 (1999).
The northward flowing Antarctic Intermediate Water (AAIW) is a major contributor to the large-scale meridional circulation of water masses in the Atlantic. Together with bottom and thermocline water, AAIW replaces North Atlantic Deep Water that penetrates into the South Atlantic from the north. On the northbound propagation of AAIW from its formation area in the southwestern region of the Argentine Basin, the AAIW progresses through a complex spreading pattern at the base of the main thermocline. This paper presents trajectories of 75 subsurface floats, seeded at AAIW depth. The floats were acoustically tracked, covering a period from December 1992 to October 1996. Discussions of selected trajectories focus on mesoscale kinematic elements that contribute to the spreading of AAIW. In the equatorial region, intermittent westward and eastward currents were observed, suggesting a seasonal cycle of the AAIW flow direction. At tropical latitudes, just offshore the intermediate western boundary current, the southward advection of an anticyclonic eddy was observed between 5°S and 11°S. Farther offshore, the flow lacks an advective pattern and is governed by eddy diffusion. The westward subtropical gyre return current at about 28°S shows considerable stability with the mean kinetic energy to eddy kinetic energy ratio being around one. Farther south, the eastward deeper South Atlantic Current is dominated by large-scale meanders with particle velocities in excess of 60 cm s-1. At the Brazil-Falkland Current Confluence Zone, a cyclonic eddy near 40°S, 50°W seems to act as injector of freshly mixed AAIW into the subtropical gyre. In general, much of the mixing of the various blends of AAIW is due to the activity of mesoscale eddies, which frequently reoccupy similar positions.
Boebel O., C. Schmid, G. Podesta, and W. Zenk. Intermediate water in the Brazil-Malvinas Confluence Zone: A Lagrangian view. Journal of Geophysical Research, 104(C9):21,063-21,082 (1999).
The subsurface flow within the subantarctic and subtropical regions around the Brazil-Malvinas Confluence Zone is studied, using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the South American shelf. The trajectories are mapped against sea-surface flow patterns as visible in concurrent satellite sea-surface temperature images, with focus on the November 1994 and October/November periods. The unprecedented employment of Lagrangian-S diagrams enables us to trace the advection of patches of fresh Antarctic Intermediate Water (AAIW) from the Confluence Zone into the subtropical region. The fresh AAIW consists of a mixture of subtropical AAIW and Malvinas Current core water. Within the subtropical gyre, these patches are discernible for extended periods and drift over long distances, reaching north to 34.26°S and east to 40.26°W. The cross-frontal migration of quasi-isobaric floats across the Confluence Zone from the subtropical to the subantarctic environment is observed on three occasions. The reverse process, float migration from a subpolar to a subtropical environment was observed once. These events were located near 40.26°S, 50.26°W, the site of a reoccurring cold core feature. Subsurface float and SST data comparison reveals similarities with analogous observations made in the Gulf Stream (Rossby, 1996) where cross-frontal processes were observed close to meander crests. The limited number of floats of this study and the complex structure of the Brazil-Malvinas Confluence Zone, however, restricts the analysis to a description of two events.
Boebel, O., R.E. Davis, M. Ollitrault, R.G. Peterson, P.L. Richardson, C. Schmid, and W. Zenk. Direct observations of the western South Atlantic intermediate depth circulation. Geophysical Research Letters, 26(21):3329-3332 (1999).
The subsurface oceanic circulation is an important part of the Earth climate system. Subsurface currents traditionally are inferred indirectly from distributions of temperature and dissolved substances, occasionally supplemented by current meter measurements. Neutrally-buoyant floats, however, now enable us to obtain for the first time directly measured intermediate depth velocity fields over large areas such as the western South Atlantic. Here, our combined data set provides unprecedented observations and quantification of key flow patterns, such as the Subtropical Gyre return flow (12 Sv; 1 Sverdrup = 106 m3 s-1), its bifurcation near the Santos Plateau and the resulting continuous narrow and swift northward intermediate western boundary current (4 Sv). This northward flowing water passes through complex equatorial flows and finally enters into the North Atlantic.
Bosart, L.F., W.E. Bracken, J. Molinari, C.S. Velden, and P.G. Black. Environmental influences on the rapid intensification of Hurricane Opal (1995) over the Gulf of Mexico. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 983-984 (1999).
No abstract.
Bourles, B., R.L. Molinari, E. Johns, W.D. Wilson, and K.D. Leaman. Upper layer currents in the western tropical North Atlantic (1989-1991). Journal of Geophysical Research, 104(C1):1361-1376 (1999).
Shipboard Acoustic Doppler Current Profiler (ADCP) measurements and hydrographic observations of temperature, salinity, and dissolved oxygen are used to examine the upper water column flow field in the North Brazil Current (NBC) retroflection region of the western tropical Atlantic Ocean. Observations are presented from six cruises, one conducted in August 1989 and the other five conducted during the Western Tropical Atlantic Experiment (WESTRAX) between January 1990 and September 1991. The upper water column is divided into two layers, an upper thermocline layer located between the surface and the 24.5 sigma theta isopycnal surface, and a lower subthermocline layer located between the 24.5 and 26.75 isopycnals. In the upper layer the NBC retroflects north of the equator to form the eastward flowing North Equatorial Counter Current (NECC). During the six cruises the retroflection appeared complete. However, data coverage did not extend shoreward of the 200 m isobath, so the possibility of a continuous flow over the shelf still remains. There were also indications of several NBC rings which had apparently separated from the NBC retroflection and drifted to the northwest towards the eastern Caribbean Sea. North of the NBC retroflection and the NECC, the North Equatorial Current (NEC) flows west as the southern limb of the subtropical gyre. Part of the NEC is observed to retroflect cyclonically to join the eastward NECC flow. In the lower layer, beneath the NBC, the North Brazil Undercurrent (NBUC) retroflects to feed the eastward North Equatorial Undercurrent (NEUC). To the north, a deeper component of the NEC recurves to also contribute to the NEUC.
Boutin, J., J. Etcheto, Y. Dandonneau, D.C.E. Bakker, R.A. Feely, H.Y. Inoue, M. Ishii, R.D. Ling, P.D. Nightingale, N. Metzl, and R.H. Wanninkhof. Satellite sea surface temperature: A powerful tool for interpreting in-situ pCO2 measurements in the equatorial Pacific Ocean. Tellus B, 51(2):490-508 (1999).
In order to determine the seasonal and interannual variability of the CO2 released to the atmosphere from the equatorial Pacific, we have developed pCO2-temperature relationships based upon shipboard oceanic CO2 partial pressure measurements, pCO2, and satellite sea surface temperature, SST, measurements. We interpret the spatial variability in pCO2 with the help of the SST imagery. In the eastern equatorial Pacific, at 5°S, pCO2 variations of up to 100 µatm are caused by undulations in the southern boundary of the equatorial upwelled waters. These undulations appear to be periodic with a phase and a wavelength comparable to tropical instability waves, TIW, observed at the northern boundary of the equatorial upwelling. Once the pCO2 signature of the TIW is removed from the Alize II cruise measurements in January 1991, the equatorial pCO2 data exhibit a diel cycle of about 10 µatm with maximum values occurring at night. In the western equatorial Pacific, the variability in pCO2 is primarily governed by the displacement of the boundary between warm pool waters, where air-sea CO2 fluxes are weak, and equatorial upwelled waters which release high CO2 fluxes to the atmosphere. We detect this boundary using satellite SST maps. East of the warm pool, DELTA-P is related to SST and SST anomalies. The 1985-1997 CO2 flux is computed in a 5° wide latitudinal band as a combination of DELTA-P and CO2 exchange coefficient, K, deduced from satellite wind speed, U. It exhibits up to a factor 2 seasonal variation caused by K-seasonal variation and a large interannual variability, a factor 5 variation between 1987 and 1988. The interannual variability is primarily driven by displacements of the warm pool that makes the surface area of the outgassing region variable. The contribution of DELTA-P to the flux variability is about half of the contribution of K. The mean CO2 flux computed using either the Liss and Merlivat (1986) or the Wanninkhof (1992) K-U parameterization amounts to 0.11 GtC yr-1 or to 0.18 GtC yr-1, respectively. The error in the integrated flux, without taking into account the uncertainly on the K-U parameterization, is less than 31%.
Bove, M.C., J.B. Elsner, C.W. Landsea, X. Niu, and J.J. O'Brien. Effect of El Niño on U.S. landfalling hurricanes, revisited. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 278-281 (1999).
No abstract.
Broecker, W.S., S. Sutherland, and T.-H. Peng. A possible 20th-century slowdown of Southern Ocean deep water formation. Science, 286(5442):1132-1135 (1999).
Chlorofluorocarbon-11 inventories for the deep Southern Ocean appear to confirm physical oceanographic and geochemical studies in the Southern Ocean, which suggests that no more than 5 × 106 cubic meters per second of ventilated deep water is currently being produced. This result conflicts with conclusions based on the distributions of the carbon-14/carbon ratio and a quasi-conservative property, PO4, in the deep sea, which seem to require an average of about 15 × 106 cubic meters per second of Southern Ocean deep ventilation over about the past 800 years. A major reduction in Southern Ocean deep water production during the 20th century (from high rates during the Little Ice Age) may explain this apparent discordance. If this is true, a seesawing of deep water production between the northern Atlantic and Southern Oceans may lie at the heart of the 1500-year ice-rafting cycle.
Broecker, W.S., E. Clark, D.C. McCorkle, T.-H. Peng, I. Hajdas, and G. Bonani. Evidence for a reduction in the carbonate ion content of the deep sea during the course of the Holocene. Paleoceanography, 14(6):744-752 (1999).
The paleo carbonate ion proxy proposed by Broecker et al. (1999) is applied in a search for trends in the Holocene acidity of waters in the transition zone between North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). A clear signal emerges that the carbonate ion content of waters in this zone declined during the last 8000 years. In order to determine whether this decline represents a strengthening of the northward penetrating tongue of low CO3 content AABW or a global reduction of CO3 ion, measurements were made on a core from the Ontong Java Plateau in the western equatorial Pacific. Evidence for a similar decline in CO3 ion over the course of the Holocene was obtained, lending support of the latter explanation. Such a drop is consistent with the recent finding by Indermuhle et al. (1999) that the CO2 content of the atmosphere (as recorded in the Taylor Dome Antarctica ice core) rose by 20 to 25 ppm during the last 8000 years.
Butler, J.H., D.B. King, and S.A. Yvon-Lewis. Computation of the air-sea exchange coefficient from halocarbon disequilibria. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S46, A31C-10 (1999).
Studies conducted by NOAA during the past decade show that it is possible to use measurements of halocarbon saturation anomalies to calculate air-sea gas transfer velocities. These methods provide independent, averaged measures of air-sea transfer in the open ocean and are based upon the exchange of halocarbon across the air-sea interface on a broad scale; the source and sink are both ubiquitous. Computations can be made for conservative halocarbons, such as CFC-11 or CFC-12, for a hydrolyzable halocarbon such as CH3CCl3, or even for a chemically and biologically reactive compound such as CH3Br, if accompanied by measures of production and degradation. During GasEx-98, we acquired data on a number of trace halocarbons from which we can estimate air-sea exchange. The method that appears to be most useful with respect to this data set involves computations from disequilibria of conservative gases (e.g., CFCs) during heating of a water mass. Unfortunately, the waters during much of the cruise were not sufficiently warm for hydrolysis of CH3CCl3 to be the dominant loss mechanism. Nevertheless, disequilibrium computations for this gas did require consideration of hydrolysis. We also attempted to obtain air profiles of halocarbons, but most gases were not sufficiently supersaturated for this to be reliable. Exceptions were CH3I and isoprene (a hydrocarbon), both of which were highly supersaturated and which, under limited sampling conditions, yielded reasonable profiles in the air.
Butler, J.H., D.B. King, S.A. Yvon-Lewis, J.M. Lobert, S.A. Montzka, and J.W. Elkins. Seasonal and temporal variability in the distribution of methyl bromide in the surface ocean. International Union of Geodesy and Geophysics, XXII General Assembly, Birmingham, England, July 18-30, July 1999. IUGG99 Abstracts, A110 (1999).
The ocean is both the largest source and the second largest sink for methyl bromide (CH3Br) in the atmosphere, yet we still don't fully understand how the ocean regulates the atmospheric burden of this gas, nor can we predict accurately how the oceanic fluxes of methyl bromide will respond to global change. From first-order calculations, it is clear that the steady-state, net flux of this gas from the ocean will act in opposition to changes in the atmospheric burden. However, the distribution of the oceanic sources and sinks of CH3Br appears to be patchy on both small and large scales. The open oceans are typically undersaturated in CH3Br, with coastal waters typically supersaturated. Warm waters tend to be undersaturated; cooler waters can be super- or undersaturated. However, there are significant exceptions to any generalities. Although the chemical degradation of dissolved CH3Br is predominantly a function of sea-surface temperature, production appears to be mainly biological and there is strong evidence for biological degradation as well. Here, we examine the distribution of methyl bromide from recent studies of its saturation in the Pacific, Atlantic, and Southern Oceans to examine spatial and temporal dependencies upon its net flux and, consequently, its production and degradation.
Cantillo, A.Y., L. Pikula, and K. Hale. Preliminary data and document rescue of material relevant to the south Florida ecosystem. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 246 (1999).
There are significant amounts of unpublished documents and data on the marine and estuarine environment of Florida that are so far unavailable to the scientific community, academia, and the general public. These data and documents are important because they represent the Florida coastal ecosystems in times past, and are the basis for comparing past with current conditions. Currently, an innovative prototype data and document rescue effort is underway that combines the expertise of a senior scientist with that of librarians. Its main purpose is to inventory unpublished documents and data, perform a quality-assurance review of the scientific content, convert the material to electronic and printed form, and make it available through printed and online resources. If the data and documents are not rescued, they will be lost as printed material physically deteriorates, personnel retire, and corporate memory disappears. Examples of rescued documents relevant to the south Florida ecosystem are presented and the data and document rescue approach discussed.
Cantillo, A.Y., K. Hale, R. Caballero, E. Collins, and L. Pikula. Environmental history of Biscayne Bay. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 218 (1999).
Biscayne Bay is surrounded on the north by the growing urban areas of Dade County, which includes Miami and Miami Beach, and on the south by the sparsely inhabited Homestead area and the northern Florida Keys. Its environmental history is closely related to the development of the Greater Miami area. Urban development of the northern part of the Bay during the 1920s began the decline that remained largely unchecked until the early 1970s. Recently, environmental degradation of the Bay has reversed. This work describes the major events impacting the Bay's ecosystem and how it has changed over time.
Carsey, T.P. Shipboard measurements of active nitrogen gases during INDOEX. AGU 1999 Fall Meeting, San Francisco, CA, December 13-17, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(46):F162, A22A-01 (1999).
A suite of active nitrogen gases (NO, NO2, and NOy) were measured on board the NOAA ship Ronald H. Brown during the INDOEX experiment during February-March 1999. The cruise track included crossing of the Indian Ocean ITCZ, as well as several air mass types in that region including clean marine and heavily anthropogenically influenced air masses. The results will be presented and discussed in the context of related meteorological and chemical data.
Checkley, D.M., P.B. Ortner, F.E. Werner, L.R. Settle, and S.R. Cummings. Spawning habitat of the Atlantic menhaden in Onslow Bay, North Carolina. Fisheries Oceanography, 8:22-36 (1999).
The Continuous, Underway Fish Egg Sampler (CUFES) was used to sample pelagic eggs of the Atlantic menhaden (Brevoortia tyrannus) from a 3-m depth off North Carolina in winter 1993-1994 and 1994-1995. Simultaneous measurements were made of temperature, salinity, and the concentration of chlorophyll a. The maximal concentration of eggs was 346 eggs m-3. Eggs were highly aggregated in patches which occurred between the Gulf Stream and mid-shelf fronts (17-23°C, 36.0-36.4 ppm). Unexpectedly, eggs were found almost exclusively in water of 20-60 m (mode 20 m) bottom depth. Thus, spawning appears related to bathymetry as well as hydrography. Variograms for egg concentration indicated a mean (± SE) patch scale of 3.6 ± 1.7 km and a high degree of spatial variance explained by CUFES sampling. Lagrangian modeling of particles moving in response to tides, winds, and a prescribed flow from the north indicated that the region of observed, maximal occurrence of eggs is favorable for the retention of eggs and larvae on the shelf adjacent to inlets used to enter nursery areas.
Cione, J.J., P.G. Black, and S.H. Houston. Cooling and drying within the hurricane near-surface environment? Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 1027-1030 (1999).
No abstract.
Cook, S.K. Vertical thermal structure of midshelf waters: Water temperatures and climatological conditions south of New England, 1974-1983. NOAA Technical Report, NMFS-134, 43 pp. (1999).
No abstract.
DeMaria, M., and J. Kaplan. An updated Statistical Hurricane Intensity Prediction Scheme (SHIPS) for the Atlantic and eastern North Pacific basins. Weather and Forecasting, 14(3):326-337 (1999).
Updates to the Statistical Hurricane Intensity Prediction Scheme (SHIPS) for the Atlantic basin are described. SHIPS combines climatological, persistence, and synoptic predictors to forecast intensity changes using a multiple regression technique. The original version of the model was developed for the Atlantic basin and was run in near-real time at the Hurricane Research Division beginning in 1993. In 1996, the model was incorporated into the National Hurricane Center operational forecast cycle, and a version was developed for the eastern North Pacific basin. Analysis of the forecast errors for the period 1993-1996 shows that SHIPS had little skill relative to forecasts based upon climatology and persistence. However, SHIPS had significant skill in both the Atlantic and east Pacific basins during the 1997 hurricane season. The regression coefficients for SHIPS were rederived after each hurricane season since 1993 so that the previous season's forecast cases were included in the sample. Modifications to the model itself were also made after each season. Prior to the 1997 season, the synoptic predictors were determined only from an analysis at the beginning of the forecast period. Thus, SHIPS could be considered a "statistical-synoptic" model. For the 1997 season, methods were developed to remove the tropical cyclone circulation from the global model analyses and to include synoptic predictors from forecast fields, so the current version of SHIPS is a "statistical-dynamical" model. It was only after the modifications for 1997 that the model showed significant intensity forecast skill.
Dickerson, R.R., K.P. Rhoads, T.P. Carsey, S.J. Oltmans, J.P. Burrows, and P.J. Crutzen. Ozone in the remote marine boundary layer: A possible role for halogens. Journal of Geophysical Research, 104(D17):21,385-21,395 (1999).
On the spring 1995 cruise of the National Oceanic and Atmospheric Administration research vessel Malcolm Baldrige, we measured very large diurnal variations in ozone concentrations in the marine boundary layer. Average diurnal variations of about 32% of the mean were observed over the tropical Indian Ocean. We simulated these observations with the Model of Chemistry in Clouds and Aerosols, a photochemical box model with detailed aerosol chemistry. The model was constrained with photolysis rates, humidity, aerosol concentrations, NO, CO, and O3 specified by shipboard observations and ozonesondes. Conventional homogeneous chemistry, where ozone photolysis to O(1D) and HOx chemistry dominate ozone destruction, can account for a diurnal variation of only about 12%. On wet sea-salt aerosols (at humidities above the deliquesence point), absorption of HOBr leads to release of BrCl and Br2, which photolyze to produce Br atoms that may provide an additional photochemical ozone sink. After eight days of simulation, these Br atoms reach a peak concentration of 1.2 × 107 cm-3 at noon and destroy ozone through a catalytic cycle involving BrO and HOBr. Reactive Br lost to HBr can be absorbed into the aerosol phase and reactivated. The model predicts a diurnal variation in O3 of 22% with aerosol-derived Br reaction explaining much, but not all, of the observed photochemical loss. The lifetime of ozone under these conditions is short, about two days. These results indicate that halogens play an important role in oxidation processes and the ozone budget in parts of the remote marine boundary layer.
Digby, S., T. Antczak, R. Leben, G. Born, S. Barth, R. Cheney, D. Foley, G.J. Goni, G. Jacobs, and L. Shay. Altimeter data for operational use in the marine environment. Proceedings, Oceans '99 MTS/IEEE Conference, Seattle, WA, September 13-16, 1999. Marine Technology Society, 605-613 (1999).
TOPEX/Poseidon has been collecting altimeter data continuously since October 1992. Altimeter data have been used to produce maps of sea surface height, geostrophic velocity, significant wave height, and wind speed. This information is of proven use to mariners as well as to the scientific community. Uses of the data include commercial and recreational vessel routing, ocean acoustics, input to geographic information systems developed for the fishing industry, identification of marine mammal habitats, fisheries management, and monitoring ocean debris. As with sea surface temperature data from the Advanced Very High Resolution Radiometer (AVHRR) in the late 1980s and early 1990s, altimeter data from TOPEX/Poseidon and ERS-1 and -2 are in the process of being introduced to the marine world for operational maritime use. It is anticipated that over the next few years companies that specialize in producing custom products for shipping agencies, fisheries, and yacht race competitors will be incorporating altimeter data into their products. The data are also being incorporated into weather and climate forecasts by operational agencies both in the United States and Europe. This paper will discuss these products, their uses, operational demonstrations, and means of accessing the data.
Doddridge, B.G., W.T. Luke, C.A. Piety, R.R. Dickerson, A.M. Thompson, J.C. Witte, J.E. Johnson, T.S. Bates, P.K. Quinn, and T.P. Carsey. Trace gas and aerosols over the Atlantic Ocean during the ACE-Aerorsols cruise. AGU 1999 Fall Meeting, San Francisco, CA, December 13-17, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(46):F163, A22A-09 (1999).
The ACE-Aerosols cruise was conducted on board the NOAA R/V Ronald H. Brown (R-104) on January 14-February 20, 1999. This paper focuses on measurements conducted during a North-South Atlantic Ocean transect from Norfolk, Virginia to Cape Town, South Africa, January 14-February 8, 1999. Hourly-averaged marine boundary layer (MBL) carbon monoxide data ranged from 105 to 200 ppbv and 45 to 75 ppbv in the northern and southern hemisphere (SH), respectively. Aerosol optical depth showed significant variability along the same transect, with elevated values dominated by upper level transport from Africa. Hourly MBL ozone data ranged from 6 to 40 ppbv, showing a diurnal cycle superimposed upon a strong hemispheric gradient, and were strongly influenced by several pollution episodes, corroborated by bulk aerosol chemistry data. Using these tracers, along with computed air parcel trajectories, cruise data indicate substantial influence of Saharan, equatorial, and SH subtropical regions of Africa on the remote Atlantic Ocean MBL.
Dodge, P.P., R.W. Burpee, and F.D. Marks. The kinematic structure of a hurricane with sea-level pressure less than 900 mb. Monthly Weather Review, 127(6):987-1004 (1999).
A National Oceanic and Atmospheric Administration aircraft recorded the first Doppler radar data in a tropical cyclone with a minimum sea level pressure (MSLP) <900 mb during a reconnaissance mission in Hurricane Gilbert on 14 September 1988, when its MSLP was ~895 mb. A previous mission had found an MSLP of 888 mb, making Gilbert the most intense tropical cyclone yet observed in the Atlantic basin. Radar reflectivity identified the hurricane eye, inner and outer eyewalls, a stratiform region between the eyewalls, and an area outside the outer eyewall that contained a few rainbands but that had mostly stratiform rain. Pseudo-dual Doppler analyses depict the three-dimensional kinematic structure of the inner eyewall and a portion of the outer eyewall. The vertical profiles of tangential wind and reflectivity maxima in the inner eyewall are more erect than in weaker storms, and winds >50 m s-1 extended to 12 km, higher than has been reported in previous hurricanes. The inner eyewall contained weak inflow throughout most of its depth. In contrast, the portion of the outer eyewall described here had shallow inflow and a broad region of outflow. The stratiform region between the two eyewalls had lower reflectivities and was the only region where the vertically incident Doppler radar data seemed to show downward motion below the freezing level. Gilbert's structure is compared with other intense Atlantic and eastern North Pacific hurricanes with MSLP >900 mb. Storms with lower MSLP have higher wind speeds in both inner and outer eyewalls, and wind speeds >50 m s-1 extend higher in storms with lower MSLP. Hurricanes Gilbert and Gloria (1985), the strongest Atlantic hurricanes yet analyzed by the Hurricane Research Division, had different outer eyewall structures. Gloria's outer eyewall had a deep region of inflow, while Gilbert's inflow layer was shallow. This may explain differences in the subsequent evolution of the two storms.
Dodge, P.P., S.H. Houston, W.-C. Lee, J.F. Gamache, and F.D. Marks. Windfields in Hurricane Danny (1997) at landfall from combined WSR-88D and airborne Doppler radar data. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 61-62 (1999).
No abstract.
Donnelly, W.J., J.R. Carswell, R.E. McIntosh, P.S. Chang, J.C. Wilkerson, F.D. Marks, and P.G. Black. Revised ocean backscatter models at C and Ku-bands under high wind conditions. Journal of Geophysical Research, 104(C5):11,485-11,498 (1999).
A series of airborne scatterometer experiments designed to collect C and Ku-band ocean backscatter data in regions of high ocean surface winds has recently been completed. Over 100 hours of data were collected using the University of Massachusetts C and Ku-band scatterometers, CSCAT and KUSCAT. These instruments measure the full azimuthal normalized radar cross section (NRCS) of a common surface area of the ocean simultaneously at four incidence angles. Our results demonstrate limitations of the current empirical models, CMOD4, SASSII and NSCAT1, that relate ocean backscatter to the near surface wind at high wind speeds. The discussion focuses on winds in excess of 15 m/sec in clear atmospheric conditions. The scatterometer data is collocated with measurements from ocean data buoys and GPS dropsondes, and a Fourier analysis is performed as a function of wind regime. A three-term Fourier series is fit to the backscatter data, and a revised set of coefficients is tabulated. These revised models, CMOD4HW and KUSCAT1, are the basis for a discussion of the NRCS at high wind speeds. Our scatterometer data show a clear over prediction of the derived NRCS response to high winds based on the CMOD4, SASSII and NSCAT1 models. Furthermore, saturation of the NRCS response begins to occur above 15 m/sec. Sensitivity of the upwind and crosswind response is discussed with implications towards high wind speed retrieval. wind speed retrieval.
Ellsberry, R.L., and F.D. Marks. The Hurricane Landfall Workshop summary. Bulletin of the American Meteorological Society, 80(4):683-685 (1999).
No abstract.
Enfield, D.B., and E.J. Alfaro. The dependence of Caribbean rainfall on the interaction of tropical Atlantic and Pacific Oceans. Journal of Climate, 12(7):2093-2103 (1999).
Seasonally-stratified analyses of rainfall anomalies over the Intra-Americas Sea and surrounding land areas and of onset and end dates of the Central American rainy season show that the variability of the tropical Atlantic sea surface temperature anomaly (SSTA) is more strongly associated with rainfall over the Caribbean and Central America than is tropical eastern Pacific SSTA. Seasonal differences include the importance of antisymmetric configurations of tropical Atlantic SSTA in the dry season but not in the rainy season. Both oceans are related to rainfall, but the strength of the rainfall response appears to depend on how SSTA in the tropical Atlantic and eastern Pacific combine. The strongest response occurs when the tropical Atlantic is in the configuration of a meridional dipole (antisymmetric across the ITCZ) and configuration of a meridional dipole (antisymmetric across the ITCZ) and the eastern tropical Pacific is of opposite sign to the tropical North Atlantic. When the tropical North Atlantic and tropical Pacific are of the same sign, the rainfall response is weaker. The rainy season in lower Central America tends to start early and end late in years that begin with warm SSTs in the tropical North Atlantic, and the end dates are also delayed when the eastern equatorial Pacific is cool. This enhancement of date departures for zonally antisymmetric configurations of SSTA between the North Atlantic and Pacific is qualitatively consistent with the results for rainfall anomalies.
Enfield, D.B., and A.M. Mestas-Nunez. Contrary tropospheric direct circulations associated with Pacific decadal variability and canonical ENSO oscillations. AGU 1999 Fall Meeting, San Francisco, CA, December 13-17, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(46):F180, A31D-07 (1999).
Our analysis shows that the intensity of the 1982-1983 and 1997-1998 El Niño events, occurring only 15 years apart, are among the three or four warmest in 130 years of trans-Pacific sampling. However, when the 130 year record of global sea surface temperatures (SST) is subjected to a complex empirical orthogonal function (CEOF) analysis, the leading mode has all the known characteristics (amplitude and phase) of the El Niño-Southern Oscillation (ENSO), yet the associated canonical variation of SST in the equatorial Pacific does not include the spectacular amplitudes of the 1980s and 1990s, seen in the unanalyzed SST data. When the equatorial reconstruction of the global ENSO mode is subtracted from the SST data, the residual equatorial variability (NINO3 region) is seen to have a pronounced decadal variability, with many of the characteristics that others have identified with the Pacific Decadal Oscillation (PDO). As much as 50% of the total amplitudes of the NINO3 SST anomalies in 1982-1983 and 1997-1998 are explained by this residual, which was unusually high after 1978. In this paper, we describe and compare the surface oceanic (SST) and atmospheric (pressure, winds) characteristics associated with these two components of the NINO3 variability (ENSO and residual). We also examine the anomalous direct circulation (Walker and Hadley circulations) of the global troposphere associated with each component. The tropospheric analysis, of greatest interest to this session, yields a startling result: the anomalous direct circulation associated with the canonical ENSO warmings in the NINO3 series is in most ways opposite to that associated with the residual (decadal) warmings. The contrary behavior of the two components extends to convection near the dateline, over the Amazon basin and over the Indian Ocean, while the Hadley circulations in the Pacific and Atlantic sectors are also affected in opposite ways. A unique feature of the decadal component is the occurrence of a stronger winter monsoon over India and northeast Africa, in association with warm background SSTs in the eastern equatorial Pacific.
Enfield, D.B., and A.M. Mestas-Nunez. Multiscale variabilities in global sea surface temperatures and their relationships with tropospheric climate patterns. Journal of Climate, 12(9):2719-2733 (1999).
El Niño-Southern Oscillation (ENSO) is a global phenomenon with significant phase propagation within and between basins. We capture and describe this in the first mode of a complex empirical orthogonal function (CEOF) analysis of sea surface temperature anomaly (SSTA) from the mid-19th century through 1991. We subsequently remove the global ENSO from the SSTA data, plus a linear trend everywhere, in order to consider other global modes of variability uncontaminated by the intra- and inter-basin effects of ENSO. An ordinary EOF analysis of the SSTA residuals reveals three non-ENSO modes of low-frequency variability that are related to slow oceanic and climate signals described in the literature. The first two modes have decadal-to-multidecadal time scales with high loadings in the Pacific. They bear some spatial similarities to the ENSO pattern but are broader, more intense at high latitudes, and differ in the time domain. A CEOF analysis confirms that they are not merely the phase-related components of a single mode and that all three modes are without significant phase propagation. The third mode is a multidecadal signal with maximal realization in the extratropical North Atlantic southeast of Greenland. It is consistent with studies that have documented connections between North Atlantic SSTA and the tropospheric North Atlantic Oscillation (NAO). All three SSTA modes have mid-tropospheric associations related to previously classified Northern Hemisphere teleconnection patterns. The relationships between SSTA modes and tropospheric patterns are consistent with the ocean-atmosphere interactions discussed in previous studies to explain low-frequency climate oscillations in the North Pacific and North Atlantic sectors. The first three leading modes of non-ENSO SSTA are most related, respectively, to the tropospheric patterns of the Pacific North American (PNA), the North Pacific (NP) and the Arctic Oscillations (AO), respectively. The 500 hPa pattern associated with the third SSTA mode also bears similarities to the NAO in its Atlantic sector. This North Atlantic mode has a region of high, positive SSTA loadings in the Gulf of Alaska, which appear to be connected to the North Atlantic SSTA by a tropospheric bridge effect in the AO.
Enfield, D.B., A.M. Mestas-Nunez, D.A. Mayer, and L. Cid-Serrano. How ubiquitous is the dipole relationship in tropical Atlantic sea surface temperatures? Journal of Geophysical Research, 104(C4):7841-7848 (1999).
Several kinds of analysis are applied to the departures of sea surface temperatures from climatology (SSTA, 1856-1991) to determine the degree to which SSTA of opposite sign in the tropical North and South Atlantic occur. Antisymmetric ("dipole") configurations of SSTA on basin scales are not ubiquitous in the tropical Atlantic. Unless the data are stratified by both season and frequency, inherent dipole behavior cannot be demonstrated. Upon removing the global ENSO signal in SSTA (which is symmetric between the North and South Atlantic) from the data, the regions north or south of the intertropical convergence zone have qualitatively different temporal variabilities and are poorly correlated. Dipole configurations do occur infrequently (12-15% of the time), but no more so than expected by chance for stochastically-independent variables. Non-dipole configurations that imply significant meridional SSTA gradients occur much more frequently, nearly half of the time. Cross-spectral analysis of seasonally averaged SSTA indices for the North and South Atlantic show marginally significant coherence with antisymmetric phase in two period bands: 8-12 years for the boreal winter-spring, and 2.3 years for the boreal summer-fall. Antisymmetric coherence is optimal for a small sub-region west of Angola in the South Atlantic, with respect to SSTA of basin scale in the tropical North Atlantic. Dipole variability, even where optimal, explains only a small fraction of the total variance in tropical Atlantic SSTA (<7%).
Enfield, D.B., A.M. Mestas-Nunez, D.A. Mayer, and L. Cid-Serrano. The dipole in tropical Atlantic SST: Common? Random? Intrinsic? Proceedings, 23rd Annual Climate Diagnostics and Prediction Workshop, Miami, Florida, October 26-30, 1998. National Weather Service, 223-226 (1999).
In this paper we clarify the confusing and apparently contradictory views regarding tropical Atlantic dipole variability. The issue is revisited by using a recently reconstructed 136-year SST anomaly (SSTA) analysis for the globe (Kaplan et al., 1998; henceforth, K98). An expanded analysis will appear in the Journal of Geophysical Research-Oceans (Enfield et al., 1999).
Esenkov, O.E., and B. Cushman-Roisin. Modeling of two-layer eddies and coastal flows with a particle method. Journal of Geophysical Research, 104(C5):10,959-10,980 (1999).
An existing particle-in-cell (PIC) numerical code is applied to lens-like anticyclonic vortices and buoyant coastal currents. A first series of experiments with initially elongated eddies reveals that motions induced in the lower layer act to increase the rate of rotation of the structure; eccentricity reduction, if any, produces a final vortex of aspect ratio between 1.8 and 1.9, in accordance with a theoretical prediction. A second series of experiments determines the maximal separation distance that can exist between two identical and circular vortices before they spontaneously merge; this distance is a function of the vortex size and ambient stratification. In a third series of experiments, vortex interactions across layers are considered; results similar to those obtained with two-layer point vortices (hetons) are obtained. Finally, the PIC method is generalized to simulate the finite-amplitude instability of a buoyant geostrophic current flowing a long a vertical coastal wall.
Etcheto, J., J. Boutin, Y. Dandonneau, D.C.E. Bakker, R.A. Feely, R.D. Ling, P.D. Nightingale, and R.H. Wanninkhof. Air-sea CO2 flux variability in the equatorial Pacific Ocean near 100°W. Tellus B, 51(3):734-747 (1999).
The interannual variability of the CO2 partial pressure (pCO2) in the surface layer of the east equatorial Pacific Ocean near 100°W is studied and compared with the sea surface temperature (SST) monitored from satellites. This variability is shown to be correlated with the SST anomaly rather than with the temperature itself. The pCO2OC variability is related to the variability of the upwelling systems (the equatorial upwelling and the upwelling along the American coast), the main influence being from the coastal upwelling via the surface water advected from the east. A method is derived to interpolate the pCO2OC measurements using the SST satellite measurements. By combining the result with the exchange coefficient (K) deduced from the wind speed provided by satellite-borne instruments, we deduce the air-sea CO2 flux and, for the first time, we continuously monitor its temporal variation. The variability of this flux is mainly due to the variability of K, with a clear seasonal variation. The flux obtained using the Liss and Merlivat (1986) relationship averaged from April 1985 to June 1997 in the region 97.5°-107.5°W, 0-5°S is 1.67 mole m-2 yr-1 of CO2, leaving the ocean with an estimated accuracy of 30%.
Etcheto, J., J. Boutin, D.C.E. Bakker, Y. Dandonneau, R.A. Feely, H.Y. Inoue, M. Ishii, R.D. Ling, L. Merlivat, P.D. Nightingale, N.Metzl, and R.H. Wanninkhof. pCO2 in the equatorial Pacific and Atlantic Oceans: Determination of air-sea CO2 flux using satellite-borne instruments. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 119-125 (1999).
No abstract.
Feely, R.A., M.F. Lamb, D.J. Greeley, and R.H. Wanninkhof. Comparison of the carbon system parameters at the global CO2 survey crossover locations in the North and South Pacific Ocean between 1990-1996. Technical Report, ORNL/CDIAC-115, Oak Ridge National Laboratory/Carbon Dioxide Information Analysis Center, 73 pp. (1999).
As a collaborative program to measure global ocean carbon inventories and provide estimates of the anthropogenic carbon dioxide (CO2) uptake by the oceans, the National Oceanic and Atmospheric Administration and the U.S. Department of Energy have sponsored the collection of ocean carbon measurements as part of the World Ocean Circulation Experiment and Ocean-Atmosphere Carbon Exchange Study cruises. The cruises discussed here occurred in the North and South Pacific from 1990 through 1996. The carbon parameters from these 30 crossover locations have been compared to ensure a consistent global data set emerges from the survey cruises. The results indicate that for dissolved inorganic carbon, fugacity of CO2, and pH, the agreement at most crossover locations are well within the design specifications for the global CO2 survey, whereas in the case of total alkalinity, the agreement between crossover locations is not as close.
Feely, R.A., C.L. Sabine, R.M. Key, and T.-H. Peng. CO2 survey synthesis results: Estimating the anthropogenic carbon dioxide sink in the Pacific Ocean. U.S. JGOFS News, 9(4):1-4 (1999).
Our results to date suggest that the cumulative amount of anthropogenic CO2 in the global ocean is somewhere between 105 and 118 PgC through the year 1996. These results can be utilized as a constraint on other global carbon model simulations, similar to Princeton/Geophysical Fluid Dynamics Laboratory Ocean Biogeochemical Model and National Center for Atmospheric Research model simulations. As we refined and complete the estimates of the oceanic uptake of anthropogenic CO2, the results will be compared to CO2 uptake estimates for the atmosphere and terrestrial biosphere.
Feely, R.A., R.H. Wanninkhof, T. Takahashi, and P. Tans. Influence of El Niño on the equatorial Pacific contribution to atmospheric CO2 accumulation. Nature, 398:597-601 (1999).
The equatorial ocean is an important CO2 source to the atmosphere, contributing annually 0.7-1.5 Pg of carbon as CO2, as much as 80% of which is attributed to the equatorial Pacific. This source is known to change significantly by ENSO events. To better understand the regional and interannual variability of CO2 fluxes from the equatorial Pacific, field measurements of the partial pressure of CO2 (pCO2) have been made in the equatorial Pacific region since 1992. Here, we report that during the 1991-1994 ENSO period the net annual sea-to-air flux of CO2 was 0.3 PgC from the fall of 1991 to the fall of 1992, 0.6 PgC in 1993, and 0.7 PgC in 1994. These fluxes are 30%-80% of the 0.9 PgC observed during the non-El Niño year of 1996. The total reduction of the sea-to-air CO2 flux during the 1991-1994 El Niño is estimated to be 0.8-1.2 PgC, which accounts for 16-36% of the atmospheric anomaly (the difference between the annual atmospheric CO2 increase in PgC yr-1 and the long-term average increase of 3.18 PgC yr-1) observed over the same period.
Feely, R.A., C.L. Sabine, R.M. Key, T.-H. Peng, and R.H. Wanninkhof. The U.S. global CO2 survey in the North and South Pacific Ocean. Preliminary synthesis results. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 193-198 (1999).
As a collaborative program to measure global ocean carbon inventories and provide estimates of the anthropogenic CO2 uptake in the oceans, the National Oceanic and Atmospheric Administration, the U.S. Department of Energy, and the National Science Foundation have co-sponsored the collection of ocean carbon measurements as part of the World Ocean Circulation Experiment (WOCE) and Ocean-Atmospheric Carbon Exchange Study (OACES). The cruises discussed here occurred in the North and South Pacific from 1990 through 1996. The new estimates for anthropogenic CO2, employing the DELTA-C* method of Gruber et al. (1996), indicate that the largest buildup of anthropogenic CO2 occurs in subtropical waters. Along 155°W, anthropogenic CO2 penetrates to a maximum depth of 900 m at about 37°N in the North Pacific and 1300 m at about 48°S in the South Pacific. Strong shoaling of anthropogenic CO2 occurs southward of 50°S and northward of 48°N. The anthropogenic CO2 inventories from the observations are smaller than the Princeton Ocean Biogeochemical Model (POBM) model estimates, primarily because the Princeton model produces too much deep convective mixing of anthropogenic CO2 in the Southern Ocean. The NCAR Climate System Ocean model, which has very different physics and biological parameterizations, appears to do a better job of reproducing the general patterns in the data-based section.
Feely, R.A., R.H. Wanninkhof, D. Hansell, M.F. Lamb, K. Lee, and R.D. Castle. Water column CO2 measurements during the GasEx 98 cruise. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S46, A31C-11 (1999).
During the recent GasEx 98 cruise in the North Atlantic aboard the NOAA Ship Ronald H. Brown, carbon measurements were performed in the area of 46°N, 20.5°W. This process study followed a warm core ring tagged with the deliberately-introduced tracer, SF6. Continuous surface water measurements were combined with vertical profiles sampled twice daily to depths up to 1000 m for carbon mass balance studies. Dissolved inorganic carbon (DIC) and fCO2 measurements were conducted onboard in both underway and discrete analysis modes. During the 25-day experiment in the tagged patch, surface water fCO2 values averaged 275 ± 9 µatm, providing a constant condition of undersaturation and flux of CO2 into the ocean. Using the Wanninkhof (1992) exchange coefficient, the estimated CO2 flux ranged from 2-10 moles m-2 yr-1. The largest CO2 flux occurred during a large storm beginning on June 6. After the storm, DIC and fCO2 values decreased for a few days as a result of increased productivity associated with the strong mixing event. The DIC were combined with the DOC, oxygen, and nutrient data to provide a mass balance for carbon within the patch. The mass balance of CO2 can be reconciled with the gas transfer velocities determined during the cruise.
Franklin, J.F., M.L. Black, and S.E. Feuer. Wind profiles in hurricanes determined by GPS dropwindsondes. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 167-168 (1999).
No abstract.
Fratantoni, D.M., P.L. Richardson, W.E. Johns, C.I. Fleurant, R.H. Smith, S.L. Garzoli, W.D. Wilson, and G.J. Goñi. The North Brazil Current Rings Experiment. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S179, OS31B-10 (1999).
North Brazil Current rings are large (400 km diameter) anticyclonic vortices shed from the retroflecting North Brazil Current (NBC) in the low-latitude western Atlantic Ocean. NBC rings carry a large volume of South Atlantic water northwestward along the coast of South America towards the islands of the southeastern Caribbean. These rings are thought to be one of several processes responsible for the northward transport of upper-ocean water across the equatorial-tropical gyre boundary and into the North Atlantic subtropical gyre. Such transport is required to close the Atlantic meridional overturning cell (MOC) forced by the high-latitude production and southward export of North Atlantic Deep Water. The objective of this multi-institutional study is to obtain, for the first time, comprehensive observations of the NBC retroflection, the NBC ring formation process, and the physical structure and evolution of NBC rings as they translate along the low-latitude western boundary. We seek to understand the process of NBC ring generation and to quantify the role of NBC rings as a component of the Atlantic MOC. To accomplish our objectives we used several complementary measurement techniques including detailed shipboard CTD/ADCP/XBT surveys, surface drifter and subsurface RAFOS float observations, moored velocity and temperature-salinity measurements, and a moored array of inverted echo sounders. We will present results obtained during the first two NBC rings cruises in November-December 1998 and February-March 1999. A total of three rings were surveyed in detail, each differing substantially from the others in intensity and vertical structure. Maximum azimuthal surface velocities were typically of order 150 cm/s at a radius of 120-150 km from the ring center. In one ring, coherent swirl velocities of 20 cm/s were observed to extend as deep as 2000 m. Two of the three rings exhibited subsurface velocity maxima near 100 m depth. We will present a summary of our shipboard and surface drifter observations and share some initial conclusions regarding the physical structure and watermass composition of NBC rings.
Gamache, J.F. Airborne Doppler observations of intensity change in eastern Pacific Hurricane Guillermo. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 325-328 (1999).
No abstract.
Garzoli, S.L., and R.L. Molinari. Ageostrophic currents in the tropical Atlantic. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S179, OS31B-09 (1999).
Between 23 June 1997 and 12 August 1997, the R/V Seward Johnson completed two basin-wide transects in the Atlantic along 6°N and 6°S and a partial transect along the equator. During this time, the vessel occupied 81 oceanographic stations at which hydrographic, CTD, and lowered acoustic Doppler current profiler (LADCP) measurements were acquired. Hull-mounted ADCP data were collected continuously along the transects. In this paper, the data collected along 6°N and 6°S are analyzed and discussed. Direct measurement of the ageostrophic transport are obtained and compared with estimates of the Ekman transports derived from wind measurements. Estimates of divergence are compared with other results in terms of upwelling. From the present analysis it may be concluded that in the tropical Atlantic, the Ekman drift plays an important role in the upper layer (<300 m) transports but does not account totally for the ageostrophic ones. At 6°N, instability waves and inertial currents are dominant. At 6°S, most of the ageostrophic transport can be attributed to Ekman with the difference explained by inertial waves.
Garzoli, S.L., P.L. Richardson, C.M. Dumcombe Rae, D.M. Fratantoni, G.J. Goni, and A.J. Roubicek. Three Agulhas rings observed during the Benguela Current Experiment. Journal of Geophysical Research, 104(C9):20,971-20,986 (1999).
A field program to study the circulation of the Benguela Current and its extension into the southeastern Atlantic Ocean has completed the survey and instrument deployment phase. We report here new observations of three Agulhas rings north and west of Cape Town, South Africa. Three mesoscale anticyclonic rings initially identified by means of TOPEX/POSEIDON altimetry were surveyed with expendable bathythermographs (XBTs), conductivity-temperature-depth-oxygen (CTDO) profiles, direct current measurements from a lowered acoustic Doppler current profiler (LADCP), a hull-mounted acoustic Doppler current profiler (ADCP), and satellite-tracked surface drifters. Characteristics of the rings are presented and their origins are discussed. Two are typical Agulhas rings surveyed at different times after their generation; the third Agulhas ring has an anomalous watermass structure whose most likely origin is the Subtropical Front.
Godin, O.A., D. Yu. Mikhin, and D.R. Palmer. Ocean current monitoring in the coastal zone. Oceanologia, 13:174 (1999).
A new technique has recently been put forward for real-time monitoring of ocean currents in the coastal zone. The acoustic technique, called matched non-reciprocity tomography (MNT), is being developed to extend traditional ocean acoustic tomography to the coastal zone. It should provide maps of the current field extending out tens of kilometers in range and throughout the water column. These maps will have applications to several important scientific problems such as measuring ocean circulation and upwelling and monitoring global climate change. Alternative approaches for monitoring currents in the coastal zone are surveyed and their limitations when compared with the MNT approach are discussed. Non-reciprocity tomography is based on recent progress in the theory of acoustic propagation in moving media and in the use of matched-field processing to solve tomographic inverse problems. The MNT technique can be viewed as an application of matched-field processing to a judiciously selected acoustic observable that is sensitive to flow velocity, but insensitive to sound speed and bathymetric variations, and leads to robust inversions for the depth-dependence of the velocity. The development of non-reciprocity tomography is reviewed in this article in the context of extended opportunities the technique offers in monitoring ocean dynamics in the coastal zone by acoustic means. Applications of the MNT technique to problems not directly related to coastal current monitoring are also noted.
Goldenberg, S.B., and C.W. Landsea. Relationships between decadal-scale fluctuations in vertical shear from NCEP/NCAR reanalysis data and Atlantic basin tropical cyclone activity. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 1089-1091 (1999).
No abstract.
Goni, G.J. Transport estimates of the Kuroshio Current from satellite altimeter data. In Ecosystem Dynamics of the Kuroshio Oyashio Transition Region, M. Terazaki, K. Ohtani, T. Sugimoto, and Y. Watanabe (eds.). Japan Marine Science Foundation, Tokyo, 1-8 (1999).
The Kuroshio, together with the Gulf Stream, its counterpart in the North Atlantic, are the two major western boundary currents in the northern hemisphere. These currents have been viewed as the principal channel of water exchange between the equatorial regions, where heat is added to the oceans to be later removed in the polar regions. The transport of the Kursohio current remains one of the largest uncertainties in the meridional heat flux estimate across the North Pacific subtropical gyre. Estimates of the Kuroshio mean transports vary from 21 Sv to 33 Sv (1 S v =106 m3 s-1). Some characteristics of the dynamics of this current and its variability will be also briefly addressed in this work. One very important issue in ocean dynamics is to constantly monitor the subsurface thermal structure and transport of a western boundary current. This work presents a methodology that uses a combination of satellite altimetry-derived sea height anomaly and inverted echosounder-derived hydrographic data to estimate the thickness of the ocean upper layer and baroclinic transport. The estimates reveal that during the end of 1996 and beginning of 1997 the Kuroshio Current presents an anomalous behavior.
Goni, G.J., and W.E. Johns. Synoptic study of North Brazil Current rings from altimeter data. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S179, OS31B-12 (1999).
TOPEX/POSEIDON-derived sea height anomaly fields from 1993 to 1998 are used to study the mesoscale variability off northeastern South America between 0 to 15°N and 40 to 65°W. The North Brazil Current (NBC) and the anticyclonic rings generated at this current's retroflection are the major sources of mesoscale variability in the region. Space-time diagrams show a very pronounced annual cycle of the sea height anomaly field. Once this annual cycle is removed, the sea height residuals clearly show the northwest translation of the North Brazil Current rings generated at the retroflection. Using a two-layer model, the sea height anomaly field is converted into an upper layer thickness field using parameters derived from historical hydrographic data, where the base of the upper layer is defined by the 20° isotherm. The maps of the upper layer thickness are used to find the trajectory of each ring, their velocities, length scales, and mass transport. These maps also show that 5 to 8 rings are formed every year, with the greatest frequency of formation being in boreal spring. The rings translation velocities range between 7 and 18 km/day. These rings seem to have preferred trajectories which are closely related to changes in bathymetry. Estimates of the baroclinic transport of the North Brazil Current from a T/P groundtrack across the upstream part of the retroflection show that peaks in the transport are usually followed by the formation of rings.
Goni, G.J., M.M. Huber, and L.K. Shay. TOPEX/POSEIDON-derived Atlantic Ocean hurricane heat content estimates. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, American Meteorological Society 79th Annual Meeting, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 1037-1042 (1999).
No abstract.
Goodwin, K.D., R.A. Varner, P.M. Crill, and R.S. Oremland. Uptake of near-ambient levels of methyl bromide by strain IMB-1, a facultative methylotrophic bacterium. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S64, A42C-06 (1999).
A bacterium isolated from agricultural soils, Strain IMB-1, is a facultative methylotroph able to grow on high levels (500 µM) of the agricultural fumigant, methyl bromide (CH3Br). Agricultural and structural fumigation can release 20 to 80% of the gas that is applied, creating a potential source of stratospheric-ozone-destroying Br radicals. Investigation of Strain IMB-1 has focused on harnessing its ability to consume high levels of CH3Br (ppmv) in order to decrease the amounts of CH3Br released during the soil fumigation process. However, agricultural soils have also been determined to irreversibly break down ambient levels of CH3Br (pptv). Strain IMB-1 was thus tested for its ability to consume near-ambient levels of CH3Br with the use of a permeation tube/dynamic dilution system during dynamic flow-through incubations. Strain IMB-1 grown in the presence of 0.3% CH3Br was able to consume CH3Br supplied at 12 parts per trillion by volume (pptv). The presence of glucose or methylamine did not inhibit CH3Br consumption. Glucose-grown cells were induced to uptake 12 pptv CH3Br by exposure to 0.3% CH3Br during either exponential or stationary phases of growth. Glucose-grown cells were induced to uptake 12 pptv by exposure to 100 pptv CH3Br only during exponential growth. The uptake rate of CH3Br by IMB-1 grown on glucose was linearly related to concentration in the range from 12 to 19,430 pptv.
Graber, H.C., M.A. Donelan, S. Atakturk, W.M. Drennan, and K.B. Katsaros. Marine flux-profile relations from an air-sea interaction spar buoy. Proceedings, Symposium on the Wind-Driven, Air-Sea Interface, Sydney, Australia, January 10-15, 1999, M. Banner (ed.). The University of New South Wales, 317-324 (1999).
The Air-Sea Interaction Spar (ASIS) is a new autonomous spar buoy designed to permit long-term measurements of processes at the air-sea interface. During a two-month deployment in the Gulf of Mexico in April/May 1997, the buoy recorded waves as high as 3.5 m and wind speeds up to 20 m/s. The ASIS buoy was instrumented to measure high resolution wave directional properties, wind stress, and four level profiles of wind speed, temperature, and humidity. These data are used to examine marine flux-profile relations and to explore the effect of a thick wave boundary layer on the validity of Monin-Obukhov similarity theory.
Gray, J. National Oceanic and Atmospheric Administration research and operation priorities. In Proceedings, South Florida Measurement Center Workshop: Establishment of a Center for Innovative Oceanography in the 21st Century, Dania, FL, February 24-26, 1999. National Science Foundation, 207-213 (1999).
No abstract.
Grima, N., A. Bentamy, K.B. Katsaros, Y. Quilfen, P. Delecluse, and C. Levy. Sensitivity of an oceanic general circulation model forced by satellite wind stress fields. Journal of Geophysical Research, 104(C4):7967-7989 (1999).
Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on European Remote Sensing satellites 1 and 2 (ERS-1 and ERS-2) are used to drive the ocean general circulation model (OGCM) "OPA" in the tropical oceans. The results of the impact of ERS winds are discussed in terms of the resulting thermocline, current structures, and sea level anomalies. Their adequacy is evaluated on the one hand by comparison with simulations forced by the Arpege-Climat model and on the other hand by comparison with measurements of the Tropical Atmosphere-Ocean (TAO) buoy network and of the TOPEX/Poseidon altimeter. Regarding annual mean values, the thermal and current responses of the OGCM forced by ERS winds are in good agreement with the TAO buoy observations, especially in the central and eastern Pacific Ocean. In these regions the South Equatorial Current, the Equatorial Undercurrent, and the thermocline features simulated by the OGCM forced by scatterometer wind fields are described. The impact of the ERS-1 winds is particularly significant to the description of the main oceanic variability. Compared to the TAO buoy observations, the high-frequency (a few weeks) and the low-frequency of the thermocline and zonal current variations are described. The correlation coefficients between the time series of the thermocline simulated by ERS winds and that observed by the TAO buoy network are highly significant; their mean value is 0.73, over the whole basin width, while it is 0.58 between Arpege model simulation and buoy observations. At the equator the time series of the zonal current simulated by the ERS winds, at three locations (110°W, 140°W, and 165°E) and at two depths, are compared to the TAO current meter and acoustic Doppler current profiler (ADCP) measurements. The mean value of the significant correlation coefficients computed with the in-situ measurements in 0.72 for ERS, while it is 0.51 for the Arpege-Climat model. Thus, ERS wind fields through the OGCM generate more realistic current variations than those obtained with Arpege climate winds, and they are particularly efficient in capturing abrupt changes ("wind bursts") which may be important regarding ocean dynamics.
Hansen, D.V., and W.C. Thacker. Estimation of salinity profiles in the upper ocean. Journal of Geophysical Research, 104(C4):7921-7934 (1999).
A new algorithm is presented for estimating salinity profiles in the upper ocean from measurements of temperature profiles and surface salinity. In application to the eastern tropical Pacific the method replicates a large fraction of the variability of salinity in the upper few tens of meters and provides modest to substantial improvement at nearly all levels. Estimated salinity profiles are able to characterize barrier layers, regions formed by a halocline within the thermal mixed layer. The rms error of geopotential-height calculations based on estimated salinity profiles is reduced more than 50 percent by this method relative to methods not using surface salinity. Even without the surface salinity measurement some reduction of error in geopotential heights can be obtained relative to previous methods.
Hellin, J., M. Haig, and F.D. Marks. Rainfall characteristics of Hurricane Mitch. Nature, 399:316 (1999).
No abstract.
Hendee, J.C. An environmental information synthesizer for expert systems. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 217 (1999).
As an enhancement to the SEAKEYS environmental monitoring network, software called the Environmental Information Synthesizer for Expert Systems (EISES) has been constructed which synthesizes knowledge from near real-time acquired meteorological and oceanographic data. This knowledge is acquired in the form of facts which can be used by expert systems designed to monitor and match environmental parameters as they meet criteria generally thought to be conducive to certain biological events. The initial expert system constructed to use the facts from EISES, which we have dubbed the Coral Reef Early Warning System (CREWS), represents a first step in the construction of a larger coral reef specific expert system. When environmental conditions are conducive to coral bleaching, according to different bleaching theories or models, CREWS produces alerts which are automatically posted to the Web and emailed to researchers so they can verify and study bleaching events as they might happen. The models are refined using feedback from field data on bleaching recorded after alerts from the expert system. CREWS has now been implemented not only for the Florida Keys National Marine Sanctuary, but also for the Great Barrier Reef Marine Park Authority, and will hopefully be developed in the future for other coral reef sanctuaries or parks throughout the world. In addition to CREWS, expert systems for Florida Bay are being developed with collaborators to model juvenile pink shrimp and fish spawning migrations (with UM/RSMAS and NOAA/NMFS) and conditions conducive to harmful algal blooms (with NOAA/NESDIS). Some other example events that might be monitored or predicted from EISES expert systems include good diving and/or fishing conditions (e.g., clear water, low winds), at remote locations, phytoplankton blooms, hypo- or hypersaline influxes from Florida Bay, and excessive dissolved nutrient encroachment (inferred from high fluorometry values).
Hood, M., R.H. Wanninkhof, and L. Merlivat. The effects of wind-induced mixing on short timescale surface variability of fCO2 and fluorescence: Results from the GasEx-98 CARIOCA buoy data. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S47, A31C-12 (1999).
During the Lagrangian deliberate tracer study in the North Atlantic, GasEx-98, hourly measurements of wind speed, sea surface temperature, fCO2, and fluorescence were made from two CARIOCA drifting buoys near 46°N and 21.5°W over a period of approximately 20 days. Shipboard measurements of fCO2 were used to calibrate the buoy data, and the hourly time series of the two buoys and the ship were in good agreement. Using these data, we investigated the air-sea flux of CO2, the importance of short-term wind-induced mixing events for longer-term estimates of flux, and the physical versus biological processes controlling surface variability of fluorescence. The air-sea flux estimate for the ~20 day experiment using the Wanninkhof (1992) gas transfer velocity formulation was -0.012 mol m-2 d-1, and using the Liss and Merlivat (1986) formulation was -0.007 mol m-2 d-1. A storm with wind speeds reaching as high as 16-17 m s-1 led to a sharp decrease in sea surface temperature and an increase in fCO2 of approximately 30 µatm. The magnitude of this sudden change in fCO2 is equal to approximately half of the annual range of fCO2 in this area and accounted for approximately 38% of the flux over the 20-day period. Approximately 16 hours after the onset of the storm, there was an increase in surface fluorescence coincident with the initial increase in fCO2. Nitrate measurements made from the ship show a sharp peak in surface concentrations about 24 hours after the increase in winds and approximately 6-8 hours after the increase in surface fluorescence. This increase in surface fluorescence that occurs in tandem with the increase in fCO2 and decrease in SST and before the arrival of nutrients to the surface suggests an upwelling of a relatively shallow chlorophyll maximum in this area. Phaeopigment to chlorophyll ratios are consistent with this mechanism. After the upwelling of the NO3, the fluorescence increases more sharply while the fCO2 decreases, consistent with biological productivity.
Houston, S.H., and M.D. Powell. Hurricanes and tropical storms in Florida Bay. Florida Sea Grant College Program, FLSGP-G-99-016, 2 pp. (1999).
No abstract.
Houston, S.H., W.A. Shaffer, M.D. Powell, and J. Chen. Comparisons of HRD and SLOSH surface wind fields in hurricanes: Implications for storm surge modeling. Weather and Forecasting, 14(5):671-686 (1999).
Surface wind observations analyzed by the Hurricane Research Division (HRD) were compared to those computed by the parametric wind model used in the National Weather Service Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model's storm surge computations for seven cases in five recent hurricanes. In six cases, the differences between the SLOSH and HRD surface peak wind speeds were 6% or less, but in one case (Hurricane Emily of 1993) the SLOSH computed peak wind speeds were 15% less than the HRD. In all seven cases, statistics for the modeled and analyzed wind fields showed that for the region of strongest winds, the mean SLOSH wind speed was 14% greater than that of the HRD and the mean inflow angle for SLOSH was 19° less than that of the HRD. The radii beyond the region of strongest winds in the seven cases had mean wind speed and inflow angle differences that were very small. The SLOSH computed peak storm surges usually compared closely to the observed values of storm surge in the region of the maximum wind speeds, except Hurricane Emily where SLOSH underestimated the peak surge. HRD's observation-based wind fields were input to SLOSH for storm surge hindcasts of Hurricanes Emily and Opal (1995). In Opal, the HRD input produced nearly the same computed storm surges as those computed from the SLOSH parametric wind model, and the calculated surge was insensitive to perturbations in the HRD wind field. For Emily, observation-based winds produced a computed storm surge that was closer to the peak observed surge, confirming that the computed surge in Pamlico Sound was sensitive to atmospheric forcing. Using real-time, observation-based winds in SLOSH would likely improve storm surge computations in landfalling hurricanes affected by synoptic and mesoscale factors that are not accounted for in parametric models (e.g., a strongly sheared environment, convective asymmetries, and stably stratified boundary layers). An accurate diagnosis of storm surge flooding, based on the actual track and wind fields, could be supplied to emergency management agencies, government officials, and utilities to help with damage assessment and recovery efforts.
Houston, S.H., G. Forbes, A. Chiu, W.-C. Lee, and P.P. Dodge. Super Typhoon Paka's (1997) surface winds. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 1032-1033 (1999).
No abstract.
Huang, H., R.E. Fergen, J.J. Tsai, and J.R. Proni. Evaluation of mixing zone models: CORMIX, PLUMES, and OMZA with field data from two Florida ocean outfalls. Proceedings, Second International Symposium on Environmental Hydraulics, Hong Kong, China, December 16-18, 1998. Environmental Hydraulics, pp. 249-254 (1999).
This paper presents an evaluation of three mixing zone models: CORMIX, PLUMES, and OMZA using field data from two Florida ocean outfalls: Hollywood and Miami-Central outfalls. The hollywood outfall has a single port outlet and the Miami-Central outfall has a multiport diffuser. Both outfalls discharge secondary effluent. For the nearfield, all of the three models predict realistic initial dilutions for the tests at the outfall except three cases in CORMIX predictions and two cases in PLUMES predictions (out of 20 cases). For the nearfield and farfield combined, CORMIX significantly overestimates dye concentrations for the tests at the Hollywood outfall but underestimates dye concentrations within the 300 m to 400 m range for the tests at the Miami-Central outfall. PLUMES predictions agree reasonably well with the filed data for the range from 300 m to 800 m but do not agree well within the 300 m range for the tests at both outfalls. OMZA predictions agree well with the field data within the 800 m range for the test at both outfalls.
Huber, M.M., L.K. Shay, and G.J. Goni. The Atlantic Ocean's role on intensity change. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, American Meteorological Society 79th Annual Meeting, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 36-39 (1999).
No abstract.
Humphrey, J.C., S.L. Vargo, J.C. Ogden, and J.C. Hendee. SEAKEYS 1999: Florida Keys monitoring initiative. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Program and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 240-241 (1999).
The Sustained Ecological Research Related to the Management of the Florida Keys Seascape (SEAKEYS) program was organized in 1991 by the Florida Institute of Oceanography (FIO) with initial funding from the John D. and Catherine T. MacArthur Foundation, and continuing funding from the South Florida Ecosystem Restoration, Prediction and Monitoring (SFERPM) program, administered by the National Oceanic and Atmospheric Administration (NOAA). The SEAKEYS environmental monitoring program, which is basically an oceanographic extension to the meteorologically-oriented Coastal-Marine Automated Network of NOAA, has accumulated an unparalleled long-term database of meteorological and oceanographic data from the Florida Straits and Florida Bay. During 1998, the SEAKEYS network was upgraded with more precise oceanographic sensors, and selected stations were augmented with fluorometers, transmissometers, and water-level sensing equipment. A seventh monitoring station, a cooperative effort between FIO and the University of South Florida's Department of Marine Science (USF/DMS), was completed in Northwest Florida Bay at 25°05'00"N, 81°05'30"W during summer, 1998. This station also contains a full suite of meteorological and oceanographic instrumentation and also transmits its data hourly via a NOAA GOES satellite. The Northwest Florida Bay station is the northwestern most station in the SEAKEYS network, as well as the southernmost link in the West Florida Coastal Ocean Monitoring and Prediction System of USF/DMS. Turbulent weather was prominent during 1998 in the Florida Keys. Severe conditions reported by the SEAKEYS stations included the Ground Hog Day Storm, Hurricane Georges, and Tropical Storm Mitch. In most cases the SEAKEYS stations contained the only instruments to measure the meteorological and oceanographic measurements accompanying these events in the Florida Keys. The Long Key station measured the highest winds (119 mph) in South Florida during the Ground Hog Day Storm of February 2, 1998. On September 25, 1998 the eye of Hurricane Georges passed over Key West at 1150 EDT as wind speeds dropped from 85.2 mph to 9.6 mph. The eye moved across the Dry Tortugas station at 1610 EDT with barometric pressures dropping to 974.4 mb. Winds gusted to hurricane force only after the eye passed at 2100 EDT. Georges' most severe winds in the Florida Keys gusted to 113 mph at Sombrero Reef, with a sustained wind speed of 94 mph. Long Key, Molasses Reef, and Fowey Rocks received gusts of tropical storm force. The tide station at Sombrero Reef reported a storm water level of 2.87 feet above mean lower low water. This contrasted with below normal levels reported at a station on Florida Bay. Hurricane Mitch passed northwest of the Florida Keys on the evening of November 4, 1998, bringing peak winds of 62.4 mph at Molasses Reef and sustained gale force winds until the following afternoon. Numerous localized tornadoes spawned by this storm caused extensive damage in the Upper Keys. Daily near real-time SEAKEYS data are available to researchers via NOAA's Coral Health and Monitoring Program (CHAMP) Web site at http://www.coral.noaa.gov, while historical data are available at http://www.neptune.noaa.gov. The Coral Reef Early Warning System (CREWS), which utilizes the near real-time data from six SEAKEYS stations, is an online expert system which monitors environmental conditions on the reef that are theoretically conducive to coral bleaching. If these conditions occur, alerts are sent via email to researchers and posted to the Web at http://www.coral.noaa.gov/sferpm/seakeys/es.
Johns, E., W.D. Wilson, and T.N. Lee. Surface salinity variability of Florida Bay and southwest Florida coastal waters. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 169-171 (1999).
No abstract.
Johns, E., W.D. Wilson, and R.L. Molinari. Direct observations of velocity and transport in the passages between the Intra-Americas Sea and the Atlantic Ocean, 1984-1996. Journal of Geophysical Research, 104(C11):25,805-25,820 (1999).
Shipboard acoustic Doppler current profiler observations of the velocity in the upper 200 m of the water column collected during 1984-1996 using the National Oceanic and Atmospheric Administration R/V Malcolm Baldrige are used to examine the velocity structure and transport in the passages between the Atlantic Ocean and the Intra-Americas Sea (IAS). Data were colected during 23 cruises along the following sections: across the Straits of Florida, in the Northwest Providence Channel (NWPC), across the northern passages into the Caribbean Sea (Windward, Mona, and Anegada), across the eastern Caribbean along 63°30'W, thereby forming a closed quadrangle, and in the Grenada Passage. The Florida Current, the eastern Caribbean, and the Grenada Passage share a similar mean velocity structure characterized by high-velocity, surface intensified flows with strong vertical and horizontal shears. The northern Caribbean passages (NWPC, Windward, Mona, and Anegada) share a different common mean velocity structure, with subsurface velocity maxima directed into the IAS, and surface-intensified counterflows along one side of each paassage. On average, there is a transport balance in the upper 200 m between waters entering and exiting the IAS, with the 16.5 ± 2.4 Sv (1 Sv = 106 m3 s-1) transport of the Florida Current at 27°N comprised of 0.4 ± 0.8 Sv from the NWPC, 2.2 ± 1.5 Sv from the Windward Passage, 2.8 ± 2.1 and 2.4 ± 2.8 Sv from the Mona and Anegada passages, respectively, and 9.5 ± 4.7 Sv across the eastern Caribbean, for a total of 17.3 Sv. The four passages north of 17°N (from NWPC to Anegada Passage) have a combined transport of 7.8 Sv, nearly half of the transport of the Florida Current in the upper 200 m. Of the 9.5 Sv flowing through the eastern Caribbean between 11°N and 17°N, 4.9 ± 2.6 Sv, or more than half, come from the Grenada Passage. This is significant to the subject of cross-equatorial exchange of mass, heat, and salt, as the Grenada Passage is where the highest transport of waters originating in the southern hemisphere is thought to enter the Caribbean.
Jones, R.W., and M. DeMaria. Further studies of the optimization of a hurricane track prediction model using the adjoint equations. Monthly Weather Review, 127(7):1586-1598 (1999).
The method of model fitting, or adjoint method, is applied to a barotropic hurricane track forecast model described by DeMaria and Jones using a large sample of forecast cases. The sample includes all Atlantic tropical cyclones that reached hurricane intensity during the 1989-1993 hurricane seasons (141 72-h forecasts of 17 storms). The cases considered by DeMaria and Jones are a subset of the present sample. Model-fitting calculations using strong, weak, strong followed by weak, or weak followed by strong model constraints are discussed for data assimilation periods varying from 6 to 72 h. Generally, the best track forecasts occur for shorter assimilation periods and for weak constraints, although only the 12-h assimilation with the weak constraint has less track error than the control forecast without assimilation, and only for the 12-h forecast. The principle reason for this lack of improvement is that the fit of the model to the observed track is good at the middle of the assimilation period, but not very good at the end where the forecast begins. When a future track position at 6 h is included in the assimilation, in order to improve the track fit at the synoptic data time, the resulting track errors average about 10% smaller than the control forecast. The control forecast may also be improved in the same way. In that case, the best assimilation forecasts have 2.5% smaller track errors than the modified control forecasts.
Jones, R.W., and H.E. Willoughby. Results of generalizing a semispectral shallow-water barotropic hurricane tracking model into a two-layer baroclinic model. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 747-750 (1999).
No abstract.
Kaplan, J., and M. DeMaria. Climatological and synoptic characteristics of rapidly intensifying tropical cyclones in the North Atlantic basin. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 592-595 (1999).
No abstract.
Kelly, P.S., K.M. Lwiza, R.K. Cowen, and G.J. Goni. Low-salinity lenses at Barbados, West Indies: Their origin, frequency, and variability. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S185, OS42C-01 (1999).
A vertical array of conductivity-temperature sensors moored west of Barbados, West Indies, from May 1996 to November 1997 revealed a heterogeneous and variable salinity pattern punctuated by six intrusions of low-salinity water (less than 34.5 psu). A typical intrusion extended to 30 m depth and lasted ~25 days, although one intrusion extended to 47 m and lasted 94 days. Water samples taken during an intrusion in May 1997 have Radium 228/226 activity ratios of approximately 1, consistent with previous measurements in Barbados of water that originated in the Amazon River mixing zone. The Amazon water likely was translated to Barbados in rings spawned from the North Brazil Current (NBC). Analysis of sea height anomaly derived from the TOPEX/Poseidon satellite altimeter supports this conclusion and reveals that, contrary to previous studies, rings are shed throughout the year, mostly during spring. The intrusions of low-salinity water and their associated velocities dramatically changed the already variable flow in our study area. The complex salinity and flow we observed represented the effects of NBC rings passing the island, perhaps disrupted by the relatively shallow Tobago-Barbados ridge. The complex velocity and water structure are interesting in their own right as evidence of the Barbados region as a mixing zone and for their influence on recruitment of larval fishes to the reef along the island's west coast.
Landsea, C.W., and J.A. Knaff. Application of the El Niño-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 8(4):34-36 (1999).
No abstract.
Landsea, C.W., and J.F. Knaff. How much "skill" did the various forecasting methods available have for the 1997-1998 El Niño event? Preprints, Second Hayes Symposium on Seasonal to Interannual Climate Variability--The 1997/1998 ENSO Cycle, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 73 (1999).
No abstract.
Landsea, C.W., R.A. Pielke, A.M. Mestas-Nunez, and J.A. Knaff. Atlantic basin hurricanes: Indices of climatic changes. Climatic Change, 42:89-129 (1999).
Accurate records of basin-wide Atlantic and U.S. landfalling hurricanes extend back to the mid 1940s and the turn of the century, respectively, as a result of aircraft reconnaissance and instrumented weather stations along the U.S. coasts. Such long-term records are not exceeded elsewhere in the tropics. The Atlantic hurricanes, U.S. landfalling hurricanes, and U.S. normalized damage time series are examined for interannual trends and multidecadal variability. It is found that only weak linear trends can be ascribed to the hurricane activity and that multidecadal variability is more characteristic of the region. Various environmental factors including Caribbean sea level pressures and 200 mb zonal winds, the stratospheric Quasi-Biennial Oscillation, the El Niño-Southern Oscillation, African West Sahel rainfall, and Atlantic sea surface temperatures, are analyzed for interannual links to the Atlantic hurricane activity. All show significant, concurrent relationships to the frequency, intensity, and duration of Atlantic hurricanes. Additionally, variations in the El Niño-Southern Oscillation are significantly linked to changes in U.S. tropical cyclone-caused damages. Finally, much of the multidecadal hurricane activity can be linked to the Atlantic Multidecadal Mode, an empirical orthogonal function pattern derived from a global sea surface temperature record. Such linkages may allow for prediction of Atlantic hurricane activity on a multidecadal basis. These results are placed into the context of climate change and natural hazards policy.
Landsea, C.W., C.A. Anderson, G. Clark, J. Fernandez-Partagas, P. Hungerford, C. Neumann, and M. Zimmer. The Atlantic hurricane database re-analysis project. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 394-397 (1999).
No abstract.
Lapitan, R.L., R.H. Wanninkhof, and A.R. Mosier. Methods for stable gas flux determination in aquatic and terrestrial systems. In Approaches to Scaling of Trace Gas Fluxes in Ecosystems, A.F. Bouwman (ed.), Elsevier, Amsterdam, 27-66 (1999).
A general description of the current approaches for measuring trace gas fluxes in aquatic and terrestrial systems is presented in this paper. Our aim is to provide an overview of the current methodologies employed in trace gas flux measurements and the most recent advancements made; with emphasis on the uncertainties observed and potential areas for future developments required to further minimize these uncertainties brought about by spatial and temporal variabilities of fluxes in the field. The increase in sensitivity and improved response time of analytical devices for measuring trace gases within the last five years, such as advancements in laser spectroscopy, have significantly improved the effectiveness of the current methods of measuring these gases in aquatic and terrestrial systems. Systematic errors in trace gas flux estimates have also been reduced with the refinements in estimates of the gas transfer velocity,k, through the use of tracers in the two systems. Footprint corrections of micrometeorological flux measurements in terrestrial systems have provided a better means of identifying the spatial sources of trace gases, and thus, have increased the scope of inference from trace gas flux measurements. Despite these improvements, however, flux measurement errors still remain high. Experimental and sampling designs that can efficiently and effectively deal with the spatial and temporal variabilities in trace gas flux measurements to the minimum are of utmost priority. The same can be said of the modeling procedures; that is, there is a need for an effective method that can reduce instead of propagate potential errors in scaling from field plot to regional or global scales.
Lee, K., R.H. Wanninkhof, R.A. Feely, F.J. Millero, and T.-H. Peng. Global distribution of total inorganic carbon in surface water. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 493-496 (1999).
No abstract.
Lee, K., R.H. Wanninkhof, T. Takahashi, S.C. Doney, and R.A. Feely. Interannual variations in oceanic uptake of anthropogenic carbon dioxide for the period of 1982-1995. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 31-34 (1999).
No abstract.
Lee, T.N., E. Williams, E. Johns, and W.D. Wilson. First year results from enhanced observations of circulation and exchange processes in western Florida Bay and connecting coastal waters, including effects of El Niño and Hurricane Georges. 1999 Florida Bay and Adjacent Marine System Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 145-147 (1999).
No abstract.
Majumdar, S.J., S.D. Aberson, C.H. Bishop, and Z. Toth. Real time hurricane track targeting using a VICBAR ensemble. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 755-756 (1999).
No abstract.
Marks, F.D., and H.A. Friedman. 1999 Hurricane Field Program Plan. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami Florida (published for limited distribution), 142 pp. (1999).
No abstract.
Marks, F.D., P.P. Dodge, and C. Sandin. WSR-88D observations of hurricane atmospheric boundary layer structure at landfall. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 1051-1054 (1999).
No abstract.
McGillis, W., J. Edson, and R.H. Wanninkhof. Direct air-sea flux measurements of carbon dioxide over the North Atlantic Ocean and the comparison to indirect methods. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22,1999. Center for Global Environmental Research (CGER-I037-99), 367-377 (1999).
To date, large uncertainties in the extent of the CO2 flux between the atmosphere and ocean have prevented us from accurately quantifying how the increasing atmospheric CO2 burden partitions between the ocean and the terrestrial biosphere. This limits our ability to accurately predict future atmospheric CO2 levels. We have recently designed a direct CO2 flux measurement system that considerably improves our estimates of air-sea gas exchange. The system measures the direct air-sea flux of CO2 in the atmospheric boundary layer using eddy correlation (direct covariance). It was successfully deployed during the large scale experiment to study air-sea gas fixes, GASES98, which was conducted in the CO2 sink region of the North Atlantic during May/June of 1998. The seasonal algal bloom caused air-sea pCO2 differences of between -80 to ~100 µatm. This large concentration gradient generated large signals for accurate measurement of the CO2 flux using a close path CO2 sensor. In addition to the CO2 gas flux, the comprehensive atmospheric flux measurement suite included momentum, heat, and moisture fluxes. Atmospheric flux and air-sea gas concentration measurements were performed for over 500 hours, providing more than 1000 observations. Wind speeds between 1 and 16 m/s were experienced over the range of these observations. Preliminary flux estimates from our system compare extremely well with previous estimates of the gas transfer velocity for wind speeds below 7 m/s. At higher wind speeds, the transfer velocities obtained from our system are as much as 20-50% higher than those estimated by empirical relationships. Based on accurate air-sea CO2 coefficients obtained by our investigation and atmospheric and surface ocean pCO2 data obtained to date, estimates of the global ocean CO2 sink are now feasible. Our findings will also provide better predictions of the seasonal and interannual variability of sea-air CO2 flux observed in various global regions.
McTaggart, K.E., G.C. Johnson, C.I. Fleurant, and M.O. Baringer. CTD/O2 measurements collected on a Climate and Global Change cruise along 24°N in the Atlantic Ocean (WOCE section A6) during January-February 1998. NOAA Data Report, ERL PMEL-68 (PB99-155194), 368 pp. (1999).
Summaries of CTD/O2 measurements and hydrographic data acquired on a Climate and Global Change cruise during the winter of 1998 aboard the NOAA ship Ronald H. Brown are presented. The majority of these data were collected along 24.5°N from 23.5°W to 69°W. Completing the transatlantic section are data collected along a northeast-southwest dogleg off the coast of Africa, and along a second, short, zonal section along 26.5°N off the coast of Abaco Island from 69°W to 77°W, jogging north along 27°N in the Straits of Florida to 80°W. Data acquisition and processing systems are described and calibration procedures are documented. Station location, meteorological conditions, CTD/O2 summary data listings, profiles, and potential temperature-salinity diagrams are included for each cast. Section plots of oceanographic variables and hydrographic data listings are also given.
Mestas-Nunez, A.M., and D.B. Enfield. Rotated global modes of non-ENSO sea surface temperature variability. Journal of Climate, 12(9):2734-2746 (1999).
A varimax rotation was applied to the EOF modes of global SST derived by Enfield and Mestas-Nuñez (1999). The SST anomaly record is more than a century long, with a global complex EOF representation of ENSO and a linear trend removed at every grid point. The rotated EOF modes capture localized centers of variability that contribute to the larger scale spatial patterns of the unrotated modes. The first rotated EOF represents a multidecadal signal with larger response in the North Atlantic. The second rotated EOF represents an interdecadal uctuation with larger response in the eastern North Pacific and out of phase fluctuations of smaller amplitude in the central North Pacific. The third rotated EOF captures interdecadal fluctuations in the eastern tropical Pacific with a dominant peak that coincides with the 1982-83 ENSO. The fourth rotated EOF has an interdecadal to multidecadal nature with larger response in the central equatorial Pacific and quasi-symmetric out of phase response in the western North and South Pacific. The fifth mode represents multidecadal fluctuations with large response at about 40°N in the North Pacific. The sixth mode has interannual to interdecadal time scales with largest response confined to the South Atlantic. Our rotated modes are dominated by intra- rather than interocean uctuations supporting the hypothesis that the non-ENSO variability is more regional than global in nature. Analyses of sea level pressure and surface wind stress show that in general the non-ENSO rotated EOFs are consistent with an ocean response to local atmospheric forcing. An exception is the eastern tropical Pacific mode which is more consistent with an atmospheric response to changes in the ocean SST.
Mestas-Nunez, A.M., and D.B. Enfield. Rotated global modes of non-ENSO sea surface temperature. Proceedings, 23rd Annual Climate Diagnostics and Prediction Workshop, Miami, Florida, October 26-30, 1998. National Weather Service, 162-165 (1999).
No abstract.
Molinari, R.L. Lessons learned from operating global ocean observing networks. Bulletin of the American Meteorological Society, 80(7):1413-1420 (1999).
The Global Ocean Observing System Center (GOOSC) at the National Oceanic and Atmospheric Administration's (NOAA) Atlantic Oceanographic and Meteorological Laboratory operates two global observing networks, a drifting buoy array, and a Voluntary Observing Ship network. The arrays provide in real time surface atmospheric and subsurface oceanographic data needed by NOAA weather and climate forecasters. The data are used in delayed mode to verify model simulations of the ocean and atmosphere, to provide in situ calibration/validation data for remote sensing observations, and to increase understanding of the dynamics of the ocean and atmosphere. The operational and research lessons learned in the operation of the GOOSC are reviewed. Operationally, it was learned that, because of costs, international participation is required to maintain global networks; data management methodology is a critical component of operations; and integrated observing systems using multiple platforms provide more accurate products. Scientifically, it was learned, for example, that accurate characterizations of the salinity field must be available in model simulations. As more data become available it is found that scales of important phenomena such as equatorial upwelling are smaller, and high-frequency signals can impact on the mean structure of the upper ocean. These findings must be considered when designing effective sampling strategies.
Molinari, R.L., S.L. Garzoli, and R.W. Schmitt. Equatorial currents at 1000 m in the Atlantic Ocean. Geophysical Research Letters, 26(3):361-364 (1999).
Twenty-seven Profiling ALACE (PALACE) floats were deployed in the equatorial Atlantic during July-August 1997. The floats were ballasted to drift at 1000 m for 10 to 14 days, return to the surface while obtaining a temperature profile, transmit data via satellite, and then after one day return to 1000 m. One-year float paths are now available. Floats deployed on the equator were launched into a deep westward jet. The jet extends some 1-2° north of the equator, with eastward motion observed in floats to the north of 2°N. The equatorial current reverses in the central basin to the east in mid-October and then back to the west in mid-February. Flow to the north also reverses. The short space and time scales contrast with earlier work based on fewer floats that inferred space scales of some 5 -10 in latitude and time scales greater than one year. The new results are consistent with models that indicate that equatorial Rossby waves are the cause of the reversing currents.
Morisseau-Leroy, N., M.K. Solomon, G.P. Momplaisir, T. Kurian, and E. Griffin. Oracle 8I SQLJ Programming. Osborne McGraw-Hill (ISBN 0072121602), 557 pp. (1999).
No abstract.
Murillo, S.T., and J.J. O'Brien. The influence of ENSO on eastern Pacific tropical cyclones. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 437-438 (1999).
No abstract.
Murillo, S.T., W.-C. Lee, K. Hondl, P.P. Dodge, C. McAdie, and F.D. Marks. Implementation of the GBVTD technique in nowcasting hurricane wind fields using the WSR-88D. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 311-312 (1999).
No abstract.
Nelsen, T.A., and J.R. Proni. Detecting, mapping, sampling, and analyzing oceanic suspended particulate matter: Methods complementary to acoustic detection of environmentally sensitive ocean outfall and dumped materials. Joint Meeting, 137th Regular Meeting of the Acoustical Society of America and 2nd Convention of the European Acoustics Association: Forum Acousticum 99, Berlin, Germany, March 15-19, 1999. Journal of the Acoustical Society of America, 105(2):1322 (1999).
Natural systems such as lakes, rivers, and oceans can be described by dissolved and particulate components. Particulate sources in coastal oceanic environments include natural materials from seaward riverine and estuarine flows and anthropogenic sources such as ocean dumping and outfalls. Plumes of suspended particulate matter (SPM) can be natural (lithogenic and biogenic), anthropogenic, and any mixture of these. Because SPM can range from environmentally neutral (i.e.,lithogenic and biogenic) to hazardous (heavy metals, bacteria), detecting, tracking, sampling, and sourcing SPM plumes can be beneficial for the environment and human health. Acoustic methods have proven successful in detecting and mapping oceanic SPM over large spatial areas but are limited in resolving internal fine structure, estimating relative contributions of merged plumes from various sources (e.g., river outflow vs. dumping), and differentiating between introduced and in-situ SPM. To complement acoustics, CTD/optical/water survey tools have been employed for guided sampling of plumes. Water samples for total suspended matter (TSM) and particle size distributions have proven useful to both calibrate acoustic measurements and provide insight into signatures provided by particle size distributions. Signatures, determined by factor and component analyses, allows mapping of SPM components, as well as estimating their dilution and long-termed budgets.
Nelsen, T.A., and J.R. Proni. Distribution and movement of discharged dredged material at the San Juan Ocean Disposal site. Final Report to the U.S. Army Corps of Engineers, MIPR No. W32CS580843181, 57 pp. (1999).
No abstract.
Nelsen, T.A., and J.R. Proni. Signatures contained in suspended particulate matter with application to coastal-ocean environmental studies. In Coastal Engineering and Marine Developments, C. Brebbia and P Anagnostopoulos (eds.). WIT Press, Southampton, 328-346 (1999).
Suspended particulate matter (SPM) samples from the New York Bight Apex collected during a sewage-dump experiment were analyzed for chemical as well as physical parameters such as particle-size distributions. The latter provided a signature of the SPMs' sewage component that allowed differentiation from other components. These results were applied to a series of eight Water Column Characterization (WCC) cruises in this area. Co-analysis of WCC and sewage dump particle-size distributions by factor analysis and Distribution Component Analysis revealed patterns that allowed differentiation of sewage-derived components for all WCC samples. From this, a long-termed budget of SPM components, including sewage-derived materials, was constructed. Given this, we conclude that useful tools are available for developing signatures of anthropogenic components of SPM plumes which are independent of study sites or subject materials. These signatures can be applied to understand the sources, pathways, and sinks of such materials in the coastal ocean, as well as constructing long-termed budgets thereof. Ultimately such estimates can be critical to waste management strategies and decisions in an ever more anthropogenically-impacted coastal ocean.
Nelsen, T.A., G. Garte, C.M. Featherstone, P.L. Blackwelder, T. Hood, C. Alvarez-Zarikian, P. Swart, H.R. Wanless, L. Tedesco, C. Souch, J. Pachut, and J. Arthur. Understanding long-term rainfall, freshwater flow, and salinity patterns with concomitant responses of benthic microfauna, stable isotopes, and pollen in Oyster and Florida Bays. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 189-190 (1999).
Salinity records exhibited variability from the decadal scale to the monthly scale that can be accounted for by changing patterns in regional rainfall. Changes in salinity, both near the outflow of the Shart River Slough at Oyster Bay, and in central Florida Bay near Jimmy Key, show a direct response to regional rainfall on these time scales. Moreover, regional rainfall, represented by the 80+ year record at Homestead, Florida, proved representative of the study area and indicated high correlation with flow into Shark River Slough prior to major watershed construction instigated in the early 1960s. During subsequent periods of water management strategies, enacted from the mid-1960s to present, results indicate essentially no correlation between regional ranfall and flow during the Monthly Allocation Plan. In contrast, correlations most closely paralleled pre-construction, apparently more natural condtions, during the Rainfall Plan. Investigated characteristics for the benthic microfaunal community (foraminifers and ostracods) such as stable isotopes, abundance, and community diversity, exhibited changes and trends that apparently more closely paralleled natural rather than anthropogenic influences over the whole period of record. At both Jimmy Key and Oyster Bay, foraminifer and ostracod data indicate direct correlation to rainfall patterns for temporal scales ranging from decadal down to the limit-of-resolution of our geochronology. An exception to this natural influence was observed from the late-1940s to mid-1950s during which time a dual transition occurred in the sediments adjacent to the Shark River Slough in Oyster Bay. Organic carbon content permanently declined from above- to below-average with concurrent onset of major increases in foraminifer and ostracod abundances. These events temporally conicided with the construction of the Everglades Agricultural Area, which impounded 700,000 acres of organic-rich swampland. These effects were not observed for sediments representing the same time period at Jimmy Key. Stable isotope (delta 18O, delta 13O) trends alone for ostracods and foraminifers at Oyster Bay and Jimmy Key showed mixed signals, with most data suggesting upcore trends to less fresh, more marine conditions. However, when long-term trends for relative abundance of salinity-sensitive species were examined, for the same time periods and locations, they confirmed a statistically valid upcore trend toward less fresh, more marine conditions at both Oyster and Florida Bay study sites. This trend was coincident with a weak decline in regional rainfall over the same time span. Changes in the stable isotopic values of these microfauna indicated, to the limits of our geochronology, direct responses to regional rainfall. Such responses more closely paralleled rainfall than freshwater runoff, even adjacent to the outflow of the Shark River Slough. At Oyster Bay, istracod stable isotope (delta18O) trends correlated better with variabions in regional rainfall than with freshwater outflow from the adjacent Shark River Slough. Crashes in microfaunal abundances at Oyster Bay and more gradual declines at Jimmy Key were salinity related. This abundance drop was concurrent with an equally dramatic drop in community diversity. The latter was characterized by survivor-mode dominance by two microfaunal species and occurred over a period of drought at both sites and the related reduced flow from Shart River Slough. A non-traditional use of pollen allowed evaluation of the degree of paleo-flushing from Shark River Slough that not only correlated well with existing flow and rainfall records but suggests validity as a flushing proxy for pre-record eras. Analysis of regional pollen indicated taxa associations that allowed discrimination of pollen zonations from coastal mangrove to upland slough environments. This, in turn, allowed reconstruction in the sediment record of historical periods of major to minor flushing from Shark River Slough.
Ooyama, K.V. Boundary-layer parameterization in a cloud-resolving model using the radical thermodynamic formulation. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 150-152 (1999).
No abstract.
Ortner, P.B., L.B. Crowder, and D.E. Hoss. The South Atlantic Bight Recruitment Experiment: Introduction and overview. Fisheries Oceanography, 8:1-6 (1999).
The South Atlantic Bight Recruitment Experiment (SABRE) brought together an interdisciplinary team of scientists to conduct research to enhance our understanding of the relationship between variation in environmental factors and the variable recruitment of "estuarine dependent" fishes within the South Atlantic Bight. The project sought to develop a new fusion of government and academic scientists, each possessing unique skills, to address the difficult problem of recruitment variability in fishes. This fusion required the development of appropriate and, at that time, novel management and administrative strategies. SABRE initially focused on recruitment dynamics of Atlantic menhaden, Brevoortia tyrannus, in the South Atlantic Bight, but expanded over time to include several estuarine-dependent species and much of the Middle Atlantic Bight as well. The project was conducted from 1991 to 1997 and resulted in a substantial improvement in our understanding of the life history and ecology of Atlantic menhaden and the potential constraints upon its recruitment. SABRE also contributed to our understanding of the physical oceanography of the western North Atlantic shelf and adjacent coastal inlets and the implications of physical dynamics upon the potential pathways for larval transport.
Ortner, P.B., M.J. Dagg, G.S. Kleppel, and C.R. Tomas. Grazing by zooplankton in Florida Bay waters. Florida Sea Grant College Program, FLSGP-G-99-012, 2 pp. (1999).
No abstract.
Palmer, D.R. Parabolic approximations for global acoustic propagation modeling. NOAA Technical Memorandum, ERL AOML-94 (PB99-171571), 54 pp. (1999).
Motivated by the difficulty in using the splitting matrix method to obtain parabolic approximations to complicated wave equations, we have developed an alternative method. It is three-dimensional, does not a priori assume a preferred direction or path of propagation in the horizontal, determines spreading factors, and results in equations that are energy conserving. It is an extension of previous work by several authors relating parabolic equations to the horizontal ray acoustics approximation. Unlike previous work, it applies the horizontal ray acoustics approximation to the propagator rather than to the Green's function or the homogenous field. The propagator is related to the Green's function by an integral over the famous "fifth parameter" of Fock and Feynman. Methods for evaluating this integral are equivalent to narrow-angle approximations and their wide-angle improvements. When this new method is applied to simple problems, it gives the standard results. In this paper, it is described by applying it to a problem of current interest: the development of a parabolic approximation for modeling global underwater and atmospheric acoustic propagation. The oceanic or atmospheric waveguide is on an Earth (or other heavenly body) that is modeled as an arbitrary convex solid of revolution. The method results in a parabolic equation that is energy conserving and has a spreading factor that describes field intensification for antipodal propagation. Significantly, it does not have the singularities in its range-sliced version possessed by many parabolic equations developed for global propagation. The work is generalized to allow for refracted geodetics and the possibility that the depth dependence of the pressure field can be described by adiabatic normal modes.
Peng, T.-H., and F. Chai. Modeling the carbon cycle in the equatorial Pacific Ocean. Proceedings, Second International Symposium on CO2 in the Ocean, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 183-189 (1999).
As part of the U.S. JGOFS SMP program, we have developed an ocean ecosystem model of the equatorial Pacific Ocean with new and export productivity regulated by Si and Fe to synthesize and to analyze data collected during the process-study-oriented survey cruises in 1992. The circulation model is based on the Modular Ocean Model of the NOAA/GFDL ocean general circulation model. The ecosystem model consists of nine components describing two size phytoplankton, two size zooplankton, two detritus pool, and three dissolved nutrients: silicate, nitrate, and ammonium. The carbonate chemistry is parameterized in the model to evaluate the variations of pCO2, and hence the CO2 flux across the air-sea interface. At this initial stage, a test case by using a 1D model is performed to simulate low-silicate, high-nitrate, and low-chlorophyll conditions in the equatorial Pacific, and to investigate how the carbon system behaves in this ecosystem structure. The model includes the vertical upwelling and diffusion processes. The upwelling rate and vertical diffusivity were initially averaged for the region 5°S to 5°N, 180°W to 90°W, the "cold tongue" of the equatorial Pacific from the parameter values of 3D model simulations. Temperature is used to calibrate model upwelling and vertical diffusion rates. Comparison of model results with the observations made during the NOAA/OACES EqPac 1992 expeditions indicates that the vertical profiles of DIC, NO3 and Si(OH)4 are consistent with the measurements made in the fall season when the ocean was in a normal non-El Niño condition. A tight fit of profiles between model and observation is not possible because of spatial variations of the observed values. A 3D simulation is required, which is in progress. The 1D model CO2 evasion rate is estimated to be 2.9 mol/m2/yr, which is within the range of estimates from measurements made during non-El Niño conditions.
Peng, T.-H., and R.H. Wanninkhof. Re-evaluation of historical carbon data based on recent high-quality measurements. AGU 1999 Fall Meeting, San Francisco, CA, December 13-17, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(46):F579, OS51E-15 (1999).
In the Indian Ocean, crossover stations between GEOSECS and recent NOAA/DOE CO2 survey sampling cruises are selected. Measurements of temperature, salinity, oxygen, TCO2, and alkalinity for samples taken below 2000 m depth at these crossover stations are compared. Because water masses below this depth are relatively stable with respect to anthropogenic disturbances, the carbon chemistry and hydrographic properties should remain unchanged in the last three decades. Hence, comparison of deep water properties between new and old data will provide information regarding the need for correction or adjustment in the older data sets. Systematic differences between the two data sets reflect the need for such correction. We apply "Linear Least-Squares Multiple Regression" of TCO2 against salinity, potential temperature, oxygen, and alkalinity of deep waters in new data sets. Using this relationship, TCO2 is predicted from these parameters measured during GEOSECS at the crossover station. The difference between the predicted TCO2 and the GEOSECS observed TCO2 is the adjustment needed for this historical data. The overall average is 21.6 ± 4.1 mol/kg, which is the mean adjustment needs to be made to all GEOSECS TCO2 measurements in the Indian Ocean.
Peng, T.-H., J.-J. Hung, R.H. Wanninkhof, and F.J. Millero. Carbon budget in the East China Sea in spring. Tellus B, 51(2):531-540 (1999).
Results of total dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements made in the East China Sea (ECS) during a geochemical expedition of KEEP (Kuroshio Edge Exchange Processes) program in May of 1996 show that ECS is a CO2 sink during the spring season. The mean difference of fCO2 (fugacity of CO2) between the atmosphere and surface water is calculated to be 28 µatm, and the resulting net CO2 invasion flux is 2.1 mol/m2/yr, which gives about 0.03 GtC/yr of CO2 uptake in this continental shelf in spring. This study supports the notion that shelf regions can be a significant CO2 sink. The riverine alkalinity, which discharges into ECS, is estimated to be 1,743 µmol/kg on the basis of a linear relationship between TA and salinity. The observed salinity-normalized alkalinity in ECS is higher than that in the open sea, and this excess alkalinity is estimated to be 42 µmol/kg. With the known rate of the Changjiang discharge, this excess TA gives a mean residence time of 1.2 years for the continental shelf water in the ECS. The DIC in the ECS is also found to be higher than that in the open sea. This excess DIC is estimated to be about 76 ± 70 µmol/kg, which is equal to a net carbon input to ECS of 3.9 ± 3.6 mol/m2/yr. Based on the riverine alkalinity input, the equivalent riverine carbon flux from Changjiang discharge is estimated to be about 1.8 mol/m2/yr. With net CO2 invasion flux of 2.1 ± 2.8 mol/m2/yr, the remaining 0 ± 4.6 mol/m2/yr could come from remineralization of organic matter derived from biological pump in the shelf or terrestrial sources. Although this preliminary carbon budget implies that gas exchange and riverine input are the main sources of excess carbon in ECS, the contribution of biological carbon flux can not be ruled out because of the large uncertainty associated with these estimates.
Pielke, R.A., and C.W. Landsea. La Niña, El Niño, and Atlantic hurricane damages in the United States. Bulletin of the American Meteorological Society, 80(10):2027-2034 (1999).
Hurricanes result in considerable damage in the United States. Previous work has shown that Atlantic hurricane landfalls in the United States have a strong relationship with the El Niño-Southern Oscillation phenomena. This paper compares the historical record of La Niña and El Niño events defined by eastern Pacific sea surface temperature with a data set of hurricane losses normalized to 1997 values. A significant relationship is found between the ENSO cycle and U.S. hurricane losses, with La Niña years exhibiting much more damage. Used appropriately, this relationship is of potential value to decision makers who are able to manage risk based on probabilistic information.
Pielke, R.A., C.W. Landsea, R.T. Musulin, and M. Downton. Evaluation of catastrophe models using a normalized historical record: Why it is needed and how to do it. Journal of Risk and Insurance, 18:177-194 (1999).
No abstract.
Powell, M.D. Hurricanes at landfall. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 107-108 (1999).
No abstract.
Powell, M.D., and S.H. Houston. Comments on "A multiscale numerical study of Hurricane Andrew (1992). Part I: Explicit simulation and verification." Monthly Weather Review, 127(7):1706-1710 (1999).
No abstract.
Powell, M.D., T.A. Reinhold, and R.D. Marshall. GPS sonde insights on boundary layer wind structure in hurricanes. Proceedings, 10th Conference on Wind Engineering, Copenhagen, Denmark, June 21-24, 1999. ICWE, 307-314 (1999).
No abstract.
Powell, M.D., P.G. Black, S.H. Houston, and T.A. Reinhold. GPS sonde insights on boundary layer structure in hurricanes. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 881-884 (1999).
No abstract.
Proni, J.R., and T.A. Nelsen. Integrated measurements of sewage effluent and dredged material discharges. In Coastal Engineering and Marine Developments, C. Brebbia and P Anagnostopoulos (eds.). WIT Press, Southampton, 368-379 (1999).
A series of measurements to characterize sewage effluent discharge plumes and dredged material discharge plumes were carried out in coastal ocean waters off the coast of Puerto Rico in April 1998. A multiple sensor suite including an acoustic backscatter profiler, a towed optical backscatter containing CTD device, a vertical cast CTD having an optical transmissometer and oxygen sensors, and an acoustic Doppler current profiler (ADCP) was utilized to determine the subsurface plume spatial distribution and dilution. The sewage effluent plumes resulted from discharges at several diffusers located approximately one or more miles from the coastline. Using the multiple sensor systems listed above, it was possible to relate measurements made at water locations distant from the diffuser to plumes emanating from various parts of the diffuser under study. That is, a "connectivity" was established so that quantities inherent in the effluent discharge could be used for dilution calculations. Typical "initial" dilutions observed were on the order of 60:1. Using inherent tracers, such as plume salinity, effluent plume distributions were determined out to several hundred meters from the diffuser. "Macro" scale comparisons of multiple sensor outputs were carried out with good general agreement on plume distributions. Comparisons between in-situ "contact" sensors, e.g., temperature and salinity probes, and in-situ remote sensor probes, e.g., optical and acoustic backscatter, optical transmissivity (transmissometry), were made with good agreement resulting.
Proni, J.R., and T.A. Nelsen. Puerto Rico outfall/dredged material disposal studies: April 13-26, 1998. Contract EPA/IAG DW13937869-01-04 (Final report). U.S. Environmental Protection Agency, 74 pp. (1999).
No abstract.
Proni, J.R., and T.A. Nelsen. Recent advances in coastal ocean pollution research and monitoring. Joint Meeting, 137th Regular Meeting of the Acoustical Society of America and 2nd Convention of the European Acoustics Association: Forum Acousticum 99, Berlin, Germany, March 15-19, 1999. Journal of the Acoustic Society of America, 105(2):1323 (1999).
Design of both real-time studies of oceanic discharges of potential pollutants such as sewage effluent, and long-term monitoring of same, are complicated by a number of factors. These factors include lack of knowledge of the space and time distribution of the discharge plume, proper placement sites for sample gathering, and lack of knowledge of the space-time distribution of "interfering" plumes (plumes from sources other than the discharge plume under study). Progress has been made in the development of "integrated sensor suites" which produce data with substantial synergistic benefits. Ocean acoustics plays a key role in integrated sensor suite data unification. In a recent study in the coastal waters off San Juan, Puerto Rico, the ability of acoustics systems to view essentially the complete oceanic water enabled a connection to be made between salinity, temperature, and turbidity measurements gathered in the upper 5 m in the water column to a specific port of a sewage effluent diffuser. Having established the "connectivity" of the distal field measurement to a specific port, a dilution value at the distal point could confidently be calculated. This example is but one of many of the synergies available from utilization of multiple sensor suites unified through acoustics.
Quilfen, Y., A. Bentamy, K.B. Katsaros, and G. Lorand. Estimation of ocean-atmosphere turbulent fluxes from satellite measurements. Proceedings, 1999 International Geoscience and Remote Sensing Symposium (IGARSS '99), Hamburg, Germany, June 28-July 2, 1999. Institute of Electrical and Electronic Engineers, 2 pp. (1999).
No abstract.
Reasor, P.D., M.T. Montgomery, and F.D. Marks. The asymmetric structure of Hurricane Olivia's inner core. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 301-304 (1999).
No abstract.
Rodbell, D.T., G.O. Seltzer, D.M. Anderson, M.B. Abbott, D.B. Enfield, and J.H. Newman. A high-resolution ~15,000 year record of El Niño driven alluviation in southwestern Ecuador. Science, 283:516-520 (1999).
Debris flows have deposited inorganic laminae in an alpine lake 75 kilometers east of the Pacific Ocean, in Ecuador. These storm-induced events are dated by radiocarbon, and the age of laminae that are less than 200 years old matches the historic record of El Niño events. From about 15,000 to about 7,000 calendar years before the present, the periodicity of clastic deposition is greater than or equal to 15 years; thereafter, there is a progressive increase in frequency to periodicities of 2-8.5 years. This is the modern El Niño periodicity, which was established about 5,000 calendar years before present. This may reflect the onset of a steeper zonal sea surface temperature gradient, which was driven by enhanced trade winds.
Rogers, R.F. Amplification of warm-core vortices by convective redevelopment: A key component of tropical cyclogenesis. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 929-932 (1999).
No abstract.
Rogers, R.F., and J.M. Fritsch. Amplification of warm-core vortices by convective redevelopment: A key component of tropical cyclogenesis. Preprints, Eighth Conference on Mesoscale Processes, Boulder, CO, June 28-July 1, 1999. American Meteorological Society, Boston, 55-60 (1999).
Theories explaining the transition of a relatively disorganized area of convection into a coherent, self-sustaining system (i.e., tropical cyclogenesis) have traditionally relied upon the presence of a vortex before genesis can occur. Observations have confirmed the need for these vortices, often detecting them in radar and satellite imagery several days prior to the formation of a tropical depression. However, observational, theoretical, and numerical studies of similar systems over land have found that the initial vortices are often confined to the mid-troposphere. Therefore, an important question to address is how these vortices grow down to the surface in maritime tropical environments, for it is not until the vortex is reflected at the surface that intensification can begin, provided the large-scale environment is not unfavorable. This study investigates how midlevel vorticity within mesoscale convective vortices (MCVs) can amplify and grow downward to the surface by the redevelopment of deep convection. It is shown that the diabatic heating within the convection can increase the magnitude of the balanced warm core of the vortex, further lowering heights beneath the warm core and causing a cyclonic circulation closer to the surface. This cyclonic vorticity can develop in the lower troposphere even in the presence of the anomalously cold air of the low-level cold pool, given a sufficiently strong warm core aloft. The factors that play a key role in governing the downward penetration of vorticity to the surface are 1) onset of deep moist convection; 2) local reduction of the Rossby radius of deformation; and 3) weakening of the surface-based cold pool. These concepts are explored by performing a 48-hour numerical simulation of an observed MCV that underwent multiple cycles of convective redevelopment, amplifying after each cycle. The model was successful in reproducing the creation and evolution of the MCV. The amplitude of the midlevel vortex increased considerably after each convective cycle, as cyclonic vorticity reached the surface during the third cycle. Conditions prior to the third cycle showed a strong southwesterly low-level jet that was transporting warm, moist air over an outflow boundary left from the previous convective cycle and underneath the existing MCV. Deep convection developed within the existing cyclonic circulation and intense latent heat release amplified the warm core. As a result of this warming, lower-tropospheric geopotential heights lowered, creating low-level convergence which increased cyclonic vorticity under the amplifying vortex. This convergence led to an intense vortex in the lower troposphere during the strongest periods of the convective cycle, despite the fact that the lower troposphere was anomalously cold during the entire period. A conceptual model incorporating these ideas is presented.
Schmid, C. On the circulation in the tropical Atlantic. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S179, OS31B-08 (1999).
The circulation in the tropical Atlantic is studied using recent and historical Lagrangian observations. The measurements of the Lagrangian velocities were performed at two levels: near the surface and at intermediate depth. The surface measurements were collected with surface drifters whose drogues were centered at 15 m depth. The intermediate layer measurements derive from an array of 17 PALACE floats deployed in the tropical Atlantic during the summer of 1997. They cycle between about 1000 m and the surface to take a temperature profile every 11 days. Between the two profiles, the PALACE floats drift at depth for 10 days. The presentation will focus on the description of the velocity field and the analysis of the seasonal variability. The available surface drifter data allow the estimation of the mean monthly circulation patterns over large parts of the tropical Atlantic. The resulting fields show the seasonal reversal of the North Equatorial Countercurrent with predominantly westward velocities in the first half of the year and eastward velocities during the second half of the year. The PALACE floats also indicate the existence of a seasonal variability at about 1000 m.
Smith, R.H. IASlinks.org: Online management and distribution of oceanographic and meteorological data for the Gulf of Mexico and Caribbean Sea. Proceedings, First Biennial Intra-Americas Sea Initiative (IASI) Science Meeting, Panama City, Panama, November 9-11, 1999. University of Miami (1999).
There is a growing recognition of the connectivity among oceanic processes within the Gulf of Mexico and Caribbean Sea region (Intra-Americas Sea). Recent technological breakthroughs in communication, specifically the Internet, provide a common denominator for scientific collaboration and data exchange among the region's institutions and government agencies that collect data and utilize data products. The growing need for regional scale models requires that interaction between research endeavors take place, enabling the creation of larger, regional data sets and a more unified approach to understanding the oceanography, climate, and ecology of the Intra-Americas Sea. The Internet web site, http://IASlinks.org, hosted by NOAA/AOML in Miami, Florida, has been developed to facilitate the sharing of resources, results, and data sets relevant to research conducted throughout the Intra-Americas Sea region. The site is presently designed with indices describing the different types of research and the different institutions, agencies, and personnel involved, with regular highlights of specific regional research topics; it is our hope that the site will continue to expand, becoming a more complete representation of observational programs presently underway in and around the Gulf of Mexico and Caribbean Sea. The usefulness of a venue such as IASlinks.org will continue to be realized as scientists and operational observing systems throughout the Intra-Americas Sea make more of their data available over the Internet. In particular, the Internet as a medium for data exchange will play a pivotal role in the forthcoming IOCARIBE-GOOS regional observing system. IASlinks will complement the IASI web site, which will emphasize research programs, education, and training. This collaborative atmosphere, where scientific information and resources are shared with one another, will provide investigators working in the region the ability to tackle larger questions regarding climate, circulation, the propagation of species, and the connectivity of regional marine environments.
Swenson, M.S., and D.V. Hansen. Tropical Pacific Ocean mixed-layer budget: The Pacific cold tongue. Journal of Physical Oceanography, 29(1):69-82 (1999).
Data from satellite-tracked drifting buoys and VOS/XBT profiles for the years 1979-1995 were used to evaluate the seasonal cycle of how major oceanic processes redistribute heat in the cold tongue region of the tropical Pacific. The most active processes for the annual cycle are local heat storage and heat export by entrainment of upwelling and by mean meridional advection. Heat export by zonal advection, however, is not negligible, and meridional eddy heat fluxes associated with tropical instability waves effect a negative feedback that offsets a considerable fraction of that produced by the mean meridional advection. All of these processes mimic the essentially one cycle per year of the surface wind stress, as do those of the depths of both the bottom of the surface mixed layer and the thermocline. Because it is associated with poleward Ekman transports, upwelling, and baroclinic adjustment near the equator, the zonal wind stress component appears to be the more important. The meridional wind stress, while weaker in the annual mean, has a larger annual variation and, therefore, has equal influence on the annual variation of the scalar stress and perhaps the mixed layer thickness. The Monin-Obukov length is found to underestimate the mixed layer thickness very considerably. Finally, we produce the first estimates of the seasonal cycle of eddy heat flux convergence, which plays a significant role in the evolution of the cold tongue, and show that the eddy heat flux convergence can be quantitatively modeled as eddy diffusion with a diffusivity derived from single-particle buoy statistics.
Takahashi, T., R.H. Wanninkhof, R.A. Feely, R.F. Weiss, D.W. Chipman, N. Bates, J. Olafsson, C.Sabine, and S.C. Sutherland. Net sea-air CO2 flux over the global oceans: An improved estimate based on the sea-air pCO2 difference. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 9-15 (1999).
No abstract.
Tedesco, L.P., C. Souch, J. Pachut, J.A. Arthur, H.R. Wanless, P.L. Blackwelder, T. Hood, C. Alvarez-Zarikian, J. Trefry, W.J. Kang, S. Metz, and T.A. Nelsen. The signature of hurricane sedimentation in the lower Everglades/Florida Bay ecosystem: Recognition of sedimentologic, geochemical, and microfaunal indicators. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 194-195 (1999).
Winter storm and hurricane resuspension and transport processes are responsible for building the bulk of the sediment sequence in the accreting bank flanks in both northwest Oyster Bay (Whitewater Bay) and Florida Bay. Repetitive resuspension by winter storms provides fine silt-sized carbonate, siliceous and organic laminae as thin event laminae, mostly a millimeter or less in thickness. As these repetitive winter storms produce similar wind and transport sequences in an area, the constituent composition and mineralogy of the laminae are similar. Vertical profiles of excess 210Pb activity in sediments from northwest Oyster Bay, Jimmy Key, and First National Bank showed that sedimentation at these sites has been in steady state during the last 40 years. However, two to three discontinuities of short duration (<2 years) in the decay profiles of excess 210Pb activities were observed in the sedimentary records from northwest Oyster Bay, Jimmy Key, and First National Bank. Based on excess 210Pb-based ages, the discontinuities occurred at about 1960, 1948, and 1935, dates coincident with major hurricanes passing through Florida Bay: Donna in September 1960 (category 4); an unnamed hurricane in September 1948 (category 3); and the Great Labor Day Hurricane in September 1935 (category 5). Hurricane layers from 1935, 1948, 1960 (Donna), and 1992 (Andrew) in Oyster Bay are identified by a sharp surface on which sand-sized shell, carbonate peloids, and organic detritus are concentrated and overlain by a white, fine sand to silt layer, 0.5-2 cm in thickness. Sedimentologic and geochemical data on discontinuity surfaces show that the base of each hurricane layer is an erosional surface from which several centimeters of sediment was eroded. This is expected as the upper 3-10 cm of the sediment in these accreting flanks is a very soft zone with as much as 80% water content that could easily be removed. Discontinuities of 210Pb profiles and, therefore, erosion were more pronounced in open water sites such as Jimmy Key and First National Bank (3-20 cm thick) relative to the more protected, mangrove coastline surrounded environment of northwest Oyster Bay (~2 cm thick). Major hurricanes (categories 4 and 5) are devastating to the red and black mangrove communities, causing destruction to 50-100% of the forest in the eye wall of the storm. This loss is reflected in the organic detritus content of sediments in cores from northwest Oyster Bay and other areas surrounded by extensive mangrove coastlines. Prior to a major hurricane, the macro-organic detritus is mainly partly decayed fragments of mangrove leaves released from the adjacent forests. Defoliation, uprooting, and death of the forest during and following the storm result in a change in the amount and composition of organic detritus in sediments. Organic detritus is composed of fine root hairs for a period of 5-10 years following the event. This reflects an extended period of erosion and release of root-hair detritus from the disrupted and decaying mangrove peat substrate. Organic detritus gradually decreases and becomes dominated by leaf detritus as the forest recovers. Hurricane-related signals in the microfaunal assemblage data (benthic ostracods and foraminifers) are both site- and event-specific. The two hurricanes that significantly modified the microfaunal assemblages from Jimmy Key and northwest Oyster Bay are the Labor Day Hurricane of 1935 and Hurricane Donna (1960). Hurricane Donna resulted in peaks in relative abundance of atypical benthic foraminifer species at both sites. At Jimmy Key, the species comprising this peak were derived from elsewhere within Florida Bay. In contrast, in northwest Oyster Bay, species were comprised of continental shelf species transported from the Gulf of Mexico by Donna's last winds. An example of hurricane-specific effects can be seen in the differing signals recorded by the 1935 and 1960 hurricanes at Jimmy Key. The 1960 hurricane left a distinct lag-type deposit, whereas the 1935 hurricane sediments were essentially barren of microfauna. High organic carbon influx and subsequent oxygen depletion associated with these hurricane events appear to be recorded in the microfaunal assemblages as well.
Thacker, W.C. Principal predictors. International Journal of Climatology, 19:821-834 (1999).
Principal predictors are linear combinations of variables from one set that efficiently describe the collective variability of those from a second set. Their defining eigenproblem is similar to that of canonical-correlation analysis, and when the two sets are taken to be the same, principal predictors reduce to principal components. Within the context of a forecast model for the circulation in the Gulf of St. Lawrence, they are shown to be capable of providing a low-dimensional characterization of high-resolution model dynamics.
Uhlhorn, E.W., P.G. Black, and A.F. Hasler. Evolution of mesoscale flow in a mature tropical cyclone as determined from satellite imagery. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 200-203 (1999).
No abstract.
Vachon, P.W., and K.B. Katsaros. Atmospheric cyclones from spaceborne SAR. Backscatter, 10(4):14-19 (1999).
No abstract.
Vachon, P.W., K.B. Katsaros, P.G. Black, and P.P. Dodge. RADARSAT synthetic aperture radar measurements of some 1998 hurricanes. Proceedings, 1999 International Geoscience and Remote Sensing Symposium (IGARSS '99), Hamburg, Germany, June 28-July 2, 1999. Institute of Electrical and Electronic Engineers, 1631-1633 (1999).
The RADARSAT synthetic aperture radar (SAR) acquired C-band and HH polarization images over four 1998 hurricanes: Bonnie, Danielle, Georges, and Mitch. We present the SAR images and discuss their quantitative use in understanding hurricane morphology. The SAR provides a complementary "view from below" that is most beneficial when considered in the context of more conventional hurricane observations.
Wang, C., R.H. Weisberg, and J.I. Virmani. Western Pacific interannual variability associated with the El Niño-Southern Oscillation. Journal of Geophysical Research, 104(C3):5131-5149 (1999).
Observations of sea surface temperature (SST), sea level pressure (SLP), surface wind, and outgoing longwave radiation (OLR) show that the El Niño-Southern Oscillation (ENSO) displays western Pacific anomaly patterns in addition to eastern Pacific anomaly patterns. During the warm phase of ENSO, warm SST and low SLP anomalies in the equatorial eastern Pacific and low OLR anomalies in the equatorial central Pacific are accompanied by cold SST and high SLP anomalies in the off-equatorial western Pacific and high OLR anomalies in the off-equatorial far western Pacific. Also, while the zonal wind anomalies over the equatorial central Pacific are westerly, those over the equatorial far western Pacific are easterly. The nearly out-of-phase behavior between the eastern and western tropical Pacific is also observed during the cold phase of ENSO, but with anomalies of opposite sign. These western Pacific interannual anomaly patterns are robust features of ENSO, independent of data sets. It is argued that equatorial easterly (westerly) wind anomalies over the far western Pacific during the warm (cold) phase of ENSO are initiated by off-equatorial western Pacific cold (warm) SST anomalies, and that these winds are important for the evolution of ENSO. An atmosphere model is employed to demonstrate that small off-equatorial western Pacific cold (warm) SST anomalies (compared to those in the east) are sufficient to produce equatorial easterly (westerly) wind anomalies as observed over the far western Pacific. The coupled ocean-atmosphere model of Zebiak and Cane is then modified to investigate the evolution of the western Pacific interannual anomaly patterns in a coupled ocean-atmosphere system, by including a meridional structure to the subsurface temperature parameterization in the western Pacific. The modified model produces both western and eastern Pacific interannual anomaly patterns.
Wang, C., R.H. Weisberg, and H. Yang. Effects of the wind speed-evaporation-SST feedback on the El Niño-Southern Oscillation. Journal of the Atmospheric Sciences, 56(10):1391-1403 (1999).
The thermodynamical process of latent heat flux is added to an analogical delayed oscillator model of the El Niño-Southern Oscillation (ENSO) that mainly considers equatorial ocean dynamics and produces regular, non-phase-locked oscillations. Latent heat flux affects the model sea surface temperature (SST) variations by a positive feedback between the surface wind speed and SST operating through evaporation which is called the wind speed-evaporation-SST feedback. The wind speed-evaporation-SST feedback in which the atmosphere interacts thermodynamically with the ocean through surface heat flux differs from the conventional zonal wind stress-SST feedback in which the atmosphere interacts dynamically with the ocean through momentum flux. The combination of equatorial ocean dynamics and thermodynamics produces relatively more realistic model oscillations. When the annual cycle amplitude of the zonal wind in the wind speed-evaporation-SST feedback is gradually increased, the model solution undergoes a transition from periodic to chaotic and then to periodic oscillations for some ranges of the parameters, whereas for other ranges of the parameters the transition goes from periodic to quasi-periodic and then to periodic oscillations. The route to chaos is the intermittency route. Along with such irregularity, the nonlinear interactions between the annual and interannual cycles operating through the wind speed-evaporation-SST feedback also produce a phase-locking of ENSO to the seasonal cycle. The model ENSO onset and peak occur in the boreal winter and spring, respectively, consistent with the observed phase-locking of ENSO in the far eastern Pacific. It is shown that ENSO decadal or interdecadal variability may result from the nonlinear interactions between the annual and interannual cycles in the tropics.
Wanninkhof, R.H. An overview of GAS EX-98. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S49, A32A-01 (1999).
The gas experiment in the North Atlantic (GAS EX-98) had as its main objective to improve our knowledge of air-sea CO2 fluxes. Understanding of the physics controlling the gas transfer in the field necessitates measuring gas transfer on the time scales of the environmental forcing (sub-hour). Conventional waterside mass balance methods have a response time of at least a day such that we must rely on micrometeorological measurements, or proxies of CO2 such as heat, along with assumption of similarities. Since micrometeorological measurements have yielded too high fluxes compared to mass balance approaches in the past, the first step was to reconcile the measurements. Micrometeorological CO2 flux estimates were obtained from gradients of CO2 and dimethyl sulfide in the (air) marine boundary layer, and by CO2 co-variance measurements. Gas transfer velocities were measured using the dual-deliberate tracer technique with 3He and SF6 in the water column. Changes of CO2 in the water column were used as overall constraints for the gas fluxes after accounting for changes of CO2 concentrations due to biology. The selection of study location was based on the site being a constrained watermass in an eddy in a large CO2 sink region. The anticyclonic (warm core) eddy inhibited dispersion of the deliberate tracers, thereby extending the duration of the experiment, and SF6 concentrations were measurable for the duration of the 24-day process study. The large CO2 sink, averaging -85 µatm during the study, improved the signal to noise for the direct flux measurements. The post-bloom environment was thought to minimize the biological signal compared to the change due to CO2 invasion in the water column mass balance. However, despite the near absence of major nutrients, several lines of evidence suggest rapid biological cycling. The independent estimates of gas transfer velocities agreed well with each other. This is the first time that such concordance is observed between the micrometeorological-based measurements and the water column mass balance based observations. The results from the co-variance data of McGillis and Edson (see abstract in this session) can be fit with a cubic dependence with wind speed. Such a relationship can be reconciled with global flux constraints based on bomb 14C. If such a relationship holds universally over the ocean, the net global CO2 uptake would increase by a half based on the monthly pCO2 climatology of Takahashi (1997).
Wanninkhof, R.H. Recent advances in determining air-sea CO2 fluxes. Proceedings, Second International Symposium on CO2 in the Oceans, Tsukuba, Japan, January 18-22, 1999. Center for Global Environmental Research (CGER-I037-99), 101-104 (1999).
Uncertainties in inverse calculations to determine regional carbon fluxes between the atmospheric, oceanic, and terrestrial reservoirs (Fan et al., 1998) have clearly indicated the need to improve our oceanic carbon flux estimate. There have been significant advances in several aspects of air-sea flux determinations to address this question, including direct estimates of fluxes by co-variance and gradient measurements in the air-boundary layer, extrapolation routines using remote sensing products, and a rapidly increasing observational database of air-sea partial pressure differences. The gas fluxes are commonly expressed as F = k s DELTA-pCO2 where F is the air-sea flux CO2 (mol m-2 day-1), k is the gas transfer velocity (m day-1), s is the solubility (mol m3 µatm-1) and DELTA-pCO2 is the air-water partial pressure difference (µatm). This overview discusses recent research aimed at improving estimates of F, k, and DELTA-pCO2.
Wanninkhof, R.H., and W.M. McGillis. A cubic relationship between air-sea CO2 and wind speed. Geophysical Research Letters, 26(13):1889-1892 (1999).
Using recent laboratory and field results we explore the possibility of a cubic relationship between gas exchange and instantaneous (or short-term) wind speed, and its impact on global air-sea fluxes. The theoretical foundation for such a dependency is based on retardation of gas transfer at low to intermediate winds by surfactants, which are ubiquitous in the world's oceans, and bubble-enhanced transfer at higher winds. The proposed cubic relationship shows a weaker dependence of gas transfer at low wind speed and a significantly stronger dependence at high wind speed than previous relationships. A long-term relationship derived from such a dependence, combined with the monthly CO2 climatology of Takahashi (1997), leads to an increase in the global annual oceanic CO2 uptake from 1.4 Gigaton C yr-1 to 2.2 Gigaton C yr-1. Although a cubic relationship fits within global bomb-14C oceanic uptake constraints, additional checks are warranted, particularly at high wind speeds where the enhancement is most pronounced.
Wanninkhof, R.H., E. Lewis, R.A. Feely, and F.J. Millero. The optimal carbonate dissociation constants for determining pCO2 from alkalinity and total inorganic carbon. Marine Chemistry, 65(3-4):291-301 (1999).
In many numerical ocean chemistry models total dissolved inorganic carbon (DIC) and total alkalinity (TA) are transported between subsurface boxes, and partial pressure pCO2 is calculated from TA and DIC in the surface box in order to account for air-sea exchange of carbon dioxide. The conversion is commonly performed by solving the thermodynamic relationships for equilibria between carbonate, bicarbonate, and aqueous CO2 using apparent carbonate dissociation constants. Four independent determinations of the constants have been performed for seawater in the past 50 years. These results have been corrected, refit, and combined by others, creating a virtual cottage industry of laboratory and field verification and cross checks. Here we show that, based on extensive field observations in three major ocean basins, the calculated surface pCO2 from TA and DIC corresponds best with the measured pCO2 of the constants proposed by Mehrbach et al.
Wanninkhof, R.H., S. Doney, T.-H. Peng, J.L. Bullister, K. Lee, and R.A. Feely. Comparison of methods to determine the anthropogenic CO2 invasion into the Atlantic Ocean. Tellus B, 51(2):511-530 (1999).
A comparison of different methods of estimating anthropogenic CO2 into the Atlantic Ocean through the center of the basin between 62°N and 42°S is performed using referenced high quality total dissolved inorganic carbon (DIC) data. The specific anthropogenic input is determined utilizing analytical procedures as described in Gruber et al. (1996), and Chen and Millero (1979) to correct for remineralization and to estimate preanthropogenic endmembers. These estimates are compared with results of the Princeton ocean biogeochemical model (OBM). The results show the specific inventories of anthropogenic carbon agreeing to within 20% but with different uptake patterns. The differences are largely caused by differing assumptions about mixing and winter outcrop endmembers. The same photosynthetic quotients (Redfield ratios) were used each methods. Varying these constants within the range of literature values causes changes in specific inventories of similar magnitude as the different methodologies. Comparison of anthropogenic CO2 uptake and chlorofluorocarbon ages, and preanthropogenic photosynthetic quotients utilizing the analytical methods suggest that anthropogenic CO2 penetration is too shallow following the procedure according to Gruber et al. (1996), and too deep using those of Chen and Millero (1979) in the North Atlantic. The results support previous observations that the uptake of CO2 in the North Atlantic is disproportionate to its surface area. This is caused by a combination of deep water formation and deep winter mixed layers.
Whung, P.-Y., C.J. Fischer, and T. Meyers. Atmospheric deposition of nitrogen and phosphorous to the South Florida Bay ecosystems. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 87 (1999).
The monitoring nutrient deposition to South Florida Bay is now underway. A 10-m meteorological tower was installed at the Keys Marine Laboratory at Long Key in April 1998. Air samples, both dry and wet deposition such as gaseous ammonia (NH3), particulate ammonium (NH4+), particulate nitrate (NO3-), organic phosphorous (org-PO4), and total phosphorous (PO4), are measured. Meteorological parameters such as wind speed, wind direction, air temperature, relative humidity, and solar radiation are also collected at the sampling site. Atmosphere nitrogen, which includes NH3, NH4+, and NO3-, was sampled using treated filter packs. The preliminary results for the gaseous nitrogen species during the period of April 1998 and March 1999 showed that the NH3 concentrations varied greatly (between 0.034 and 0.76 ug/m3), with relatively higher concentrations in the summer season. The averaged particulate NH4+ and NO3- concentrations were 1.20 ug/m3 and 2.17 ug/m3, respectively. The observed atmospheric NH3 concentrations in South Florida Bay were similar to the averaged NH3 concentrations in other coastal regions (such as Tampa Bay and Chesapeake Bay). Since late October 1998, aerosol monitoring of phosphorous and wet deposition of nitrogen has been underway. The sampling protocol, sample analysis, and shipping logistics have been worked out in collaboration with the laboratory at the Illinois State Water Survey who conducted the analysis for the National Atmospheric Deposition Program (NADP). Samples collected through mid-February have been analyzed. For this period, the average dry deposition rate of ammonium aerosol was estimated to be about 0.18 mg/m2/wk, compared to an average wet deposition rate of 0.1 mg/m2/wk. The averaged weekly wet deposition rate of nitrate was on the order of 0.7 mg/m2/wk. For phosphorous, there has only been one week in which the wet deposition data were above the detectable limit. However, measurable air concentrations have been obtained each week in order to obtain a dry deposition rate. At this time, the averaged weekly PO4- deposition rate was estimated to be about 0.1 mg/m2/wk. The analysis for organic contributions (that do not show up as PO4) (which includes the organic fraction) have been 30% higher than the inorganic fractions. Further analyses of elemental ratios will be used to determine the possible origin of this organic fraction.
Wilkerson, J.C., J.R. McCollum, and J.R. Proni. A methodology for validating satellite estimates of rainfall over the ocean using underwater acoustic techniques. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S99, H21A-05 (1999).
Current methods for validating satellite estimates of precipitation over the open ocean use rain gauge or radar data. The rain gauge data come from low-lying islands and atolls or from moored buoys. The intercomparison of satellite and rain gauge estimates leads to uncertainties in the satellite error estimates due largely to the differences in spatial coverage. Satellite rainfall estimates cover tens to hundreds of km2 while the representative area measured by a rain gauge is only several cm2. In addition to sampling uncertainties, most of these gauges are in the tropical Pacific, while satellite estimation errors depend upon location on the globe. Radar rainfall estimates have sufficient spatial resolution for comparisons with satellite estimates, but the amount of radar data from coastal sites or ships is scarce. In addition, satellite rainfall estimation techniques based on passive microwave emission cannot be applied to grid boxes containing coast, which further limits the amount of comparison data. Due to the current difficulties in validation of oceanic rainfall estimates, we have examined the possibility of utilizing underwater acoustics for oceanic rainfall estimation. It has subsequently been shown that underwater sound can, in fact, be used to detect and classify rainfall in coastal ocean regions and that rainfall estimation to useful accuracy appears feasible. The acoustic technique is now being tested in the deep ocean at the U.S. Navy Atlantic Undersea Test and Evaluation Center located in the Tongue of the Ocean, Bahamas. A 12-hydrophone array tethered to the ocean floor at a depth of 1.5 km has been made available to NOAA for investigation. Acoustic data from the array, covering a 500 km2 area of the ocean surface, is sampled continuously once every 12 seconds giving temporal and spatial data coverage comparable to that of satellite rainfall estimates. This paper presents results of an initial comparison of four satellite rainfall products for the acoustic site with concurrent estimates of rainfall from the underwater array made at comparable time and space scales. These data are supported by independent measurements of rainfall over the array from a WR 74C weather radar located at Nassau, 60 km distant. Products from the Geostationary Operational Environmental Satellite (GOES) include estimates from the Global Precipitation Index (GPI), the GOES Multi-Spectral Rainfall Algorithm (GMSRA), and the Auto Estimator. Rainfall observations from the Special Sensor Microwave Imager (SSM/I) on the Defense Meteorological Satellite Program (DMSP) polar orbiting satellites are also examined.
Willis, P.T. An evaluation of NEXRAD (WSR88D) data as a measure of fresh water flux into the Florida Bay/Everglades system. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 153 (1999).
The radar measurement of rain provides excellent spatial and temporal resolution over a large area. This is true even over water areas, where a dense gauge network may be impossible or prohibitively expensive. But, since the radar does not measure rainfall rate directly, but measures the sixth moment of the raindrop size distribution (dsd), the measurement requires a definitive relation between rainfall rate and the shape of the drop size distribution. The shape of the dsd is not uniquely related to the rainfall rate. This is a source of error, and scatter, in the radar rainfall rate measurements. A major thrust of the project has been to characterize the shape of raindrop size distributions in south Florida. The project described herein involves the measurement of dsd's at a site at the ENP Research Center, and a comparison of the radar rain measurements to the gauge measurements from the extensive gauge network associated with the Florida Bay/Everglades Restoration project. The raw radar data has a spatial scale of approximately 1 x 1 km and a time resolution of 5-6 min. The NEXRAD hydrologic product (dpa) has been smoothed to a spatial scale of 4 x 4 km and a time resolution of 1 hr. This can be easily averaged to larger scales, and longer times to provide desired products. The radar data are empirically related to the gauge data using a probability matching methodology (PMM) which forces the overall match of the radar mean rainfall rate and the mean gauge rainfall and also forces an empirical match in data bin intervals. From extensive data comparisons between the dpa and 1-hr gauge data it is found that the radar significantly underestimates the higher rainfall rates, and overestimates the lower rainfall rates. This is true even from a smaller sample of the full resolution radar data, and high-resolution gauge and disdrometer data. The match provided by the PMM is virtually the same as that from the 4 km/1 hr data. The stability of this relation is being checked with an additional year of radar and gauge data, and the result will be reported. A single gauge/radar rainfall product that retains the best features of each data type is being developed using a cokriging methodology. Sample one-month mean radar data, and combined products using the empirical calibrations, are presented. Planned improvements and future work are also presented.
Willis, P.T. The WSR-88D tropical Z-R relationship in south Florida. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 237-240 (1999).
No abstract.
Willoughby, H.E. Hurricane heat engines. Nature, 401:649-650 (1999).
No abstract.
Willoughby, H.E. Vortex tracking semispectral hurricane models. Preprints, 23rd Conference on Hurricanes and Tropical Meteorology, Dallas, TX, January 10-15, 1999. American Meteorological Society, Boston, 662-665 (1999).
No abstract.
Wilson, W.D. Atlantic western boundary currents. Proceedings, South Florida Measurement Center Workshop: Establishment of a Center for Innovative Oceanography in the 21st Century, Dania, FL, February 24-26, 1999. National Science Foundation, 131-140 (1999).
No abstract.
Wilson, W.D., E. Johns, R.H. Smith, T.N. Lee, and E. Williams. Interaction of freshwater riverine discharges from the Everglades with the Gulf of Mexico and Florida Bay: Preliminary results from a moored array and shipboard surveys. 1999 Florida Bay and Adjacent Marine Systems Science Conference, Programs and Abstracts, Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 175-177 (1999).
No abstract.
Wilson, W.D., S.L. Garzoli, G.J. Goni, W.E. Johns, R.H. Smith, C.I. Fleurant, P.L. Richardson, and D.M. Fratantoni. The North Brazil Current Retroflection: Two recent surveys. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union,80(17):S179, OS31B-11 (1999).
The North Brazil Current is the low-latitude western boundary current that flows northward across the equator in the western Atlantic along the coast of Brazil. The NBC is the main source of inter-hemispheric warm water transport in the Atlantic. Its retroflection supplies water to equatorial zonal currents at various latitudes and depths, and rings separate from the retroflection at irregular intervals and propagate into the western tropical Atlantic. Because of its broad spatial extent, and non-linear and rapidly changing nature, synoptic surveys that adequately describe the NBC are difficult to perform. Two such surveys, by far the most complete to date, were conducted as part of the North Brazil Current Rings Experiment in November/December 1998 and February/March 1999. Surveys contain data from XBT, CTD, and shipboard and lowered ADCP data sources, providing water properties and current velocities to 2000 m. Continuity between cruises is provided by satellite altimetry. In November/December, 1998, the near-surface currents of the retroflection reached to nearly 9°N, 52°W, and a closed recirculation center was evident, which separated shortly thereafter to form an NBC ring. At sub-thermocline level, only the closed circulation of the ring was seen, with the subsurface retroflection completely turning eastward near 4° to 5°N, east of 48°W. During the February/March 1999 survey, the retroflection was found further to the south, its northernmost tip extending to only 7°N, 51°W, with a newly formed NBC ring found just northwest of the retroflection.
Yvon-Lewis, S.A., J.H. Butler, D.B. King, S.A. Montzka, J. Rodriguez, J.M. Lobert, and M. Ko. The oceanic contribution to organic bromine in the atmosphere. International Union of Geodesy and Geophysics, XXII General Assembly, Birmingham, England, July 18-30, July 1999. IUGG99 Abstracts, A110 (1999).
The ocean delivers considerable organic bromine into the troposphere. Although many of the oceanic, bromine-containing compounds are short-lived in the troposphere, they can be convected periodically into the stratosphere, where they contribute to the destruction of stratospheric ozone. Methyl bromide (CH3Br) and the halons are recognized as being the primary carriers of bromine into the stratosphere, but contributions from other compounds may be significant. Some of these other trace gases include CH2Br2, CHBr3, CH2BrCl, CHBr2Cl, and CHBrCl2. All of these gases are produced to some extent in the ocean and their collective sea-air flux is of the same order as the total flux of CH3Br from all sources. We have been measuring CH3Br, CH2Br2, CHBr3, and other bromine-containing compounds in air and surface seawater samples on research cruises in the Pacific, Atlantic, and Southern Oceans since 1994. Results show CH3Br undersaturations throughout much of the ocean, suggesting that the ocean is a net sink for this brominated trace gas. However, results for CH2Br2, CHBr3, and the other bromine-containing compounds show these trace gases to be supersaturated throughout much of the ocean, often with higher degrees of saturation in the tropics and subtropics. These data are presented here and will be used in conjunction with a two-dimensional model to examine the role that the oceans play in the cycling of atmospheric organic bromine.
Zhang, J.-Z. Ship determination of nM nitrite and nitrate by gas-segmented continuous flow analysis with a liquid waveguide capillary flow cell. AGU 1999 Fall Meeting, San Francisco, CA, December 13-17, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(46):F46, B12B-09 (1999).
Incorporation of a 2-m long liquid waveguide capillary flow cell to a gas-segmented continuous flow auto-analyzer significantly enhances the sensitivity of automated colorimetric analysis. Nanomolar concentrations of nitrite and nitrate in oligotrophic surface seawater can be accurately determined. Using this technique the diel cycle of nitrate at nM level in oligotrophic water was observed. The advantages of this technique are low detection limit, high precision, and automation for rapid analysis of a large numbers of samples. This technique has been successfully used on shipboard measurements of about 1000 seawater samples during a one-month cruise in North Atlantic.
Zhang, J.-Z., C.J. Fischer, and P.B. Ortner. Laboratory glassware as a contaminant in silicate analysis of natural water samples. Water Research, 33(12):2879-2883 (1999).
When glassware is used for the storage of water samples, reagents, and standard solutions, dissolution of silicate from the glass containers can contaminate the samples. Experimental results demonstrate that dissolution from glassware can introduce micromolar silicate within a few hours. The extent of dissolution depends upon contact time, salinity, and pH of the solution, and the size and shape of the containers.
Zhang, J.-Z., C.J. Fischer, and P.B. Ortner. Optimization of performance and minimization of silicate interference in continuous flow phosphate analysis. Talanta, 49(2):293-304 (1999).
Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH >0.5. At final pH of 0.78, there is maximum interference from silicate in the sample. We recommend, therefore, as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction, and a [H+]/Mo ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.
Zhang, J-Z., R.H. Wanninkhof, and K. Lee. New production estimated from diel cycle of nutrient and oxygen in the mixed layer. AGU 1999 Spring Meeting, Boston, MA, June 1-4, 1999. Supplement to EOS, Transactions, American Geophysical Union, 80(17):S50, A32A-03 (1999).
New production can be estimated from accurate measurement of inventory change in nutrient at nM level in the mixed layer. A strong diel cycle was observed in nutrient concentration in response to photosynthesis in an anticyclonic eddy in North Atlantic during the GASEX-98 cruise. During a diel study, nitrate concentration was about 92 nM in the morning and decreased to 12 nM at 6 p.m. Nitrate concentration increased after dark, presumably due to the diffusive flux from the nitracline. Oxygen data in the mixed layer also showed a similar diel cycle. The oxygen production during the day caused concentrations to increase by about 2 uM. Under steady state conditions, eddy diffusion is a dominant process for transportation of nutrient to the euphotic zone to sustain the new production. The vertical eddy diffusion coefficients were derived from temporal changes in concentrations of a deliberate tracer, SF6, in the upper thermocline. Together with vertical nitrate distributions, the nitrate flux from nitracline could be estimated. Such a diffusive flux throughout the night can account for a nitrate concentration of 102 nM by morning, which is in good agreement with measured nitrate of 92 nM at 6 a.m. The new production estimated from changes of nitrate inventory in the mixed layer during the day was 28 mmole C/m2, which is in good agreement with 31 mmole C/m2 estimated from the oxygen inventory change. Increases in mixed layer nutrients were observed during a storm event that deepened the mixed layer and brought the nutrient to the surface (1.2 uM nitrate). A good correlation between wind speed and the concentrations of nitrate and nitrite is observed. Addition of nitrate to the mixed layer by the storm disappeared within two days, indicating a rapid nutrient cycle by marine organisms. The relative importance of sporadic storm events versus daily diffusive flux in supply nutrient to new production can be estimated from accurate measurement of inventory change of nutrient and oxygen in the mixed layer.
Zhang, J.-Z., C.J. Fischer, C.R. Kelble, and F.J. Millero. Phosphate distribution coefficients for suspended sediments in Florida Bay. 1999 Florida Bay and Adjacent Marine System Science Conference, Programs and Abstracts Key Largo, FL, November 1-5, 1999. University of Florida Sea Grant Program, 77 (1999).
The distribution coefficient Kd (Kd = Cs/Cw, where Cs is concentration of phosphorus on particle surface and Cw in seawater) is a key parameter that governs phosphorus partitioning between seawater and particle surface. To estimate the distribution coefficient for phosphorus partitioning between suspended sediments and seawater, surface sediments were collected from Florida Bay at various locations with different environmental conditions. The sediments were equilibrated with low nutrient seawater for 24 hours at constant temperature. The particles were then separated from seawater by filtration. The phosphate concentrations in equilibrated seawater were determined by spectrophotometric method using an autoanalyzer. The sediments were then equilibrated with a 1 M MgCl2 solution at pH of 8 for 4 hours. The sorbed and desorbable phosphorus was then extracted into the solution by a complexing reaction with MgCl2. The extracted phosphate was determined after separation from the suspended sediments. The results showed a linear correlation between phosphate concentrations in seawater and exchangeable phosphate on the sediments surface. Preliminary estimated Kd is of 100 L/kg. Further experiments are underway to study the effect of salinity and temperature on the Kd. A fitted equation of Kd as a function of salinity and temperature can be used in a water quality model to predict the fate of input phosphorus in Florida Bay.
**1998**
Aberson, S.D. Five-day tropical cyclone track forecasts in the North Atlantic basin. Weather and Forecasting, 13(4):1005-1015 (1998).
Statistical analyses of the most recent 40 years of hurricane tracks (1956-1995) are presented, leading to a version of the North Atlantic climatology and persistence (CLIPER) model that exhibits much smaller forecast biases but similar forecast errors compared to the previously used version. Changes to the model involve the inclusion of more accurate historical tropical cyclone track data and a simpler derivation of the regression equations. Nonlinear systems analysis shows that the predictability timescale in which the average errors increase by a factor e is approximately 2.5 days in the Atlantic basin, which is larger than that found by similar methods near Australia. This suggests that five-day tropical cyclone track forecasts may have some benefit, and, therefore, a version of CLIPER extended to five days to be used as a baseline to measure this skill is needed.
Aberson, S.D. Impact of the Gulfstream-IV jet aircraft on hurricane forecasts. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C. (paper was mistakenly omitted from the Minutes) (1998).
No abstract.
Aberson, S.D. Targeted observations to improve tropical cyclone forecasts. Scientific Programme, XXIII General Assembly, European Geophysical Society, Nice, France, April 20-24, 1998. European Geophysical Society, 256 (1998).
No abstract.
Aberson, S.D., M.A. Bender, and R.E. Tuleya. Ensemble forecasting of tropical cyclone intensity. Preprints, Symposium on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 150-153 (1998).
No abstract.
Aberson, S.D., M.A. Bender, and R.E. Tuleya. Ensemble forecasting of tropical cyclone tracks. Preprints, 12th Conference on Numerical Weather Prediction, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 290-292 (1998).
No abstract.
Aberson, S.D., M.A. Bender, and R.E. Tuleya. Ensemble forecasting of tropical cyclone tracks and intensity. Scientific Programme, XXIII General Assembly, European Geophysical Society, Nice, France, April 20-24, 1998. European Geophysical Society, 255 (1998).
No abstract.
Aberson, S.D., R.E. Tuleya, and M.A. Bender. Ensemble forecasting of hurricane track and intensity using the GFDL model during 1997. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C.,143-145 (1998).
Tropical cyclone track predictions have shown considerable skill past three days, and intensity predictions are beginning to show some skill. While most forecasts are good, great variability in the utility of individual forecasts occurs. Ensemble forecasting provides a mechanism by which the inherent uncertainty in model forecasts can be assessed. During the 1996 and 1997 hurricane seasons, more than 100 sets of ensemble forecasts using a two-mesh version of the Geophysical Fluid Dynamics Laboratory (GFDL) hurricane model have been run, based upon the bred growing modes produced operationally at the National Centers for Environmental Prediction (NCEP). Results of these track and intensity forecasts will be presented, including information as to how well the models conform to the "perfect model" scenario, whether the forecasts envelope the evolution of the atmosphere, and whether information on the utility of individual model forecasts can be obtained from the ensembles. Plans to continue ensemble forecasting runs during the 1998 hurricane season will be presented.
Aberson, S.D., R.E. Tuleya, and J. Heming. Five-day forecasts of tropical cyclone tracks in the Atlantic basin. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C. (paper was mistakenly omitted from the Minutes) (1998).
Tropical cyclone track predictions have improved so that skill, as assessed by the improvement of forecasts over a forecast provided by a simple statistical model based upon climatology and persistence, averages more than 30% at 72 h, the current standard length of forecasts. Because of the possibility of such skill levels at longer forecast times during the 1997 Atlantic hurricane season, four tropical cyclone track models produced quasi-operational 120 h forecasts. The models were a new version of CLIPER, with which to assess skill, and extensions of the currently run VICBAR, GFDL, and UKMO models. Individual track forecasts and skill assessments for the various models will be shown, and recommendations for future work in this area, both operationally and for research, will be made.
Alfaro, E., L. Cid, and D.B. Enfield. Relationships between the start and end date of the rainy season in Central America and the tropical Atlantic and Pacific Oceans. Investigaciones Marinas, 26:59-69 (1998).
In recent years, several studies have shown that anomalies in the sea surface temperature of the tropical Atlantic and Pacific Oceans are related to variations in the intensity and timing of the rainy season in Central America. In order to study anomalous behavior of the rainy season over Central America, tropical Atlantic and Pacific Oceans indices are used to produce correlation series with the starting and ending date (IELL and TELL) of the rainy season. The North Atlantic (ATN) and SOI-Niño3 indices show the main correlations with the IELL and the TELL respectively.
Amat, L.R., M.D. Powell, and S.H. Houston. WANDA: HRD's real-time tropical cyclone "Wind Analysis Distributed Application." Preprints, 16th Conference on Weather Analysis and Forecasting, Symposium on the Research Foci of the U.S. Weather Research Program, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, J29-J31 (1998).
No abstract.
Asher, W.E., and R.H. Wanninkhof. The effect of bubble-mediated gas transfer on purposeful dual gaseous-tracer experiments. Journal of Geophysical Research, 103(C5):10,555-10,560 (1998).
For air-water gas exchange across unbroken surfaces, the only gas-dependent parameter affecting the transfer velocity is the molecular diffusivity of the transferring species. In contrast, bubble-mediated transfer processes can cause the transfer velocity to depend on both molecular diffusivity and aqueous-phase solubility. This can complicate the analysis of data from dual-gaseous tracer gas transfer experiments. Bubble effects also complicate the estimation of transfer velocities for other gases from the transfer velocity calculated using the dual-tracer data. Herein, a method for incorporating the effects of bubble-mediated gas transfer processes on the transfer velocity is presented. This new procedure is used to analyze the data from two recent dual-tracer gas transfer experiments. Transfer velocities that include the effect of bubbles are calculated using the data from two previous oceanic dual-gaseous tracer experiments. Comparing these transfer velocities with transfer velocities calculated by neglecting the effect of bubbles shows that bubble-mediated transfer increased the transfer velocity of helium 3 by 5% at a wind speed of 10.6 m s-1. However, when using the transfer velocities form helium 3 to calculate transfer velocities for carbon dioxide under the same conditions, including the effect of bubbles, decreases the transfer velocity of carbon dioxide by 18%. This shows that bubble-mediated transfer does not have a large effect on the analysis of dual-tracer data, but it is important in relating transfer velocities determined using helium 3 and sulfur hexafluoride to transfer velocities of more soluble gases at wind speeds above 10 m s-1.
Asher, W.E., and R.H. Wanninkhof. Transient tracers and air-sea gas transfer. Journal of Geophysical Research, 103(C8):15,9393-15,958 (1998).
This paper provides a review of the physics and chemistry associated with air-sea gas transfer of transient atmospheric trace gases and the available laboratory and field measurement techniques used to study air-water gas transfer. The mechanistic principals and their relation to the measurement techniques are used to show that the error associated with estimating air-sea transfer velocities of transient tracers from transfer velocities measured using proxy tracers can be significant if an incorrect dependence of the transfer velocity on molecular diffusivity is assumed. Bubble-mediated transfer processes are also demonstrated to have a significant effect on the parameterization of the transfer velocity.
Atakturk, S.S., and K.B. Katsaros. Estimates of surface humidity and wind speed obtained from satellite data in the stratocumulus regime in the Azores region. In Remote Sensing of the Pacific Ocean by Satellites, R.A. Brown (ed.). Southwood Press, Marrickville, Australia, 16-22 (1998).
No abstract.
Bauer, S., M.S. Swenson, A. Griffa, A.J. Mariano, and K. Owens. Eddy-mean flow decomposition and eddy-diffusivity estimates in the equatorial Pacific. Journal of Geophysical Research, 103(C13):30,855-30,872 (1998).
The ocean-atmospheric dynamics of the tropical Pacific Ocean create longitudinally coherent zonal flow () with strong meridional shear () in the large-scale mean and energetic mesoscale (O(100 km)) component. Parameterization of the effects of the mesoscale field depends on the separation of the large-scale mean and mesoscale eddy components in order to compute meaningful eddy diffusivity estimates in flow regimes that demonstrate strong currents and strong shear. Large gradients in the large-scale mean have precluded diffusivity estimation by traditional binning techniques. In this first of two publications, a method is developed for using Lagrangian data to estimate the diffusivity addressing the inhomogeneity of the mean flow. The spatially dependent estimate of the mean field is computed with a least squares bicubic smoothing spline interpolation scheme with an optimized roughness parameter which guarantees minimum energy in the fluctuation field at low frequencies. Numerical simulations based on a stochastic model of a turbulent shear flow are used to validate our approach in a conceptually simple but realistic scenario. The technique is applied to near-surface drifter observations obtained from 1979-1996 from two dynamically distinct time-space regions of the tropical Pacific Ocean. The first region, in the SEC, is characterized by a linear zonal shear mean flow and an approximately exponential autocovariance structure in the residuals. The residual velocity variance is s2 ~ 130 cm2 s-2 for both components and horizontal diffusivities are 7 × 107 cm2 s-1, and 3 × 10 cm2 s-1. The second region, in the NECC and the NEC, has a mean flow with a strong zonal shear and a weak northward velocity. The autocovariance is approximately exponential for the zonal component while the meridional component has a negative lobe at about 10 days probably due to the presence of instability waves. The variance is approximately tripled compared to the SEC region estimate while the meridional diffusivity estmate is nearly the same magnitude. The zonal diffusivity is estimated to be 15 × 107 cm2 s-1.
Black, M.L., S.H. Houston, and G. Carter. AFRES-NOAA flight-level data comparisons. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C. (paper was mistakenly omitted from the Minutes) (1998).
A coordinated flight between an Air Force Reserve (AFRES) C-130 aircraft and both National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft was conducted on 12 July 1997. This mission was the third in recent years and resulted from a recommendation made at the 49th Interdepartmental Hurricane Conference. The AFRES and NOAA aircraft each recorded, at 1-sec intervals, the standard suite of flight-level meteorological data (winds, temperature, dew point, pressure) and navigational information (e.g., position, true air speed, heading, etc.). The data were collected during clear and moderate-wind conditions along the Florida west coast, about 100 miles north of Tampa. The NOAA and AFRES aircraft conducted "fly-bys" adjacent to an Air Force Aerostat balloon which was carrying a NOAA calibrated instrument package. The balloon approaches were at altitudes ranging from 1,000 to 10,000 feet and provide the basis for the intercomparisons. A GPS dropwindsonde was released along the coast to supply another set of independent measurements. Comparisons between the flight-level data collected from the balloon, the dropsonde, and the NOAA and AFRES aircraft will be presented. Recommendations, if any, will be made to improve the data collection, processing, and strategies for future intercomparison flights. Additionally, the calibration information gained from this flight will be used to investigate the data quality from concurrent flights into tropical cyclones by both the NOAA and AFRES aircraft this past hurricane season.
Black, P.G., and L.K. Shay. Observations of tropical cyclone intensity change due to air-sea interaction processes. Preprints, Symposium on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 161-168 (1998).
No abstract.
Black, P.G., F.D. Marks, P. Dodge, I. Popstefanija and R. Pauwl. First observations from the vertically scanning Doppler radar (VSDR): A key to G-IV reconnaissance operations. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A236-A256 (1998).
No abstract.
Boebel, O., C. Duncombe Rae, S.L. Garzoli, J. Lutjeharms, P. Richardson, T. Rossby, C. Schmid, and W. Zenk. Float experiment studies interocean exchanges at the tip of Africa. EOS, Transactions, American Geophysical Union, 79(1):7-8 (1998).
No abstract.
Bosart, L.F., W.E. Bracken, J. Molinari, C.S. Velden, and P.G. Black. Environmental influences on the rapid intensification stage of Hurricane Opal (1995) over the Gulf of Mexico. Preprints, Symposium on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 105-112 (1998).
No abstract.
Bove, M.C., J.J. O'Brien, J.B. Eisner, C.W. Landsea, and X. Niu. Effect of El Niño on U.S. landfalling hurricanes, revisited. Bulletin of the American Meteorological Society, 79(11):2477-2482 (1998).
Changes in the frequency of U.S. landfalling hurricanes with respect to the El Niño-Southern Oscillation (ENSO) cycle are assessed. Ninety-eight years (1900-1997) of U.S. landfalling hurricanes are classified, using sea surface temperature anomaly data from the equatorial Pacific Ocean, as occurring during an El Niño (anomalously warm tropical Pacific waters), La Niña (anomalously cold tropical Pacific waters), or neither (neutral). The mean and variance of U.S. landfalling hurricanes are determined for each ENSO phase. Each grouping is then tested for Poisson distribution using a chi-squared test. Resampling using a "bootstrap" technique is then used to determine the 5% and 95% confidence limits of the results. Last, the frequency of major U.S. landfalling hurricanes (sustained winds of 96 kt or more) with respect to ENSO phase is assessed empirically. The results indicated that El Niño events show a reduction in the probability of a U.S. landfalling hurricane, while La Niña shows an increase in the chance of a U.S. hurricane strike. Quantitatively, the probability of two or more landfalling U.S. hurricanes during an El Niño is 28%, of two or more landfalls during neutral conditions is 48%, and of two or more landfalls during La Niña is 66%. The frequencies of landfalling major hurricanes show similar results. The probability of one or more major hurricane landfall during El Niño is 23% but is 58% during neutral conditions and 63% during La Niña.
Broecker, W.S., and T.-H. Peng. Greenhouse Puzzles, Part I, Keeling's World: Is CO2 Greening the Earth? Eldigio Press, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, 111 pp. (1998).
This section's hero is Charles David Keeling. In the late 1950s, he had the wisdom to establish two stations for the continuous precise measurement of atmospheric carbon dioxide, one high on Hawaii's extinct volcano Mauna Loa and the other at the South Pole. The records from these stations provide the foundation upon which all studies of man's perturbation of the Earth's carbon cycle rest. Not only did Keeling have the foresight to establish these stations but also the tenacity to make sure that year in and year out they produced accurate results. Keeling took on this task as part of a career-long effort to understand the flux of CO2 gas through the atmosphere, into the ocean and into and out of the terrestrial biosphere. He was the first to realize the wealth of information contained in the spatial and seasonal texture of the atmosphere's CO2 content. In addition to his direct scientific contribution, he fostered a secondary one. Son, Ralph, is doing for atmospheric O2 all the kinds of things papa did for atmospheric CO2.
Broecker, W.S., and T.-H. Peng. Greenhouse Puzzles, Part II, Martin's World: CO2's Glacial Hideout? Eldigio Press, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, 73 pp. (1998).
The selection of the hero of this section has proven difficult. Under consideration were those who first measured the low CO2 contents of air trapped in glacial age ice, those who used carbon isotope ratios and cadmium contents in foraminifera to set constraints on scenarios designed to explain this drop, and those who demonstrated that the high latitude outcrops of the deep sea dictated the CO2 content of the entire surface ocean and, in turn, that of the atmosphere. But in the end, we initially selected a dark horse, David Archer, who at the time this book was being written, put his finger on what appeared to be the mechanism responsible for the atmosphere's glacial to interglacial CO2 cycle. He obtained microelectrode O2 and pH data from the upper few centimeters of deep sea sediments which clearly demonstrated the importance of bacterial respiration as a driver of calcite dissolution. Encouraged by preliminary boron-isotope-based paleo pH measurements which suggested large deep sea CO=3 concentrations during glacial time, Archer showed that an increase in the rain rate of organic matter could generate the required CO=3 ion change with little or no change in lysocline depth. But alas, now five years later, Archer's hypothesis has like its predecessors fallen on hard times. Danny Sigman, while a graduate student at Woods Hole, demonstrated that the requisite large separation between the saturation horizon and the lysocline could not be sustained. So in this second edition, we replace David Archer with the late John Martin who pioneered the concept that the availability of iron limits plant productivity in many parts of the oceans. He also pointed out that the large excess of iron carried to the sea during glacial time by the several-fold higher dust rain may have been responsible for the CO2 drawdown.
Broecker, W.S., and T.-H. Peng. Greenhouse Puzzles, Part III, Walker's World: CO2 , Chemical Traffic Controller? Eldigio Press, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, 93 pp. (1998).
This section's hero is James C.G. Walker, a space physicist at the University of Michigan. In 1981, together with his colleagues P.B. Hays and J.F. Kasting, he published a paper which lays out in beautiful simplicity the role of atmospheric CO2 as the chemical policeman controlling the flow of continental weathering products to the sea, and thereby maintaining a balance between the rate of outgassing of CO2 gas from our planet's interior and the rate of CO2 removal to sea floor sediments as calcite. The important consequence of this police action is its influence on Earth climate. Walker and his colleagues pointed out that early in the Earth's history the tendency toward cooler temperatures related to the faintness of the young Sun was mostly likely compensated by higher atmospheric CO2 contents. In an attempt to explain the cooling of the Earth over the last 100 million years, the role of Walker's mechanism was subsequently expanded by Berner, Lasaga and Garrels, who postulated that the cooling was driven by a decrease in the planetary outgassing rate related to a progressive slowing of plate motions. This suggestion was met with wide interest and became known as the BLAG hypothesis in honor of its creators. In the enthusiasm to explore all the aspects of BLAG, the earlier contribution of Walker tended to be forgotten. Hopefully, in naming this section, we will help to return the credit for the CO2 policing concept to its originator, James C.G. Walker.
Broecker, W.S., S.L. Peacock, S. Walker. R. Weiss, E. Fahrbach, M. Schroeder, U. Mikolajewicz, C. Heinze, R. Key, T.-H. Peng, and S. Rubin. How much deep water is formed in the Southern Ocean? Journal of Geophysical Research, 103(C8):15,833-15,843 (1998).
Three tracers are used to place constraints on the production rate of ventilated deep water in the Southern Ocean. The distribution of the water mass tracer PO4* ("phosphate star") in the deep sea suggests that the amount of ventilated deep water produced in the Southern Ocean is equal to or greater than the outflow of North Atlantic Deep Water from the Atlantic. Radiocarbon distributions yield an export flux of water from the North Atlantic which has averaged about 15 Sv over the last several hundred years. CFC inventories are used as a direct indicator of the current production rate of ventilated deep water in the Southern Ocean. Although coverage is as yet sparse, it appears that the CFC inventory is not inconsistent with the deep water production rate required by the distributions of PO4* and radiocarbon. It has been widely accepted that the major part of the deep water production in the Southern Ocean takes place in the Weddell Sea. However, our estimate of the Southern Ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the Weddell Sea, which lie in the range 1-5 Sv. Possible reasons for this difference are discussed.
Bryan, G.H., R.F. Rogers, and J.M. Fritsch. Cloud-scale resolution simulations in moist absolutely unstable layers. Preprints, Eighth Pennsylvania State University/National Center for Atmospheric Research's Mesoscale Model Users Workshop, Boulder, CO. National Center for Atmospheric Research, 59-62 (1998).
No abstract.
Butler, J.H., J.W. Elkins, S.A. Montzka, T.M. Thompson, T.H. Swanson, A.D. Clarke, F.L. Moore, D.F. Hurst, P.A. Romashkin, S.A. Yvon-Lewis, J.M. Lobert, M. Dicorleto, G.S. Dutton, L.T. Lock, D.B. King, R.E. Dunn, E.A Ray, M. Pender, P.R. Wamsley, and C. M. Volk. Nitrous oxide and halocompounds. In Climate Monitoring and Diagnostics Laboratory Summary Report No. 24, D.J. Hofmann, J.T. Peterson, and R.M. Rosson (eds.). National Technical Information Services, Springfield, VA, 91-121 (1998).
No abstract.
Castle, R.D., R.H. Wanninkhof, J.L. Bullister, S.C. Doney, R.A. Feely, B.E. Huss, E. Johns, F.J. Millero, K. Lee, D. Frazel, D. Wisegarver, D. Greeley, F. Menzia, M. Lamb, G. Berberian, and L.D. Moore. Chemical and hydrographic profiles and underway measurements from the eastern North Atlantic during July and August of 1993. NOAA Data Report, ERL AOML-32 (PB98-131865), 82 pp. (1998).
From July 4-August 30, 1993, the National Oceanic and Atmospheric Administration's (NOAA) Ocean-Atmosphere Carbon Exchange Study (OACES) and Radiatively Important Trace Species (RITS) programs participated in an oceanographic research cruise aboard the NOAA ship Malcolm Baldrige. The objectives of the OACES component were to determine the source and sink regions of CO2 in the equatorial and North Atlantic during the summer and to establish a baseline of total carbon inventory in the region. Data were collected from 5°S to Iceland along a nominal longitude of 20°W. This report presents only the OACES-related data from legs 1, 2A, and 2B, including hydrography, nutrients, carbon species, dissolved oxygen, total inorganic carbon, chlorofluorocarbons, total alkalinity, pH, and salinity. Included are contour plots of the various parameters and descriptions of the sampling techniques and analytical methods used in data collection.
Chen, G., B. Chapron, J. Tournadre, K.B. Katsaros, and D. Vandemark. A new look at the diurnal variation of global oceanic precipitation from the ocean TOPography EXperiment (TOPEX) and the TOPEX Microwave Radiometer (TMR). International Journal of Remote Sensing, 19(1):171-180 (1998).
New results on the diurnal variation of global oceanic precipitation are obtained by using one year's TOPEX (ocean TOPography EXperiment) and TMR (TOPEX Microwave Radiometer) data, derived from the dual-frequency (Ku and C band) capacity of the altimeter and the non-Sun-synchronous orbit of the satellite. The diurnal variation is characterized by a three-maximum structure which peaks at 00:00, 08:00, and 16:00 local time. The midnight-morning-afternoon maxima and dawn-noon-evening minima pattern seems to correlate with the results of most previous studies and to offer a unified picture of the diurnal variation of oceanic rainfall. A slight daytime (06:00-18:00) preference of oceanic precipitation appears to be significant in all seasons with the day/night ratio varying from 1.032 to 1.141 and the annual mean being 1.082. Examination of the geographical distribution of the timing of diurnal variation shows that the majority of the world oceans favor an afternoon maximum and an evening minimum. Moreover, the northern hemisphere is more coherent in reaching its maximum, while the southern hemisphere in reaching its minimum. In addition, the mechanisms responsible for the diurnal variations are discussed.
Chen, G., B. Chapron, J. Tournadre, K.B. Katsaros, and D. Vandemark. Identification of possible wave damping by rain using TOPEX and TMR data. Remote Sensing of Environment, 63(1):40-48 (1998).
A global picture of wave damping by rain (WDBR), a phenomenon familiar to seafarers for centuries, has been so far unavailable owing to the fact that neither rules nor tools exist for its systematic measurement. The situation has changed following the launch of the first dual-frequency (5.3 GHz and 13.6 GHz) radar altimeter TOPEX, along with the three-frequency (18 GHz, 21 GHz, and 37 GHz) radiometer TMR (TOPEX Microwave Radiometer). In this study, a scheme for detecting possible WDBR using TOPEX/TMR data is proposed. The geographical distribution of identified WDBR is consistent with the simultaneous presence of high sea state and intensive rainfall. Frequent occurrences of WDBR are observed in the midlatitude of the two hemispheres, particularly in the Pacific Ocean. In contrast, WDBR rarely occurs in the majority of the tropical and subtropical oceans. The global seasonality of WDBR is found to be weak as a result of the hemispheric phase opposition of sea state and rainfall in their annual variations. Knowledge of spatial distribution and temporal variation of WDBR is useful in dealing with potential systematic biases in satellite wind and wave measurements due to rain/sea interaction. It would have been interesting to compare the WDBR with coincident estimates of global rainfall from the SSM/I (Special Sensor Microwave/Imager).
Cione, J.J., and P.G. Black. Surface thermodynamic observations within the tropical cyclone inner core. Preprints, Symposium on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 141-145 (1998).
No abstract.
Cione, J.J., S. Raman, L.J. Pietrafesa, R.A. Neuherz, K. Keeter, and X. Li. The use of pre-storm low-level baroclinicity in determining and implementing the Atlantic surface cyclone intensification index. Boundary Layer Meteorology, 89:211-224 (1998).
The lateral motion of the Gulf Stream off the eastern seaboard of the United States during the winter season can act to dramatically enhance the low level baroclinicity within the coastal zone during periods of offshore cold advection. The relative close proximity of the Gulf Stream current off the mid-Atlantic coast can result in the rapid and intense destabilization of the marine atmospheric boundary layer directly above and shoreward of the Gulf Stream within this region. This airmass modification period oftentimes precedes either wintertime coastal cyclogenesis or the cyclonic re-development of existing mid-latitude cyclones. A climatological study investigating the relationship between the severity of the pre-storm, cold advective period, and subsequent cyclogenic intensification was undertaken by Cione et al. in 1993. Findings from this study illustrate that the thermal structure of the continental airmass, as well as the position of the Gulf Stream front relative to land during the pre-storm period (i.e., 24-48 h prior to the initial cyclonic intensification), are linked to the observed rate of surface cyclonic deepening for storms that either advected into or initially developed within the Carolina-southeast Virginia offshore coastal zone. It is a major objective of this research to test the potential operational utility of this pre-storm low level baroclinic linkage to subsequent cyclogenesis in an actual National Weather Service (NWS) coastal winter storm forecast setting. The ability to produce coastal surface cyclone intensity forecasts recently became available to North Carolina State University researchers and NWS forecasters. This statistical forecast guidance utilizes regression relationships derived from a nine-season (January 1982- April 1990), 116-storm study conducted by Cione et al. (1993). During the period between February 1994 and February 1996, the Atlantic Surface Cyclone Intensification Index (ASCII) was successfully implemented in an operational setting by the NWS at the Raleigh-Durham forecast office for 10 winter storms. Analysis of these ASCII forecasts will be presented.
Crane, M.L. Project ACCESS: Community coastal monitoring for year 2007. Earth System Monitor, 8(4):12-16 (1998).
No abstract.
Donelan, M.A., H.C. Graber, S. Ataktürk, W.M. Drennan,, E.A. Terray, and K.B. Katsaros. Marine flux-profile relations from an air-sea interaction spar buoy. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS99, OS31J-09 (1998).
During the Spring of 1997, the Air Sea Interaction Spar (ASIS) buoy was deployed in the northeastern Gulf of Mexico. Continuous data on profiles of wind speed, temperature, and humidity were obtained with concurrent wind stress, heat flux, and wave directional properties. This paper examines the flux-profile relations and the effect of non-local or non-equilibrium wave fields on them.
Doney, S.C., J.L. Bullister, and R.H. Wanninkhof. Climatic variability in upper ocean ventilation rates diagnosed using chlorofluorocarbons. Geophysical Research Letters, 25(9):1399-1402 (1998).
The chlorofluorocarbon CFC-12 (CCl2-F2) distributions from two occupations of a meridional hydrographic section in the eastern North Atlantic are used to describe the oceanic penetration of CFCs and change in the integrated ventilation patterns over the five years from 1988 to 1993. The CFC-12 water-column inventories increased by 30-40%, despite a slowing atmospheric growth rate (14%), because of continuing uptake by undersaturated subsurface water masses whose response is lagged by the ventilation time-scales. After removing the long-term CFC temporal trend using a tracer age based normalization technique, we observe a distinct dipole pattern in upper ocean ventilation, with reduced convection in the subpolar gyre and enhanced production of saline subtropical underwater in 1993. These differences are discussed in relation to interannual variability in atmospheric surface forcing, upper ocean anomalies, and convection patterns associated with the North Atlantic Oscillation.
Duncombe Rae, C., S.L. Garzoli, P. Richardson, and D. Fratantoni. Hydrography of some rings in the southeast Atlantic. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS131, OS41D-02 (1998).
Mesoscale rings and eddies in the southeast Atlantic Ocean have three potential sources: the Brazil-Malvinas Current Confluence, the Agulhas Current Retroflection, and the South Atlantic Subtropical Front. Previous hydrographic surveys have identified Agulhas rings and Brazil eddies in the region of the Cape Basin. During a component cruise of KAPEX (Cape of Good Hope Experiment), an experiment to track the flow of intermediate water around the southern tip of Africa and through the Benguela Current, three large eddies were encountered in the Cape Basin and east of the Mid-Atlantic Ridge during September 1997. The eddies were detected in satellite altimetry before the cruise and surveyed with XBT, CTD and LADCP profiles. One of the rings, closest to the Agulhas retroflection, appeared a typical Agulhas ring in its first year after shedding, with a single surface isothermal stad of 16.1°C down to 280 m. The ring furthest from the supposed shedding point exhibited two lenses, 130-210 m and 320-420 m depth, at 15.27°C and 14.45°C, respectively, in addition to the surface mixed layer, 17.6°C, suggesting an Agulhas ring which had experienced two winter mixing periods since leaving the retroflection. The middle ring had a stad of 12.22°C between 440 and 600 m and showed little evidence of convective overturning events above that level, apart from a surface mixed layer (160 m, 16.7-16.8°C) which was evident also in the background water column. The origin, structure, and temperature-salinity characteristics of these three eddies are examined. It is surmised that these eddies were shed from the Agulhas retroflection and subsequently modified by atmospheric cooling, convective overturning during winter, and possibly interaction with the Subtropical Front.
Dunion, J., S.H. Houston, C. Velden, M.D. Powell, and P.G. Black. Use of GOES high-density low-level VIS winds to improve the estimation of tropical cyclone outer wind radii. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A72-A87 (1998).
UW-CIMSS recently began providing real-time GOES low-level VIS winds in the vicinity of tropical cyclones on a demonstrational basis to NOAA's Hurricane Research Division (HRD). These data were included in many of HRD's real-time tropical cyclone surface wind analyses which were sent to NHC forecasters on an experimental basis during 1997. These wind analyses are used as guidance in their tropical cyclone advisories and warnings. The satellite observations provide essential coverage in the periphery of hurricanes where conventional in-situ observations (e.g., ships, buoys, etc.) are often widely spaced or non-existent and reconnaissance aircraft do not normally fly. The GOES VIS winds were adjusted to the surface using a PBL model. These adjusted data were used in real-time surface wind analyses for Hurricanes Danny and Erika of 1997 and were available for post-storm analyses in 1996 Hurricanes Edouard, Fran, Hortense, and Lili. The satellite observations improved the estimation of the 34 kt wind radii in many cases and also helped place the 50 kt wind radii for some cases. Examples of the impact of these data on hurricane surface wind analyses will be shown. Statistics on comparisons (>100 cases) of the adjusted and unadjusted GOES VIS winds with in-situ surface measurements will be presented. Also, in some cases GPS-sonde profiles were available in the vicinity of the GOES VIS winds. Comparisons of these highly detailed soundings with the satellite winds and their height assignments will be shown. The potential for further improvement of outer wind radii estimation through joint use of GOES VIS winds and satellite-based scatterometer surface winds will be discussed.
Durand, P., H. Dupuis, D. Lambert, B. Bénech, A. Druilhet, K.B. Katsaros, P.K. Taylor, and A. Weill. Comparison of sea surface flux measured by instrumented aircraft and ship during SOFIA and SEMAPHORE experiments. Journal of Geophysical Research, 103(C11):25,125-25,136 (1998).
Two major campaigns (Surface of the Oceans, Fluxes and Interactions with the Atmosphere (SOFIA) and Structure des Echanges Mer-Atmosphére, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale (SEMAPHORE)) devoted to the study of ocean-atmosphere interaction were conducted in 1992 and 1993, respectively, in the Azores region. Among the various platforms deployed, instrumented aircraft and ship allowed the measurement of the turbulent flux of sensible heat, latent heat, and momentum. From coordinated missions we can evaluate the sea surface fluxes from (1) bulk relations and mean measurements performed aboard the ship in the atmosphere surface layer and (2) turbulence measurements aboard aircraft, which allowed the flux profiles to be estimated through the whole atmospheric boundary layer and therefore to be extrapolated toward the sea surface level. Continuous ship fluxes were calculated with bulk coefficients deduced from inertial-dissipation measurements in the same experiments, whereas aircraft fluxes were calculated with eddy-correlation technique. We present a comparison between these two estimations. Although momentum flux agrees quite well, aircraft estimations of sensible and latent heat flux are lower than those of the ship. This result is surprising, since aircraft momentum flux estimates are often considered as much less accurate than scalar flux estimates. The various sources of errors on the aircraft and ship flux estimates are discussed. For sensible and latent heat flux, random errors on aircraft estimates, as well as variability of ship flux estimates, are lower than the discrepancy between the two platforms, whereas the momentum flux estimates cannot be considered as significantly different. Furthermore, the consequence of the high-pass filtering of the aircraft signals on the flux values is analyzed; it is weak at the lowest altitudes flown and cannot therefore explain the discrepancies between the two platforms but becomes considerable at upper levels in the boundary layer. From arguments linked to the imbalance of the surface energy budget, established during previous campaigns performed over land surfaces with aircraft, we conclude that aircraft heat fluxes are probably also underestimated over the sea.
Eads, L.J., H.A. Friedman, and D.J. Garcia. From humble beginnings as the Inner City Marine Project to selection as a National School of Excellence. Preprints, Seventh Symposium on Education, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 162-165 (1998).
The evolution of the MAST Academy (Maritime and Science Technology High School), a Dade County Magnet School of Choice, from its predecessor, the Inner City Marine Project (ICMP), is described. ICMP originated after Dade County experienced civil unrest in the Black community in 1984. At that time, Dr. Linda J. Eads, currently MAST Academy's principal, was assigned to design a program in maritime education which emphasized career exploration for minorities. The ICMP operated from the District Office of the Dade County Public Schools and targeted elementary and middle schools in the inner city with high minority populations. When the MAST Academy opened its doors in 1991, the ICMP became the MAST Academy Outreach Department which continued to provide programs for the targeted schools. The MAST Academy presently carries on the tradition of the ICMP by providing high school students with specialized marine-theme science and technology courses. In 1996, the MAST Academy was selected as a U.S. Department of Education National Blue Ribbon School of Excellence.
Ellis, G., P. Swart, M. Lutz, C. Alvarez-Zarikian, P. Blackwelder, T.A. Nelsen, H. Wanless, and J. Trefry. The stable isotope composition of foraminifera, ostracods, and organic material in a dated core from Whitewater Bay. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 2 pp. (1998).
No abstract.
Ellsberry, R.L., and F.D. Marks. U.S. Weather Research Program Hurricane Landfall Workshop Report. Technical Note, NCAR/TN-442, 40 pp. (1998).
No abstract.
Feely, R.A., R.H. Wanninkhof, C.D. Cosca, and K. Lee. The impact of the 1997-1998 El Niño on the air-sea exchange flux of CO2 in the oceans. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F507, OS41H-08 (1998).
As part of the NOAA Ocean Atmosphere Carbon Exchange Study (OACES), measurements of CO2 partial pressure were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific from 1992 to 1998. Surface water pCO2 data indicate significant diurnal, seasonal, and interannual variations. The largest variations were associated with the 1997-98 ENSO event, which reached maximum intensity in the winter of 1997-1998. The lower surface pCO2 values during the 1997-98 ENSO period were the result of the combined effects of both remotely and locally forced physical processes: (1) development of a low-salinity surface cap as part of the formation of the warm pool in the western and central equatorial Pacific; and (2) deepening of the thermocline by propagating Kelvin waves in the eastern Pacific. Both these processes serve to reduce pCO2 values towards near equilibrium values at the height of the warm phase of ENSO. These changes resulted in a lower-than-normal CO2 flux to the atmosphere. The annual average fluxes indicate that strong ENSOs exchange about 0.3-0.4 GtC/yr to the atmosphere; whereas, during non-El Niño years the equatorial Pacific exchanges about 0.9-1.0 GtC/yr to the atmosphere. This difference is enough to account for approximately one-third of the atmospheric anomaly during an El Niño. Our models suggest that this effect occurs in temperate and polar regions as well. Thus, the ENSO process is the major controlling factor of the interannual variability of the air-sea exchange of CO2 in the oceans. During decades dominated by strong ENSO events, such as this one, as much as 2-3 Gt more C are retained by the oceans compared with normal decades. Clearly, the equatorial Pacific is a very important region for studying climate feedbacks of greenhouse warming.
Feely, R.A., R.H. Wanninkhof, H.B. Milburn, C.E. Cosca, M. Stapp, and P.P. Murphy. A new automated underway system for making high precision pCO2 measurements onboard ships of opportunity. Analytica Chimica Acta, 377:185-191 (1998).
We have developed a new temperature-controlled, automated underway system for making atmospheric and surface ocean pCO2 measurements onboard research vessels equipped with an uncontaminated seawater intake system. Uncontaminated seawater is supplied to a showerhead plexiglass equilibrator at the rate of approximately 50 liters/minute. After about 3 minutes, the air trapped in the equilibrator is equilibrated with seawater. This air is sampled six times per hour. In addition, atmospheric air is sampled three times per hour from the intake on the bow flagstaff through 3/8" DekabonTM tubing to the underway system. The CO2 measurements are made with a differential, non-dispersive, infrared analyzer LiCorTM (model 6252). The underway system operates on an hourly cycle with the first quarter of each hour devoted to calibration with three CO2 standards, each measured for 5 minutes. A second order polynomial calibration curve is calculated from the voltage values of the standards. The remaining time in each hour is used to measure equilibrator air (15 min), bow air (15 min), and equilibrator air once again (15 min). To date, we have successfully used the underway pCO2 system on 12 cruises of the NOAA Ship Ka'imimoana in the equatorial Pacific. The analytical precision of the system is approximately 0.3-0.4 ppm for seawater and for air.
Ffield, A., C.I. Fleurant, R.L. Molinari, and W.D. Wilson. NOAA Ship Malcolm Baldrige 1995 cruises: MB95-02, MB95-04, and MB95-07 hydrographic data. LDEO-98-1, Technical Report, 310 pp. (1998).
No abstract.
Fleurant, C.I., and R.L. Molinari. Comparison of bottle salinity and bottle oxygen values from WHP repeat lines I7N, I1W, I8N, and I8S. International WOCE Newsletter, 33:27-29 (1998).
No abstract.
Franklin, J.L., and M.L. Black. GPS dropwindsonde data in hurricanes. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A111-A142 (1998).
The 1997 hurricane season was the first with both NOAA WP-3D aircraft equipped with the new NCAR GPS dropwindsonde system. The GPS sonde replaces the old Omega-based ODW, in use since the early 80's on the P-3s. During the season, the first successful dropwindsonde releases (of any kind) were made in a hurricane eyewall (Guillermo). These were followed by additional eyewall releases in Hurricane Erika. The wind profiles show that surface winds in the eyewall may be much higher than what is typically inferred from flight-level reconnaissance data. Very strong jets resolved by the GPS dropsondes in and just above the boundary layer may be indicative of peak surface gusts.
Fratantoni, D.M., P.L. Richardson, C.M. Duncombe Rae, and S.L. Garzoli. Three warm-core rings in the eastern south Atlantic. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS131, OS41D-04 (1998).
During the September 1997 Benguela Current Experiment, three large (300 km) anticyclonic rings were identified and surveyed near 30°S in the eastern South Atlantic. Preliminary analysis suggests that these rings were formed from the retroflecting Agulhas Current south of Africa. Two of the rings were observed west of the Walvis Ridge and appear to have been freely translating for nearly two years. The transport of intermediate water (approximate depth range 400-1000 m) within Agulhas rings is thought to be an important interbasin transport pathway associated with the global-scale thermohaline circulation. Employing an array of Lagrangian floats and drifters, this experiment and others associated with the U.S., German, and South African KAPEX (Cape of Good Hope Experiment) program constitute the first direct examination of this pathway. In-situ hydrographic and direct velocity measurements were performed aboard the R/V Seward Johnson. Nominal ring positions were estimated prior to departure using satellite altimetry. During the cruise intensive shipboard XBT and ADCP surveys revealed the three-dimensional structure of temperature and velocity associated with each ring and facilitated a determination of the ring center. Multiple acoustically-tracked subsurface RAFOS floats (at 700 m depth) and satellite-tracked surface drifters were then launched near the center of each ring to measure ring translation and the evolution of core properties over a two-year period. Additional floats and drifters were deployed along 30°S and 7°W to characterize the background flow of surface and intermediate water in the Benguela Current and the eastern South Atlantic subtropical gyre. In this poster we describe the horizontal structure of these large (300 km diameter) and energetic (40 cm/s) warm-core rings using both in-situ and Lagrangian measurements. We present synoptic plan-view depictions of thermocline depth, upper-ocean velocity, and integrated heat content for each ring. The scale and intensity of each ring is discussed in the context of a translation history compiled from archived TOPEX/Poseidon altimetry. Finally, surface drifter trajectories are used to assess ring translation and to describe the temporal evolution of azimuthal velocity structure and intensity.
Friedman, H.A., and D.J. Garcia. Tropical cyclone public awareness programmes: Preparing for the twenty-first century. Preprints, Seventh Symposium on Education, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 166-168 (1998).
During the period from 1969 to 1993, a total of 1551 tropical cyclones, typhoons, and hurricanes occurred worldwide. Literally millions of lives are affected each year, and billions of dollars are lost as a result of these storms. At present, we can do little, if anything, to lessen the occurrence, frequency, or intensity of tropical cyclones, or to influence their paths. But over the past three decades, significant advances have been made in mankind's capability to prepare for and mitigate their damaging effects. Concerted international scientific efforts have resulted in better understanding the phenomenon of tropical cyclones, their formation, characteristics, path of movement, and effects. Technical advances in weather monitoring equipment satellites, computers, improved radar systems, and other space age meteorological tools enable scientists today to vigilantly monitor cyclones as they form, track them as they move, and predict with some accuracy where they are likely to impact on land and people. Correspondingly, meteorological services in many countries have been substantially improved in recent years. Cyclone monitoring equipment has been installed in most cyclone-prone regions of the world. National systems have been linked to regional and international networks through which meteorological data is shared and warnings of approaching cyclones conveyed. In many localities, local communication systems and administrative procedures have been strengthened to ensure that information about approaching cyclones is passed to communities most at risk. While great strides have been made in our ability to understand and live with cyclones, still more must be done. We must strive to further expand our basic knowledge about tropical cyclones, upgrade tools needed for weather monitoring and prediction, improve the warning and communications network, and strengthen meteorological services. It is a useful reminder that the primary objectives of these varied activities is to prevent the loss of lives and prevent or minimize property damage from cyclones. The need for continued effort is reconfirmed by the deaths and destruction left in the wake of each tropical cyclone that affects populated areas today; a problem that is likely to continue and increase in seriousness as coastal populations enlarge. The goal of preventing loss of life and reducing property damage from tropical cyclones, however, can not be achieved simply through improved technical and meteorological services. Accurate prediction and timely notice are critically important, but loss of life and property can only be minimized if officials and the general public are knowledgeable of the hazards faced, understand the warnings provided, and take the proper actions to protect life and property before, during, and after a cyclone. The process required to achieve a public state of readiness is commonly referred to as an awareness program. A resource guide, designed to provide a framework for the development and implementation of local tropical cyclone awareness programs, will be discussed. The Internet was used extensively to obtain up-to-date information on worldwide issues concerning tropical cyclones. The guide's design encourages interactive use by disaster preparedness officials and educators at the local level. Questionnaires and community-specific checklists are provided to elicit local participation in the process of creating tropical cyclone awareness.
Garcia, D.J., H.A. Friedman, and L.J. Eads. MAST Academy outreach: Serving the community with marine theme programs. Preprints, Seventh Symposium on Education, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 169-171 (1998).
The MAST Academy's Outreach Department provides marine theme enrichment programs which emphasize career opportunities for targeted schools with high minority enrollments. Enrichment programs include the Land SHARC (Science Hands-on and Related Careers) and WOW (Weather On Wheels) mobile laboratories, environmental field trips, internships, and the MAST Mariners Program, a middle school summer course focused on, but not exclusively for, minority students. The role of NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML) and other outside agencies in providing school year and summer internships for MAST Academy students is discussed. Meteorologists from AOML's Hurricane Research Division serve as advisory board members for the WOW; their contributions to the program are presented.
Garzoli, S.L., C. Duncombe Rae, D. Fratantoni, G.J. Goni, J. Mantel, A. Roubicek, P. Fratantoni, and C. Whittle. Benguela Current Experiment. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS131, OS41D-01 (1998).
Although intermediate water is an important component of the northward-flowing meridional circulation cell in the Atlantic, the pathways, velocity, and variability of this water are poorly known. In order to study the northward flow of intermediate water in the Benguela Current and its extension, a program was initiated by scientists of WHOI, NOAA/AOML, and Sea Fisheries (South Africa). The main objective was to obtain the first subsurface Lagrangian float measurements of the northward flow of intermediate water in t he eastern South Atlantic and to measure the characteristics of this water. This program is a component of KAPEX (Cape of Good Hope Experiment), a joint U.S., Germany, and South Africa effort. During September 1997, we participated in a cruise aboard the RV Seward Johnson from Cape Town to Recife. The main objectives of this cruise were: to launch an array of RAFOS floats and surface drifters; to perform an intensive survey to determine the characteristics of the flow; and to search for and study Agulhas rings in the area. Agulhas rings are considered to be one of the main carriers of Indian Ocean waters into the Atlantic. Hydrographic casts (CTD-O2) and direct measurements of currents (ADCP/LADCP) were performed along 30°S (between 14°E and 7°W) and along 7°W (between 33°S and 18°S) to study the characteristics and paths of the intermediate water flow at the time of deployments. Three anticyclonic rings were identified through intensive XBT surveys guided by satellite images of sea surface height. CTD/LADCP stations were performed and RAFOS floats and drifters launched in a radial from the center of the rings. The eddies are tentatively identified as being Agulhas rings, although a deep (600 m), cold (12.2°C), mixed layer in one ring raises questions about its origin. Thirty-two RAFOS floats and 11 surface drifters were launched along the sections and in the rings. This poster will provide an overview of the Benguela Current Experiment and the preliminary results from the September 1997 cruise.
Goni, G.J., and S.L. Garzoli. Origin and evolution of the Benguela Current Experiment rings by altimetry. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS131, OS41D-03 (1998).
Historical hydrographic data is used to compute the mean upper layer thickness and reduced gravity in the southeastern Atlantic. These parameters, along with the altimeter-derived sea surface height anomaly, are used to derive the upper layer thickness of the ocean. This product proved to be an efficient means to identify and track anticyclonic rings. In September 1997, as part of the Benguela Current Experiment, a cruise on the R/V Seward Johnson guided by the TOPEX/POSEIDON product identified and surveyed three rings. The water mass characteristics of these rings indicate that at least two of them could have their origin in the Agulhas retroflection. The third ring has hydrographic characteristics that raise questions about its origin. This poster shows the results of a study of these rings based on altimetry. Synoptic maps of the upper layer thickness are analyzed to determine the trajectories of the rings in the region for a period of two years previous to the Benguela Current Experiment. The origins and evolution of the three rings observed during the September 1997 cruise are established and discussed. The translation velocity, available potential energy, and heat content are calculated from the altimeter data. A comparison between the shipboard and altimeter-derived values of the upper layer thickness is also presented.
Graber, H.C., M.A. Donelan, S. Atakturk, W.M. Drennan, and K.B. Katsaros. Evaluation of NSCAT scatterometer winds with wind stress measurements in the Gulf of Mexico. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F417, OS72G-03 (1998).
Wind vectors and radar backscatter observed by the NASA scatterometer (NSCAT) are compared with wind and wind stress measurements from an air-sea interaction spar (ASIS) buoy and wind measurements from a nearby NDBC discus buoy. ASIS is a new autonomous spar buoy designed to permit long-term measurements of interfacial processes. During a two-month deployment in the Gulf of Mexico in April 1997, the buoy experienced several fronts associated with rapid changes in wind speed and direction. The ASIS buoy was equipped for motion-corrected measurements of the wind stress vector, as well as high resolution wave directional properties. These are used to explore wind and backscatter measurements of scatterometers. Time difference and spatial separation between NSCAT and buoy observations were limited to less than 30 minutes and 25 km, respectively.
Gray, W.M., C.W. Landsea, J.A. Knaff, P.W. Mielke, and K.J. Berry. Verification of the 1997 seasonal hurricane forecasts and a prediction for 1998. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A331-A338 (1998).
No abstract.
Hacker, E., E. Firing, W.D. Wilson, and J.C. Kindle. Evidence for a North Equatorial Countercurrent in the eastern Indian Ocean during the northeast monsoon. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS75, OS21J-02 (1998).
Data collected during February and March 1995 as part of the WOCE Hydrographic Program Expedition in the Indian Ocean provide evidence for an eastward-flowing countercurrent, a possible North Equatorial Countercurrent (NECC), extending from 80°E south of Sri Lanka to about 92°E. The current is associated with a local surface salinity maximum (34.5 psu) representing its probable northwest Indian Ocean source. At 80°E, the combination of shipboard and lowered acoustic Doppler current profiler (ADCP) data shows weak flow to the east between 2°N and 2.8°N near the surface, with flow to the east extending from 1.5°N to 4°N at a depth of 100 m. The eastward flow is imbedded in a westward flow of lower salinity water extending from 3°S to 6°N. The westward flow represents a combination of the outflow of fresher, surface Bay of Bengal water and westward return flow of the eastward-flowing South Equatorial Countercurrent water. At 92°E, the NECC is part of an intense circulation feature with eastward flow extending from 3°N to 6°N and peak speed of 0.8 m/s. NOAA data from the repeat hydrographic line along 80°E during late October 1995, during the monsoon transition period, show evidence of a weak eastward flow in the upper 100 m between 4°N to 5°N imbedded in a broader westward flow between 1°N and 6°N. The observations are compared to model circulation features from the NRL high-resolution, three-layer, non-linear, model forced by ECMWF winds. Although the NRL model does not show an NECC south of Sri Lanka, it does show a weak countercurrent trough further to the east between 4°N and 7°N. The temporal and spatial smoothing of historical data products may be the reason that the NECC has not been reported previously.
Hansen, D.V., and M.S. Swenson. Application of oceanic heat budgets to evaluation of surface heat flux climatologies. Proceedings, First International Conference on Reanalyses, Washington, D.C., October 27-31, 1997. World Climate Research Programme, 40 (1998).
We are using the extensive WOCE/TOGA data sets from drifting buoys and VOS/XBT measurements for quantification of climatological heat budget processes in the equatorial cold tongue and NECC regions of the eastern tropical Pacific Ocean. One interesting application of the results is in their implication for the net surface heat flux. Early results suggest that the heat flux climatology generated from the NCEP/NCAR Reanalysis Project is superior to other popular climatologies. A major factor in the improvement appears to be the annual cycle of downward shortwave radiation.
Hasler, A.F., K. Palaniappan, C. Kambhammetu, P.G. Black, E.W. Uhlhorn, and D. Chesters. High-resolution wind fields within the inner core and eye of a mature tropical cyclone from GOES 1-min images. Bulletin of the American Meteorological Society, 79(11):2483-2496 (1998).
Mesoscale wind fields have been determined for a mature hurricane with high spatial and temporal resolution, continuity, and coherency. These wind fields, near the tropopause in the inner core and at low levels inside the eye, allow the evolution of mesoscale storm features to be observed. Previously, satellite-derived winds near hurricanes have been determined only at some distance from the eye over a typical time period of 1V2 h. Hurricane reconnaissance aircraft take 30 min to 1 h to complete an inner-core pattern. With the long observation periods of these previous methods, steady-state conditions must be assumed to give a complete description of the observed region. With the advent of 1-min interval imagery, and fourfold improvement of image dynamic range from NOAA's current generation of GOES satellites, there is a new capability to measure inner-core tropical cyclone wind fields near the tropopause and within the eye, enabling mesoscale dynamical processes to be inferred. These measurements give insights into the general magnitude and structure of the hurricane vortex, along with very detailed measurements of the cloud-top wind's variations in response to convective outbursts. This paper describes the new techniques used to take advantage of the GOES satellite improvements that, in turn, allowed the above innovations to occur. The source of data for this study is a nearly continuous 12-h sequence of 1-min visible images from NOAA GOES-9 on 6 September 1995. These images are centered on Hurricane Luis with maximum winds of 120 kt (CAT4) when it was 250 km northeast of Puerto Rico. A uniform distribution of long-lived cirrus debris with detailed structure is observed in the central dense overcast (CDO), which has been tracked using the 1-min images. The derived wind field near the tropopause at approximately 15 km in the CDO region has a strong closed circulation with speeds up to 25 m s-1, which pulses in response to the convective outbursts in the eyewall. Cloud displacements are computed at every pixel in every image, resulting in a quarter-million uVv winds in each of 488 hurricane images observed at 1- to 4-min intervals over 12 h. For analysis and presentation, these ultradense wind fields are reduced to 8- or 16-km grids using a 7-min time base by smoothing displacement vectors in space and time. Cloud structures were tracked automatically on a massively parallel processing computer, but with manual spot-checking. Manual tracking has been used to follow CDO structure over long time periods, up to 90 min for a small test sample. Cloud tracking for the wind fields presented here is accomplished using a Massively Parallel Semi-Fluid Motion Analysis (MPSMA) automatic technique. This robust deformable surface-matching algorithm has been implemented on the massively parallel Maspar supercomputer. MPSMA automatic tracking typically follows a feature for 7 min. For this time base the error of these winds is estimated to be 1.5 m s-1. However, systematic navigation and height assignment errors in the moderately sheared hurricane environment must still be considered. Spatial and temporal smoothing of the wind field have been performed to reduce systematic navigation errors and small-scale turbulent noise. The synthesis used here to compute the wind fields gives an order of magnitude reduction in the amount of data presented compared to the amount of data processed. Longer tracking could give higher accuracy but would smooth out the smaller-scale spatial and temporal features that appear dynamically significant. The authors believe that the techniques described in this paper have great potential for further research on tropical cyclones and severe weather as well as in operational use for nowcasting and forecasting. United States and foreign policymakers are urged to augment the GOES, GMS, FY2, and Meteosat geostationary satellite systems with dual imaging systems such that 1-min observations are routinely taken.
Hendee, J.C. An expert system for marine environmental monitoring in the Florida Keys National Marine Sanctuary and Florida Bay. Proceedings, 2nd International Conference on the Coastal Environment, Cancun, Mexico, September 8-10, 1998. Computational Mechanics Publications/WIT Press, Southampton, 57-66 (1998).
The National Oceanic and Atmospheric Administration's (NOAA, U.S. Department of Commerce) Atlantic Oceanographic and Meteorological Laboratory (AOML) works cooperatively with the Florida Institute of Oceanography (FIO) in the implementation of the SEAKEYS (Sustained Ecological Research Related to Management of the Florida Keys Seascape) network, which is situated along 220 miles of coral reef tract within the Florida Keys National Marine Sanctuary (FKNMS). This network is itself actually an enhanced framework of seven Coastal-Marine Automated Network (C-MAN) stations for long-term monitoring of meteorological parameters (wind speed, wind gusts, air temperature, barometric pressure, relative humidity). To the C-MAN network, SEAKEYS adds oceanographic parameters (sea temperature, photosynthetically active radiation, salinity, fluorometry, optical density) to the stations. As a recent enhancement to the SEAKEYS network, an expert system shell is being employed to provide daily interpretations of near real-time acquired data for the benefit of scientists, fishermen, and skin divers. These interpretations are designed to be automatically emailed to Sanctuary managers and to the FIO maintainers of the network. The first set of interpretations include those dealing with environmental conditions conducive to coral bleaching. Other marine environmental interpretations are slated to follow.
Hendee, J.C., C. Humphrey, and T. Moore. A data-driven expert system for producing coral bleaching alerts. Proceedings, 7th International Conference on the Development and Application of Computer Techniques to Environmental Studies, Las Vegas, Nevada, November 10-12, 1998. Computational Mechanics Publications/WIT Press, Southampton, 139-147 (1998).
As a recent enhancement to the SEAKEYS (Sustained Ecological Research Related to Management of the Florida Keys Seascape) environmental monitoring network, an expert system shell was employed to provide daily interpretations of near real-time acquired combinations of meteorological and oceanographic parameters as they meet criteria generally thought to be conducive to coral bleaching. These interpretations were automatically posted to the World-Wide Web and emailed to Florida Keys National Marine Sanctuary managers and scientists so they could witness and study bleaching events as they might happen, and so that a model could be developed with greater precision in identifying physical factors conducive to coral bleaching. The expert system, as a model, was successful in showing that certain assumptions by experts regarding coral bleaching apparently do not hold at Sombrero Reef.
Henderson-Sellers, A., H. Zhang, G. Berz, K. Emanuel, W. Gray, C.W. Landsea, G. Holland, J. Lighthill, S.-L. Shieh, P. Webster, and K. McGuffie. Tropical cyclones and global climate change: A post-IPCC assessment. Bulletin of the American Meteorological Society, 79(1):19-38 (1998).
The very limited instrumental record makes extensive analyses of the natural variability of global tropical cyclone activities difficult in most of the tropical cyclone basins. However, in the two regions where reasonably reliable records exist (the North Atlantic and the western North Pacific), substantial multidecadal variability (particularly for intense Atlantic hurricanes) is found, but there is no clear evidence of long-term trends. Efforts have been initiated to use geological and geomorphological records and analysis of oxygen isotope ratios in rainfall recorded in cave stalactites to establish a paleoclimate of tropical cyclones, but these have not yet produced definitive results. Recent thermodynamical estimation of the maximum potential intensities (MPI) of tropical cyclones shows good agreement with observations. Although there are some uncertainties in these MPI approaches, such as their sensitivity to variations in parameters and failure to include some potentially important interactions such as ocean spray feedbacks, the response of upper-oceanic thermal structure and eye and eyewall dynamics do appear to be an objective tool with which to predict present and future maxima of tropical cyclone intensity. Recent studies indicate the MPI of cyclones will remain the same or undergo a modest increase of up to 10%-20%. These predicted changes are small compared with the observed natural variations and fall within the uncertainty range in current studies. Furthermore, the known omissions (ocean spray, momentum restriction, and possibly also surface to 300-hPa lapse rate changes) could all operate to mitigate the predicted intensification. A strong caveat must be placed on analysis of results from current GCM simulations of the "tropical-cyclone-like" vortices. Their realism, and hence prediction skills (and also that of "embedded" mesoscale models), is greatly limited by the coarse resolution of current GCMs and the failure to capture environmental factors that govern cyclone intensity. Little, therefore, can be said about the potential changes of the distribution of intensities as opposed to maximum achievable intensity. Current knowledge and available techniques are too rudimentary for quantitative indications of potential changes in tropical cyclone frequency. The broad geographic regions of cyclogenesis and, therefore, also the regions affected by tropical cyclones are not expected to change significantly. It is emphasized that the popular belief that the region of cyclogenesis will expand with the 26 C SST isotherm is a fallacy. The very modest available evidence points to an expectation of little or no change in global frequency. Regional and local frequencies could change substantially in either direction, because of the dependence of cyclone genesis and track on other phenomena (e.g., ENSO) that are not yet predictable. Greatly improved skills from coupled global ocean-atmosphere models are required before improved predictions are possible.
Hitchcock, G.L., C. Wiebinga, and P.B. Ortner. CTD hydrographic data from the Global Ocean Ecosystem Dynamics (GLOBEC) Indian Ocean cruises. University of Miami Technical Report, 97-006, 69 pp. (1998).
No abstract.
Hitchcock, G., G.A. Vargo, T. Lee, E. Johns, E. Williams, and J. Jurado. The influence of circulation on nutrient distributions in western Florida Bay. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 98-99 (1998).
No abstract.
Hood, T., C. Alvarez-Zarikian, P. Blackwelder, P. Swart, T.A. Nelsen, H.R. Wanless, J.H. Trefry, and L. Tedesco. The sediment record as a monitor of natural and anthropogenic changes in the lower Everglades/Florida Bay ecosystem. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 33-34 (1998).
No abstract.
Houston, S.H., and M.D. Powell. Reconstruction of surface wind fields for hurricanes affecting Florida Bay. Preprints, Second Conference on Coastal Atmospheric and Oceanic Prediction and Processes, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 241-244 (1998).
Hurricanes constitute episodic events which affect the physical and oceanographic processes within Florida Bay. These effects are manifested by significant changes in water-levels, waves, currents, and sediment transport processes. In addition, these storms impact plant and animal life in the Bay and the surrounding areas. Hurricane wind fields are now being made available to researchers, such as oceanographers and biologists, on a Hurricane Research Division World Wide Web site (http://www.aoml.noaa.gov/hrd). Researchers can use the wind fields to estimate the potential impacts of future tropical cyclones on the south Florida ecosystem and especially on Florida Bay. The hurricanes used in this study were the Labor Day Hurricane of 1935, Donna of 1960, Betsy of 1965, Felix of 1987, and Andrew of 1992. These tropical cyclones represented vastly different scenarios for the type of event that might be expected over extreme south Florida. The 1935 hurricane was a category 5 storm and is the most intense hurricane known to have struck the USA. This hurricane had a relatively small, concentrated wind field when it crossed the Florida Keys and Florida Bay. Hurricane Donna (1960) was a category 4 hurricane with a much broader wind field that crossed the Keys and Bay on a similar track to the 1935 Hurricane. Hurricane Andrew was a fast moving category 4 hurricane when it struck south Florida recently. However, its strongest winds covered only a very small area, especially to the south of the storm track. The direct impact of Andrew on Florida Bay appears to have been minimal, but decomposing organic storm debris in the Everglades likely contributed to water quality problems in the Bay.
Houston, S.H., and M.D. Powell. Surface wind field in Florida Bay hurricanes. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 35 (1998).
No abstract.
Houston, S.H., and M.D. Powell. Surface wind fields in hurricanes. Proceedings, Third International Symposium, Waves '97, Virginia Beach, VA, November 3-7, 1997. American Society of Civil Engineers (ASCE), 1391-1399 (1998).
No abstract.
Houston, S.H., and M. D. Powell. The potential impact of GPS sondes in real-time surface wind analyses for hurricanes. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 26-30, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-110 (1998).
During the 1996 and 1997 hurricane seasons, GPS sondes were dropped within the inner core of some tropical cyclones (i.e., Josephine of 1996; Danny, Erika, Guillermo, and Linda of 1997). The data from these sondes provided some highly detailed boundary layer profiles and surface measurements of each tropical cyclone's wind and thermodynamic properties after the fact. During the upcoming 1998 hurricane season, two potential developments may make the GPS sonde data useful for defining the hurricane's surface wind structure in real-time: (1) The GPS sonde "temp drop message" sent from AFRES and NOAA missions in and near hurricanes (including drops from the NOAA G-IV) may include additional essential information that will likely enhance the real-time use of these sondes. For example, the splash location and time are two additional parameters that may be available in the drop messages. (2) When it is deemed necessary by NHC for the issuance of warnings and (or) other critical factors, GPS sondes may be dropped along the flight-track of tasked reconnaissance flights. These drops have the potential to provide estimates of the peak surface winds and may help define some of the wind radii (i.e., 34, 50, and/or 64 kt wind radii) in those quadrants where the drops are made. This study examines the potential impacts additional wind and thermodynamic observations from sondes might have on surface wind analyses in hurricanes, which are currently provided to NHC's forecasters in real-time by HRD on an experimental basis. Some examples of post-storm analyses in 1997 hurricanes utilizing these new data in addition to conventional data sources will be presented and the potential impacts will be assessed. In addition, some preliminary comparisons of the boundary layer measurements from GPS sondes with reliable in-situ surface observations (e.g., buoys, C-MAN's, etc.) of wind, temperature, and pressure in the vicinity of tropical cyclones will be shown.
Houston, S.H., M. Lawrence, S. Spisak, and S.T. Murillo. A verification of National Hurricane Center forecasts of surface wind speed radii in hurricanes. Preprints, Symposium on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 139-140 (1998).
The National Hurricane Center (NHC) issues a position and intensity forecast every six hours on all tropical cyclones in the Atlantic and eastern Pacific basins. This forecast is contained in the forecast/advisory product and includes a forecast of the horizontal distribution of the surface wind field. This distribution is given as radii in four quadrants from the center of the tropical cyclone to three wind speed values: 17.5, 25.7, and 32.9 m s-1 (i.e., 34, 50, and 64 kt, respectively). A set of opportunistic marine observations w ere collected to determine the wind speed radii from the center of each tropical cyclone to the observation site. This can be done when a tropical cyclone's wind field affects a measurement platform with the required wind speeds. The wind speed radii based on the marine platform data were used to verify the official NHC radii forecasts described above. The preliminary results are for 17.5 m s-1 wind speeds and are based on only 25 cases. Statistics will be presented showing that the mean absolute error of the 25 cases of verification is about 83 km (45 nm) at the initial (i.e., 0 h) forecast period and decreases about 25% by the 36 h forecast. There is a positive bias (the forecasts were larger than observed) of about 37 km (20 nm) for these cases, which also appears to decrease with longer forecast periods. The small number of cases limits our analysis to simple averages. This is the first time that such a data set has been prepared and that forecasts of tropical cyclone intensity in terms of wind speed radii have been verified. Details on the method of verification will be given along with the final statistics of the study, including 17.5 and 25.7 m s-1 radii verification.
Huang, H., R.E. Fergen, J.R. Proni, and J.J. Tsai. Initial dilution equations for buoyancy-dominated jets in currents. Journal of Hydraulic Engineering, 124:105-108 (1998).
Initial dilution of submerged, single, round, buoyancy-dominated jets in a current is considered. Two simple semi-empirical equations, one for centerline dilution and the other for minimum surface dilution, are presented. These equations are derived based on the continuity equation for the buoyant jet flow with a hypothesis that shear entrainment and forced entrainment can be added. Available laboratory and field data are used to determine the constants in the equations. Unlike asymptotic equations which apply for the limiting flow regimes, the proposed equations span all flow regimes, from the buoyancy-dominated near field (BDNF), to the transition, and to the buoyancy-dominated far field (BDFF), providing continuous predictions for dilutions.
Jameson, A.R., A.B. Kostinski, and R.A. Black. The texture of clouds. Journal of Geophysical Research-Atmospheres, 103(D6):6211-6220 (1998).
Using a precise definition of clustering, it is shown that in two tropical cumulus clouds, droplets appear to be bunched over distances ranging from at least a kilometer or more down to several centimeters. A statistical framework is proposed for quantifying clustering in terms of a Poisson probability mixture. While these observations require further substantiation in many different clouds, droplet clustering may play a role in diverse phenomena from the coalescence growth of raindrops to the scattering of radiation by clouds.
Johns, E., and W.D. Wilson. Direct observations of velocity structure in the passages between the Intra-Americas Sea and the Atlantic Ocean, 1984-1996. Proceedings, Conference on the Transports and Linkages of the Intra-Americas Sea (IAS), Cozumel, Mexico, November 1-5, 1997. IOC/IOCARIBE/MMS, 36 (1998).
Shipboard acoustic Doppler current profiler (ADCP) velocity data collected between 1984 and 1996 in connection with several NOAA research programs have been used to examine the mean and variability of the velocity structure within the Straits of Florida, the Northwest Providence Channel, a northern approach to the Windward Passage, the Mona and Anegada Passages, and across the eastern Caribbean Sea. Historically, direct velocity data collection in these important passages between the Gulf of Mexico, the Caribbean Sea, and the Atlantic Ocean has been very sparse. Herein, we examine the transport and velocity structure in the passages using a more complete data set than previously available. This newer data set allows computation of statistically significant mean and standard deviations of the transport and velocity fields, and examination of the temporal (seasonal to interannual) variability of these fields. Comparison will be made of the mean and varying flow fields with the results of previous studies and with available time series of regional forcing functions such as the COADS wind stress data set. Most importantly, the mean transports should prove useful to numerical modelers of the Intra-Americas Sea for calibration and refinement of model boundary conditions.
Johns, E., W.D. Wilson, and T.N. Lee. Interaction of Florida Bay waters with the Gulf of Mexico and the Atlantic Ocean. Proceedings, 1998 Meeting of the Oceanography Society and the Intergovernmental Oceanographic Commission on Coastal and Marginal Seas, Paris, France, June 1-4, 1998. Oceanography, 11, No. 2 supplement, 38 (1998).
As part of the South Florida Ecosystem Restoration program, an observational study of the circulation of Florida Bay and its connection with the surrounding waters of the Gulf of Mexico, the southwest Florida shelf, and the Atlantic Ocean is presently underway. Measurement systems include moored arrays equipped with current meters, bottom pressure sensors and conductivity-temperature sensors, satellite-tracked surface drifters, and shipboard ADCP. Bimonthly interdisciplinary surveys include continuous thermosalinograph observations of surface salinity, temperature, and fluorescence. Early results show that there is a net southeastward flow of 1 to 4 cm/s which transports waters from the Gulf of Mexico and the Everglades across western Florida Bay and through the channels of the Florida Keys, on a time scale of 1 to 3 months depending on local wind forcing. This net flow, with a volume transport of 1000 to 2000 m3/s, has the potential to deliver harmful algal blooms and excess nutrients out to the environmentally sensitive coral reefs of the Florida Keys National Marine Sanctuary. The ongoing study now focuses on refining and quantifying the flow between the Gulf of Mexico, Florida Bay, and the Atlantic and its response to seasonal and episodic meteorological forcing. In addition, new emphasis is placed on examining the fate of the freshwater river discharges from the Everglades into the Gulf of Mexico, and the relation of the river plume dispersion to regional wind and rainfall distributions.
Kaplan, J., and M. DeMaria. Climatological and synoptic characteristics of rapidly intensifying tropical cyclones in the North Atlantic basin. Preprints, Symposiuim on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 119-123 (1998).
No abstract.
Katsaros, K.B. Microwave remote sensing with radiometers. In Remote Sensing of the Pacific Ocean by Satellites, R.A. Brown (ed.). Southwood Press, Marrickville, Australia, 13-15 (1998).
No abstract.
Katsaros, K.B. Turbulent flux of water vapor in relation to the wave field and atmospheric stratification. In Physical Processes in Lakes and Oceans, J. Imberger (ed.). Coastal and Estuarine Studies, Volume 54, American Geophysical Union, 37-46 (1998).
Field measurements of evaporation rate, momentum, and heat flux together with mean meteorological quantities allow inferences to be drawn concerning the sheltering of air in the troughs of large waves and the possible differences between moisture and heat fluxes in very stable regimes over water. Interpretation of the measurements in terms of the processes near the surface are based on the Monin-Obukhov similarity theory. The results presented indicate that in the presence of water waves and under strong atmospheric stable stratification further detailed measurements are needed to fully explain the processes at work and that Monin-Obukhov theory may need modification.
King, D.B., S.A. Yvon-Lewis, S.A. Montzka, and J.H. Butler. Dependence of trace halocarbon saturation anomalies on sea-surface properties. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F429, OS11F-02 (1998).
If global warming results in an increase in sea surface temperature, the saturations and air-sea fluxes of trace gases in the surface ocean are also likely to change. Since many of these gases are involved in tropospheric chemistry, global warming, and even the destruction of stratospheric ozone, it would be useful to predict how their fluxes into and out of the oceans might be altered as a result of climate change. Although such an effort requires an intricate examination of biological and chemical activity, a first step in understanding the nature of this behavior is mapping their degree of saturation in waters of different temperature, location, and chemical properties. As part of a joint expedition to the Atlantic and Pacific Oceans, we have measured the saturation anomalies of a number of trace gases in surface waters in an effort to evaluate the dependence of their air-sea fluxes upon sea-surface properties. Data collected on this cruise demonstrate that the fates of some compounds may be easier to predict than others. Some gases are conservative in seawater, and their integrated fluxes over a year are small. Other gases are consumed by chemical reaction. For example, methyl chloroform, an anthropogenic trace gas that is no longer emitted in significant amounts to the atmosphere, was undersaturated in warm surface waters, but not in cooler waters, which is consistent with enhanced hydrolysis in warmer water. Other compounds, such as the methyl halides, are produced and consumed by a variety of processes. Methyl bromide was generally undersaturated at sea surface temperatures above 25°C, becoming supersaturated at colder temperatures. Yet, there were several regions where it was supersaturated in the warmer waters, indicating that the concentration of this gas in the surface ocean is controlled by more than just chemical removal. Methyl chloride and methyl iodide were supersaturated for the duration of the cruise, with the degree of saturation decreasing with surface water temperature. If the saturation of these compounds were controlled solely by chemical removal, the trend would have been the opposite of what was observed. We relate the measured saturation anomalies to pertinent sea-surface properties, including those measurable by satellite (e.g., SeaWiFS), to see if any useful correlations can be derived.
Landsea, C.W., and R.A. Pielke. Trends in U.S. hurricane losses, 1925 1995. Preprints, Ninth Symposium on Global Change Studies, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 210-212 (1998).
No abstract.
Landsea, C.W., J. Kaplan, and M. DeMaria. The differing roles of the large-scale environment in the intensity changes of recent Atlantic hurricanes. Preprints, Symposium on Tropical Cyclone Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 113-114 (1998).
No abstract.
Landsea, C.W., N. Nicholls, and J. Gill. Australian region tropical cyclones: Recent trend and interannual predictions. Preprints, Ninth Conference on Interaction of the Sea and Atmosphere, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 1-4 (1998).
No abstract.
Landsea, C.W., G.D. Bell, W.M. Gray, and S.B. Goldenberg. The extremely active 1995 Atlantic hurricane season: Environmental conditions and verification of seasonal forecasts. Monthly Weather Review, 126(5):1174-1193 (1998).
The 1995 Atlantic hurricane season was a year of near-record hurricane activity with a total of 19 named storms (average is 9.3 for the base period 1950-1990) and 11 hurricanes (average is 5.8), which persisted for a total of 121 named storm days (average is 46.6) and 60 hurricane days (average is 23.9), respectively. There were five intense (or major) Saffir-Simpson category 3, 4, or 5 hurricanes (average is 2.3 intense hurricanes) with 11.75 intense hurricane days (average is 4.7). The net tropical cyclone activity, based upon the combined values of named storms, hurricanes, intense hurricanes and their days present, was 229% of the average. Additionally, 1995 saw the return of hurricane activity to the deep tropical latitudes: seven hurricanes developed south of 25°N (excluding all of the Gulf of Mexico) compared with just one during all of 1991-1994. Interestingly, all seven storms that formed south of 20°N in August and September recurved to the northeast without making landfall in the United States. The sharply increased hurricane activity during 1995 is attributed to the juxtaposition of virtually all of the large-scale features over the tropical North Atlantic that favor tropical cyclogenesis and development. These include extremely low vertical wind shear, below-normal sea level pressure, abnormally warm ocean waters, higher than average amounts of total precipitable water, and a strong west phase of the stratospheric quasi-biennial oscillation. These various environmental factors were in strong contrast to those of the very unfavorable conditions that accompanied the extremely quiet 1994 hurricane season. The favorable conditions for the 1995 hurricane season began to develop as far back as the previous winter. Their onset well ahead of the start of the hurricane season indicates that they are a cause of the increased hurricane activity, and not an effect. The extreme duration of the atmospheric circulation anomalies over the tropical North Atlantic is partly attributed to a transition in the equatorial Pacific from warm episode conditions (El Niño) to cold episode conditions (La Niña) prior to the onset of the hurricane season. Though the season as a whole was extremely active, 1995's Atlantic tropical cyclogenesis showed a strong intraseasonal variability with above-normal storm frequency during August and October and below normal for September. This variability is likely attributed to changes in the upper-tropospheric circulation across the tropical North Atlantic, which resulted in a return to near-normal vertical shear during September. Another contributing factor to the reduction in tropical cyclogenesis during September may have been a temporary return to the near-normal SSTs across the tropical and subtropical North Atlantic, caused by the enhanced tropical cyclone activity during August. Seasonal hurricane forecasts for 1995 issued at Colorado State University on 30 November 1994, 5 June 1995, and 4 August 1995 correctly anticipated an above-average season, but underforecast the extent of the extreme hurricane activity.
Landsea, C.W., W.M. Gray, J.A. Knaff, P.W. Mielke, and K.J. Berry. Verification of the 1997 seasonal hurricane forecast and a prediction for 1998. Minutes, 52nd Interdepartmental Hurricane Conference, Clearwater, FL, January 27, 1998. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-331-A-338 (1998).
The forecast for the 1998 Atlantic hurricane season issued by Dr. Bill Gray and collaborators (including myself) will be discussed. This prediction, to be issued in early December 1997, will be updated in early April, early June, and early August. Uncertainties in the predictors, especially in El Niño, Atlantic sea surface temperatures, and Sahel rainfall, will be discussed in how they may impact the number and intensity of tropical cyclones this year. I will also analyze and discuss the performance of the 1997 forecasts.
Lee, K., R.H. Wanninkhof, T. Takahashi, S.C. Doney, and R.A. Feely. Low interannual variability in recent oceanic uptake of atmospheric carbon dioxide. Nature, 396(12):155-158 (1998).
An improved understanding of the partitioning of carbon between the atmosphere, terrestrial biosphere, and ocean allows for more accurate predictions of future atmospheric CO2 concentrations under various fossil-fuel CO2 emission scenarios. One of the more poorly quantified relevant processes is the interannual variability in the uptake of fossil-fuel CO2 from the atmosphere by the terrestrial biosphere and ocean. Existing estimates, based on atmospheric measurements, indicate that the oceanic variability is large. Here we estimate the interannual variability in global net air-sea CO2 flux using changes in the observed wind speeds and the partial pressure of CO2 (pCO2) in surface seawater and the overlying air. Changes in seawater pCO2 are deduced from interannual anomalies in sea surface temperature and the regionally and seasonally varying temperature-dependence of seawater pCO2, assuming that variations in sea surface temperature reflect seawater pCO2 changes caused by thermodynamics, biological processes, and water mixing. The calculated interannual variability in oceanic CO2 uptake of 0.4 Gt C yr-1(2 sigma) is much less than that inferred from the analysis of atmospheric measurements. Our results suggest that variable sequestration of carbon by the terrestrial biosphere is the main cause of observed year-to-year variations in the rate of atmospheric CO2 accumulation.
Lee, T.N., E. Johns, W.D. Wilson, and E. Williams. Florida Bay circulation and exchange study. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 43-44 (1998).
No abstract.
Marks, F.D., and H.A. Friedman. 1998 Hurricane Field Program Plan. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida (published for limited distribution), 144 pp. (1998).
The objective of the National Oceanic and Atmospheric Administration (NOAA) hurricane research field program is the collection of descriptive data that are required to support analytical and theoretical hurricane studies. These studies are designed to improve the understanding of the structure and behavior of hurricanes. The ultimate purpose is to develop improved methods of hurricane prediction. Ten major experiments have been planned, by principal investigators at the Hurricane Research Division (HRD)/Atlantic Oceanographic and Meteorological Laboratory (AOML) of NOAA and the Mission Planning Committee for the National Aeronautics and Space Administration (NASA) Third Convection and Moisture Experiment (CAMEX-3), for the 1998 Hurricane Field Program. These experiments will be conducted with the NOAA/Aircraft Operations Center (AOC) WP-3D and Gulfstream IV-SP aircraft and the NASA DC-8 and ER-2 aircraft.
Marks, F.D., and L.K. Shay. Landfalling tropical cyclones: Forecast problems and associated research opportunities. Preprints, 16th Conference on Weather Analysis and Forecasting, Symposium on the Research Foci of the U.S. Weather Research Program, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 520-523 (1998).
No abstract.
Marks, F.D., L.K. Shay, and PDT-5 (Fifth Prospectus Development Team). Landfalling tropical cyclones: Forecast problems and associated research opportunities. Report of the Fifth Prospectus Development Team to the U.S. Weather Research Program. Bulletin of the American Meteorological Society, 79(8):305-323 (1998).
The Fifth Prospectus Development Team of the U.S. Weather Research Program was charged to identify and delineate emerging research opportunities relevant to the prediction of local weather, flooding, and coastal ocean currents associated with landfalling U.S. hurricanes specifically, and tropical cyclones in general. Central to this theme are basic and applied research topics, including rapid intensity change, initialization of and parameterization in dynamical models, coupling of atmospheric and oceanic models, quantitative use of satellite information, and mobile observing strategies to acquire observations to evaluate and validate predictive models. To improve the necessary understanding of physical processes and provide the initial conditions for realistic predictions, a focused, comprehensive mobile observing system in a translating storm-coordinate system is required. Given the development of proven instrumentation and improvement of existing systems, three-dimensional atmospheric and oceanic data sets need to be acquired whenever major hurricanes threaten the United States. The spatial context of these focused three-dimensional data sets over the storm scales is provided by satellites, aircraft, expendable probes released from aircraft, and coastal (both fixed and mobile), moored, and drifting surface platforms. To take full advantage of these new observations, techniques need to be developed to objectively analyze these observations, and initialize models aimed at improving prediction of hurricane track and intensity from global-scale to mesoscale dynamical models. Multinested models allow prediction of all scales from the global, which determine long-term hurricane motion to the convective scale, which affect intensity. Development of an integrated analysis and model forecast system optimizing the use of three-dimensional observations and providing the necessary forecast skill on all relevant spatial scales is required. Detailed diagnostic analyses of these data sets will lead to improved understanding of the physical processes of hurricane motion, intensity change, the atmospheric and oceanic boundary layers, and the air-sea coupling mechanisms. The ultimate aim of this effort is the construction of real-time analyses of storm surge, winds, and rain, prior to and during landfall, to improve warnings and provide local officials with the comprehensive information required for recovery efforts in the hardest hit areas as quickly as possible.
Masters, J.C., and R.H. Wanninkhof. Continuous pCO2 measurements as a method to characterize upwelling along the northwestern Arabian Sea boundary. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS52, OS21G-11 (1998).
Upwelling zones are identified using surface water pCO2 and other biogeochemical parameters in the northwestern Arabian Sea based on observations from May through August 1995. This time frame encompasses the beginning of the southwest monsoon through the first monsoonal break. The Ekman dynamics associated with the wind stress create an upwelling structure along the northwestern boundary of the Arabian Sea. The characteristics of upwelled water are low temperature, high nutrients, high dissolved inorganic carbon (DIC), and high pCO2 relative to the surrounding waters. Each parameter has a unique response time and can be used to characterize the upwelling zone. An underway monitoring system collected pCO2 data from the surface water and the marine boundary air. The pCO2 measurements, taken at 4-minute intervals, were plotted against the ship track and produced a high-resolution representation of the upwelling structure, boundaries, and water mass movement though time. Temperature, salinity, fluorescence, and nitrate values were used to further define the water mass and upwelling zones. Satellite sea surface temperature images were used to produce a more complete two-dimensional picture of the water mass movement on the surface. When upwelled water reaches the surface, the physical and chemical characteristics of the water are affected by incident radiation, wind stress, and photosynthesis. As the primary production consumes nutrients, the concentration of chlorophyll a increases and pCO2 decreases. The parameters change as a function of the time the water mass spends on the surface. By the time the upwelled water warms to adjacent conditions, the pCO2 has decreased but remains elevated compared to the surrounding waters. The nutrients are depleted and there are high chlorophyll a concentrations. Thus, in conjunction with concentrations of chlorophyll a and nutrients, pCO2 can be used as a non-conservative tracer of an upwelled water mass. The results show that coastal upwelling took place during the entire five-month period at approximately 10°N, 51°E, 19°N, 58°E, and 22°N, 59.5°E. During the southwest monsoon, the upwelling in these areas strengthened, as manifested by lower sea surface temperatures (29°C in May to 20°C in August) and higher pCO2 (430 ppm to 720 ppm). The mass transport of upwelled water moves offshore in "squirts" or "jets" as shown by large changes in pCO2 over approximately 20 km scales. These narrow jets diffuse offshore into a larger surface area and their pCO2 decreases as a function of time, slower than the time it takes for the water temperature to equilibrate with its surroundings.
Mayer, D.A., and R.H. Weisberg. El Niño-Southern Oscillation-related ocean-atmosphere coupling in the western equatorial Pacific. Journal of Geophysical Research, 103(C9):18,635-18,648 (1998).
Using 43 years of Comprehensive Ocean-Atmosphere Data Set (COADS) and related data for the period 1950-1992, an examination is made into the regional dependence of ocean-atmosphere coupling in relation to the El Niño-Southern Oscillation (ENSO). The cross correlation between sea surface temperature (SST) and sea level pressure (SLP) anomalies over the global tropics shows two patterns of significant negative correlation consistent with a local hydrostatic response of SLP to SST: (1) the eastern Pacific, where the correlation is symmetric about and largest on the equator; and (2) the western Pacific, where symmetric regions of negative correlation are found off the equator, separated by a region of positive correlation on the equator. Anomalies within these two patterns vary out of phase with each other. While the SLP anomalies on both sides of the basin are of similar magnitude, the SST anomalies in the east are much larger than those in the west. Despite this disparity in the SST anomaly magnitudes between the eastern and western Pacific, we argue that the ocean-atmosphere couplings in the western and west-central Pacific are important for ENSO. The off-equator SST anomalies in the west enhance the SLP anomalies there and they appear to initiate easterly wind anomalies over the far western Pacific during the peak El Niño phase of ENSO. As these easterlies evolve, their effect upon the ocean tends to oppose that of the westerly wind anomalies found over the west-central Pacific. These competing effects suggest a mechanism that may contribute to coupled ocean-atmosphere system oscillations. The west-central equatorial Pacific (the region separating the eastern and western patterns), while exhibiting large momentum and heat flux exchanges, shows minimum correlation between SST and SLP. Thus, neither the SST and SLP anomaly magnitudes nor the correlation between them are alone indicative of ocean-atmosphere coupling, and the regional dependence for such coupling in relation to ENSO appears more complicated than mechanistic interpretations of ENSO would suggest.
Mayer, D.A., G.J. Goni, and R.L. Molinari. Comparison of hydrographic and altimetric estimates of sea level height variability in the Atlantic Ocean. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10,1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F432, OS12A-06 (1998).
Hydrographic estimates of dynamic height (DH) derived from expendable bathythermograph (XBT) data and average temperature salinity (TS) relationships are compared to sea height anomalies (SHA) derived from TOPEX/Poseidon (T/P) altimeter data along two sections of the Atlantic Ocean. Our inquiry examines the relationship between the variability of dynamic effects in the upper 500 m of the water column and SHA over seasonal to interannual time scales for the period 1993 through 1997. Our spatial domain extends from 30°S to 50°N. Emphasis is on two well sampled sections representative of the western and eastern regions of the Atlantic. Both the XBT and T/P data are matched by time and location within 2° of latitude by 4° of longitude quadrangles and then binned by month. The SHA signal is compared to DH derived with respect to reference depths ranging from 50 m to 500 m. DH is estimated from T/P data by computing their linear correlations along both sections. The subtropics show correlations that remain relatively constant throughout most of the water column. This reveals the dominant effects of seasonal heating on SHA due to surface fluxes. In contrast, correlations in the tropics can be sharply depth dependent, suggesting the effects of ocean dynamics (thermocline depth) on SHA due to the seasonal cycle of the zonal currents and their system of ridges and troughs. Correlations are generally significant at the 90% significance level (SL). With a few exceptions, most of the relationship between SHA and DH is a consequence of the annual cycle. Correlations degrade well below the 90% SL if the annual cycle is removed before the correlations are computed. In both the tropics and subtropics, most of the dynamic height signal can be accounted for by using reference depths of 500 m. However, the DH does not fully account for the SHA by a factor of 2 or more in some instances. This discrepancy can be attributed to factors such as the use of average historical TS relationships, the spatial averaging within each 2° by 4° quadrangle, reference depths to only 500 m, and barotropic effects.
Mayer, D.A., R.L. Molinari, and J.F. Festa. The mean and annual cycle of upper layer temperature fields in relation to Sverdrup dynamics within the gyres of the Atlantic Ocean. Journal of Geophysical Research, 103(C9):18,545-18,566 (1998).
Using 28 years of expendable bathythermograph data (1967-1994), we describe the mean and annual cycle of the upper ocean temperature fields in the Atlantic from 30°S to 50°N in the context of the basin-scale wind-driven gyres (Sverdrup stream function field) which provide a framework for describing the oceanographic measurements. We examine the circulation field implied by the temperature distributions which are used as a proxy for the field of mass. Similarities between the temperature and stream function fields increase with depth. In the lower to subthermocline depths of the tropical and equatorial gyres, the zonal currents form a closed circulation. A Southeastward Boundary Current is suggested near and below 150 m that provides closure for the tropical gyre, and the equatorial gyre axis is southward of that suggested by the stream function field. Higher in the water column, the North Equatorial Countercurrent (NECC) may be a surface manifestation of the North Equatorial Undercurrent (NEUC) where the latter can be interpreted as the southern limb of the tropical gyre. Because there are large vertical shears in the tropics, the equatorial gyre is not clearly indicated in the vertically integrated temperature field but appears below about 200 m. Here, the South Equatorial Undercurrent (SEUC) can be interpreted as the eastward flowing northern limb of the equatorial gyre and is opposite in direction to the westward flowing South Equatorial Current above. Both the NEUC and SEUC are analagous to currents in the Pacific that are governed by non-Sverdrup dynamics. Despite the shortcomings of the data, the mean annual cycle appears to be relatively stable, and we have discounted the possibility that in regions where it represents a significant percentage of the total variance, it is changing slowly over the 28 years of record. The wind-forcing fields, which undergo large meridional movements (5-6 of latitude) during their annual cycle, with some exceptions, have essentially no counterpart in gyre movements between their seasonal extremes. Most of the variability associated with the annual cycle is confined to the upper 300 m. Greatest variability, where ranges exceed 6°C, occurs in the northwestern Atlantic in late winter and early spring. During this time of year south of the Gulf Stream and below about 100 m, water temperatures exhibit a systematic phase lag with depth. The next largest area of variability, where ranges can also exceed 6°C, resides in the tropical western basin between the equator and 10°N just below 100 m. In the eastern basin, ranges decrease and shoal. Additionally, the phase fields are consistent with the intensification and relaxation of the tropical ridge-trough system where the NECC disappears in March in the west but the NECC/NEUC complex is strongest in September.
McElligott, S., R.H. Byrne, K. Lee, R.H. Wanninkhof, F.J. Millero, and R.A. Feely. Discrete water column measurements of CO2 fugacity and pHT in seawater: A comparison of direct measurements and thermodynamic calculations. Marine Chemistry, 60(1-2):63-73 (1998).
The NOAA Equatorial Pacific CO2 system data set (~2500 water samples) has been evaluated to assess the internal consistency of measurements and calculations involving CO2 fugacity and pHT. This assessment represents the first large scale field comparison of pHT and fCO2 data. Comparisons of direct discrete CO2 fugacity (fCO2) measurements with CO2 fugacity calculated from total inorganic carbon (CT), total alkalinity (AT), and spectrophotometric pH (pHT = -log[H+]T) indicate that a variety of improvements are needed in the parameter measurements and thermodynamic relationships used to relate fCO2, CT, AT, and pHT in seawater. CO2 fugacity calculated from CT and pHT or AT and pHT agree with direct measurements to no better than 1%. Comparisons of measured fugacity, fCO2 (measured), and CO2 fugacity calculated from CT and pHT, fCO2 (CT, pHT), indicate that the precision of fCO2 calculations is good relative to direct measurements. In contrast, due to the extreme sensitivity of fCO2 and [H+]T calculations to relatively small errors in both CT and AT, CO2 fugacity, as well as [H+]T, calculated from CT and AT are very imprecise and render comparisons with direct measurements of little use. Consequently, precise calculations of fCO2 require the use of direct pHT measurements.
Mestas-Nunez, A.M., and D.B. Enfield. Rotated global modes of multiyear sea surface temperature variability. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS75, OS22H-04 (1998).
El Niño-Southern Oscillation (ENSO) is a global phenomenon with significant phase propagation which we capture in the first mode of a complex empirical orthogonal function (EOF) analysis of sea surface temperature anomaly (SSTA) from the mid-19th century through 1991. We subsequently remove the global ENSO from the SSTA data, plus a linear trend everywhere, in order to consider other global modes of variability uncontaminated by the effects of ENSO. An ordinary EOF analysis of the SSTA residuals reveals three non-ENSO modes that are related to slow oceanic and climate signals described in the literature. The first two modes both have an interdecadal time scale with high loadings in the Pacific. The third mode is a multidecadal signal with maximal realization in the extratropical North Atlantic southeast of Greenland. It also has high loadings in the tropical Atlantic, anticorrelated across the intertropical convergence zone, and strong variability of opposite sign in the eastern tropical Pacific. Unlike ENSO and the secular global warming, it is not known if the variability at intermediate (decadal to multidecadal) time scales is global or regional in nature. To investigate the presence of localized centers of variability, we perform a varimax rotation of the ordinary non-ENSO EOFs. The first rotated mode has multidecadal scales with maximal realization in the North Atlantic. The second rotated mode has interdecadal scales with maximal realization in the western tropical Pacific and captures the interdecadal warm anomaly that contributed to the strong ENSO of 1983. These first two rotated modes capture the Atlantic and western tropical Pacific counterparts of the third Atlantic multidecadal unrotated mode. The third rotated mode is a multidecadal signal with maximal realization in the mid-latitude eastern North Pacific. The relation of these and higher order rotated modes to the unrotated modes and to published climatic signals are discussed.
Millero, F.J., and J.-Z. Zhang. Adsorption of phosphate on calcium carbonate. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 115 (1998).
No abstract.
Millero, F.J., W. Yao, K. Lee, J.-Z. Zhang, and D.M. Campbell. Carbonate system in the waters near the Galapagos Islands. Deep-Sea Research II, 45(6):1115-1134 (1998).
During the IRONEX cruise in the equatorial Pacific Ocean, the carbonate parameters TA (total alkalinity), TCO2 (total inorganic carbon), pH, and fCO2 (fugacity of CO2), were determined both in a small (8 × 8 km) patch of water fertilized with Fe and in the waters around the Galapagos Islands. The CO2 parameters, along with hydrographic properties, were found to be uniform in the surface waters of the study area before the addition of iron. A significant decrease of the surface TCO2 (7 µmol kg-1) and fCO2 (11 µatm) in the patch was detected within 48 h of the iron release. This decrease, however, did not continue and was lower than expected from the complete utilization of NO3- due to the addition of iron. The shipboard iron a ddition experiments (3 nM fe) resulted in a continual decrease of TCO2 (up to 48 µmol kg-1) and complete consumption of the nutrients. A good correlation was found between TCO2, pH, and fCO2 with temperature in the surface waters around the Galapagos Islands. The salinity (S = 35) normalized alkalinities were quite uniform (NTA = 2310 ± 9 mol kg-1) throughout the region. The effect of high primary production on the CO2 system in the downstream plume is overshadowed by the upwelling waters with high CO2.
Millero, F.J., D.G. Purkerson, P. Steinberg, E. Peltola, K. Lee C. Edwards, J. Goen, and M.P. Roche. The carbon dioxide system in the Ross Sea during the JGOFS Southern Ocean Process Study. University of Miami Technical Report, RSMAS-98-001, 159 pp. (1998).
In the austral summer of 1996 and austral fall of 1997, we participated in the Joint Global Ocean Flux Study (JGOFS) supported by the National Science Foundation (NSF) in the Southern Ocean aboard the R/V Nathaniel B. Palmer. The first cruise was a survey across the Antarctic Convergence Zone from Port Lyttelton, New Zealand to the Ross Sea and back. The Process 1 and 3 cruises were in the Ross Sea. The first process cruise originated in Port Lyttelton, New Zealand and ended in McMurdo Station, Antarctica. The third process cruise originated and ended in Port Lyttelton, New Zealand. This report gives the results of our pH, total alkalinity (TA), and total inorganic carbon dioxide (TCO2) measurements made during these cruises. The pH, TCO2, and TA results were obtained by potentiometric titration of seawater samples with hydrochloric acid (HCl), while the TCO2 was determined by coulometry. Spectroscopic pH measurements were also made. Measurements of pH, TA, and TCO2 were made on certified reference material (CRM) throughout the cruises to assess the quality of the measurements. The reproducibility of these CRM measurements by potentiometric titration were ±1.6 µmol kg-1 in TA, ±2.2 µmol kg-1 in TCO2, and ±0.005 in pH. The reproducibility in TCO2 by coulometry were ±1 µmol kg-1 and ±0.001 in the spectroscopic values of pH. The at sea measurements agreed with the assigned values of ±2 µmol kg-1 in TA, ±5 µmol kg-1 in TCO2, and ±0.002 in pH. All the measurements done at sea were adjusted for these differences. The values of pH, TA, and TCO2 for the measurements in the Ross Sea are examined for the process studies along with surface nutrients and pCO2.
Molinari, J., S. Skubis, D. Vollaro, F. Alsheimer, and H.E. Willoughby. Potential vorticity analysis of tropical cyclone intensification. Journal of the Atmospheric Sciences, 55(6):2632-2644 (1998).
The interaction of marginal Tropical Storm Danny (1985) with an upper-tropospheric positive potential vorticity anomaly was examined. The intensification mechanism proposed earlier for mature Hurricane Elena appears to be valid for Danny as well, despite significant differences in the synoptic-scale environment and in the stage of the tropical cyclone prior to the interaction. Both storms experienced rapid pressure falls as a relatively small-scale positive upper potential vorticity anomaly began to superpose with the low-level tropical cyclone center. The interaction is described in terms of a complex interplay between vertical wind shear, diabatic heating, and mutual advection among vortices at and below the level of the outflow anticyclone. Despite this complexity, the superposition principle appears to be conceptually useful to describe the intensification of tropical cyclones during such interactions.
Molinari, R.L., H.F. Bezdek, M. Latif, and A. Groetzner. A comparison of modeled and observed mean and decadal time-scale Atlantic air-sea structure. Proceedings, Atlantic Climate Variability Meeting, Palisades, New York, September 24-26, 1997. University Corporation for Atmospheric Research, 78-79 (1998).
No abstract.
Molinari, R.L., R.A. Fine, W.D. Wilson, J. Abell, M. McCartney, and R. Curry. A fast-track for recently formed Labrador Sea Water: The Deep Western Boundary Current of the North Atlantic. Proceedings, Atlantic Climate Variability Meeting, Palisades, New York, September 24-26, 1997. University Corporation for Atmospheric Research, 80 (1998).
No abstract.
Molinari, R.L., R.A. Fine, W.D. Wilson, R.G. Curry, J. Abell, and M.S. McCartney. The arrival of recently formed Labrador Sea Water in the Deep Western Boundary Current at 26.5°N. Geophysical Research Letters, 25(13):2249-2252 (1998).
The Deep Western Boundary Current (DWBC) of the North Atlantic is a principal conduit between the formation region for Labrador Sea Water (LSW) and the oceanic interior to the south. Time series (1985-1997) of hydrographic properties obtained in the DWBC at 26.5°N show that prior to 1994, temperature, salinity, and transient tracer properties within the LSW density range showed little indication of recently formed parcels. Properties characteristic of a newer version of LSW (cooler, fresher, and higher tracer concentrations) were observed beginning in 1994 and continuing through 1997. Longer time series of temperature and salinity, developed from a regional data base, show both the 1994 and a 1980-1981 event in the Abaco region. Both events are consistent with anomalies in the Labrador Sea that occurred some 10 years earlier. The 10-year transit time from the Labrador Sea to 26.5°N is less than the 18-year transit time inferred from earlier studies.
Murphy, P.P., R.A. Feely, and R.H. Wanninkhof. On obtaining high-precision measurements of oceanic pCO2 using infrared analyzers. Marine Chemistry, 62(1-2):103-115 (1998).
Assessments of ocean carbon uptake using the air-sea disequilibrium of CO2 require very high quality measurements of pCO2 in the atmosphere and in surface seawater. These measurements are often collected and analyzed using infrared detectors. Laboratory data are presented here which suggest that errors of the order of several parts per million in xCO2 can result if the analyzer temperature and pressure are not carefully matched during calibration and sampling. Field data were examined to address questions about the importance of measuring analysis temperature and pressure under more extreme conditions, sample averaging, and calibration frequency. The results indicate that calibration frequency can be minimized without significant compromises in data quality if the analyzer temperatures and pressures are suitably monitored and/or controlled. Daily calibrations gave results to within 0.4 ppm of the results obtained by hourly calibration when the temperature of the analyzer was controlled to ±0.2°C and the voltages were corrected for pressure differences between calibration and sampling.
Nelsen, T.A., H. Wanless, P. Blackwelder, T. Hood, C. Alvarez-Zarikian, P. Swart, J. Trefry, W.-J. Kang, L. Tedesco, and M. O'Neil. The sediment record as a monitor of anthropogenic changes in the lower Everglades/Florida Bay ecosystem. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program (1998).
Florida Bay is a shallow subtropical estuary (~2200 km2, mean depth ~2 m) that lies at the southern end of peninsular Florida and is subject to both natural and anthropogenically-induced changes. Nearshore areas receive not only atmospheric input but also freshwater input from natural sheetflow, major and minor creeks (Shark River and Taylor Sloughs respectively), an unquantified input from groundwater and direct precipitation, as well as anthropogenic sources (c-111 canal). A paleoecological evaluation of this region was instigated using high-resolution retrospective analysis of regional sediments. It integrated sedimentology, geochronology (PB210, Cs137), biology (foraminifera and ostracods), chemistry (organic carbon, heavy metals, stable isotopes), and palynology to allow a broad scope of characterization. These data were complemented with an analysis of historical rainfall, freshwater flow, and limited nearshore salinity data. Placed within a temporal context by geochronology, sediment accumulation rates of ~1 cm per year in recovered sequences permitted evaluation back to about the turn of the century, thus allowing high-resolution evaluation of other co-sampled parameters over a time period that encompasses both natural and anthropogenic changes. Results from geochronology that were supported by other co-sampled parameters indicated disburbed horizons that temporarily correlate with major hurricanes. Moreover, foraminifera and ostracod community structures showed changes that temporally correlated with both natural rainfall patterns and anthropogenic effects such as water management practices. Sediment burdens of heavy metals also showed time-based changes that temporally correlated with documented anthropogenic usage patterns.
Nelsen, T.A., H.R. Wanless, P. Blackwelder, T. Hood, C. Alvarez-Zarikian, P. Swart, J.H. Trefry, W.-J. Kang, L. Tedesco, and M. O'Neal. The sediment record as a monitor of natural and anthropogenic changes in the lower Everglades/Florida Bay ecosystem. Proceedings, ASLO/ESA Land-Water Interface: Science for a Sustainable Biosphere, St. Louis, Missouri, June 8-13, 1998. American Society of Limnology and Oceanography, A-64 (1998).
Florida Bay is a shallow subtropical estuary (~2200 km2, mean depth ~2 m) that lies at the southern end of peninsular Florida and is subject to both natural and anthropogenically-induced changes. Nearshore areas receive not only atmospheric input but also freshwater input from natural sheetflow, major and minor creeks (Shark River and Taylor Sloughs respectively), an unquantified input from groundwater and direct precipitation, as well as anthropogenic sources (c-111 canal). A paleoecological evaluation of this region was instigated using high-resolution retrospective analysis of regional sediments. It integrated sedimentology, geochronology (Pb210, Cs137), biology (foraminifera and ostracods), chemistry (organic carbon, heavy metals, stable isotopes) and palynology to allow a broad scope of characterization. These data were complemented with an analysis of historical rainfall, freshwater flow, and limited near-shore salinity data. Placed within a temporal context by geochronology, sediment accumulation rates of ~1 cm per year in recovered sequences permitted evaluation back to about the turn of the century, thus allowing high-resolution evaluation of other co-sampled parameters over a time period that encompasses both natural and anthropogenic changes. Results from geochronology, that were supported by other co-sampled parameters, indicated disturbed horizons that temporally correlate with major hurricanes. Moreover, foraminifera and ostracod community structures showed changes that temporally correlated with both natural rainfall patterns and anthropogenic effects such as water management practices. Sediment burdens of heavy metals also showed time-based changes that temporally correlated with documented anthropogenic usage patterns.
Nicholls, N., C.W. Landsea, and J. Gill. Recent trends in Australian region tropical cyclone activity. Meteorology and Atmospheric Physics, 65:197-205 (1998).
No abstract.
Niyogi, D.S., J.J. Cione, and S. Raman. Gulf Stream influence on the North Carolina mesoclimate. Preprints, 2nd Conference on Coastal Atmospheric and Oceanic Prediction, American Meteorological Society 78th Meeting, Phoenix, AZ, January 12-16, 1998. American Meteorological Society, Boston, 421-424 (1998).
No abstract.
Ogden, J.C., S.L. Vargo, J.C. Hendee, R. Timko, J.C. Humphrey, and T.C. Moore. SEAKEYS 1998: An enhanced Florida Bay monitoring initiative. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 118 (1998).
No abstract.
Ortner, P.B., M.J. Dagg, G.S. Kleppel, R. Brenner, and C. Tomas. Trophic pathways in the pelagic environment of Florida Bay. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 143-145 (1998).
No abstract.
Ozgokmen, T.M., and O.E. Esenkov. Asymmetric fingers induced by the nonlinear-equation of state. Phys. Fluids, 10(8):1882-1890 (1998).
No abstract.
Ozgokmen, T.M., O.E. Esenkov, and D.B. Olsen. A numerical study of layer formation due to fingers in double-diffusive convection in a vertically-bounded domain. Journal of Marine Research, 56:463-487 (1998).
No abstract.
Peltola, E., R. Wanninkhof, R. Molinari, B.E. Huss, R. Feely, J. Bullister, J.-Z. Zhang, F. Chavez, A. Dickson, A. Ffield, D. Hansell, F. Millero, P. Quay, R. Castle, G. Thomas, R. Roddy, T. Landry, M. Roberts, H. Chen, D. Greeley, K. Lee, M. Roche, J.A. Goen, F. Millero, K. Buck, M. Kelly, F. Menzia, A. Huston, T. Waterhouse, S. Becker, and C. Mordy. Chemical and hydrographic measurements during the Indian Ocean I8 repeat cruise (IR8N) in September and October 1995. NOAA Data Report, ERL AOML-34 (PB99-126948), 176 pp. (1998).
This document contains data and metadata from the I8 repeat cruise in the Indian Ocean cruise in 1995 from Fremantle, Australia to Male in the Maldives. From September 22 to October 25, 1995, the National Oceanic and Atmospheric Administration (NOAA) sponsored an oceanographic research cruise conducted aboard the NOAA Ship Malcolm Baldrige. This report presents the analytical and quality control procedures and data from the cruise that was conducted for the Ocean-Atmosphere Carbon Exchange Study (OACES). Samples were taken at 101 stations. The data presented in this report includes hydrography, nutrients, total dissolved inorganic carbon dioxide (DIC), fugacity of carbon dioxide (fCO2), total alkalinity (TA), pH, total organic carbon and nitrogen data (TOC/TON), chlorofluorocarbons, 13C, and biological parameters.
Peng, T.-H., and F. Chai. Modeling of the carbon cycle in the equatorial Pacific Ocean. AGU 1998 Western Pacific Geophysics Meeting, Taipei, Taiwan, July 21-24, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(24):W41, OS41A-10 (1998).
As a part of the U.S. JGOFS program, field data relating to hydrographic, chemical, and biological properties in the equatorial Pacific have been collected during the process-study-oriented survey cruises in 1992. To synthesize and analyze these data for a better understanding of the carbon cycle dynamics, an ocean ecosystem model of the equatorial Pacific Ocean has been developed. The circulation model is based on the Modular Ocean Model of the NOAA/GFDL ocean general circulation model. It consists of five components describing phytoplankton, zooplankton, detritus, and two forms of dissolved inorganic nitrogen: nitrate and ammonium. The carbonate chemistry is parameterized in the model to evaluate the variations of pCO2, and hence the CO2 flux across the air-sea interface. At this initial stage, a test case by using a one-dimensional model is performed to investigate how the carbon system behaves in the ecosystem structure. The model includes the vertical upwelling and diffusion processes. The upwelling rate and the diffusivity were averaged for the region 5°S to 5°N, 180° to 90°W, the "cold tongue" of the equatorial Pacific. Results of this one-dimensional testing model and comparison with the observed data collected in 1992 will be presented.
Peng, T.-H., R. Key, and H.G. Ostlund. Temporal variations of bomb radiocarbon in the Pacific Ocean. Marine Chemistry, 60:3-14 (1998).
The natural and anthropogenic components of the radiocarbon measurements from seawater samples can be successfully separated by an improved method, which is based on a very well-defined relationship between natural radiocarbon and dissolved silica observed mainly during the GEOSECS survey for waters beneath 1000 m depth. This relationship is further reconfirmed by the 14C measurements from large volume samples taken in the deep waters in the Pacific Ocean during the recent WOCE survey program. Analysis of upper ocean 14C measurements made along 152°W, and north of 20°'N, in the northeastern Pacific Ocean during the NOAA's CGC91 cruise, which is a part of the WOCE survey program, indicates that the bomb 14C inventory in this part of the ocean has increased by 22% since the GEOSECS measurements made in 1974. This increase is consistent with the model prediction of 25% for the northern hemisphere ocean. Change of the surface water bomb 14C values during this period is insignificant. This feature is also consistent with the model simulation. Results of this new analysis will provide useful information of the temporal variations of bomb 14C inventory in the ocean, in addition to the spatial distribution, which can be used as powerful constraints in calibrating the global ocean carbon cycle models, especially those based on three dimensional ocean general circulation models, for estimating the uptake of CO2 by the ocean.
Peng, T.-H., R.H. Wanninkhof, J.L. Bullister, R.A. Feely, and T. Takahashi. Quantification of decadal anthropogenic CO2 uptake in the Indian Ocean based on dissolved inorganic carbon measurements. Nature, 396(10):560-563 (1998).
The increase of total dissolved inorganic carbon (DIC) in the ocean caused by the uptake of fossil fuel CO2 is estimated mostly by ocean models. These model estimates need to be verified using field measurements. However, the direct detection of the anthropogenic CO2 signal in the ocean has been hampered by the relatively small annual increase in DIC in seawater (~1 µmol/kg/yr, as compared with background DIC of ~2000 µmol/kg) and by lack of high-precision measurements in the past. With the recent improvement in DIC analyses techniques, it has now become possible to detect the anthropogenic CO2 signal on decadal time scales. Here we report a significant increase in DIC between the GEOSECS survey in 1978 and the recent NOAA-OACES survey in 1995 in the Indian Ocean. The anthropogenic CO2 signal is 12 ± 4.5 µmol/kg at ~300 m (potential density, sigmatheta = 26.6) and the signal decreases on denser isopycnal horizons down to undetectable near ~1000 m (sigmatheta = 27.2). The data are used to illustrate the isopycnal analysis and corrections necessary to determine the anthropogenic CO2 increase over time. The work can be used as a guide for future observational strategies to assess uptake of anthropogenic CO2.
Pielke, R.A., and C.W. Landsea. Normalized hurricane damages in the United States: 1925-1995. Weather and Forecasting, 13(3):621-631 (1998).
Hurricanes are the costliest natural disasters in the United States. Understanding how both hurricane frequencies and intensities vary from year to year, as well as how this is manifested in changes in damages that occur, is a topic of great interest to meteorologists, public and private decision makers, and the general public alike. Previous research into long-term trends in hurricane-caused damage along the U.S. coast has suggested that damage has been quickly increasing within the last two decades, even after considering inflation. However, to best capture the year-to-year variability in tropical cyclone damage, consideration must also be given toward two additional factors: coastal population changes and changes in wealth. Both population and wealth have increased dramatically over the last several decades and act to enhance the recent hurricane damages preferentially over those occurring previously. More appropriate trends in the United States hurricane damages can be calculated when a normalization of the damages are done to take into account inflation and changes in coastal population and wealth. With this normalization, the trend of increasing damage amounts in recent decades disappears. Instead, substantial multidecadal variations in normalized damages are observed: the 1970s and 1980s actually incurred less damages than in the preceding few decades. Only during the early 1990s does damage approach the high level of impact seen back in the 1940s through the 1960s, showing that what has been observed recently is not unprecedented. Over the long term, the average annual impact of damages in the continental United States is about $4.8 billion (1995 $), substantially more than previous estimates. Of these damages, over 83% are accounted for by the intense hurricanes (Saffir-Simpson categories 3, 4, and 5), yet these make up only 21% of the U.S.-landfalling tropical cyclones.
Powell, M.D., and S.D. Aberson. How well do we forecast the position and time of hurricane landfall? Preprints, 16th Conference on Weather Analysis and Forecasting, Symposium on the Research Foci of the U.S. Weather Research Program, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 9-12 (1998).
No abstract.
Powell, M.D., and S.H. Houston. Surface wind fields of 1995 Hurricanes Erin, Opal, Luis, Marilyn, and Roxanne at landfall. Monthly Weather Review, 126(5):1259-1273 (1998).
Hurricanes Erin, Opal, Luis, Marilyn, and Roxanne were the most destructive hurricanes of 1995. At landfall, Luis and Marilyn contained maximum sustained winds (marine exposure) estimated at near 60 and 46 m s-1, respectively. The strongest landfalling storm of the 1995 season, Luis, decreased in intensity from a category 4 to 3 on the Saffir-Simpson scale shortly before the eyewall crossed the Islands of Antigua, Barbuda, St. Kitts-Nevis, St. Barthelemy, St. Martin, and Anguilla. Hurricane Marilyn strengthened as it approached the U.S. Virgin Islands, with St. Thomas bearing the brunt of the north and south eyewall winds of 46 m s-1 (marine exposure) and St. Croix being affected by the relatively weak western eyewall peak winds of 35-40 m s-1 (marine exposure). For Luis and Marilyn, only surface winds with marine exposures were analyzed because of unknown small-scale interactions associated with complex island terrain with 500-1000-m elevations. Wind engineering studies suggest that wind acceleration over blunt ridges can increase or "speed up" winds by 20%-80%. Topographic effects were evident in damage debris analyses and suggest that an operational method of assessing terrain-induced wind gusts (such as a scaled down mesoscale model) is needed. After landfall as a marginal hurricane over central Florida, Hurricane Erin regained strength over the Gulf of Mexico with a well-defined radar reflectivity structure. Erin struck the Florida panhandle near Navarre Beach with maximum sustained surface winds of 35-40 m s-1 affecting the Destin-Ft. Walton area. Hurricane Opal made landfall in nearly the identical area as Erin, with maximum sustained surface winds of 40-45 m s-1, having weakened from an intensity of nearly 60 m s-1 only 10 h earlier. Opal was characterized by an asymmetric structure that was likely related to cold front interaction and an associated midlevel southwesterly jet. Roxanne struck Cozumel, Mexico, with sustained surface winds (marine exposure) of 46 s-1, crossed the Yucatan, and meandered in the southwest Gulf of Mexico for several days. While in the Bay of Campeche, Roxanne's large area of hurricane-force winds disabled a vessel, which led to the drowning deaths of five oil industry workers. High-resolution wind records are critical to preserving an accurate extreme wind climatology required for assessment of realistic building code risks. Unfortunately, power interruptions to Automated Surface Observing Stations (ASOS) on the U.S. Virgin Islands (St. Croix, St. Thomas) and Destin, Florida, prevented complete wind records of the eyewall passages of Marilyn and Opal, respectively.
Powell, M.D., and S.K. Rinard. Marine forecasting at the 1996 centennial olympic games. Weather and Forecasting, 13(3):764-782 (1998).
A team of meteorologists from the United States, Canada, and Australia provided marine weather support to the sailing events of the 1996 Centennial Olympic Games, held in Wassaw Sound near Savannah, Georgia. The team conducted research on the weather and climate and developed a set of forecast products designed to inform athletes, volunteers, and race managers of the wind, tidal current, wave, and weather behavior expected each day during the pre-Olympic and Olympic periods. The Olympic period proved to be a challenge with thunderstorms delaying, abandoning, or postponing races on half of the days. Thunderstorm development and movement was linked to the timing and strength of the sea breeze as well as the direction and speed of the gradient wind. Numerous thunderstorm warnings were issued with the assistance of the WSR-88D radar and the Warning Decision Support System. Frequent lightning was a legitimate safety concern due to the long distances between race courses and lack of suitable shelter; fortunately no one was injured during the lightning episodes. Forecasters benefited from access to a variety of monitoring tools and models including real-time Olympic buoy wind and current time series displays; satellite and radar imagery animation; 2-, 8-, and 10-km resolution mesoscale models; a live video feed of race coverage; and communications with forecasters aboard patrol craft offshore. Official wind forecasts, mesoscale models, and a simple vector addition model performed better than climatology and persistence as defined by mean vector error and rms wind direction error. Climatology was difficult to beat on the basis of wind speed error.
Powell, M.D., S.H. Houston, L.R. Amat, and N. Morisseau-Leroy. The HRD real-time hurricane wind analysis system. Journal of Wind Engineering and Industrial Aerodynamics, 77&78:53-64 (1998).
The HRD real-time wind analysis system is currently undergoing evaluation in the operational forecasting environment of the National Hurricane Center. The system is an object-oriented, distributed, three-tiered client-server application that assimilates disparate observations and processes the data into a common framework for exposure, height, and averaging time. The data are then examined collectively or by type, quality controlled, and passed on to a scale-controlled objective analysis algorithm. Several products are derived from the analysis wind field and storm track, yielding effective tools for disaster assessment, emergency management, and recovery.
Proni, J.R., and J.C. Wilkerson. Underwater acoustic monitoring for satellite rainfall estimation validation. Proceedings, 6th International Conference for Precipitation, Mauna Lani Bay, Hawaii, June 29-July 1, 1998. NASA/NOAA, 2-10 (1998).
Application of underwater acoustic techniques to the monitoring of rainfall over water is demonstrated at four acoustically distinct ocean sites based on information in the 4-30 kHz frequency band. Rainfall detection and classification as to type (convective or stratiform) are possible because underwater sound spectral characteristics of rain are different from the normally prevailing underwater background noise in the ocean, and because there are distinct differences in the sound levels and spectral shapes of the acoustic signature of the two rain types. Rain type classification is determined by an acoustic discriminant, DR, which is defined as the difference in the average spectral levels between the 10-30 and 4-10 kHz bands. Rainfall estimation potential is based on the high correlation between sound spectral levels in decibels (in the 4-10 kHz frequency band) and radar reflectivity dBz. Data obtained from a spatially distributed 12-hydrophone array on the ocean floor, at a depth of 1.5 km, demonstrates the potential of monitoring rainfall at the sea surface on spatial (420 km2) and temporal (five samples/minute) scales suitable for validating precipitation estimates from remote sensors carried on geostationary and polar orbiting satellites.
Proni, J.R., and J.C. Wilkerson. Wind-generated acoustic spectral effects in the surf zone in the presence and absence of rainfall at Duck, North Carolina. Proceedings, 16th International Congress on Acoustics and 135th Meeting of the Acoustical Society of America, Seattle, Washington, June 20-26, 1998. Journal of the Acoustical Society of America, 103(5):2865-2866 (1998).
Concurrent underwater sound, wind, radar, and rainfall measurements were made on November 5, 1992, off Duck, North Carolina. A wind speed increment from 5 m/s to 13 m/s in 90 seconds resulted in a reduction in the rainfall sound spectrum level beginning at about 50 kHz and extending downward in frequency with time to about 10 kHz. The reduction in rainfall-generated sound spectrum level with time is thought to be due to sound absorption by the evolving wind-generated bubble field.
Proni, J.R., C. McArthur, and G. Schuster. Adaptive dredged material discharge for the Port of Miami. Proceedings, Ports '98, Long Beach, California, March 8-11, 1998. American Society of Civil Engineers, 1249-1257 (1998).
In a joint effort of the U.S. Army Corps of Engineers, the U.S. Environmental Protection Agency, the National Oceanic and Atmospheric Administration, the State of Florida, the Port of Miami, and the University of Miami, a novel, environmentally adaptively controlled procedure was developed, wherein a vital port expansion and maintenance dredging operation was carried out while affording maximum protection to sensitive coral reefs. After establishing the existence and spatial disposition of a residual water column discharge plume, via acoustic backscattering methods, a real-time current measurement system was established at the offshore dredged material disposal site to be utilized. Dredged material discharges then proceeded on a schedule in conformity with the ambient currents, so that material transport to the coral reefs of concern was minimized.
Quilfen, Y., B. Chapron, T. Elfouhaily, K.B. Katsaros, and J. Tournadre. Observations of tropical cyclones by high-resolution scatterometry. Journal of Geophysical Research, 103(C4):7767-7786 (1998).
Unprecedented views of surface wind fields in tropical cyclones (hereafter TCs) are provided by the European Remote Sensing Satellite (ERS) C-band scatterometer. Scatterometer measurements at C band are able to penetrate convective storms clouds, observing the surface wind fields with good accuracy. However, the resolution of the measurements (50 × 50 km2) limits the interpretation of the scatterometer signals in such mesoscale events. The strong gradients of the surface wind existing at scales of a few kilometers are smoothed in the measured features such as the intensity and location of the wind maxima and the position of the center. Beyond the ERS systems, the scatterometers on-board the ADEOS and METOP satellites, designed by the Jet Propulsion Laboratory and by the European Space Agency, respectively, will be able to produce measurements of the backscattering coefficient at about 25 × 25 km2 resolution. A few sets of ERS-1 orbits sampling TC events were produced with an experimental 25 × 25 km2 resolution. Enhancing the resolution by a factor of 2 allows location of the wind maxima and minima in a TC with a much better accuracy than at 50 km resolution. In addition, a better resolution reduces the geophysical noise (variability of wind speed within the cell and effect of rain) that dominates the radiometric noise and, hence, improves the definition of the backscattering measurements. A comprehensive analysis of the backscattering measurements in the case of high winds and high sea states obtained within TCs is proposed in order to refine the interpretation of the wind vector derived from a backscattering model that is currently only calibrated up to moderate winds (<20 m/s) in neutral conditions. Observations of the TOPEX-POSEIDON dual-frequency altimeter are also used for that purpose. Patterns of the surface winds in TCs are described and characteristic features concerning asymmetries in the maximum winds and in the divergence field are discussed.
Roubicek, A.J., S.L. Garzoli, P.L. Richardson, C.M. Dumcombe Rae, and D.M. Fratantoni. Benguela Current Experiment, R/V Seward Johnson Cruise SJ9705, Cape Town, September 4, 1997-Recife, September 30, 1997. NOAA Data Report, ERL AOML-33 (PB98-164775), 215 pp. (1998).
The main objective of this program is to study the pathways, velocity, transport, and variability of the Benguela Current and its extension with emphasis on tracking floats in the intermediate water. It is expected that the results of this program will make a significant contribution towards the understanding of inter-ocean (Indian to Atlantic) and inter-basin (South and North Atlantic) exchange of intermediate water and its role in heat and mass exchanges. This program is a component of KAPEX (Cape of Good Hope Experiment), a joint U.S., German, and South African experiment. In March 1997, a German cruise on the Polarstern led by W. Zenk and O. Boebel launched 35 RAFOS floats and five sound sources (including one of the U.S. sources near 20°S, 4°E) in the general area west and southwest of Cape Town. During August 1997, a U.S. cruise on the R/V Seward Johnson led by T. Rossby launched three sound sources east and southeast of Cape Town; 50 RAFOS floats will be launched in the Agulhas Current starting in November 1997. During the Benguela Current Experiment cruise on the RV Seward Johnson in September 1997, 32 RAFOS floats and two sound sources were launched in the general area west and northwest of Cape Town. During KAPEX, over 100 RAFOS floats and nine sound sources will measure ocean trajectories for the first time in the Agulhas Current, in its rings which enter the South Atlantic, and in the Benguela Current and its extension, which is the source of water moving northward through the Atlantic in the meridional overturning circulation cell. In addition, temperature, salinity, and velocity profiles will document the water mass and velocity structure of the Benguela Current, its extension, and several Agulhas rings.
Shapiro, L.J., and S.B. Goldenberg. Atlantic sea surface temperatures and tropical cyclone formation. Journal of Climate, 11(4):578-590 (1998).
It has long been accepted that interannual fluctuations in sea surface temperature (SST) in the Atlantic are associated with fluctuations in seasonal Atlantic basin tropical cyclone frequency. To isolate the physical mechanism responsible for this relationship, a singular value decomposition (SVD) is used to establish the dominant covarying modes of tropospheric wind shear and SST, as well as horizontal SST gradients. The dominant SVD mode of covarying vertical shear and SST gradients, which comprises equatorially confined near-zonal vertical wind shear fluctuations across the Atlantic basin, is highly correlated with both equatorial eastern Pacific SST anomalies (associated with El Niño) and west African Sahel rainfall. While this mode is strongly related to tropical storms, hurricanes, and major hurricane frequency in the Atlantic, it is not associated with any appreciable Atlantic SST signal. By contrast, the second SVD mode of covarying vertical shear and horizontal SST gradient variability, which is effectively uncorrelated with the dominant mode, is associated with SST fluctuations concentrated in the main tropical cyclone development region between 10°N and 20°N. This mode is significantly correlated with tropical storm and hurricane frequency but not with major hurricane frequency. Statistical tests confirm the robustness of the mode, and lag correlations and physical reasoning demonstrate that the SST anomalies are not due to the developing tropical cyclones themselves. Anomalies of SST and vertical shear during years where the mode has substantial amplitude confirm the resemblance of the individual fields to the modal structure, as well as the association of hurricane development with the warmer SSTs. Although SSTs are of secondary importance to vertical shear in modulating hurricane formation, explaining only 10% of the interannual variability in hurricane frequency over the 50% explained by vertical shear, the results support the conclusion that warmer SSTs directly enhance development. The lack of correlation with major hurricanes implies that the underlying SSTs are not a significant factor in the development of these stronger systems.
Shay, L., G.J. Goni, F.D. Marks, J.J. Cione, and P.G. Black. Role of warm ocean features on intensity change: Hurricane Opal. Preprints, Symposium on Tropical Intensity Change, American Meteorological Society 78th Annual Meeting, Phoenix, AZ, January 11-16, 1998. American Meteorological Society, Boston, 131-138 (1998).
No abstract.
Sheinbaum, J., J. Candela, W.D. WILSON, J. Ochoa, and A. Badan. Shipboard ADCP and lower ADCP observations in the Yucatan Channel. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS125, OS32P-01 (1998).
Observations obtained during two cruises in December 1996 and in May/June 1997 within the CANEK Project are discussed. The cruises were onboard the R/V Justo Sierra, equipped with a ship-mounted RDI 75 kHz ADCP, usually measuring up to 400 m depth, and covered the area around the Yucatan Channel within 20° to 22.5°N. Both cruises show a persistent and swift Yucatan Current flowing towards the Gulf of Mexico, on the western side of the Channel, with surface magnitudes as large as 2 m/s. Transport estimates in the upper 300 m indicate that this current was transporting around 8 Sv into the Gulf during both cruises, for an equivalent cross-shelf section about 50 km in length at around 22°N and oriented nearly in west-east direction. A complete cross-Channel section between Isla Contoy, Yucatan and Cabo San Antonio, Cuba, during the May cruise, gives a total transport of 19 Sv into the Gulf in the upper 300 m. Ship-mounted ADCP velocities from the top 300 m are used to reference velocity measurements from a Lower-ADCP (LADCP), an RDI 300 kHz acoustic Doppler current profiler attached to a CTD-rosette frame which samples the whole water column. Total and deep transport estimates, together with methods to filter out tidal transports, are also discussed.
Sheinbaum, J., J. Candela, J. Ochoa, A. Badan, I. Gonzalez, W.D. Wilson, and R.H. Smith. Velocity and transport measurements with a lower-acoustic Doppler current profile in the Yucatan Channel: Some preliminary results. Proceedings, Conference on the Transports and Linkages of the Intra-Americas Sea (IAS), Cozumel, Mexico, November 1-5, 1997. IOC/IOCARIBE/MMS, 57 (1998).
We present preliminary results from the extensive surveys carried out onboard UNAM'S R/V Justo Sierra using a shipboard ADCP and a CTD/LADCP during December 1996 and May 1997 in the Yucatan Channel. These cruises were part of the CANEK Project, a collaborative effort between CICESE, ICMyL-UNAM, UAM (Mexico), NOAA (USA), and IOC (Cuba), to measure the exchange between the Carribean Sea and the Gulf of Mexico. Velocity measurements and transport estimates from both instruments are analyzed and compared. The May 1997 cruise had a standard GPS instrument to fix ship positions, which were recorded almost continuously (every second) during the whole cruise. These data were filtered before velocity and transport calculations were carried out. Details of the data processing and sensitivity of absolute velocity estimates from the LADCP instrument to the ship's position are discussed.
Swart, P., K.S. White, D.B. Enfield, P. Milne, and R.E. Dodge. Stable oxygen isotopic composition of corals from the Gulf of Guinea as indicators of periods of extreme precipitation conditions in the sub-Sahara. Journal of Geophysical Research, 103(C12):27,885-27,891 (1998).
Analyses of scleractinian coral skeletons from the Gulf of Guinea in the eastern Atlantic reveal that the corals from this region can be used to identify periods of severe drought and above average precipitation in the Subsahara. Data presented in this paper show a positive correlation between the magnitude of the Sahel drought and the d18O values of the Principe coral skeleton. The explanation for this positive correlation is that the salinity of the Gulf of Guinea is strongly influenced by the outflow of the Niger and Zaire Rivers. The outflow of these rivers is also correlated with the fluorescence of the Principe coral. These periods of high freshwater input correlate with periods of higher rainfall in the Subsahara and have affected the d18O values of the coral skeleton. The correlations between Principe coral d18O values and Atlantic NATL (r = -0.34), the dipole (r = -0.45), and the latitudinal position of the ITCZ (r = -0.37) illustrate that the d18O values in the Principe coral reflect climate dynamics of the region that affect the precipitation patterns in the Subsahara.
Swenson, M.S., and D.V. Hansen. Drifter-based estimates of the seasonal cycle of heat advection in the NECC of the eastern tropical Pacific. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F431, OS12A-05 (1998).
Drifter-based estimates of the seasonal cycle of heat advection in the NECC of the eastern tropical Pacific is based on over 2500 estimates of weekly averaged velocity and DT/Dt from drifting buoys and over 2100 XBT casts in the region 4°N-11°N, 145°W-115°W from the historical data base in the Pacific for 1979-1996. This is the region of the North Equatorial Countercurrent (NECC) over which the Intertropical Convergence Zone is usually found. The NECC exhibits a strong seasonal cycle in zonal velocity and mixed-layer depth structure. We estimate the contribution to the mixed layer heat budget in this region arising from horizontal advection and diffusion during the march of the seasonal cycle. These contributions are compared with estimates of the remaining terms in an attempt to close the budget and identify the mechanisms which dominate during different seasons. The estimates will include eddy heat flux estimates. Finally, we will attempt to evaluate existent surface flux climatologies based on the balances we find.
Swenson, M.S., and H.F. Bezdek. On ocean-atmosphere coupling in the North Atlantic. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS77, OS22I-08 (1998).
We explore the geographical variability of the structure of the cross correlation function between sea surface temperature anomalies (SSTA) and anomalies of the sum of the latent and sensible heat fluxes (LSHFA) in the North Atlantic based on summaries from the Comprehensive Ocean Atmosphere Data Set (COADS) summaries from 1947-1990. Two distinct cross correlation structures emerge, one of which dominates in the open ocean at midlatitudes and the other of which dominates in the western boundary current and in the tropics. The former is characterized by a strong antisymmetry, while the latter is one-sided with a peak at zero-lag. A simple stochastic model (vector first-order auto-regressive model) is proposed to account for the observed structure. This is the simplest auto-regressive model that can produce the antisymmetric aspect in the cross correlation found in the open ocean midlatitude region. The model reproduces the results with great fidelity, but requires essential mutual coupling between SSTA and LSHFA to reproduce the open ocean midlatitudes result. The residuals from the fit contain low-frequency behavior with decadal time scales.
Thomas, G.G., R. Benway, S. Cook, Y.-H. Daneshzadeh, and W.S. Krug. Surface salinity and temperature from ships of opportunity. Proceedings, Ocean Community Conference '98, Baltimore, MD, November 16-19, 1998. Marine Technology Society, 160-165 (1998).
Thermosalinograph (TSG) data collected aboard both NOAA research vessels and ships participating in the National Oceanic and Atmospheric Administration's (NOAA) Volunteer Observing Ship (VOS) program plays an important role in the study of meridional circulation in the world's oceans. Sea surface temperature (SST) and sea surface salinity (SSS) are valuable measurements in our attempt to understand the interaction between the world's oceans and global climate. The ability to collect and calibrate these data sets to insure a high standard of data quality is necessary to validate their use in NOAA's Global Ocean Observing System (GOOS) Center data base at the Atlantic Oceanographic and Meteorological Laboratory (AOML) located in Miami, Florida.
Wang, C., and R.H. Weisberg. Climate variability of the coupled tropical-extratropical ocean atmosphere system. Geophysical Research Letters, 25(21):3979-3982 (1998).
Observations show that tropical and extratropical Pacific SST anomalies vary out-of-phase, and that the atmospheric meridional Hadley and zonal Walker Circulations are related to these variations. A tropical-extratropical model is constructed to show oscillations consistent with observations. The positive feedback introduced by the Walker Circulation causes tropical warming so that the air rises and flows toward the subtropics where it sinks. When the sinking air approaches the sea surface, it flows both equatorward and poleward enhancing tropical easterly and extratropical westerly winds, respectively. Enhanced extratropical westerlies increases wind speed and hence evaporation, resulting in extratropical cooling. The Walker and Hadley Circulations thus result in tropical warming and extratropical cooling, respectively. The tropical warming and extratropical cooling increase the meridional SST difference and hence the meridional heat transport which erodes the tropical warming and extratropical cooling. Enhanced tropical easterlies due to the Hadley Circulation cools the tropical ocean through ocean dynamics. These negative feedbacks help the system to switch from warm to cold phases, and vice versa.
Wang, C., and R. H. Weisberg. Observations of meridional scale frequency dependence in the coupled tropical ocean-atmosphere system. Journal of Geophysical Research, 103(C2):2811-2816 (1998).
It is generally observed in models of the coupled tropical ocean-atmosphere system that the meridional scales for oscillations at interannual periods are larger than an oceanic equatorial Rossby radius of deformation. Using nine years of the high-resolution Optimum Interpolation sea surface temperature (SST) product of the NOAA/NCEP, analyses are made on the frequency dependence of the observed meridional scales, with emphasis on the latitudinal structures in the central Pacific at 140°W. On the relatively short intraseasonal and seasonal time scales the SST variations are found to occur over a meridional scale of the oceanic equatorial Rossby radius of deformation suggested by conventional equatorially trapped wave theory. In contrast to this, on the longer annual and interannual time scales the meridional scales are found to increase beyond the oceanic equatorial Rossby radius of deformation. A physical explanation for this meridional scale increase with decreasing frequency in the coupled tropical ocean-atmosphere system is discussed.
Wanninkhof, R.H., and R.A. Feely. fCO2 dynamics in the Atlantic, Pacific, and South Indian Oceans. Marine Chemistry, 60(1-2):15-31 (1998).
Subsurface fugacities of CO2 (fCO2(20)) can be used in combination with total dissolved inorganic carbon (DIC) to precisely calculate total alkalinity. Thus, it can be used to determine dissolution of calcium carbonate (hard tissue) and remineralization of organic material (soft tissue), to quantify saturation constants of calcite and aragonite in seawater, and to characterize water masses. fCO2(20) is a good tracer of biological transformation since it is thermodynamically related to the other inorganic carbon system parameters and it has a dynamic range from 200 to 2000 µatm in the world's ocean. Precision of fCO2 measurements is better than 0.3% and the values are well calibrated using compressed gas reference standards. Increases of fCO2(20) are observed as the water masses age during movement from the Atlantic to the Indian and South Pacific Oceans. As an example of the determination of the ratio of soft tissue remineralization to hard tissue dissolution from fCO2(20) and DIC, the trends along the 27.2 isopyncal for the subtropical gyres of the three basins are investigated. Little CaCO3 dissolves along this isopycnal in the Atlantic and the South Pacific while the soft tissue remineralization to hard tissue dissolution ratio in the Indian Ocean is 4.5:1. The difference in this ratio along the 27.2 isopycnal appears to be a combination of the calcite and aragonite saturation levels and the supply of aragonite tests.
Weisberg, R.H., and D.A. Mayer. Interhemisphere and intergyre exchange processes. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F484, OS31F-10 (1998).
Given that tropical ocean and atmosphere property fields have large annual cycles, intergyre and interhemisphere exchanges are likely to be seasonally dependent. Using COADS, we describe the annual variability of the tropical Atlantic Ocean wind-driven circulation and its implications for property exchanges. Focus is on three gyres: the anticyclonic northern hemisphere subtropical gyre, the cyclonic tropical gyre north of the equator, and the clockwise equatorial gyre. In the tropical gyre, the Sverdrup circulation argues against a continuous western boundary current for transporting water between the equatorial region and the Caribbean in boreal winter. Instead, the Sverdrup circulation implies a southeastward flowing boundary current, bringing to question the mechanisms for the interhemisphere and intergyre exchanges of heat and mass. A conceptual model is proposed involving two stages. First, the western boundary current closing the clockwise equatorial gyre is instrumental in transporting heat across the equator and storing warm water mass between the North Equatorial Countercurrent ridge and the North Equatorial Current trough in boreal summer. Transport farther north into the subtropical gyre in boreal winter is then accomplished by Ekman transport, as the seasonal change in wind stress deepens the thermocline, allowing for northward Sverdrup transport over the region of warmest waters. Once in the subtropical gyre, the Ekman transport continues to be northward despite the Sverdrup transport reversing to be southward. These stages constitute a rectification of the annual cycle wherein different regions play additive roles during different times of year. With Ekman and geostrophic transports being important, we also look at how they combine to form divergence on the equator. We use vertical velocity estimates from an equatorial central Pacific array of moorings deployed during TIWE. Upwelling (downwelling) is observed above (below) the EUC core, and while the divergence is centered on the equator, poleward surface and equatorward subsurface flows are larger at 1°S than at 1°N. The results are consistent with interior fluid pathways to the equator in the central Pacific. These gyre and vertical velocity analyses demonstrate that three-dimensional and time dependent processes are at work in transporting properties across hemispheres and gyres.
Whung, P.-Y., and C.J. Fischer. Input of atmospheric nitrogen species in the Florida Bay area: Its role in the nitrogen budget of Florida Bay. Proceedings, 1998 Florida Bay Science Conference, Miami, Florida, May 12-14, 1998. Florida Sea Grant College Program, 71 (1998).
No abstract.
Willoughby, H.E. Tropical cyclone eye thermodynamics. Monthly Weather Review, 126(12):3053-3067 (1998).
In intense tropical cyclones, sea level pressures at the center are 50-100 hPa lower than outside the vortex, but only 10-30 hPa of the total pressure fall occurs inside the eye between the eyewall and the center. Warming by dry subsidence accounts for this fraction of the total hydrostatic pressure fall. Convection in the eyewall causes the warming by doing work on the eye to force the thermally indirect subsidence. Soundings inside hurricane eyes show warm and dry air aloft, separated by an inversion from cloudy air below. Dewpoint depressions at the inversion level, typically 850-500 hPa, are 10-30 K rather than the 100 K that would occur if the air descended from tropopause level without dilution by the surrounding cloud. The observed temperature and dewpoint distribution above the inversion can, however, be derived by 100 hPa of undilute dry subsidence from an initial sounding that is somewhat more stable than a moist adiabat. It is hypothesized that the air above the inversion has remained in the eye since it was enclosed when the eyewall formed and that it has subsided at most a few kilometers. The cause of the subsidence is the enclosed air's being drawn downward toward the inversion level as the air below it flows outward into the eyewall. Shrinkage of the eye's volume is more than adequate to supply the volume lost as dry air is incorporated into the eyewall or converted to moist air by turbulent mixing across the eye boundary. The moist air below the inversion is in thermodynamic contact with the sea surface. Its moisture derives from evaporation of seawater inside the eye, frictional inflow of moist air under the eyewall, and from moist downdrafts induced as condensate mixes into the eye. The moist air's residence time in the eye is much shorter than that of the dry air above the inversion. The height of the inversion is determined by the balance between evaporation, inflow, and inward mixing on one hand and loss to the eyewall updrafts on the other.
Wilson, W.D. Constructing an IAS regional Global Ocean Observing System. Proceedings, Conference on the Transports and Linkages of the Intra-Americas Sea (IAS), Cozumel, Mexico, November 1-5, 1997. IOC/IOCARIBE/ MMS, 66 (1998).
The Global Ocean Observing System (GOOS) was established as an international program in 1993 by the IOC, WMO, UNEP, and ICSU. The main elements are the collection and timely distribution of oceanic data and products, including assessments, assimilation of data into numerical prediction models, the development and transfer of technology, and capacity building within participating member states to develop analysis and application capability. To date, national GOOS operational activities worldwide are primarily split between global programs (supported almost entirely by a small number of highly developed countries) and regional networks of linked coastal and nearshore programs, such as EURO-GOOS in the EU and NEAR-GOOS in northeastern Asia. The IOC suggests that "...In regions having existing IOC Sub-Commissions (e.g., IOCARIBE), countries organizing regional GOOS activities will do so in consultation with the Sub-Commission." Subsequently, both IOC and IOCARIBE have expressed support for the development of an IAS regional GOOS. Because of the nature of the IOCARIBE member states, which contain far fewer autonomous national oceanographic programs than eastern Asia or western Europe, the IAS GOOS paradigm will have a somewhat different structure than NEAR-GOOS or EURO-GOOS. It is hoped that this talk will promote a dialogue about planning for the implementation of an IAS regional GOOS. For discussion purposes, some important issues to be addressed in planning an IAS GOOS include: (1) identification of customer concerns, e.g., fisheries, climate studies, pollution management, etc., in keeping with the primary GOOS goal of providing practical benefits to society; (2) Design of a scientifically sound, expandable pilot observing system for continual monitoring; (3) model development to provide a framework for data synthesis and program expansion; (4) utilization of existing and planned regional programs and regional parts of global programs as components for cost-efficiency; and (5) regional dispersal of technology and capacity building for synoptic data acquisition, management, and utilization.
Wilson, W.D., and W.E. Johns. Measurements of transport and water mass exchange in the passages to the Caribbean Sea. AGU 1998 Ocean Sciences Meeting, San Diego, CA, February 9-13, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(1):OS125, OS32P-03 (1998).
Physical oceanographic measurements from 14 cruises during 1991-1997 in the Antilles island passages have been analyzed to study water exchange between the Atlantic Ocean and the Caribbean Sea. This region is generally thought to be an important site for the entrainment of upper ocean waters of South Atlantic origin into the North Atlantic circulation system, a process necessary to balance southward North Atlantic outflow in deeper layers. The magnitude of this exchange, comprising the North Atlantic thermohaline Meridional Overturning Circulation (MOC), is thought to be around 15 Sv. While earlier cruises were concentrated on passages south of 15°N (Wilson and Johns, 1997, DSR, 44[3]), recent results also include five occupations of the more northern passages of the Lesser Antilles, allowing estimation of significant mean transports through all the passages. Net transport above 800 m in the passages south of Dominica (15°N) is estimated to be 12.2 Sv, partitioned among Grenada (6.1), St. Vincent (2.8), St. Lucia (2.0), and Dominica (1.3). The northern passages, Guadeloupe (1.0), Antigua (2.9), and Anegada (2.8), account for an additional 6.7 Sv. Allowing a maximum of 1 Sv of unresolved inflow, approximately 20 Sv of the 32 Sv that leaves the Straits of Florida at 27°N enters through the passages of the Lesser Antilles. This is quite consistent in total and in spatial distribution with geostrophic transports relative to 800 m calculated from high-resolution historical T-S data at 60°W. Too few sections in the Mona and Windward passages are available to estimate mean transports there. Consideration of these data, historical data, Sverdrup theory, and numerical model results suggests that very little of the mean inflow through the southern passages can be attributed to wind-driven circulation, and that most of that transport is derived from South Atlantic waters crossing the equator in the upper limb of the Atlantic thermohaline cell. The remainder of the upper ocean thermohaline likely follows a different route into the subtropical gyre, possibly flowing northward in the interior and entering the Caribbean through the northern passages.
Wilson, W.D., W. Johns, and E. Johns. Atlantic-Caribbean water exchange: A quantitative summary of observations. Proceedings, Conference on the Transports and Linkages of the Intra-Americas Sea (IAS), Cozumel, Mexico, November 1-5, 1997. IOC/IOCARIBE/MMS, 65 (1998).
The need for good models of IAS circulation is growing as regional researchers seek input for studies of air-ocean-land interaction, climate variability, fisheries management, and pollution control. Proper boundary conditions will be essential to the operation and validation of these models. The water masses that enter, transit, and exit the IAS are determined by interaction between the Atlantic thermohaline and wind-driven circulations as well as regional modifications within the IAS itself. Existing data on transports into, within, and out of the IAS are quantitatively summarized to aid understanding of the IAS general circulation, provide initial conditions, and serve as benchmarks for model evaluation. Passages are categorized as inflows (passages of the Antilles and Bahamas), internal (Pedro Banks, Yucatan Channel, western Straits of Florida), or outflows (northern Straits of Florida). Inflow passages are further subdivided by geographic location (southern/northern); transport and water mass characteristics vary markedly between northern and southern due to their location relative to the western Atlantic gyre and wind field structure. Range of variability as well as mean flow values are estimated when possible, as this is important to evaluation of model dynamics. A significant result of this summary is a "best estimate" of mean transport distribution and variability by region, passage, and depth levels. These values are compared to transports derived from mean hydrographic and wind fields.
Wilson, W.D., D. Wallace, R. Olivacce, R.A. Watlington, and W.E. Johns. Monitoring the pulse of the DWBC in the Anegada Passage. Proceedings, Conference on the Transports and Linkages of the Intra-Americas Sea (IAS), Cozumel, Mexico, November 1-5, 1997. IOC/IOCARIBE/MMS, 63 (1998).
A serial station in the Anegada Passage, site of significant surface transport and of the deepest exchange between the Atlantic Ocean and the Caribbean Sea, is contributing to earlier observations at this location to provide a useful background against which variability of the Deep Western Boundary Current (DWBC) can be contrasted. Profiles of dissolved inorganic carbon, dissolved oxygen, chlorofluorocarbons, and standard hydrographic variables have successfully portrayed the several water masses transiting this location at depths down to 1900 m. Significantly, the southward advance of the prodigious flow Labrador Sea Water observed at Abaco is expected to manifest itself at this station within the coming year. ACTS is a project of the University of the Virgin Islands conducted in partnership with Brookhaven National Laboratory and the NOAA Atlantic Oceanographic and Meteorological Laboratory. The study, in itself, represents a successful collaborative model whereby long-term oceanic observations are conducted at minimal expense.
Yvon-Lewis, S.A., J.H. Butler, P.A. Matrai, E.S. Saltzman, D.B. King, R. Tokarczyk, K. Sullivan, B. Yocis, W. Grosko, and H. Wright. An investigation into the use of SeaWiFS data to study the biogeochemical cycling of methyl bromide. AGU 1998 Fall Meeting, San Francisco, CA, December 6-10, 1998. Supplement to EOS, Transactions, American Geophysical Union, 79(45):F429, OS11F-01 (1998).
The objectives of this study are to evaluate the effects of oceanic biological degradation and production of methyl bromide (CH3Br) on its uptake by and emission from the ocean, to relate the derived parameters to satellite measurements of oceanic and atmospheric properties, and to evaluate the use of satellite data in modeling oceanic fluxes of this gas. Results of this study will have a direct, and likely significant, impact upon our understanding of the lifetime and budget of atmospheric methyl bromide and may be useful in future assessments of the budget of atmospheric CH3Br as anthropogenic emissions decrease. The first step in this investigation was completed during a cruise in the North Atlantic in May and June 1998, where in-situ measurements of CH3Br saturation anomalies and measurements of biological degradation and production rates for CH3Br were made. Results from these measurements will be included in a global model if the production rates, degradation rates, and/or saturation anomalies can be linked to a property or properties that are recorded by satellite, particularly ocean color from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Here, we will present the preliminary results from the field measurements described above and results from our initial efforts to correlate these measurements with a SeaWiFS data product.
Zegowitz, V., and S.K. Cook. World Meteorological Organization-Volunteer Observing Ship Program. Proceedings, Ocean Community Conference '98, Baltimore, MD, November 16-19, 1998. Marine Technology Society, 6 pp. (1998).
As one of our astute, well-informed political figures said recently, "What do we need the Weather Service for, we have the Weather Channel!" Just where DOES the data come from to make a good marine forecast? Even those of you who have wandered here by mistake are about to be exposed to a little bit of information about a big contributor to this process, the World Meteorological Organization (WMO) Voluntary Observing Ship (VOS) program.
Zhang, J.-Z., and P.B. Ortner. Effect of thawing conditions on the recovery of reactive silicic acid from frozen natural water samples. Water Research, 32(8):2553-2555 (1998).
A method for thawing frozen samples for silicic acid analysis is recommended. The maximum recovery of silicic acid is achieved by thawing the frozen samples in a refrigerator (at 4°C) in the dark for at least four days. This method significantly improves the recovery of silicic acid from frozen fresh water samples. It also permits close to 100% recovery of reactive silicic acid from frozen seawater samples even after three months storage.
**1997**
Aberson, S.D. Adaptive observations in a hurricane environment. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 308-309 (1997).
No abstract.
Aberson, S.D. Five-day statistical hurricane track forecasts. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Support Research, Washington, D.C., A-3 (1997).
A dimensional analysis of five-day hurricane tracks is presented to calculate the number of predictors necessary to accurately predict tracks. While the dimensions of the hurricane tracks are large, statistical analyses can still be used as a benchmark by which other methods can be assessed. A new version of CLIPER is developed which eliminates problems with the original dependent data sets and extends the forecasts to five days. The new version updates the original CLIPER, which used data from 1930 through 1970, a time during which many tracks are conjecture and many are missed completely. The new version eliminates the Gulf of Mexico tropical cyclones from the Atlantic basin, and corrects for problems in the original Gulf of Mexico data. The new version also eliminates non-physical cross-terms in the multiple linear regression. Independent forecasts are made for the 1996 hurricane season and compared to the older version of the model. Model biases of the two versions are compared.
Aberson, S.D. The prediction of the performance of a nested barotropic hurricane track forecast model. Weather and Forecasting, 12(1):24-30 (1997).
Linear multiple regression and discriminant analyses provide estimates of the errors of track forecasts from a nested barotropic hurricane track forecast model (VICBAR), which was run in the North Atlantic Basin during the 1989-94 hurricane seasons. Predictors are determined from the synoptic situation, the magnitude of atmospheric changes in the environment of the tropical cyclone, the consistency between current and past predictions, and the past performance of the model for each particular storm. This technique distinguishes cases in which VICBAR performs well from those for which it performs poorly and can provide skillful operational predictions of model performance to forecasts.
Acero-Schertzer, C.E., D.V. Hansen, and M.S. Swenson. Evaluation and diagnosis of surface currents in the NCEP ocean analyses. Journal of Geophysical Research, 102(C9):21,037- 21,048 (1997).
Ensemble average currents from the 15 m depth level of the NCEP analyses of the tropical Pacific Ocean are evaluated against surface mixed layer current observations obtained from an extensive set of satellite-tracked drifting buoys. These averages display many climatological characteristics of the region, but are not intended to serve as a climatology because the data from the analyses are trimmed to match the time-space distribution of the observations. Substantial discrepancies between the analyses and the observations are revealed. First, the near-equatorial meridional currents and divergence have approximately twice the magnitude in the analyses as in the observations. This discrepancy is largely independent of whether temperature profile data are assimilated or not, and is attributed to the parameterization of vertical viscosity. Second, the zonal flow in both the NECC and the SEC is much stronger in the analyses than in the observations, especially in the western Pacific. This discrepancy is associated with assimilation of temperature profile data. It arises because salinity is an active variable in the underlying analysis model, but is not controlled by boundary fluxes or other observations. Under the uncontrolled influence of advection and strong horizontal diffusion, the salinity distribution becomes nearly homogeneous. Consequently, the analyses do not account for observed temperature-salinity correlations when density is computed following assimilation of temperature profile data. This leads to erroneous pressure gradients that drive excessively strong geostrophic currents and force large accelerations near the western boundary. Our results indicate that it is important to consider the consequences on the density structure of neglecting salinity during the assimilation of temperature data. We recommend that surface salinity observations from drifting buoys and volunteer observing ships be initiated to improve the ocean analyses.
Baringer, M.O., and J.F. Price. Mixing and spreading of the Mediterranean Outflow. Journal of Physical Oceanography, 27(8):1654-1677 (1997).
Hydrographic and expendable current profiler (XCP) data taken during the Gulf of Cadiz Expedition on September 21-27, 1988 were analyzed to diagnose the mixing, spreading, and descent of the Mediterranean Outflow. The theta/S properties and the thickness and width of the outflow were very similar to that seen in earlier surveys (for example, by Heezen and Johnson, 1969). The transport of pure Mediterranean water (S=38.4) was estimated to be about half a Sv, which is considerably lower than historical estimates, most of which were indirect, but comparable to other recent estimates made from direct velocity observations. The total outflow transport was about 0.7 Sv at the west end of the Strait of Gibraltar, and increased to about 1.9 Sv within the western Gulf of Cadiz. This increase in transport occurred by entrainment of fresher North Atlantic Central Water (NACW), and the salinity anomaly of the outflow was rapidly eroded. The velocity-weighted salinity decreased to 36.7 within 60 km of the Strait, during the initial descent of the continental slope, and decreased by about another 0.1 before the deeper portion of the outflow began to float off of the bottom near Cape St. Vincent. Entrainment appears to have been correlated with the occurrence of bulk Froude numbers slightly greater than 1. In the western Gulf of Cadiz, where entrainment was much weaker, Froude numbers were well below 1. The outflow began in the eastern Strait of Gibraltar as a narrow (10 km wide) current having a very narrow range of theta/S properties (theta varies by < 0.5°C). The outflow broadened as it descended the continental slope of the northern Gulf of Cadiz, and reached a maximum width of 90 km in the western Gulf of Cadiz. The descent of the outflow was very asymmetric: the offshore and downslope edge of the flow descends rapidly, while the onshore and shallower edge of the outflow descends slowly. The northern, nearshore side remained considerably higher in the water column and thus entrained relatively warm and salty NACW. This caused the outflow to develop horizontal theta/S variability and, by about 100 km downstream, the across-stream variation in temperature on an isopycnal was more than 2°C. Much of the volume transport in the western Gulf of Cadiz was contained in two preferred modes, often called cores, apparently because of topographic steering effects. The deeper, offshore core had a central sigmatheta = 27.8, and the shallower nearshore core, which was still in contact with the bottom in the Gulf of Cadiz, had a central sigmatheta = 27.5.
Baringer, M.O., and J.F. Price. Momentum and energy balance of the Mediterranean Outflow. Journal of Physical Oceanography, 27(8):1678-1692 (1997).
Hydrographic and expendable current profiler (XCP) data taken during the Gulf of Cadiz Expedition in September 1988 were analyzed to describe some aspects of the dynamics of the Mediterranean Outflow. During the initial descent of the continental slope, the outflow current executes a 90 degrees right turn that appears to be approximately inertial. The estimated geostrophic velocity greatly underestimated the actual current, and the estimated curvature Rossby number is about 0.5. A form of the Bernoulli function was evaluated to infer the total stress (entrainment stress and bottom drag) acting on the outflow. Total stress was as large as 5 Pa where the outflow begins to descend the continental slope and where currents were in excess of 1 m/s. The entrainment stress, estimated independently from property fluxes, reached a maximum of only about 1 Pa, which was less than the inferred bottom stress. By about 100 km downstream, the current was aligned approximately along the topography. The current amplitude and the estimated stress were much less, about 0.3 m/s and less than 0.5 Pa. The entrainment stress was very small in the region well downstream of the Strait. Bottom stress thus appears to be the crucial element in the dynamics of the Mediterranean Outflow, allowing or causing the outflow to descend some 1000 m into the North Atlantic. In the regions of strongest bottom stress the inferred drag coefficient was about 3 × 10- 3. Entrainment stress was much smaller by comparison, but the entrainment effect upon the density anomaly was crucial in eroding the density anomaly of the outflow.
Black, M.L., and J.R. Parrish. The structure of the hurricane eyewall at altitudes reached by the NOAA Gulfstream-IV aircraft. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-16 (1997).
Starting with the 1997 Atlantic hurricane season, the recently acquired and specially instrumented NOAA Gulfstream-IV (G-IV) jet aircraft will conduct synoptic reconnaissance missions in the periphery of tropical cyclones. The missions are designed to sample, via dropsondes, vertical profiles of the environmental air from flight altitudes of 40,000-45,000 ft. The flights are intended to avoid the convectively active eyewall and rainband regions of the storms. In future seasons, however, research and reconnaissance needs may warrant high altitude penetrations of the hurricane core. Before conducting flights directly into tropical cyclones, the structure of the deep convection, especially in the eyewall, needs to be assessed to determine the types of flight conditions the G-IV might experience. The purpose of this report is to use the remote-sensing capabilities of the NOAA WP-3D aircraft to document and describe the structure of the hurricane eyewall at high altitudes. Vertcally-pointing Doppler radials from the tail radars on the NOAA P-3 aircraft yield estimates of the two-dimensional (radius-height plane) reflectivity and vertical velocity structure. Observations from more than 200 radial legs through the eyewalls of tropical cyclones have shown that vertical velocity extrema with magnitudes >10 m/s can occur at heights up to 15 km, well above the maximum attainable altitude of the G-IV. These extrema occur infrequently (<10% chance) but can contain steep vertical velocity gradients that may produce moderate to severe turbulence, similar to that experienced by the P-3 aircraft at lower altitudes. Examples of the various types of vertical velocity structures that the G-IV may encounter in eyewall penetrations will be presented.
Black, M.L., R.W. Burpee, and F.D. Marks. The asymmetric distribution of vertical motions and precipitation in the hurricane eyewall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 100-101 (1997).
No abstract.
Black, M.L., J.F. Gamache, H.E. Willoughby, C.E. Samsury, F.D. Marks, and R.W. Burpee. Airborne radar observations of shear-induced asymmetries in the convective structure of Hurricane Olivia (1994). Proceedings, 28th Conference on Radar Meteorology, September 9-12, 1997, Austin, TX. American Meteorological Society, Boston, 577-578 (1997).
The Hurricane Research Division of NOAA conducted dual aircraft experiments on successive days in eastern Pacific Hurricane Olivia. The flights occurred on 24 September 1994 while Olivia was intensifying and 25 September when the hurricane was initially at maximum intensity followed by a period of rapid filling. The data collected from the flights into Hurricane Olivia provide a unique opportunity to investigate and describe the interplay between environmental wind shear, eye-wall convection, and intensity changes. Radar systems on the WP-3D research aircraft recorded radar reflectivity from the horizontally-scanning, lower-fuselage (LF) radar (5-cm), and reflectivity and Doppler radials from the tail radar (3-cm) which scans in a plane perpendicular to the aircraft track. On September 24th, the hurricane was embedded in weak easterly shear and observations from the LF radar showed that the convection in Olivia's eyewall was highly asymmetric. The deepest convection and highest reflectivities were concentrated in the south and southeast portions of the eyewall, while the northern portions contained a stratiform-like precipitation structure. Vertical profiles of reflectivity and vertical velocity derived from vertically-pointing radials from the tail Doppler radar further describe the nature of these asymmetries. Large and strong updrafts were located just upwind of the heaviest precipitation while downward motion dominated in the eyewall region slightly downwind of the precipitation maximum. Much weaker and smaller up- and downdrafts existed in the low-reflectivity region of the northern eyewall. Olivia intensified during the 24-hour period between flights while the environmental shear was weak, ahead of a mid-tropospheric trough. On the 25th, when the aircraft first arrived near the center, Olivia's eyewall appeared on LF radar images as a highly symmetric, nearly continuous ring of high reflectivities (>40 dBZ). Doppler radar observations of the vertical velocity structure, however, still showed an asymmetric structure, albeit not as pronounced as the previous day. During the flight, westerly shear increased dramatically, Olivia's central pressure rose, and large asymmetries in the eyewall reflectivity field developed in an apparent response to the changing vertical wind shear. Olivia's weakening may also have been partially due to the storm moving over a region of cooler sea-surface temperatures. Convective cells with strong updrafts formed in the eastern eyewall (downshear), and advected around to the high-reflectivity region of the northern eyewall. Strong downdrafts appeared to form at high altitudes, adjacent to and slightly downwind of the large and strong updrafts, and rotated around the eyewall to the weak-reflectivity region of the western eyewall (upshear). Near the end of the flight, the magnitude of the updrafts decreased and the convective tops were lower in altitude, conditions that are consistent with a weakening hurricane.
Black, R.A. Giant raindrops observed from large aircraft. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 494-495 (1997).
No abstract.
Boebel, O., C. Schmid, and W. Zenk. Flow and recirculation of Antarctic Intermediate Water across the Rio Grande Rise. Journal of Geophysical Research, 102(C9):20,967-20,986 (1997).
The flow of the low-salinity Antarctic Intermediate Water (AAIW) at 700-1150 m depth across the Rio Grande Rise and the lower Santos Plateau is studied under the auspices of the World Ocean Circulation Experiment (WOCE) in the context of the Deep Basin Experiment. Our data set consists of several hydrographic sections, a collection of 15 RAFOS float trajectories, and records from 14 moored current meters. The data were gathered during different intervals between 1990 and 1994. The inferred flow field strongly supports a basinwide anticyclonic recirculation cell in the subtropical South Atlantic underneath the wind-driven gyre. Its center, which appears to be southeast of the Rio Grande Rise, separates the eastward advection of AAIW below the South Atlantic Current from the westward flowing, recirculating AAIW. The two near-shelf limbs closing the circumference of AAIW flow are formed in the east by the deep Benguela Current, potentially modulated by salty inflow of Indian Ocean Intermediate Water, and in the west by the Brazil Current system. Further important circulation elements are the Brazil-Falkland (Malvinas) Confluence Zone at 40°S and an unnamed divergence at 28°S close to the 1000 m isobath. The resulting broad southward flow of AAIW augments the share of modified, i.e., saltier, intermediate water in the source region of the South Atlantic Current, while the smaller northward flow marks the source of a narrow equatorward Western Intermediate Boundary Current, ultimately leaving the South Atlantic. This shelf-trapped jet is clearly documented in hydrographic data from 19°S and in nearby current meter records. The jet contrasts a sluggish flow across this latitude east of 35°W. A continuous flow of AAIW from its subpolar region in the southwestern Argentine Basin all along the western slope toward the equator appears unlikely between 35°S and 25°S.
Bringi, V.N., K.Knupp, A. Detwiler, L. Liu, I.J. Caylor, and R.A. Black. Evolution of a Florida thunderstorm during the Convection and Precipitation Experiment: The case of August 9, 1991. Monthly Weather Review, 125(9):2131-2160 (1997).
The relationships among kinematic, microphysical, and electric field properties within a multicell Florida thunderstorm are investigated using observations from three Doppler radar (one with multiple wavelength and polarization diversity capabilities), four instrumented penetrating aircraft, a surface-based electric field mill network, and other observation facilities. The storm was convectively active for about 1 h and at least five primary cells developed within the storm during this time, one of which went through three consecutive development cycles. The updrafts in this storm were 2-4 km wide, exhibited bubble-like evolution, and had lifetimes of 10-20 min. The maximum updraft determined by the multiple Doppler analysis was about
20 m s-1. A differential reflectivity (ZDR) "column," indicating regions containing millimeter-size raindrops, extending above the freezing level, was associated with each cell during its developing stages. This column reached altitudes exceeding 6 km (-8°C) in the stronger updrafts. As the ZDR columns reached maximum altitude, a "cap" of enhanced linear depolarization ratio (LDR) and enhanced 3-cm wavelength attenuation (A3) formed, overlapping the upper regions of the ZDR column. These parameters indicate rapid development of mixed-phase conditions initiated by freezing of supercooled raindrops. Lightning was observed only in the central and strongest convective cell. Electric fields exceeding 10 k V m-1 were noted during aircraft penetrations in this as well as several other cells that did not produce lightning. Fields exceeding 1 k V m-1 were noted by the instrumented aircraft at midcloud levels within a few minutes of development of mixed-phase conditions at these levels or aloft. The first intracloud lightning was detected by the surface field mill network within 5 min of development of mixed-phase conditions aloft in the first cycle of development in the central cell, and the first cloud-to-ground event was noted within 9 min of this development. Lightning continued through two additional cycles of updraft growth in this central region and diminished as the convection subsided after about 30 min. Aircraft-measured electric fields and lightning retrievals from the surface field meter network are consistent with a tendency for negative charge to accumulate above the 6.5 km (-12°C) level within regions of radar reflectivity maxima and for positive charge to accumulate in the anvil region well above 9 km (-30°C).
Butler, J.H., and S.A. Yvon-Lewis. Estimating lifetimes of atmospheric trace gases with respect to oceanic loss: Two approaches. AGU 1997 Spring Meeting, Baltimore, MD, May 27-30, 1997. Supplement to EOS,Transactions, American Geophysical Union, 78(17):S90, A42E-12 (1997).
The flux of a gas across the air-sea interface typically is estimated as the product of the air-sea, gas-transfer coefficient and the difference in the partial pressure of the gas between the water and the air. Although there is some uncertainty in the value and mechanism selected for the transfer coefficient, this approach is generally considered a reasonable way to evaluate the rate at which a gas passes between the ocean and the atmosphere. Problems can arise, however, when one tries to compute the partial lifetime of this gas in the atmosphere with respect to its loss in the ocean. So long as the gas is not produced in the ocean, this calculated flux can be used to derive a partial lifetime. However, if the gas is simultaneously produced and consumed in the ocean, the lifetime estimate calculated in this way will be too long. This can be accounted for if one considers that the calculated flux from the atmosphere to the ocean is a net flux and that it will change in opposition to changes in the atmospheric burden of the gas. In this sense, the ocean acts as a "buffer" for the gas in the atmosphere, yet the effect is calculable. An alternative approach, involving the separation of inward and outward fluxes, gets past the lifetime and emission problem and allows for an accurate calculation of the partial atmospheric lifetime. This approach also provides for the computation of emissions from undersaturated waters or uptake by supersaturated waters. Each approach is internally consistent and both can be used, along with information on other non-oceanic fluxes, to describe the budgets of atmospheric trace gases. However, each carries with it certain caveats and limitations that must be considered in constructing these budgets. This talk will address these issues, with specific emphasis on methyl bromide and other trace gases of interest in ozone depletion and global warming.
Carsey, T.P., D.D. Churchill, M.L. Farmer, C.J. Fischer, A.A. Pszenny, V.B. Ross, E.S. Saltzman, M. Springer-Young, and B. Bonsang. Nitrogen oxides and ozone production in the North Atlantic marine boundary layer. Journal of Geophysical Research, 102(D9):10,653-10,665 (1997).
Measurements of reactive nitrogen gases (NO, NO2, NOy), as well as related chemical (O3, CO, aerosol black carbon, radon, selected nonmethane hydrocarbons) and meteorological parameters, were made on board the R/V Malcolm Baldrige prior to and subsequent to the 1992 ASTEX (Atlantic Stratocumulus Transition Experiment) in the North Atlantic Ocean during June and July 1992. Results showed indications of well-defined plumes from North America and Europe from both chemistry and back trajectory data. Elevated ozone concentrations were also observed in air masses from uninhabited continental regions. Chemical and meteorological data were incorporated into a simple photochemical model in which ozone destruction predominated over generation. The principal reaction leading to ozone destruction was O(1D) + H2O - 2OH.
Checkley, D.M., P.B. Ortner, L.R. Settle, and S.R. Cummings. A continuous, underway fish egg sampler (CUFES). Fisheries Oceanography, 6(2):58-73 (1997).
We describe a method to sample the highly contagious distribution of pelagic fish eggs. CUFES, the continuous, underway fish egg sampler, consists of a submersible pump, concentrator, electronics, and sample collector. This system operates continuously and under nearly all sea conditions, providing a real-time estimate of the volumetric abundance of pelagic fish eggs at pump depth, usually 3 m. CUFES-derived estimates of volumetric abundance agree well with those from nets towed at pump depth and with a real abundance estimated from vertically-integrated plankton tows. CUFES has been used successfully to sample the eggs of menhaden, pinfish, sardine, and anchovy off the coasts of the eastern and western United States and South Africa. Two large patches of eggs of the Atlantic menhaden were sampled off North Carolina in winter 1993-1994, had a linear scale of 5-10 km, and were found in waters between the Gulf Stream and mid-shelf front. Spawning location may be related to bathymetry. CUFES is now being used to estimate spawner biomass by the Daily Egg Production Method. An optical plankton counter provided accurate estimates of the number of Atlantic menhaden eggs sampled by CUFES. Automation of egg counting in CUFES is under development.
Chelton, D.B., and A.M. Mestas-Nunez. The large-scale, wind-driven response of the North Pacific. International WOCE Newsletter, 25:3-6 (1997).
In this note, we present the results of an investigation of the validity of the time-varying Sverdrup balance in the North Pacific based on analysis of three years of: (1) a simple flat bottom Sverdrup model; (2) the primitive equation global ocean circulation model developed by the Parallel Ocean Program (POP) at the Los Alamos National Laboratory; and (3) observations of sea surface height (SSH) by the TOPEX/POSEIDON (T/P) altimeter. The three-year period considered here is October 1992 through November 1995. We conclude that much of the large-scale, low-frequency variability in the North Pacific can be accounted for by simple Sverdrup dynamics.
Chen, G., B. Chapron, J. Tournadre, K.B. Katsaros, and D. Vandemark. Global oceanic precipitation: A joint view by TOPEX and the TOPEX microwave radiometer. Journal of Geophysical Research, 102(C5):10,457-10,471 (1997).
The TOPEX/POSEIDEN mission offers the first opportunity to observe rain cells over the ocean by a dual-frequency radar altimeter (TOPEX) and simultaneously observe their natural radiative properties by a three-frequency radiometer (TOPEX microwave radiometer (TMR)). This work is a feasibility study aimed at understanding the capability and potential of the active/passive TOPEX/TMR system for oceanic rainfall detection. On the basis of past experiences in rain flagging, a joint TOPEX/TMR rain probability index is proposed. This index integrates several advantages of the two sensors and provides a more reliable rain estimate than the radiometer alone. One year's TOPEX/TMR data are used to test the performance of the index. The resulting rain frequency statistics show quantitative agreement with those obtained from the Comprehensive Ocean-Atmosphere Data Set (COADS) in the Intertropical Convergence Zone (ITCZ), while qualitative agreement is found for other regions of the world ocean. A recent finding that the latitudinal frequency of precipitation over the Southern Ocean increases steadily towards the Antarctic continent is confirmed by our result. Annual and seasonal precipitation maps are derived from the index. Notable features revealed include an overall similarity in rainfall pattern from the Pacific, the Atlantic, and the Indian Oceans and a general phase reversal between the two hemispheres, as well as a number of regional anomalies in terms of rain intensity. Comparisons with simultaneous Global Precipitation Climatology Project (GPCP) multisatellite precipitation rates and COADS rain climatology suggest that systematic differences also exist. One example is that the maximum rainfall in the ITCZ of the Indian Ocean appears to be more intensive and concentrated in our result compared to that of the GPCP. Another example is that the annual precipitation produced by TOPEX/TMR is constantly higher than those from GPCP and COADS in the extratropical regions of the northern hemisphere, especially in the northwest Pacific Ocean. Analyses of the seasonal variations of prominent rainy and dry zones in the tropics and subtropics show various behaviors such as systematic migration, expansion, and contraction, merging and breakup, and pure intensity variations. The seasonality of regional features is largely influenced by local atmospheric events such as monsoon, storm, or snow activities. The results of this study suggest that TOPEX and its follow-on may serve as a complementary sensor to the special sensor microwave/imager in observing global oceanic precipitation.
Chereskin, T.K., W.D. Wilson, H.L. Bryden, A. Ffield, and J. Morrison. Observations of the Ekman balance at 8°30'N in the Arabian Sea during the 1995 southwest monsoon. Geophysical Research Letters, 24(21):2541-2544 (1997).
The Ekman transport is estimated from two sets of hydrographic and shipboard acoustic Doppler current profiler (ADCP) velocity observations made during June and September 1995, during the southwest monsoon in the Arabian Sea. Both sets of measurements were made along latitude 8°30'N, designated as World Ocean Circulation Experiment (WOCE) line I1W, from Somalia to Sri Lanka. The Ekman transport estimates calculated from ageostrophic velocity were southward: 17.6 ± 2.4 106 m3 s-1 in June and 7.9 ± 2.7 106 m3 s-1 in September. These direct estimates were in good agreement with those predicted by the Ekman balance using both shipboard and climatological winds. The vertical structure of the ageostrophic velocity and the stratification were quite different between the two occupations of the transect. The wind-driven momentum was confined to a very shallow layer in June (about 50 m) and the surface layer was strongly stratified, with a maximum salinity layer at depths between 50 and 70 m. The ageostrophic velocity penetrated much deeper in September (to about 160 m) and the pycnocline was correspondingly deeper. In both cases, the Ekman transport penetrated beneath the mixed layer, to the top of the pycnocline.
Cione, J.J., and S. Raman. The impact of SST gradients on propagating low-level mesovortices near the Gulf Stream. Preprints, Conference on Coastal Oceanic and Atmospheric Prediction, Atlanta, GA, January 28- February 2, 1996. American Meteorological Society, Boston, 204-211 (1997).
No abstract.
DeMaria, M., and J. Kaplan. An operational evaluation of a statistical intensity prediction scheme (SHIPS). Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 280-281 (1997).
No abstract.
Dietrich, D.E., C.A. Lin, A.M. Mestas-Nunez, and D.-S. Ko. A high resolution numerical study of Gulf of Mexico fronts and eddies. Meteorology and Atmospheric Physics, 64:187-201 (1997).
The Gulf of Mexico (GOM) circulation is simulated using the DieCAST ocean model, with a horizontal resolution of 1/12 degree and 20 vertical layers. The results compare well with observations of both large and small scale features, including Loop Current frontal occlusions associated with frontal eddies. The simulation is carried out without any data assimilation. The frontal eddies tend to be spaced at about 90 degree intervals around the Loop Current, leading to a Loop Current head shaped like a square with rounded corners. The pattern rotates as eddies circle the Loop, and frontal eddies elongate as they squeeze through the Florida Strait. Major warm core eddies separate regularly from the Loop Current and propagate to the western GOM. Old warm core eddies in the western Gulf dissipate through bottom drag effects, which also generate cyclonic parasitic eddies. Newly arrived warm core eddies merge with old ones in the western GOM. Recently separated elongated Loop Current eddies can rotate and reattach temporarily to the Loop Current. The barotropic flow component develops eddies between the main separated warm core eddy and the Loop Current due to eastward dispersion, as the main eddy itself propagates westward into the Gulf.
Dodge, P.P., S.H. Houston, and J.F. Gamache. Three-dimensional windfields in Hurricane Fran (1996) at landfall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 115-116 (1997).
No abstract.
Dodge, P.P., S.H. Houston, and J.F. Gamache. Windfields in Hurricane Fran (1996) at landfall from combined WSR-88D and airborne Doppler radar data. Proceedings, 28th Conference on Radar Meteorology, Austin, TX, September 9-12, 1997. American Meteorological Society, Boston, 575-576 (1997).
The Hurricane Research Division's (HRD) Tropical Cyclone Windfields at Landfall Experiment collects data in landfalling tropical cyclones from NOAA aircraft to improve real-time and post- storm surface wind analyses that are prepared by HRD. The real-time analyses are provided to forecasters at the Tropical Prediction Center. Airborne Doppler radar data are combined with National Weather Service WSR-88D radar data in three-dimensional analyses to document the evolution of tropical cyclones at landfall, and to provide corroborating data for testing WSR-88D tropical cyclone algorithms. From 2056 UTC, 5 September 1996, to 0348, 6 September 1996, the NOAA research aircraft RF42 flew in Hurricane Fran as it moved ashore in North Carolina. A "figure 4" pattern at 5,000 ft, overflights of marine and coastal surface platforms, and several passes along radials from the Wilmington and Morehead City WSR-88D radars in North Carolina provided flight-level wind data that were included in HRD's surface wind analyses. The research flight concluded with an overland "figure 4" pattern at 14,000 ft that passed near the Raleigh WSR-88D, and then through Fran's center when it was 70 km north-northwest of the Wilmington WSR-88D. The portable Doppler radar on wheels from the University of Oklahoma also recorded data at the Wilmington airport during the landfall, so there is a rich data set to describe convective and mesoscale features in Hurricane Fran. At the conference, we will present windfields synthesized from the airborne and WSR-88D radars that describe the kinematic structure as Fran moved over the coast. The comparison of vertical structure of the wind fields near the coast and 200 km inland should be particularly interesting. We will also discuss the problems of combining airborne and ground-based Doppler radar data.
Donelan, M.A., W.M. Drennan, and K.B. Katsaros. The air-sea momentum flux conditions of wind sea and swell. Journal of Physical Oceanography, 27(10):2087-2099 (1997).
During the Surface Wave Dynamics Experiment, direct measurements of momentum, heat, and water vapor fluxes were obtained from a mast on the foredeck of a SWATH (small water-plane area, twin hull) ship in deep water off the state of Virginia. Directional wave spectra were obtained simultaneously from a six or three-wire wave-staff array mounted at the bow of the ship. One hundred and twenty-six 17-minute runs of flux and wave data obtained with the ship steaming slowly into the wind are examined for the effects of the relative direction of the wind sea and background swell on the momentum transfer. The adequacy of the inertial dissipation method, which depends on the high-frequency turbulent fluctuations for evaluating the wind stress, is also examined for any effects of swell. The results show that the presence of counter- and cross-swells can result in drag coefficients that are much larger than the value for a pure wind sea. The eddy correlation and inertial dissipation methods for measuring wind stress are found to diverge during the complex sea conditions. The authors interpret the latter observations as an indication that the traditional inertial dissipation method, in which the pressure and transport terms in the kinetic energy balance equation are assumed to be in balance, may be unsuitable for use in a marine boundary layer disturbed by swell.
Drennan, W.M., M.A. Donelan, E.A. Terray, and K.B. Katsaros. On waves, oceanic turbulence, and their interaction. Geophysica, 33:17-28 (1997).
No abstract.
Dupuis, H., P.K. Taylor, A. Weill, and K.B. Katsaros. Inertial dissipation method applied to derive turbulent fluxes over the ocean during the Surface of the Fluxes and Interactions with the Atmosphere/Atlantic Stratocumulus Transition Experiment (SOFIA/ASTEX) and Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiments with low to moderate wind speeds. Journal of Geophysical Research, 102(C9):21,115-21,129 (1997).
The transfer coefficients for momentum and heat have been determined for 10 m neutral wind speeds (U10n) between 0 and 12 m/s using data from the Surface of the Ocean, Fluxes and Interactions with the Atmosphere (SOFIA) and Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiments. The inertial dissipation method was applied to wind and pseudo virtual temperature spectra from a sonic anemometer, mounted on a platform (ship) which was moving through the turbulence field. Under unstable conditions the assumptions concerning the turbulent kinetic energy (TKE) budget appeared incorrect. Using a bulk estimate for the stability parameter, Z/L (where Z is the height and L is the Obukhov length), this resulted in anomalously low drag coefficients compared to neutral conditions. Determining Z/L iteratively, a low rate of convergence was achieved. It was concluded that the divergence of the turbulent transport of TKE was not negligible under unstable conditions. By minimizing the dependence of the calculated neutral drag coefficient on stability, this term was estimated at about -0.65 Z/L. The resulting turbulent fluxes were then in close agreement with other studies at moderate wind speed. The drag and exchange coefficients for low wind speeds were found to be Cen × 103 = 2.79 U10n-1 + 0.66 (U10n < 5.2 m/s), Cen × 103 = Chn × 103 = 1.2 (U10n > 5.2 m/s), and Cdn × 103 = 11.7 U10n-2 + 0.668 (U10n < 5.5 m/s), which imply a rapid increase of the coefficient values as the wind decreased within the smooth flow regime. The frozen turbulence hypothesis and the assumptions of isotropy and an inertial subrange were found to remain valid at these low wind speeds for these shipboard measurements. Incorporation of a free convection parameterization had little effect.
Elfouhaily, T., B. Chapron, K.B. Katsaros, and D. Vandemark. A unified directional spectrum for long and short wind-driven waves. Journal of Geophysical Research, 102(C7):15,781-15,796 (1997).
Review of several recent ocean surface wave models finds that while comprehensive in many regards, these spectral models do not satisfy certain additional, but fundamental, criteria. We propose that these criteria include the ability to properly describe diverse fetch conditions and to provide agreement with in-situ observations of Cox and Munk (1954), Jahne and Riemer (1990), and Hara et al. (1994) data in the high-wavenumber regime. Moreover, we find numerous analytically undesirable aspects such as discontinuities across wavenumber limits, nonphysical tuning or adjustment parameters, and noncentrosymmetric directional spreading functions. This paper describes a two-dimensional wavenumber spectrum valid over all wavenumbers and analytically amenable to usage in electromagnetic models. The two regime model is formulated based on the Joint North Sea Wave Project (JONSWAP) in the long-wave regime and on the work of Phillips (1985) and Kitaigorodskii (1973) at the high wavenumbers. The omnidirectional and wind-dependent spectrum is constructed to agree with past and recent observations including the criteria mentioned above. The key feature of this model is the similarity of description for the high- and low-wavenumber regimes; both forms are posed to stress that the air-sea interaction process of friction between wind and waves (i.e., generalized wave age, u/c) is occurring at all wavelengths simultaneously. This wave age parameterization is the unifying feature of the spectrum. The spectrum's directional spreading function is symmetric about the wind direction and has both wavenumber and wind speed dependence. A ratio method is described that enables comparison of this spreading function with previous noncentrosymmetric forms. Radar data are purposefully excluded from this spectral development. Finally, a test of the spectrum is made by deriving roughness length using the boundary layer model of Kitaigorodskii. Our inference of drag coefficient versus wind speed and wave age shows encouraging agreement with Humidity Exchange Over the Sea (HEXOS) campaign results.
Enfield, D.B., and D.A. Mayer. Tropical Atlantic sea surface temperature variability and its relation to El Niño-Southern Oscillation. Journal of Geophysical Research, 102(C1):929-945 (1997).
Past analyses of tropical Atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics, across the Intertropical Convergence Zone (ITCZ). By analyzing an improved 43-year (1950-1992) record of SST (Smith et al., 1996) and other data derived from the Comprehensive Ocean-Atmosphere Data Set (COADS), it is shown that the regions north and south of the ITCZ are statistically independent of each other at the seasonal to interannual time scales dominating the data, confirming the conclusions of Houghton and Tourre (1992). Some dipole behavior does develop weakly during the boreal spring season, when there is a tendency for SST anomaly west of Angola to be opposite of that in the tropical North Atlantic. It is further shown that tropical Atlantic SST variability is correlated with Pacific El Niño-Southern Oscillation (ENSO) variability in several regions. The major region affected is the North Atlantic area of northeast trades west of 40°W along 10°N-20°N and extending into the Caribbean. There, about 50-80% of the anomalous SST variability is associated with the Pacific ENSO, with Atlantic warmings occurring 4-5 months after the mature phases of Pacific warm events. An analysis of local surface flux fields derived from COADS data show that the ENSO-related Atlantic warmings occur as a result of reductions in the surface northeast trade wind speeds, which in turn reduce latent and sensible heat losses over the region in question, as well as cooling due to entrainment. This ENSO connection is best developed during the boreal spring following the most frequent season of maximum ENSO anomalies in the Pacific. A region of secondary covariability with ENSO occurs along the northern edge of the mean ITCZ position and appears to be associated with northward migrations of the ITCZ when the North Atlantic warmings occur. Although easterly winds are intensified in the western equatorial Atlantic in response to Pacific warm events, they do not produce strong local changes in SST. Contrary to expectations from studies based on equatorial dynamics, these teleconnected wind anomalies do not give rise to significant correlations of SST in the Gulf of Guinea with the Pacific ENSO. As the teleconnection sequence matures, strong southeast trades at low southern latitudes follow the development of the North Atlantic SST anomaly and precede by several months the appearance of weak negative SST anomalies off Angola and stronger positive anomalies extending eastward from southern Brazil along 15°-30°S.
Enfield, D.B., and A.M. Mestas-Nunez. Global modes of ENSO and non-ENSO sea surface temperature variability. AGU 1997 Fall Meeting, San Francisco, CA, December 8-12, 1997. Supplement to EOS, Transactions, American Geophysical Union, 78(46):F349, OS21D-05 (1997).
El Niño-Southern Oscillation (ENSO) is a global phenomenon with significant phase propagation within and between basins, which we capture and describe in the first mode of a complex empirical orthogonal function (CEOF) analysis of sea surface temperature anomaly (SSTA) from the mid-19th century through 1992. We subsequently remove the global ENSO from the SSTA data, plus a linear trend everywhere, in order to consider other global modes of variability uncontaminated by the intra- and inter-basin effects of ENSO. An ordinary EOF analysis of the SSTA residuals reveals three non-ENSO modes of low-frequency variability that are related to slow oceanic and climate signals described in the literature. The first two modes both have an interdecadal time scale with high loadings in the Pacific; they bear some spatial similarities to the ENSO pattern but are broader and differ in the time domain. A CEOF analysis confirms that they are not merely the phase-related components of a single mode and that all three modes are without significant phase propagation. The third mode is a multidecadal signal with maximal realization in the extratropical North Atlantic southeast of Greenland. It also has high loadings in the tropical Atlantic, anticorrelated across the intertropical convergence zone (ITCZ), and strong variability of opposite sign in the eastern tropical Pacific. All three modes have significant loadings over the central and/or eastern equatorial Pacific. Temporal extrema in the first and third modes during 1982-1983 explain the large magnitude of that ENSO event, which in the global ENSO mode is large but equalled or exceeded by four other events.
Faber, T., L.K. Shay, S.D. Jacob, S.H. Houston, and P.G. Black. Observed air-sea interactions during Hurricane Emily. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 433-434 (1997).
No abstract.
Feely, R.A., R.H. Wanninkhof, C. Goyet, D.E. Archer, and T. Takahashi. Variability of CO2 distributions and sea- air fluxes in the central and eastern equatorial Pacific during the 1991-1994 El Niño. Deep-Sea Research II, 44(9-10):1851-1867 (1997).
As part of the U.S. JGOFS Program and the NOAA Ocean-Atmosphere Carbon Exchange Study (OACES), measurements of CO2 partial pressure were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992, the spring of 1993, and the spring and autumn of 1994. Surface-water pCO2 data indicate significant diurnal, seasonal, and interannual variations. The largest variations were associated with the 1991-1994 ENSO event, which reached maximum intensity in the spring of 1992. The lower values of surface-water DELTApCO2 observed during the 1991-1994 ENSO period were the result of the combined effects of both remotely and locally forced physical processes. The warm pool, which reached a maximum eastward extent in January-February of 1992, began in September of 1991 as a series of westerly wind events lasting about 30 days. Each wind event initiated an eastward-propagating Kelvin wave which caused a deepening of the thermocline. By the end of January 1992 the thermocline was at its maximum depth, so that the upwelled water was warm and CO2-depleted. In April of the same year, the local winds were weaker than normal, and the upwelling was from shallow depths. These changes resulted in a lower-than-normal CO2 flux to the atmosphere. The results show that for the one-year period from the fall of 1991 until the fall of 1992, approximately 0.3 GtC were released to the atmosphere; 0.6 GtC were released in 1993, and 0.7 GtC in 1994, in good agreement with the model results of Ciais et al. (Science, 269, 1098-1102; J. Geophys. Res., 100, 5051-5070). The net reduction of the ocean-atmosphere CO2 flux during the 1991-1994 El Niño was on the order of 0.8-1.2 GtC. Thus, the total amount of CO2 sequestered in the equatorial oceans during the prolonged 1991-1994 El Niño period was about 25% higher than the severe El Niño of 1982-1983.
Festa, J.F., and R.L. Molinari. Comparison of thermal statistics derived from observational data sets in the tropical Atlantic and Pacific Oceans. NOAA Technical Memorandum, ERL AOML-91 (PB97-208177), 78 pp. (1997).
Statistical analysis of surface and subsurface temperature data in the tropical Atlantic and Pacific Oceans is presented. The statistics were estimated from the Comprehensive Ocean-Atmospheric Data Set (COADS) and the historical expendable bathythermograph (XBT) observations. Spatial structure functions (semivariograms) for the anomaly fields of sea surface temperature and the temperature at 200 m and 400 m were estimated for a 2 degree by 2 degree grid in the tropical oceans. Dominant scales of spatial variability are identified and compared with other investigations.
Ffield, A., J. Toole, and W.D. Wilson. Seasonal circulation in the South Indian Ocean. Geophysical Research Letters, 24(22):2773-2776 (1997).
Two World Ocean Circulation Experiment hydrographic cruises in March and June 1995, along with Topex-Poseidon altimeter data and National Meteorological Center wind data, are used to estimate seasonal changes in the South Indian Ocean subtropical gyre. Mean annual curves derived from the altimeter and wind data reveal strengthening of the anticyclonic gyre in March and September, and weakening in June and December. The seasonal changes correspond to variations in the wind field south of 30 S at the equinoxes and solstices. In addition, the wind-driven gyre is further north in July, and further south in March. These variations in strength and location of the South Indian Ocean gyre may influence inter-ocean transports south of Africa. Despite the inferred mean annual seasonal variations in the South Indian Ocean gyre, volume transports estimated in 1995 from the hydrographic data are close to mean values. Apparently, a mesoscale eddy in March disrupts the stronger fall gyre, whereas in June the weaker winter gyre is delayed by 1 month.
Gamache, J.F. Evaluation of a fully three-dimensional variational Doppler analysis technique. Proceedings, 28th Conference on Radar Meteorology, Austin, TX, September 9-12, 1997. American Meteorological Society, Boston, 422-423 (1997).
A method is described that deduces the three-dimensional wind field from two or more independent Doppler observations and from the continuity equation, using a simultaneous three-dimensional variational solution of the Doppler projection equations and the continuity equation. The solution minimizes a cost function that includes (1) the difference between observed Doppler radial velocities (corrected for precipitation fall speed) and the projection of the analysis velocities upon the observed Doppler pointing angles, (2) the error in the discretized continuity equation, and (3) and the difference between a velocity component and the surrounding six grid points. The third part of the cost function is included to quiet noise in the solution. A much higher weight is given to the second term since it represents the solution to the continuity equation at only one grid cell. Otherwise, when all grid cells are combined there would be substantial "leakage" in the continuity equation. Errors in the discretized continuity equation are less than 10-6 s-1 at individual grid points. Analytical wind fields will be resampled and the ability of the variational analysis to repeat the analytical field will be discussed at the conference. The technique has already been applied to the core of several hurricanes, convection within a developing tropical storm, and several cases in TOGA COARE. By the time of the conference it may also have been applied to a VORTEX case. Bubble-like features have been seen in several of these cases, and the bubble locations are very consistent with the radar reflectivity presentation. Several of these examples will be shown at the conference.
Gamache, J.F. Wind shear and sea surface temperature in hurricanes observed by airborne Doppler radar. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-17-A-18 (1997).
The relationships between sea surface temperature (SST), vertical wind shear, and hurricane structure and intensity change are described for two eastern Pacific hurricanes. Two NOAA WP-3D Doppler-equipped aircraft observed Hurricane Jimena on 23 September 1991 and Hurricane Olivia on 24 and 25 September 1994. Aircraft flight tracks were coordinated for optimum Doppler wind analysis of inner core (radius <30 km) winds. Hurricane Jimena maintained virtually steady intensity for 24 hours, while Hurricane Olivia deepened 1-2 mb/hr during the mission on the 24th and filled at 3 mb/hr during the mission on the 25th. The missions yielded four wind analyses in Hurricane Jimena and seven for each of the two days in Olivia. The average interval between analyses is about 35 minutes. At the time of the mission, Jimena was located at 13.3°N, 109.6°W over warm tropical waters. The shear between 1 and 10 km was southeast at 15 m/s, and the hurricane remained at a nearly constant intensity. Hurricane Olivia intensified into a hurricane early on 24 September 1994. As the aircraft first reached Olivia, it was located near 15.2°N,118.0°W. During three hours on station the central pressure decreased by about 6 mb. The hurricane had a mean shear during the mission of east at 7 m/s between 1 and 9 km, and the asymmetric distribution of greater precipitation to the south was sustained throughout the mission. During the 24th the hurricane traveled west-northwestward and was over warm tropical water (28.2°C). As the aircraft began their penetrations on 25 September, Olivia was near its maximum intensity. The radar presentation was highly symmetric, and the shear between 1 and 9 km was 3 m/s from the west. In three hours the shear had increased to 15 m/s from west-northwest, and are highly asymmetric precipitation pattern had developed with dBZ greater than 50 seen to the north of center and nothing above 40 dBZ to the south of center. Mean winds at the 9-km level decreased by 15 m/s. The role of shear in producing this change may be confused by Olivia passing the SST front as it travelled nearly northward at 5 m/s, so the SST by the end of the mission was 27°C. Another interesting feature that may be described at the Interdepartmental Conference is a highly convective feature in the northeast eyewall late on 25 September in Olivia that had an elevated echo maximum and apparently a low-reflectivity vault where the strongest updrafts were. Analysis has just begun of this feature. Hopefully, it will be described at the next conference.
Gamache, J.F., H.E. Willoughby, M.L. Black, and C.E. Samsury. Wind shear, sea surface temperature, and convection in hurricanes observed by airborne Doppler radar. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 121-122 (1997).
No abstract.
Garzoli, S.L., G.J. Goni, A.J. Mariano, and D.B. Olson. Monitoring the upper southeastern Atlantic transports using altimeter data. Journal of Marine Research, 55(3):453-481 (1997).
A large in-situ data set, collected in the southeastern Atlantic Ocean, is merged with the TOPEX/POSEIDON altimeter observations in order to verify the use of altimeter data in monitoring the transports of the Agulhas/Benguela system. Comparisons between altimeter observations and either moored current meters or inverted echo sounder measurements shows that the sea surface elevation anomaly is significantly correlated with the thermocline depth and the surface dynamic height, respectively. Knowing the least-squares regression parameters, it is possible to calculate the transports by using geostrophy and either a two-layer or a continuously-stratified model. The transports obtained from fits of dynamic height to altimeter sea surface height are similar to the ones calculated with the moored instruments. In the southern part of the area under analysis, around 35°S, close to the Agulhas retroflection, the transports obtained from the two-layer model are overestimated. Across the Benguela Current, at 30°S, transports are still overestimated but of the same order as the measured ones. In this part of the region, the two-layer model can be successfully used to calculate the total and barotropic transports of the Benguela Current. Analysis of the three years of geostrophic transport obtained from the altimeter data indicate that the mean Benguela Current transport does not change interannually more than 20%. However, the primary interannual variability derives from the source water that forms the Benguela Current.
German, C.R., D.L. Bourles, E.T. Brown, J. Hergt, S. Colley, N.C. Higgs, E.M. Ludford, T.A. Nelsen, R.A. Feely, G. Raisbeck, and F. Yiou. Hydrothermal scavenging on the Juan de Fuca Ridge: 230Thxs, 10Be, and REE in ridge-flank sediments. Geochimica et Cosmochimica Acta, 61(19):4067-4078 (1997).
We have investigated the geochemistry of a hydrothermally-enriched sediment core recovered from the western flank of the N.Cleft Segment, Juan de Fuca Ridge, 8 km west of the "MegaPlume" area previously identified near 45°N. The core contains varying biogenic, lithogenic, and hydrothermal components, as reflected in CaCO3, Al, and Fe contents, respectively. Horizons of pronounced hydrothermal input, in core-top sediments and at depth, exhibit increased concentrations of Fe, Cu, Zn, Pb, and shifts in Pb isotopic compositions toward nonradiogenic (MORB/hydrothermal) values. REE concentrations co-vary with hydrothermal Fe down-core, and shale-normalized REE distributions patterns exhibit both negative Ce-anomalies and positive Eu-anomalies, indicative of input from plume-particle fall-out. Unsupported 230Thxs activities down-core are consistent with continuous slow sediment accumulation rates of 0.54 cm/ky for 200 ky since the deposition of the deeper Fe-rich horizon. 10Be(0) and 9Be isotope concentrations also co-vary with hydrothermal Fe down-core and exhibit 10Be(0) 9Be ratios which approach that of Pacific Ocean deep water, indicative of a seawater-scavenging source. 10Be(0) 230Thxs(0) ratios throughout most of Core GC88-6 are greater than mean Pacific Ocean values, indicating that hydrothermal scavenging can lead to significant net removal of dissolved 10Be into ridge-flank sediments.
Goldenberg, S.B., C.W. Landsea, and L.J. Shapiro. Are we seeing the beginning of a long-term upturn in Atlantic basin major hurricane activity? Proceedings, Tropical Cyclone Symposium, Melbourne, Australia, December 9-13 1996. U.S. Office of Naval Research, 10 pp. (1997).
No abstract.
Goldenberg, S.B., L.J. Shapiro, and C.W. Landsea. Are we seeing a long-term upturn in Atlantic basin major hurricane activity related to decadal-scale SST fluctuations? Preprints, 7th Conference on Climate Variations, Long Beach, CA, February 2-6, 1997. American Meteorological Society, Boston, 305-310 (1997).
No abstract.
Goldenberg, S.B., L.J. Shapiro, and C.W. Landsea. Mounting evidence for a decadal-scale upturn in Atlantic basin tropical cyclone activity. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 507-508 (1997).
No abstract.
Goldenberg, S.B., L.J. Shapiro, and C.W. Landsea. The hyperactive 1995 Atlantic hurricane season: Just a spike or a harbinger of things to come? Proceedings, 21st Climate Diagnostics and Prediction Workshop, Hunstville, AL, October 28-November 1, 1996. American Meteorological Society, Boston, 9-12 (1997).
For over 25 years the North Atlantic hurricane basin has experienced a relative lull in tropical cyclone activity, in particular, in major hurricane (maximum sustained surface winds of at least 50 m/s) activity and in overall activity in the deep tropics. After the experience of renewed "normal" activity in 1988 and 1989, it was suggested that the Atlantic basin was returning to a long-term period of higher activity such as what was experienced back in the decades of the 1950s and 1960s and some earlier periods. The renewed activity in 1988 and 1989 was followed, however, by a marked downturn in activity from 1991 to 1994. In fact, the inhabitants of the regions surrounding the Caribbean experienced no hurricanes from 1990-1994. As a result of the resumption of the below-normal activity, primarily attributed to the highly anomalous, long-lasting warm event (El Niño) in the tropical Pacific, the notion that the Atlantic basin had entered a high-activity decade was pretty much discarded. The warm event in the Pacific finally ended in early 1995 and was followed by one of the most active hurricane seasons in the Atlantic on record, including renewed activity in the Caribbean, and with almost every measure of activity over twice the long-term mean. Of particular note was that the season produced five major hurricanes for the first time since 1964. Most of the major hurricanes in the North Atlantic basin form from easterly (African) wave disturbances and are especially sensitive to fluctuations in the tropical climate on the interannual and interdecadal time scales. The chief issue that will be addressed in the current study is whether or not the activity of the 1995 season was simply an anomalous "spike" or a harbinger of longer-term climate shifts signaling the probability of greater activity over the next decade or so.
Goldenberg, S.B., L.J. Shapiro, and C.W. Landsea. The hyperactive 1995 Atlantic hurricane season: A spike or a harbinger of things to come? Workshop Proceedings, Climate Change and Climate Variability in the Atlantic, Halifax, Nova Scotia, December 3-6, 1996. American Meteorological Society, Boston, 113-119 (1997).
No abstract.
Goni, G.J., S.L. Garzoli, A.J. Roubicek, D.B. Olson, and O.B. Brown. Agulhas ring dynamics from TOPEX/POSEIDON satellite altimeter data. Journal of Marine Research, 55(5):861-883 (1997).
The transfer of warm water from the Indian Ocean into the South Atlantic subtropical gyre takes place in the form of rings and filaments formed when the Agulhas Current retroflects south of Africa between 15°E and 25°E. A survey of the rings formed from September 1992 until December 1995 in the retroflection region was carried out using TOPEX/POSEIDON altimeter data. A two-layer model was used to estimate the upper layer thickness from the altimeter-derived sea surface height anomaly data. An objective analysis scheme was used to construct a map of upper layer thickness every 10 days. Seventeen rings and their trajectories were identified using these maps. The shedding of rings from the Agulhas Current was neither continuous nor periodic, and for long periods there is no formation of rings. Several rings remained in the region for more than a year and, at any given time, two to six rings coexisted in the region east of the Walvis Ridge. The results showed that the number of rings translating simultaneously in this region is larger during the first half of each year. The upper layer transport of the Agulhas Current in the retroflection region was computed and a close association between high variations in transport and ring shedding was found. Rings translated west-northwest at translation speeds ranging from 5-16 km day-1 following formation. The values of available potential energy computed for the rings place them among the most energetic rings observed in the world oceans, with values of up to 70 × 1015 J. Transport computations indicate that each ring contributes in the average approximately 1 Sv of Agulhas Current waters to the Benguela Current.
Gordon, A.L., S. Ma, D.B. Olson, P. Hacker, A. Ffield, L.D. Talley, W.D. Wilson, and M.O. Baringer. Advection and diffusion of Indonesian throughflow within the Indian Ocean South Equatorial Current. Geophysical Research Letters, 24(21):2573-2576 (1997).
Warm, low salinity Pacific water weaves through the Indonesian Seas into the eastern boundary of the Indian Ocean. The Indonesian Throughflow Water (ITW) adds freshwater into the Indian Ocean as it spreads by the advection and diffusion within the Indian Ocean's South Equatorial Current (SEC). The low salinity throughflow trace, centered along 12°S, stretches across the Indian Ocean, separating the monsoon dominated regime of the northern Indian Ocean from the more typical subtropical stratification to the south. ITW is well represented within the SEC thermocline, extending with concentrations above 80% of initial characteristics from the sea surface to 300-m within the eastern half of the Indian Ocean, with 60% concentration reaching well into the western Indian Ocean. The ITW transport within the SEC varies from 4 to 12 × 106 m3 sec-1, partly in response to variations of the injection rate at the eastern boundary and to the likelihood of a zonally elongated recirculation cell between the Equatorial Counter Current and the SEC within the Indian Ocean. Lateral mixing disperses the ITW plume meridionally with an effective isopycnal mixing coefficient of 1.1 to 1.6 × 104 m2 sec-1.
Gray, W.M., J.D. Sheaffer, and C.W. Landsea. Climate trends associated with multi-decadal variability of Atlantic hurricane activity. In Hurricanes, Climate, and Socioeconomic Impacts, H.F. Diaz and R.S. Pulwarty (eds.). Springer, Berlin, 15-53 (1997).
No abstract.
Haddad, Z.S., D.A. Short, S.L. Durden, E. Im, S. Hensley, M.B. Grable, and R.A. Black. A new parameterization of the rain drop size distribution. IEEE, Transactions of Geoscience and Remote Sensing, 35(3):532-539 (1997).
This paper revisits the problem of finding a parametric form for rain drop size distribution (DSD) which (1) is an appropriate model for tropical rainfall, and (2) involves statistically-independent parameters. Using TOGA/COARE data, we derive a parameterization which meets these criteria. This new parameterization is an improvement on the one that was derived in [3], using TRMM ground truth data from Darwin, Australia. The new COARE data allows us to verify that the spatial variability of the two "shape" parameters is relatively small, thus confirming that this parameterization should be particularly useful for remote sensing applications. We also derive new DSD-based radar-reflectivity-rain-rate power laws, whose coefficients are directly related to the shape parameters of the DSD. Perhaps most important, since the coefficients are independent of the rain-rate itself, and very little spatially, the relations are ideally suited for rain retrieval algorithms. It should also prove straightforward to extend this method to the problems of extimating cloud hydrometeors from remote-sensing measurements.
Hasler, A.F., P.G. Black, V.M. Karyampudy, M. Jentoft-Nilsen, K. Palaniappan, and D. Chesters. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 201-202 (1997).
No abstract
Hendee, J.C. Object-oriented analysis and design of a near real-time marine environmental data acquisition and reporting system. Proceedings, 8th International Coral Reef Symposium, Panama City, Panama, June 24-28, 1996. Smithsonian Tropical Research Institute, 2:1569-1574 (1997).
The National Oceanic and Atmospheric Administration's Coral Health and Monitoring Program has cooperated with the Florida Institute of Oceanography in developing a near real-time marine environmental monitoring and reporting system. Using an object-oriented analysis technique, this report describes how data are retrieved from satellite data and archiving facilities, then reformatted for presentation via a Remote Bulletin Board system and facsimile. Using an object-oriented design technique, a new system is designed using a requirements analysis of the original system.
Hitchcock, G.L., W.J. Wiseman, W.C. Boicourt, A.J. Mariano, N. Walker, T.A. Nelsen, and E. Ryan. Property fields in an effluent plume of the Mississippi River. Journal of Marine Systems, 12:109-126 (1997).
Surface property distributions were mapped in the Mississippi River plume during May and August 1993 while following surface drifters. Prevailing winds were the primary factor controlling the orientation of the plume. In May, under typical southeasterly winds, the plume turned anticyclonically towards the coast, while in August, under anomalous westerly winds, the plume turned east. Remote imagery of sea surface temperature and suspended sediments confirmed the direction of the plume. Optimally interpolated maps of surface salinity, temperature, chlorophyll a fluorescence, and transmissivity from underway sampling, and periodic nutrient samples, reveal the plume structure. In May, concentrations of nitrate, silicate, and phosphate decreased linearly with increasing salinity. Chlorophyll a increased to peak concentrations of 10 µg 1-1 in the plume, although higher pigment biomass was observed near the coast. In August, nitrate and silicate concentrations decreased conservatively near the mouth of Southwest Pass, except where pigment biomass was enhanced in a convergent surface front. Surface nutrient concentrations in the plume also decreased with increasing salinity. The observations provide the first Lagrangian view of surface property distributions in the Mississippi River plume, and indicate that significant temporal variability exists in physical and biological properties within a day after waters are discharged from the river delta.
Ho, D.T., L.F. Bliven, R.H. Wanninkhof, and P. Schlosser. The effect of rain on air-water gas exchange. Tellus, 49B:149-158 (1997).
The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain- Sea Interaction Facility (RSIF) using several SF6 evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with 18 different rain rates (7 to 110 mm h-1) and 1 of 2 dropsizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and dropsize. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.
Ho, D.T., R.H. Wanninkhof, J.C. Masters, R.A. Feely, and C.E. Cosca. Measurement of underway fCO2 in the eastern equatorial Pacific on NOAA ships Malcolm Baldrige and Discoverer from February to September 1994. NOAA Data Report, ERL AOML-30 (PB97-169056), 58 pp. (1997).
From February through September 1994, underway measurements of the fugacity (partial pressure) of carbon dioxide (fCO2) were performed in the eastern equatorial Pacific as part of the Ocean Atmosphere Carbon Exchange Study (OACES) of the National Oceanic and Atmospheric Administration (NOAA). The measurements were performed with semi-autonomous instruments which measured the fugacity in the air and in the headspace of an equilibrator drawing water from the bow of the ship, from which the fCO2 of the surface water is calculated. From the difference in fugacity in air and water, the CO2 flux from the equatorial Pacific can be estimated. On the NOAA ship Malcolm Baldrige the system measured three reference standards, three air values, and eight water values per hour. The system on the Discoverer measured three standards, one 19-minute average air sample, and one 20-minute average water sample per hour. This report contains a description of the methodology and reduction of the fCO2 and ancillary measurements. The results from the cruises of the Malcolm Baldrige in the equatorial Pacific in the (boreal) spring and fall of 1994 and from the Discoverer along nominally 110°W in the spring of 1994 are shown in a series of graphs with fCO2 air and water versus latitude as top panel and temperature and salinity versus latitude as bottom panel.
Hopkins, M., M. DeMaria, and J. Kaplan. Evaluation of an empirical inland wind model for the landfall of Hurricane Fran (1996). Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-22 (1997).
A simple empirical model for predicting the winds from landfalling hurricanes has been developed for the Gulf and east coasts of the U.S. This model was originally developed to estimate the maximum sustained surface winds near the center of landfalling storms, but was generalized to predict the two-dimensional field of maximum winds (wind swath). The performance of the model during the landfall of Hurricane Fran will be evaluated by comparing the predicted winds with all available surface observations. Plans for improving the swath part of the model using a combined wind data set from several recent landfalling storms will also be described.
Houston, S.H., M.D. Powell, and P.P. Dodge. Surface wind fields for Hurricanes Bertha and Fran (1996). Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-23 (1997).
Hurricanes Bertha and Fran made landfall near Wilmington, North Carolina within two months of each other in 1996. These tropical cyclones contained maximum sustained surface winds (marine exposure at 10 m) estimated to be 46 m s-1 and
50 m s-1, respectively, at the time of landfall. Fran caused more loss of life and greater estimated U.S. property damage (34 deaths and $3.2 billion) than Bertha (8 deaths and $250 million). In both storms, the property losses were primarily due to storm surge and waves along the coast rather than directly from the wind. Fran also caused considerable damage due to inland flooding resulting from heavy rainfall across a large swath of the eastern U.S. as it moved northward after landfall. The Hurricane Research Division (HRD) has been providing real-time tropical cyclone surface wind fields to forecasters at the National Hurricane Center (NHC) since 1993; there were 134 of these analyses made in 1996. The analysis system contains adjustment techniques for exposure and interactive data quality control that produce a field of input observations conforming to a common framework for exposure, height, and averaging period. In Hurricane Bertha, HRD transmitted 14 real-time surface wind fields to NHC. The real-time and post-storm surface wind analyses indicate that the peak sustained surface winds in Bertha were primarily over the Atlantic Ocean at the time of landfall. The storm rapidly weakened after landfall and, based on the HRD wind fields, it is very unlikely that the peak sustained surface winds were observed at any point along the coastline of North Carolina. During Hurricane Fran, HRD produced 28 real-time surface wind fields for NHC. These, together with post-storm analyses, indicated that Fran's surface winds at landfall were stronger and spread over a larger area north and east of the center than Bertha. Unlike Bertha, the coastal areas were affected by Fran's strongest winds, especially in advance of landfall. Real-time and post-storm surface wind analyses in Hurricanes Bertha and Fran will be discussed, along with their utility for NHC's marine forecasts, emergency management, and storm surge forecasting.
Houston, S.H., M.D. Powell, and P.P. Dodge. Surface wind fields in 1996 Hurricanes Bertha and Fran at landfall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 92-93 (1997).
No abstract.
Humphrey, J.C., T.C. Moore, J.C. Hendee, and J.C. Ogden. SEAKEYS: Real-time monitoring of the Florida Keys reef tract and Florida Bay. 28th Meeting Association of Marine Laboratories of the Caribbean (ALMC-97), San Pedro, Costa Rica, July 21-25, 1997. University of Costa Rica, 51 (1997).
No abstract.
Johns, E., R.A. Fine, and R.L. Molinari. Deep flow along the western boundary south of the Blake Bahama Outer Ridge. Journal of Physical Oceanography, 27(10):2187-2208 (1997).
In June-July 1990, hydrographic, chloroflourocarbon (CFC), and direct velocity observations were taken in the western North Atlantic between the Blake Bahama Outer Ridge (BBOR) at 30°N and San Salvador Island at 24°N. The deep flow in the region, dominated by the Deep Western Boundary Current (DWBC), forms a pattern of strong, narrow currents and cyclonic gyres close to the continental slope, with broad, weaker southward flow offshore. The CFCs reveal that in general the most recently ventilated water (i.e., having the highest CFC concentrations) is found along the western boundary as two distinct cores within the DWBC between potential temperatures 4-6°C and 1.9-2.4°C. Geostrophic transport streamlines are constructed for the DWBC layers, referenced using direct velocity observations at 26.5°N and assuming mass conservation between closed areas bounded by the hydrographic sections. The tracers and transports are used to define the spatial scales and strengths of the recirculation gyres and to examine their relationship to bottom topography and their role in ventilating the interior. Geostrophic transports for the DWBC layers which transit the region and continue equatorward along the western boundary are approximately 5 Sv for the 4-6°C layer; 14 Sv for the 2.4-4.0°C layer; 9 Sv for the 1.9-2.4°C layer; and 3 Sv below 1.9°C, for a total equatorward DWBC transport of 31 Sv below 6°C. A cyclonic gyre with one or more embedded gyres extends out to about 74°W, transporting 12 Sv of water intermediate CFC concentrations. Farther offshore, a broad band of southward flow contributes an additional 16 Sv of water with lower CFC concentration to the total equatorward transport. This flow may be connected to a much larger elongated cyclonic recirculation gyre which reaches equatorward to the Guiana Basin off northeastern Brazil. The close correspondence of the tracer distributions with the regional topography indicates that the major topographic features in this region strongly influence the circulation, particularly in the deep and bottom layers. It appears that the most recently ventilated water, between 4-6°C and 1.9-2.4°C, does not reach the southern top of the BBOR, but rather it bypasses the BBOR to the north of the study region and turns back westward following the isobaths toward the western boundary north of 30°N. Only in the coldest layer (<1.9°C) are the relatively highest CFCs observed south of 30°N on the BBOR. The layer containing the shallow CFC core (4-6°C) is apparently less constrained by the bottom topography; 3 Sv are carried westward across the axis of the BBOR forming an extended zonal high CFC and salinity distribution related to the Gulf Stream recirculation. South of the BBOR, due to the steep topography west of the Blake Basin, the DWBC is channeled into a narrow equatorward boundary flow. At the San Salvador Spur, some of the more recently ventilated water appears to be deflected northward following the isobaths in a cyclonic gyre around the extension of the Bahama Ridge. The cyclonic gyres between the BBOR and the San Salvador Spur appear to be localized features close to the western boundary that may have little impact on the larger scale deep North Atlantic circulation. Nevertheless, the gyres serve to ventilate the interior by diluting the tracer concentration carried equatorward by the DWBC.
Jones, R.W., and H.E. Willoughby. Sensitivity of a spectral shallow-water barotropic vortex to variations of domain size and spectral truncation. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 577-578 (1997).
Recent studies by Willoughby (1992, 1994, 1995) discuss the motion of a vortex on a beta plane for various environmental flows with a linear and non-linear version of the model. The domain size was 3000 km. Experiments for a 6000 km domain show small 50-km track differences by 10 days for an all cyclonic vortex with no environmental flow. Experiments with environmental flows will also be reported. The spectral truncation is wave number 3 for the non-linear model. Spectral truncations at wave numbers 2 and 4 will be reported. The purpose of these calculations is to show that highly truncated models are good enough to describe the dynamics of vortex motion on a beta plane with environmental flows. In the future, a baroclinic model will be developed for theoretical studies and for application to real-time hurricane tracking.
Kaplan, J., C.W. Landsea, M. DeMaria, and J.J. Cione. The differing roles of the large-scale environment in the intensity changes of three 1996 Atlantic hurricanes. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 358-359 (1997).
No abstract.
Knaff, J.A., and C.W. Landsea. An El Niño-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Weather and Forecasting, 12(3):633-652 (1997).
A statistical prediction method is developed for the El Niño-Southern Oscillation (ENSO) phenomena which is based entirely on the optimal combination of persistence, month-to-month trend of initial conditions and climatology. The selection of predictors is by design intended to avoid any pretense of predictive ability based on "model physics" and the like, but rather is to specify the optimal "no-skill" forecast as a baseline comparison for more sophisticated forecast methods. Multiple least squares regression using the method of leaps and bounds is employed to test a total of fourteen possible predictors for the selection of the best predictors, based upon 1950-1994 developmental data. A range of zero to four predictors were chosen in developing twelve separate regression models, developed separately for each initial calendar month. The predictands to be forecast include the Southern Oscillation (pressure) Index (SOI) and the Niño 1+2, Niño 3, Niño 4 and Niño 3.4 SST indices for the equatorial eastern and central Pacific at lead times ranging from zero seasons (0-2 months) through seven seasons (18-20 months). Though hindcast ability is strongly seasonally dependent, substantial improvement is achieved over simple persistence wherein largest gains occur for two to seven season (6 to 21 months) lead times. For example, expected maximum forecast ability for the Niño 3.4 SST region, depending on the initial date, reaches 92, 85, 64, 41, 36, 24, 24 and 28 percent of variance for leads of zero to seven seasons. Comparable maxima of persistence only forecasts explain 92, 77, 50, 17, 6, 14, 21 and 17 percent, respectively. More sophisticated statistical and dynamical forecasting models are encouraged to utilize this ENSO-CLIPER model in place of persistence when assessing whether they have achieved forecasting skill; to this end, real-time results for this model are made available via a Web site.
Lamb, M.F., J.L. Bullister, R.A. Feely, G.C. Johnson, D.P. Wisegarver, B. Taft, R.H. Wanninkhof, K.E. McTaggart, K.A. Krogslund, C.W. Mordy, K. Hargreaves, D. Greeley, T. Lantry, H. Chen, B.E. Huss, F.J. Millero, R.H. Byrne, D.A. Hansell, F.P. Chavez, P.D. Quay, P.R. Guenther, J.-Z. Zhang, W. Gardner, M.J. Richardson, and T.-H. Peng. Chemical and hydrograph measurements in the eastern Pacific during the CGC94 expedition (WOCE section P18). NOAA Data Report, ERL PMEL-61 (PB97-158075), 235 pp. (1997).
No abstract.
Landsea, C.W. Comments on "Will greenhouse gas-induced warming over the next 50 years lead to higher frequency and greater intensity of hurricanes?" Tellus, 49A:622-623 (1997).
No abstract.
Landsea, C.W. Indices of global tropical cyclone activity. CLIVAR/GCOS/WMO Workshop on Indices and Indicators for Climate Extremes, Asheville, North Carolina, 10 pp. (1997).
No abstract.
Landsea, C.W., G.D. Bell, W.M. Gray, and S.B. Goldenberg. The hyperactive 1995 Atlantic hurricane season: A juxtaposition of favorable conditions. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 505-506 (1997).
No abstract.
Landsea, C.W., N. Nicholls, W.M. Gray, and L.A. Avilia. Reply to comment by R.W. Wilson on "Downward trend in the frequency of intense Atlantic hurricanes during the past five decades. Geophysical Research Letters, 24(17):2205-2206 (1997).
No abstract.
Landsea, C.W., W.M. Gray, P.W. Mielke, K.J. Berry, and J.A. Knaff. A seasonal hurricane forecast for 1997. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., B-183 (1997).
The forecast for the 1997 Atlantic hurricane season issued by Dr. Bill Gray and collaborators (including myself) will be discussed. This prediction was issued in early December 1996 and will be updated in early April, early June, and early August. Uncertainties in the predictors, especially in El Niño and Sahel rainfall, will be discussed in how they may impact the number and intensity of tropical cyclones this year. I will also briefly discuss the performance of the 1996 forecasts.
Lee, K., F.J. Millero, and R.H. Wanninkhof. The carbon dioxide system in the Atlantic Ocean. Journal of Geophysical Research, 102(C7):15,693-15,708 (1997).
During the National Oceanic and Atmospheric Administration's Ocean Atmosphere Carbon Exchange Study expedition in the eastern North Atlantic in summer 1993, measurements of four CO2 parameters, along with hydrographic properties, were made: fugacity of CO2, fCO2 (measured at 20°C and in situ); pH (measured at 20°C); total inorganic carbon, TCO2; and total alkalinity, TA. The major objective of this cruise was to establish a benchmark against which future measurements of the transient invasion of CO2 can be made. The large-scale distributions of surface water CO2 parameters were related to temperature and salinity in this region. The subsurface TA and TCO2 measurements were fitted to multiple linear functions of salinity, in situ temperature, apparent oxygen utilization, and silicate. The measurements of the inorganic carbon system were also used to examine the internal consistency of the carbonate system in this area. The measurements were internally consistent to ±1.3% in fCO2, ±0.006 in pH, ±3 µmol kg- 1 in TCO2, and ±3 µmol kg-1 in TA if proper carbonic acid dissociation constants are used for different input combinations. The thermodynamic constants of Goyet and Poisson (1989), Roy et al. (1993), Millero (1995), and Lee and Millero (1995) were most consistent with the measurements of pH (at 20°C), TCO2, and TA. However, if fCO2 (at 20°C) is used in thermodynamic calculations, the constants of Mehrbach et al. (1973) gave the best representation of measurements. The constants of Lee and Millero (1995) were also in reasonable agreement with these measurements.
Lobert, J.M., S.A. Yvon-Lewis, J.H. Butler, S.A. Montzka, and R.C. Myers. Undersaturations of CH3Br in the Southern Ocean. Geophysical Research Letters, 24(2):171-172 (1997).
Dry mole fractions of methyl bromide (CH3Br) in marine boundary layer air and air equilibrated with surface seawater were measured in the Southern Ocean. Saturation anomalies were consistently negative at -36 ± 7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH3Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at -21 (-11 to -32) Gg y-1.
Marks, F.D., and P.P. Dodge. Hurricane concentric eyewall characteristics as revealed by airborne Doppler radar analyses. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 102-103 (1997).
No abstract.
Marks, F.D., and H.A. Friedman. 1997 Hurricane Field Program Plan. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida (published for limited distribution), 132 pp. (1997).
The objectives of the National Oceanic and Atmospheric Administration (NOAA) hurricane research field program is the collection of descriptive data that are required to support analytical and theoretical hurricane studies. These studies are designed to improve the understanding of the structure and behavior of hurricanes. The ultimate purpose is to develop improved methods for hurricane prediction. Ten major experiments have been planned, primarily by principal investigators at the Hurricane Research Division (HRD)/Atlantic Oceanographic and Meteorological Laboratory (AOML) of NOAA, for the 1997 hurricane field program. These experiments will be conducted with the NOAA/Aircraft Operations Center (AOC) WP-3D and Gulfstream IV-SP aircraft.
Marks, F.D., and L.N. Shay. Landfalling tropical cyclones: Forecast problems and associated research opportunities: Report of the Fifth Prospectus Development Team of the U.S. Weather Research Program. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A-26 (1997).
The Fifth Prospectus Development Team (PDT-5) of the U.S. Weather Research Program was charged to identify and delineate emerging research opportunities relevant to the prediction of local weather, flooding, and coastal ocean currents associated with landfalling U.S. hurricanes, specifically, and tropical cyclones, in general. Central to this theme are fundamental and applied issues including: rapid intensity change; initialization of and parameterization in dynamical models; coupling of atmospheric and oceanic models; quantitative use of satellite information; and optimal adaptive observing strategies to validate predictive models. To acquire the necessary understanding and provide the initial conditions for improved prediction, a focused, comprehensive observing system in a translating storm-coordinate system is required. With the development of proven instrumentation and improvement of existing systems, three-dimensional wind and thermodynamic data sets can be obtained whenever major hurricanes threaten the United States. Satellites, aircraft, expendable probes released from aircraft, and coastal, moored, and drifting surface platforms are needed to estimate the upper-ocean temperatures and currents, air-sea interactions, the distribution of storm surge, boundary layer winds, rainfall, and potential damage. In the hurricane core, airborne Doppler radar, supplemented by a suite of other instruments, would measure tropospheric winds including critical areas of the boundary layer and outflow region. Microwave systems would determine surface winds, ocean waves, and storm surge. On the hurricane periphery, dropsondes would be released from turboprop and jet aircraft to map the atmospheric temperature, humidity, and wind structure. Satellites would acquire both storm-scale and surrounding environmental data. To take full advantage of these new observations, techniques need to be developed to objectively analyze these observations, and initialize models aimed at improving prediction of hurricane track and intensity from global-scale and mesoscale dynamical models. Multi-nested models allow prediction of all scales from the global, which determine long-term hurricane motion, to the convective-scale, which affect intensity. Development of an integrated analysis and model forecast system optimizing the use of observations and providing the necessary forecast skill on all relevant spatial scales is required. Detailed diagnostic analyses of these data sets will lead to improved understanding of the physical processes of hurricane motion, intensity change, the atmospheric boundary layer, and air-sea coupling. Ultimately, the aim is on development of real-time analyses of storm surge, winds, and rain, before and during landfall, to improve warnings and provide local officials with the information needed to focus recovery efforts in the hardest hit areas as quickly as possible.
Martin, D., M. Tsivou, B. Bonsang, C. Abonnel, T.P. Carsey, M. Springer-Young, and A.A. Pszenny. Hydrogen peroxide (H2O2) in the marine atmospheric boundary layer during the ASTEX/MAGE experiment in the eastern subtropical North Atlantic. Journal of Geophysical Research, 102:6003-6015 (1997).
No abstract.
Masters, J.C., R.H. Wanninkhof, D.T. Ho, M. Steckley, R.A. Feely, and C. Cosca. Continuous air and surface seawater measurements of fCO2 on board the NOAA ship Malcolm Baldrige around-the-world cruise in 1995. NOAA Data Report, ERL AOML-31 (PB98-105950), 65 pp. (1997).
From February 1995 through January 1996 the NOAA ship Malcolm Baldrige conducted scientific operations on an around-the-world tour. The majority of work occurred in the Indian Ocean. The CO2 groups of the National Oceanic and Atmospheric Administration's (NOAA) Atlantic Oceanographic and Meteorological Laboratory (AOML) and Pacific Marine Environmental Laboratory (PMEL) operated a continuously flowing partial pressure carbon dioxide analyzer. Samples were taken from both the surface water and the overlying atmosphere to determine carbon dioxide flux across the gas/water interface. Other parameters such as salinity, barometric pressure, and temperature were used to reduce the data and calculate the fugacity of CO2*. Total dissolved inorganic carbon (DIC) samples of surface water were also collected. Data were collected on each leg of the cruise. Leg 1 was a transit from Miami to Durban, South Africa. Leg 2 operated from Durban to Colombo, Sri Lanka. Leg 3 operated from Colombo to Muscat, Oman. Leg 4 operated from Muscat to Victoria, Seychelles. Leg 5 operated from Victoria to Muscat, Oman. Leg 6 operated from Muscat to Diego Garcia. Leg 7 consisted of a transit from Diego Garcia to Fremantle, Australia followed by the major scientific operations between Fremantle and Male, Maldive Islands. Leg 8 included another transit from Male to Darwin, Australia. Operations began after leaving Darwin and headed into the western equatorial Pacific. The ship inported in American Samoa and continued to Panama, Miami, Florida and finished in Charleston, South Carolina. Descriptions of sampling methods and graphical data summaries are given in this report.
McCarthy, M.C., L.D. Talley, and M.O. Baringer. Deep upwelling and diffusivity in the southern Central Indian Basin. Geophysical Research Letters, 24(22):2801-2804 (1997).
Transport of the deepest water westward through a gap at 28°S in the NinetyEast Ridge between the Central Indian Basin and the West Australia Basin is calculated from hydrographic data collected as part of the WOCE Hydrographic Program section I8N. Zero reference velocity levels at mid-depth were chosen through consideration of water masses. The small transport of 1.0 Sv westward through the gap of water denser than sigma4 = 45.92 kg/m3 must all upwell in the southern Central Indian Basin. Of this, 0.7 Sv upwells between the central and western sill sections, that is, close to the sill itself. Using the areas covered by the isopycnal, we calculate an average vertical velocity of 3.3 × 10-3 cm/s close to the sill and of 4.2 × 10-4 cm/s west of the sill. Associated average vertical diffusivities are 105 cm2/s close to the sill and 13 cm2/s west of the sill, in this very near bottom layer.
McCartney, M.S., R.G. Curry, and H.F. Bezdek. The interdecadal warming and cooling of Labrador Sea Water. ACCP Notes, 1-10 (1997).
No abstract.
McLeish, W., D.V. Hansen, and J.R. Proni. Coastal currents induced by Hurricane Andrew. Florida Scientist, 60(4):254-264 (1997).
Ocean current meters in 18 and 24 m depth water along the southeast Florida coast recorded water motions as Hurricane Andrew crossed the narrow continental shelf with the storm center 32 km from the southernmost current meter. Wind speeds up to 48 m s-1 at the meter closest to the storm path were associated with recorded mean current speeds up to 94 cm s-1. The greatest water speeds, however, were transient motions from the wind waves. These motions caused major changes to the bottom and to objects lying on it. Direct and remotely sensed observations showed an increasing degree of turbulence in the water as the hurricane approached, stirring both air bubbles and bottom sediment throughout the water and mixing the water so that vertical shear in the current was suppressed. Thus, beneath the strong wind stress there was not a mean water flow in the direction of the wind at the surface and a flow in the opposite direction near the bottom, as had been indicated in previous studies. Some of the water that had been forced toward shore by the strong west moving wind in the hurricane eyewall moved northward along the coast. In a region where the wind speed was less but still of hurricane force, water was displaced offshore contrary to the direction of the wind stress. At the same time that the offshore current developed, wave motions became much more severe: it appears that the new countercurrent may have induced major hurricane waves to break in this farther offshore location.
Mielke, P.W., K.J. Berry, C.W. Landsea, and W.M. Gray. A single-sample estimate of shrinkage in meteorological forecasting. Weather and Forecasting, 12(4):847-858 (1997).
An estimator of shrinkage based on information contained in a single sample is presented and the results of a simulation study are reported. The effects of sample size, amount, and severity of nonrepresentative data in the population, inclusion of noninformative predictors, and least (sum of) absolute deviations and least (sum of) squared deviations regression models are examined on the estimator. A single-sample estimator of shrinkage based on drop-one cross-validation is shown to be highly accurate under a wide variety of research conditions.
Molinari, R.L., D.A. Mayer, J.F. Festa, and H.F. Bezdek. Multi-year variability in the near surface temperature structure of the midlatitude western North Atlantic Ocean. Journal of Geophysical Research, 102(C2):3267-3278 (1997).
Between 1966 and 1995, subsurface temperature data have been collected in the western North Atlantic Ocean using expendable bathythermographs. Data coverage is sparse in both time and space, but evidence for decadal variability in the upper 400 m of the water column is found. The data were averaged by month onto a 2 degree of latitude by 4 degree of longitude grid. Thirty-one quadrangles in the region bounded by 17°N and 43°N and 78°W and 66°W have sufficient data to provide consistent results. Anomaly time series at 0, 100, 200, 300, and 400 m were estimated by subtracting a mean monthly climatology. The individual records were detrended and filtered to highlight the longer period signals. The analysis resulted in 25-year records (1969-1993) for study. Within the thermocline of the subtropical gyre and the Gulf Stream at 100 and 200 m, periods of predominately positive temperature anomaly end in 1971, 1982, and 1990, while periods of negative anomaly end in 1976 and 1985. Only the events ending in 1971, 1976, and 1990 are in the majority of the records at 300 and 400 m. Most of the events also appear in the sea surface temperature (SST) records, but are somewhat masked by significant noise at the surface. Meridional-vertical temperature sections through the subtropical gyre show that transitions from negative to positive anomaly events are characterized by a deepening of the isotherms throughout the section and transitions from positive to negative events by a rising of the isotherms. Significant lateral migration of the axis of the Gulf Stream, although possibly masked by the 2 degree averaging, is not necessary to explain either type of event. The transitions in the SST and 100 m temperature time series occur at essentially the same time as the transitions in an index of the North Atlantic Oscillation (NAO) that has also been detrended (i.e., 1971, 1976, 1980, 1984, 1988). The 1971, 1976, and 1988 NAO events are also observed at 300 and 400 m as described earlier. Periods of positive (negative) subsurface temperature anomaly are coincidental with periods of positive (negative) NAO index. Thus, earlier results showing connections between the NAO and western Atlantic SST at decadal time scales are now extended to at least 400 m in the water column. Trends were computed from the individual 25-year records. The trends at all depths are predominately negative (positive) north (south) of 38°N. Inferences from the horizontal distribution of the trends and results from earlier studies suggest that the 1969-1993 period may be a phase of a 30- to 50-year signal observed in the northern Atlantic since the beginning of the century.
Murillo, S.T., S.H. Houston, and M.D. Powell. Composites of surface marine observations for hurricanes during 1975-1996. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 78-79 (1997).
No abstract.
Ooyama, K.V. Footnotes to "conceptual evolution." Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 13-18 (1997).
No abstract.
Ooyama, K.V. The semi-implicit integration of a nested spectral model and the result of tests in squall-line simulation. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 531-532 (1997).
No abstract.
Parrish, J.R., and M.L. Black. The NOAA G-IV and the tropical cyclone environment. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 123-124 (1997).
No abstract.
Powell, M.D., and S.H. Houston. Surface wind fields of 1995 Hurricanes Erin, Opal, Luis, Marilyn, and Roxanne at landfall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 90-91 (1997).
No abstract.
Proni, J.R., and T.A. Nelsen. Final Report: Deep Ocean Relocation Project, Phase II: Application of acoustical and tracer methodologies to the deep ocean relocation of dredge material. Contract Report ARPAC 558.AOO, Naval Research Laboratory, Washington, D.C., 37 pp. (1997).
One of the major challenges facing the United States today is disposal of contaminated dredged material. Inexorable economic and population pressures assure that this challenge will exist for the foreseeable future. One concept for dealing with this material is deep ocean disposal or deep ocean relocation (DOR). A key component of DOR concepts is monitoring of the geosynthetic fabric containers (GFCs), which will be used to contain the dredged material, during descent through the oceanic water column to the ocean bottom. The present report deals with the use of acoustical and tracer methodologies for monitoring DOR-associated plumes. Discussed herein is the feasibility of utilizing active acoustical systems to monitor both GFCs and any escaping plumes. A discussion of nepheloid layer characteristics of relevance to GFC detection is presented.
Proni, J.R., and R.G. Williams. Acoustic measurements of currents and effluent plume dilutions in the western edge of the Florida Current. In Acoustic Remote Sensing Applications, S.P. Singal (ed.). Narosa Publishing House, New Delhi, India, 537-550 (1997).
The Southeast Florida Outfall Experiment (SEFLOE), carried out in the western boundary of the Florida Current off southeast Florida, USA, between 1988 and 1993, was the most extensive application of acoustics to wastewater effluent studies performed in the United States. The objective was to provide a scientific basis for managerial regulations for effluent discharges. This article describes the acoustical measurements to map effluent plume distributions, and the three-dimensional current regime. Current meters were installed near each outfall near the top and bottom of the water column. An acoustic Doppler current profiler (ADCP) was deployed on the bottom in the vicinity of the outfalls. Research ships towed active acoustical systems over the diffusers. Examples are given of the outfall plume distribution and the principal current regimes. A conceptual three-dimensional model is developed to compare with observed data. The acoustical measurements are shown to serve as a surrogate for the effluent constituent distributions.
Rhoads, K.P., P. Kelley, R.R. Dickerson, T.P. Carsey, and M.L. Farmer. Composition of the troposphere over the Indian Ocean during the monsoonal transition. Journal of Geophysical Research, 102(D15):18,981-18,996 (1997).
The atmosphere over the equatorial Indian Ocean is a unique environment in which to study the chemical and radiative effects of an intense source of anthropogenic emissions from the northern hemisphere directly coupled to the relatively pristine background conditions present in the southern hemisphere. As an initial investigation into the role of the intertropical convergence zone (ITCZ) on interhemispheric transport of pollutants, a number of trace atmospheric species were measured aboard the National Oceanic and Atmospheric Administration (NOAA) R/V Malcolm Baldrige between Durban, South Africa, and Colombo, Sri Lanka, from March 12 to April 22, 1995. Sharp increases in the concentrations of carbon monoxide (CO), carbon dioxide (CO2), and aerosols were associated with four distinct meteorological regimes transected by the cruise track from 33°S to 9°N. Across the ITCZ, aerosol concentrations, including non-sea-salt sulfate, nitrate, and ammonium, increased by a factor of 4. Surface zone measurements showed a latitudinal gradient with a minimum near the equator and a strong diurnal variation in the equatorial regions. The latitudinal profile of gas-phase reactive nitrogen paralleled ozone and was higher in the remote southern hemisphere than in the remote northern hemisphere. Evidence of direct anthropogenic impact on the region was observed more than 1500 km from the southern tip of India. Back trajectories, calculated with NOAA's medium range forecast data using the Hybrid Single Particle Lagrangian Integrated Trajectory (HY- SPLIT) program, identified the origin of the air mass regimes characterized by the trace gas and aerosol data. Continental emissions in the northern hemisphere were shown to have a major impact on the radiative properties and oxidizing capacity of the marine atmosphere.
Rogers, R.F. A component of tropical cyclogenesis: Convective redevelopment within a warm-core mesovortex. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Fort Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 555-556 (1997).
Theories explaining the transition of a relatively disorganized area of convection into a coherent self-sustaining system (i.e., tropical cyclogenesis) have traditionally relied upon the presence of a vortex before genesis can occur. Observations have confirmed the need for these vortices, often detecting them in radar and satellite imagery several days prior to the formation of a tropical depression. However, observational, theoretical, and numerical studies of similar systems over land have found that the initial vortices are confined to the mid-troposphere. Therefore, an important question to address is how these vortices grow down to the surface in maritime tropical environments, for it is not until the vortex is reflected at the surface that intensification can begin, provided the large-scale environment is not unfavorable. Viewing these vortices in the framework of potential vorticity (PV) allows a consideration of their penetration depth, which describes the vertical extent of the effects of the anomaly. This depth is a function of the magnitude of the PV anomaly itself--strengthening the PV anomaly will increase the penetration depth. One mechanism to explain how a vortex can grow downward is to increase the strength of the PV anomaly by initiating convection within the existing anomaly. Observations indicating successive cycles of convection before a named storm exists support this hypothesis. Understanding the mechanisms responsible for these repeated "internal" convective cycles is therefore critical to understanding whether a vortex will penetrate to the surface. Theories have been advanced in the literature as to how vortices are instrumental in initiating new convective outbreaks. However, the scale of the systems have prevented detailed observational studies which could verify or refute these hypotheses, necessitating the use of a high-resolution numerical model. In this study, a case of multiple convective regeneration by a mesoscale convective system (MCS)-generated mesovortex was investigated using the Penn State/NCAR mesoscale model MM5. The case involved a vortex that developed in an MCS in Colorado and tracked across the country over a three-day period, initiating five distinct convective cycles during its lifetime. Preliminary results of the simulation of one of the convective redevelopments will be reported, with the goal of examining and comparing to theory the processes whereby the vortex induces this redevelopment. The effect of the convective redevelopment on the vortex size and strength will also be examined.
Samsury, C.E., M.L. Black, P.P. Dodge, and R.E. Orville. Utilization of airborne and NEXRAD data in the analysis of cloud-to-ground lightning in 1995 and 1996 tropical cyclones. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 125-126 (1997).
No abstract.
Slansky, C.M., R.A. Feely, and R.H. Wanninkhof. The stepwise linear regression method for calculating anthropogenic CO2 invasion into the North Pacific Ocean. In Biogeochemical Processes in the North Pacific, S.Tsunogai (ed.). Japan Marine Science Foundation, 70-79 (1997).
No abstract.
Takahashi, T., R.A. Feely, R.F. Weiss, R.H. Wanninkhof, D.W. Chipman, S.C. Sutherland, and T.T. Takahashi. Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 difference. Proceedings, National Academy of Science, USA 94:8292-8299 (1997).
Approximately 250,000 measurements made for the pCO2 difference between surface water and the marine atmosphere, DELTApCO2, have been assembled for the global oceans. Observations made in the equatorial Pacific during El Niño events have been excluded from the data set. These observations are mapped on the global 4° × 5° grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Niño year. Monthly global distributions of DELTApCO2 have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO2 across the sea surface has been computed using DELTApCO2 distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C • yr-1 depending on different formulations used for wind speed dependence on the gas transfer coefficient. These estimates are subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of DELTApCO2 over the global oceans. Temperate and polar oceans of both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans. The Indian and Southern Oceans take up about 20% each.
Talley, L.D., and M.O. Baringer. Preliminary results from WHP sections I8N/I5E in the central Indian Ocean. Geophysical Research Letters, 24(22):2789-2792 (1997).
The R/V Knorr departed Colombo, Sri Lanka on March 10, 1995 and arrived in Fremantle, Australia on April 15, 1995 to carry out its third WOCE hydrographic leg in the Indian Ocean. Basic technical support was provided by Scripps Institution of Oceanography's Oceanographic Data Facility. Acoustic Doppler current profiler (ADCP) operations were carried out by the University of Hawaii (Firing). The basic sampling program was accomplished very smoothly. The full cruise report can be obtained from the author. The cruise track is shown in the overview figure for this newsletter, labeled I8N and I5E. The latter portion was a nominal repeat of the 1987 section (Toole and Warren, 1993). The goals of the sampling were to obtain a section through the center of the Central Indian Basin, and to repeat the crossing of the northward flow of deep water just to the west of Australia. Particular attention was paid to a potential source of deep water for the Central Indian Basin, through a sill in the NinetyEast Ridge, located at about 28°S. It was also possible to deviate from the 32°S section, and sample in the deep water south of Broken Ridge instead of along the top of the ridge. Between Broken Ridge and Australia we chose to move the section slightly north of the original position of I5E in order to resolve whether the deep flow splits around Dirck Hartog Ridge. All stations were to within 10 m of the bottom and included a 36-bottle rosette/CTD cast with lowered ADCP. A ship-mounted ADCP was operated throughout. Basic station spacing was 30 nmi, and was reduced at the equator, Sri Lankan, and Australian coasts and crossings of the NinetyEast and Broken Ridges. The CTD data stream consisted of elapsed time, pressure, two temperature channels, conductivity, oxygen, altimeter, and transmissometer signals. Water samples were collected for analyses of salt, oxygen, silica, phosphate, nitrate, and nitrite on all stations and of CFC-11, CFC-12, carbon tetrachloride, helium-3, helium-4, tritium, AMS C14, pCO2, total dissolved inorganic carbon, alkalinity, and barium on selected stations. Water sample results were compared with preliminary data acquired on prior WOCE legs and with earlier data. The comparisons are available in the cruise report and show that the WOCE data collected on legs 1 through 3 are a uniform data set; they also show significant differences from Geosecs salinity and phosphate which are attributable to measurement precision.
Thacker, W.C., and R. Lewandowicz. A comparison of low-dimensional representations of sea-surface temperature anomalies in the North Atlantic. International Journal of Climatology, 17:953-967 (1997).
Correlation-matrix principal components of North Atlantic sea-surface temperature anomalies for the interval 1950-1970 account for the anomalous variability observed during the interval 1972-1992 better than do similar numbers of covariance-matrix principal components, regional averages, or carefully selected local anomalies. When drift in the seasonal cycle is taken into account, local anomalies for the 127 6° × 4° longitude-by-latitude North Atlantic cells could be recovered with an average skill as high as 0.79. Surprisingly, skill increased monotonically with increasing numbers of principal components, and the maximum value was not obtained until 62 were used to characterize the field. Clearly, far more principal components carry useful information about local details than has been previously suspected.
Thacker, W.C., and R. Lewandowicz. Partitioning the North Atlantic into regions of similar seasonal sea-surface temperature anomalies. International Journal of Climatology, 17:3-23 (1997).
Mean sea-surface temperatures were computed within 127 6° × 4° longitude-by-latitude cells comprising most of the North Atlantic for 171 three-month seasons from 1950 through 1992, the mean seasonal cycle was removed, and cells with correlated seasonal anomalies were clustered into regions of coherent thermal behavior. Clustering algorithms consistently produced smaller thermal regions in the vicinity of the Gulf Stream, and while the regions were generally contiguous, a disjoint region was consistently found near the Grand Banks. Examining within-region variability as a function of the number of regions revealed no obvious "best" number of regions. For 26 regions, correlations between pairs of cells within a common region were typically 0.7; for 13 regions, a sizeable fraction were less than 0.5; and for only seven regions, within-region correlations were distributed fairly uniformly between 0.2 and 0.8.
Vaughan, S.L., and R.L. Molinari. Temperature and salinity variability in the Deep Western Boundary Current. Journal of Physical Oceanography, 27(5):749-761 (1997).
A ten-year time series (1984-1993) of repeat hydrographic sections from offshore Abaco Island, the Bahamas (26.5°N), is used to define the mean and time dependent characteristics of the Deep Western Boundary Current (DWBC). The DWBC flow is divided into four vertical layers based on chlorofluorocarbon (CFC) concentration and formations regions (upper layer, CFC core, theta ~ 3.9-5.0°C; second layer, classical Labrador Sea Water, theta ~ 3.2-3.9°C; third layer, CFC minimum, theta ~ 2.4-3.2°C; deepest layer, CFC core, theta ~ 1.85-2.4°C). Time series analysis of mean layer properties and their anomalies showed that the temperature and salinity of each layer did not increase or decrease monotonically with time. Variations in temperature and salinity were characterized by two to three-year period oscillations. Variability between years is illustrated by subtracting repeat sections of temperature and salinity along levels of both constant pressure and constant potential density. To determine an original water mass modification that could be responsible for the observed variability in the section differences, an analytical method, which uses both types of differencing schemes, was applied to the DWBC data. Variability in the upper layer between 1987 and 1993 was shown to originate primarily from an increased salinity of the source waters for this layer. Variability in the second layer was shown to arise from a combination of cooling and salinification. Variability in the two deepest layers seemed to be almost entirely due to vertical movement of the isopycnals. Increases in potential temperature and salinity observed in a sublayer of the second layer defined by sigma1.5 ~ 34.68-34.74 (classical Labrador Sea Water) from 1991 to 1993 was shown to be mainly the result of cooling. It is suggested that this cooling may have originally occurred in the central Labrador Sea during the period of active deep water renewal in the early 1970s.
Wanninkhof, R.H., and W.E. Asher. Use of the deliberate dual-gaseous tracer method to measure gas transfer velocities. 1997 AGU Spring Meeting, Baltimore, MD, May 27-30, 1997. Supplement to EOS, Transactions, American Geophysical Union, 78(17):S89, A42E-06 (1997).
Use of the deliberate dual-gaseous tracer method to measure gas transfer velocities, the deliberately injected gases, helium-3 (3He) and sulfur hexafluoride (SF6), have been used in the past decade to measure air-sea gas transfer velocities in coastal oceans. The method relies on knowledge of the relative exchange rates of the gases. It is successful because the exchange rates of the two gases differ by about a factor of three and because both gases can be measured at extremely low levels. Our results from two different field experiments and laboratory studies indicate that the measurements are robust and quantitative at low to intermediate wind speeds. The field results are in accordance with independently-determined gas exchange-wind speed relationships by the authors. Interpretation of the dual tracer results at higher wind speeds is problematic because of the influence of bubbles. In particular, the conversion of the 3He gas transfer results to gas transfer velocities of climate-relevant gases is uncertain. We will give an overview of the methodology, present results of two coastal gas transfer experiments, and discuss the power and shortcomings of the technique.
Wanninkhof, R.H., G. Hitchcock, W.J. Wiseman, G. Vargo, P.B. Ortner, W.E. Asher, D.T. Ho, P.Schlosser, M.-L. Dickson, R. Masserini, K. Fanning, and J.-Z. Zhang. Gas exchange, dispersion, and biological productivity on the west Florida shelf: Results from a Lagrangian tracer study. Geophysical Research Letters, 24(14):1767-1770 (1997).
A Lagrangian tracer study was performed on the west Florida shelf in April 1996 using deliberately injected trace gases. Although such studies have been performed previously, this work is the first where the deliberate tracers, in conjunction with carbon system parameters, are used to quantify changes in water column carbon inventories due to air-sea exchange and net community metabolism. The horizontal dispersion and the gas transfer velocity were determined over a period of 2 weeks from the change in both the concentrations and the concentration ratio of the two injected trace gases, sulfur hexafluoride (SF6) and helium-3 (3He). Horizontal diffusion estimates were about an order of magnitude greater than calculated from empirical equations, and the difference is attributed to vertical shear. The second moment of the patch grew to 1.6 × 103 km2 over a period of 11 days. The gas transfer velocity, normalized to CO2 exchange at 20°C, was 8.4 cm hr-1 at an average wind speed, U10, of 4.4 m s-1 for the duration of the experiment, which is in good agreement with empirical estimates. Remineralization rates exceeded productivity, causing an increase in dissolved inorganic carbon of about 1 µmol kg-1 day-1 in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to community remineralization and 20% due to invasion of atmospheric CO2. This net remineralization is in accordance with in situ and on-deck incubation experiments.
Weisberg, R.H., and C. Wang. A western Pacific oscillator paradigm for the El Niño-Southern Oscillation. Geophysical Research Letters, 24:779-782 (1997).
A data-based hypothesis is presented on the mechanism of the El Niño-Southern Oscillation (ENSO), a major determinant of interannual global climate variability. The hypothesis emphasizes the importance of off-equator sea surface temperature and sea level pressure variations west of the dateline for initiating equatorial easterly winds over the far western Pacific. These winds compete with westerly winds over the equatorial central Pacific enabling the coupled ocean-atmosphere system to oscillate. Consistent with this hypothesis, an analogical oscillator model is constructed that produces ENSO-like oscillations. The proposed mechanism differs from the delayed oscillator paradigm in that wave reflection at the western boundary is not a necessary condition for the coupled ocean-atmosphere system to oscillate.
Weisberg, R.H., and C. Wang. Slow variability in the equatorial west-central Pacific in relation to ENSO. Journal of Climate, 10(8):1998-2017 (1997).
Six years of upper ocean velocity, temperature and surface wind data collected in the west-central Pacific at 0°, 170°W reveal a slow ocean dynamical mode associated with the El Niño-Southern Oscillation (ENSO). Latent and sensible heat flux calculations using the basin-wide Tropical Atmosphere Ocean (TAO) array data show a coincident, slow ocean-atmosphere thermodynamical mode. Beginning with the La Niña conditions in 1988 through the peak El Niño conditions in 1992, the Equatorial Undercurrent (EUC) speed decreased along with the surface zonal wind stress and the zonal pressure gradient. Simultaneous with these were increasing trends in the Richardson number above the EUC core and in sea surface temperature (SST). After peak warming was achieved the variations in all of these quantities reversed in a movement toward their previous La Niña conditions. As this evolved within the ocean the sensible and latent heat fluxes increased with large values emanating eastward from the western Pacific. The largest interannual perturbations, then, for both the surface momentum and heat flux quantities during this recent ENSO cycle were within the west-central Pacific, the transition region between the warmest waters found in the western Pacific warm pool and the coldest waters found in the eastern Pacific cold tongue. The observed ocean and atmosphere variability represents a positive feedback. This raises a question about the origin of negative feedback that is necessary for the coupled system to oscillate. Arguing from the standpoint of a Gill atmosphere and observed SST/sea level pressure correlation patterns, the paper draws a connection between condensation heating in the equatorial west-central Pacific and easterly winds over the equatorial western Pacific during the mature phase of El Niño. The formation of such easterlies by ocean-atmosphere coupling over the western Pacific is hypothesized as providing a negative feedback for reversing the sign of anomalous SST in the equatorial central Pacific. This mechanism may complement, but it is different from, the delayed oscillator mechanism for ENSO.
Willis, P.T., P.P.Dodge, F.D. Marks, D. Smith, and D. Churchill. Evaluation of the accuracy of the NEXRAD radar rainfall estimates in tropical summer convective rainfall over the Everglades/Florida Bay. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, Boston, 679-680 (1997).
No abstract.
Willoughby, H.E. More about hurricane eye thermodynamics. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, May 19-23, 1997, Ft. Collins, Colorado. American Meteorological Society, Boston, 96-97 (1997).
No abstract.
Wilson, W.D., and W.E. Johns. Velocity structure and transport in the Windward Islands Passages. Deep Sea Research, 44(3):487-520 (1997).
During 1991-1994, repeated measurements of current structure and water mass properties were made in the major southern passages to the Caribbean Sea between Trinidad and Dominica. A total of 10 cruises were performed in different seasons, consisting primarily of serial station occupations in the Grenada, St. Vincent, St. Lucia, and Dominica Passages. This data set is by far the most comprehensive available in these passages and better determines the mean flow and range of variability than do previous studies. The flow structure in these passages is characterized by a strong and relatively stable inflow above the thermocline (approximately the upper 100 m), and a more highly variable flow regime within and below the thermocline. Typical near-surface inflow velocities in Grenada and St. Vincent passages were 40-60 cm/s, with maximum observed currents of 90 cm/s. Frequently, counterflows were observed below this surface layer flowing out of the Caribbean, trapped to the southern side of the passages. This subsurface counterflow appeared to be strongest and most prevalent in Grenada Passage, where outflow speeds as large as 30 cm s-1 were observed.
Yvon-Lewis, S.A., and J.H. Butler. The oceanic lifetime and budget of atmospheric methyl bromide. 1997 AGU Spring Meeting, Baltimore, MD, May 27-30, 1997. Supplement to EOS, Transactions, American Geophysical Union, 78(17):S90, A42E-12 (1997).
Methyl bromide (CH3Br) has become of interest recently because of its involvement in the depletion of stratospheric ozone. However, unlike the chlorofluorocarbons, which are entirely anthropogenic, methyl bromide has both natural and anthropogenic sources. At ~10 parts per trillion in the troposphere, methyl bromide is believed to be the single largest contributor of stratospheric Br. Once in the stratosphere, Br is estimated to be 40 to 100 times more effective in depleting stratospheric ozone than chlorine. Known sinks for atmospheric methyl bromide include photolysis at high altitudes and reaction with OH, uptake by the oceans and loss to soils. In the ocean, dissolved methyl bromide is degraded via hydrolysis and chloride substitution. Recently, it has been shown that methyl bromide also undergoes biological degradation, which may be due to bacterial uptake. Results from field studies, showing large undersaturations in polar and sub-polar waters, also suggest an additional, perhaps biological, sink mechanism. Previous calculations of the partial atmospheric lifetime of methyl bromide with respect to oceanic degradation have only considered the chemical degradation mechanisms. We use a global, coupled ocean-atmosphere box model to examine the potential effect that biological degradation and its distribution can have on the lifetime of atmospheric methyl bromide. The results of this study show that both the value of the oceanic degradation rate constant and its global distribution are important in determining the calculated atmospheric lifetime. The "best" estimate of the partial lifetime of atmospheric methyl bromide with respect to oceanic loss now comes to 1.7-1.8 y with a full possible range of 0.85-3.7 y, which, together with other, non-oceanic losses, yields a total atmospheric lifetime of 0.7 y with a range of 0.5-0.9 y due only to uncertainty in the oceanic lifetime. A subsequent revision of the budget for atmospheric methyl bromide indicates that a source or sources of methyl bromide totaling 90 to Gg/y (1/2 of the total sink strength) has not yet been identified.
Yvon-Lewis, S.A., and J.H. Butler. The potential effect of oceanic biological degradation on the lifetime of atmospheric CH3Br. Geophysical Research Letters, 24(10):1227-1230 (1997).
We use a global, coupled ocean-atmosphere box model to examine the potential effect that biological degradation and its distribution can have on the lifetime of atmospheric CH3Br. The results of this study show that both the value of the oceanic degradation rate constant and its global distribution are important in determining the calculated atmospheric lifetime. The "best" estimate of the partial lifetime of atmospheric CH3Br with respect to oceanic loss now comes to 1.7-1.8 y with a full possible range of 0.85-3.7 y, which, together with other, non-oceanic losses, yields a total atmospheric lifetime of 0.7 y (0.5-0.9 y). A subsequent revision of the budget for atmospheric CH3Br indicates that estimated sinks of CH3Br today exceed estimated sources by about 90 Gg y-1.
Yvon-Lewis, S.A., and J. H. Butler. The uptake of atmospheric trace gases by the ocean. AGU 1997 Fall Meeting, San Francisco, CA, December 8-12, 1997. Supplement to EOS, Transactions, American Geophysical Union, 78(46):F93, OS21D-05 (1997).
A global ocean-atmosphere model was developed to study the uptake of CH3Br by the oceans. With this model we significantly reduced the uncertainties in the partial atmospheric lifetime of CH3Br with respect to its oceanic uptake (to, CH3Br) (Yvon and Butler, Geophys. Res. Lett., 23(1), 53-56, 1996). Results from this model have also demonstrated that the distribution of the oceanic degradation term is important in caculating the partial atmospheric lifetime of a trace gas with respect to oceanic loss processes and, consequently, its total atmospheric lifetime (Yvon-Lewis and Butler, Geophys. Res. Lett., 24(10):1227-1230, 1997). It is now possible to determine the partial atmospheric lifetime with respect to oceanic degradation of any trace gas for which the oceanic degradation rate constant can be calculated. The results from model runs for several trace gases including, CH3Br, CH3Cl, and CH3I, suggested that the total atmospheric lifetimes of these trace gases should be reduced by 38%, ~3%, and ~2%. These reductions are due solely to the inclusion of the oceanic chemical degradation loss process. When adapted for CH3CCl3, the model results reduced an earlier estimate for the partial atmospheric lifetime of this trace gas with respect to oceanic uptake by 31%. For some gases, these reductions are even greater when biological removal is included. The results from the study of these and other gases, including some HCFCs, will be presented.
Zhang, J.-Z. Distinction and quantification of carry-over and sample interaction in gas segmented continuous flow analysis. Journal of Automatic Chemistry, 19(6):205-212 (1997).
The formulae for calculation of carry-over and sample interaction are derived for the first time in this study. A scheme proposed by Thiers et al. (two samples of low concentration followed by a high concentration sample and low concentration sample) is verified and recommended for the determination of the carry-over coefficient. The derivation demonstrates that both widely used schemes of a high concentration sample followed by two low concentration samples, and a low concentration sampled followed by two high concentration samples, actually measure the sum of the carry- over coefficient and sample interaction coefficient. A scheme of three low concentration samples followed by a high concentration sample is proposed and verified for determination of the sample interaction coefficient. Experimental results indicate that carry-over is a strong function of cycle time and a weak function of ratio of sample time to wash time. Sample dispersion is found to be a function of sample time. Fitted equations can be used to predict the carry-over, absorbance, and dispersion given sample times, and wash times for an analytical system. Results clearly show the important role of intersample air segmentation in reducing carry-over, sample interaction, and dispersion.
Zhang, J.-Z., and G.A. Berberian. Determination of dissolved silicate in estuarine and coastal waters by gas segmented continuous flow colorimetric analysis. In Methods for the Determination of Chemical Substances in Marine and Estuarine Environmental Matrices, Supplement 1. Environmental Protection Agency, EPA 600/R-97072, 366.0-1-366.0-2 (1997).
No abstract.
Zhang, J.-Z., P.B. Ortner, and C.J. Fischer. Determination of nitrite in estuarine and coastal waters by gas segmented continuous flow colorimetric analysis. In Methods for the Determination of Chemical Substances in Marine and Estuarine Environmental Matrices, Supplement 1. Environmental Protection Agency, EPA 600/R-97072, 353.4-1-353.4-2 (1997).
No abstract.
Zhang, J.-Z., P.B. Ortner, C.J. Fischer, and L.D. Moore. Determination of ammonia in estuarine and coastal waters by gas segmented continuous flow colorimetric analysis. In Methods for the Determination of Chemical Substances in Marine and Estuarine Environmental Matrices, Supplement 1. Environmental Protection Agency, EPA 600/R-97072, 349.0-1-349.0-2 (1997).
No abstract.
**1996**
Asher, W.E., and R.H. Wanninkhof. The effect of breaking waves on the analysis of dual-tracer gas exchange measurements. Proceedings, Third International Symposium on Air-Water-Gas Transfer, Heidelberg, Germany, July 24-27, 1995. Aeon Verlag and Studio, 517-528 (1996).
The dual-gaseous tracer technique is a new and reliable method for directly measuring air-sea gas transfer velocities. However, analysis of data from these experiments requires the assumption that the dependence of the transfer velocity on molecular diffusivity is constant. Modeling and laboratory studies indicate that this could be an invalid assumption when gas transfer through bubbles generated by breaking waves is a significant portion of the sea-to-air gas flux. Here, a parameterization of the transfer velocity in terms of wind speed and fractional area whitecap coverage is developed that includes the effects of bubble-mediated exchange processes. It is shown that transfer velocities estimated using this parameterization are consistent with available oceanic gas exchange measurements. The parameterization is then used to investigate the consequences of including whitecap-related transfer processes in the analyses of data derived from dual-tracer experiments. In the case of the tracer pair, sulfur hexafluoride and helium-3, it is shown that assuming a constant diffusivity dependence underestimates transfer velocities of helium-3 by up to 20% at high wind speeds. It is also shown that using the parameterization to normalize the transfer velocity for helium-3 to carbon dioxide results in a 6% decrease in the estimated transfer velocity compared to constant-diffusivity dependence estimates.
Asher, W.E., B.J. Higgins, L.M. Karle, P.J. Farley, C.R. Sherwood, W.W. Gardiner, R.H. Wanninkhof, H. Chen, T.P. Lantry, M. Steckley, E.C. Monahan, Q. Wang, and P.M. Smith. Measurements of gas transfer, whitecap coverage, and brightness temperature in a surf pool: An overview of WABEX-93. Proceedings, Third International Symposium on Air-Water-Gas Transfer, Heidelberg, Germany, July 24-27, 1995. Aeon Verlag and Studio, 205-216 (1996).
Toward a method for estimating air-sea gas transfer velocities, kL, from remote measurements of fractional area whitecap coverage, WC, a gas exchange experiment was conducted in an outdoor surf pool during the October 1993 Wave Basin Experiment (WABEX-93). For both spilling and plunging breaking waves, measurements were made of WC; air-water fluxes of carbon dioxide, helium, nitrous oxide, oxygen, and sulfur hexafluoride; microwave brightness temperature of the water surface, sigma; aqueous-phase turbulence velocities; and bubble size spectra. The data show that kL, scales as a common, linear relation with WC for both spilling and plungin breaking waves. The gas transfer data have been used to develop an empirical parameterization for predicting kL from WC, Schmidt number, and solubility.
Bishop, J.R., and W.P. Dammann. Cabling and mooring a remotely operated ADCP for real-time data acquisition. Proceedings, Ocean 96 MTS/IEEE, Ft. Lauderdale, Florida, September 23-26, 1996. Marine Technological Society, Vol. 1, 116-119 (1996).
As part of a joint U.S. Army Corps of Engineers, Port of Miami, State of Florida, U.S. EPA, University of Miami (Rosenstiel School), National Oceanic and Atmospheric Administration (NOAA) offshore dredged material disposal program, a real time current monitoring system (RTCMS) was designed by the Ocean Acoustics Division (OAD) of the Atlantic Oceanographic and Meteorological Laboratory (AOML) for deployment offshore of Miami. This system consists of an acoustic Doppler current profiler (ADCP) moored on the ocean floor at a point southwest of the Offshore Dredge Material Disposal Site (ODMDS) and cabled to a nearshore site. The nearshore site chosen was a range marker at the Miami Harbor entrance. From the range marker the data is transmitted via radio modem to the NOAA/AOML/OAD offices on Virginia Key. The high current regime and the requirement for periodic maintenance of the ADCP added unique challenges to the design of the cable and mooring system. Cable selection and routing was performed so as to minimize risk of damage due to recreational activities. For purposes of deployment and serviceability, the cabling and mooring system was divided into three sections. The first section extends from the range marker to a common point in 60 feet of water. The cable was laid and anchored in sandy areas where possible in order to avoid reef impact. The second section connects the common point to the first mooring point at a depth of 400 feet. The final section couples the first mooring point to the ADCP mooring point. The ADCP mooring section consists of a two-point moor with a subsurface center float to suspend the cable above the bottom. The deployment of the system was accomplished in two days on board a 95-foot research vessel equipped with a stern mounted A-frame and deck winches. Divers were utilized to attach the cable to anchors in the shallow water sections, and to inspect the cable after installation.
Black, M.L., R.W. Burpee, and F.D. Marks. Vertical motion characteristics of tropical cyclones determined with airborne Doppler radial velocities. Journal of the Atmospheric Sciences, 53(13):1887-1909 (1996).
Vertical motions in seven Atlantic hurricanes are determined from data recorded by Doppler radar on research aircraft. The database consists of Doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through hurricane centers. The vertical motions are estimated throughout the depth of the troposphere from the Doppler velocities and bulk estimates of particle fallspeeds. Portions of the flight tracks are subjectively divided into eyewall, rainband, stratiform, and "other" regions. Characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire data set and each of the four regions. In all of the regions, more than 70% of the vertical velocities range from -2 to 2 m s-1. The broadest distribution of vertical motion is in the eyewall region where ~5% of the vertical motions are >5 m s-1. Averaged over the entire data set, the mean vertical velocity is upward at all altitudes. Mean downward motion occurs only in the lower troposphere of the stratiform region. Significant vertical variations in the mean profiles of vertical velocity and reflectivity are discussed and related to microphysical processes. In the lower and middle troposphere, the characteristics of the Doppler-derived vertical motions are similar to those described in an earlier study using flight-level vertical velocities, even though the horizontal resolution of the Doppler data is ~750 m compared to ~125 m from the in-situ flight-level measurements. The Doppler data are available at higher altitudes than those reached by turboprop aircraft and provide information on vertical as well as horizontal variations. In a vertical plane along the radial flight tracks, Doppler up- and downdrafts are defined at each 300-m altitude interval as vertical velocities whose absolute values continuously exceed 1.5 m s-1, with at least one speed having an absolute value greater than 3.0 m s-1. The properties of the Doppler drafts are lognormally distributed. In each of the regions, updrafts outnumber downdrafts by at least a factor of 2 and updrafts are wider and stronger than downdrafts. Updrafts in the eyewall slope radially outward with height and are significantly correlated over larger radial and vertical extents than in the other three regions. If the downwind (tangential) slope with height of updrafts varies little among the regions, updrafts capable of transporting air with relatively large moist static energy from the boundary layer to the upper troposphere are primarily in the eyewall region. Downdrafts affect a smaller vertical and horizontal area than updrafts and have no apparent radial slope. The total upward or downward mass flux is defined as the flux produced by all of the upward or downward Doppler vertical velocities. The maximum upward mass flux in all but the "other" region is near 1-km altitude, an indication that boundary-layer convergence is efficient in producing upward motion. Above the sea surface, the downward mass flux decreases with altitude. At every altitude, the total net mass flux is upward, except for the lower troposphere in the stratiform region where it is downward. Doppler-derived up- and downdrafts are a subset of the vertical velocity field that occupy small fractions of the total area, yet they contribute a substantial fraction to the total mass flux. In the eyewall and rainband regions, for example, the Doppler updrafts cover less than 30% of the area but are responsible for >75% and >50% to the total upward mass flux, respectively. The Doppler downdrafts typically encompass less than 10% of the area yet provide ~50% of the total downward mass flux in the eyewall and ~20% of the total downward flux in the rainband, stratiform, and "other" regions.
Black, M.L., S.H. Houston, R.G. Carter, A.B. Damiano, and R. McNamara. AFRES-NOAA flight-level data comparisons. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.8 (1996).
A coordinated flight between an Air Force Reserve (AFRES) aircraft and both National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft was conducted on 24 October 1995. This mission resulted from a recommendation made at the 49th Interdepartmental Hurricane Conference. The AFRES and NOAA aircraft each recorded, at 1-sec intervals, the standard suite of flight-level meteorological data (winds, temperature, dew point, pressure) and navigational information (e.g., position, true air speed, heading, etc.). The data were collected during clear and light-wind conditions along the Florida west coast, north of Tampa. During portions of the flight, the WP-3D aircraft flew in close formation and executed calibration maneuvers. The NOAA and AFRES aircraft conducted "fly-bys" adjacent to an Air Force Aerostat balloon which was carrying a NOAA calibrated instrument package. The balloon approaches were at altitudes ranging from 1,000 to 15,000 feet and provide the basis for the intercomparisons. Comparisons between the flight-level data collected from the balloon, NOAA, and AFRES aircraft will be presented. Recommendations, if any, will be made to improve the data collection, processing, and strategies for future intercomparison flights. Additionally, the calibration information gained from this flight will be used to investigate the data quality from concurrent flights into tropical cyclones by both the NOAA and AFRES aircraft this past hurricane season. One or more examples of flight-level data collected in hurricane flights will be presented.
Black, P.G., J.R. Proni, J.C. Wilkerson, and C.E. Samsury. Oceanic rainfall detection and classification in tropical and subtropical mesoscale convective systems using underwater acoustic methods. Monthly Weather Review, 125(9):2014-2042 (1996).
Measurements of the underwater sound produced by rain were made at three U.S. coastal sites in a study to determine the feasibility and limitations of the acoustic detection and classification of rainfall over water. In the analysis of the rain sound spectra, concurrent radar reflectivity observations were used to identify convective and stratiform regions of the precipitating clouds overhead. It was found that acoustic classifications of rainfall as to type, based on information in the 4-30 kHz frequency band, were in general agreement with radar-derived classifications. The classification technique is based on use of an acoustic discriminant, DR, defined as the difference in average spectral levels between the 10-30 kHz and 4-10 kHz bands. A high correlation was found between sound spectrum levels (in dB) in the 4-10 kHz frequency band and radar reflectivity, dBZ, suggesting the possible use of the 4-10 kHz band sound spectral level as a classification tool in the same way that radar reflectivity is used in classifying precipitation. Our results demonstrate the feasibility of the acoustic method for detecting and classifying rainfall at sea.
Black, P.G., M.D. Powell, S.H. Houston, M.L. Black, and M. Hopkins. An air-deployable drifting buoy observing system for monitoring hurricane surface structure in critical air-sea interaction and landfall situations. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.5 (1996).
The 1995 hurricane season illustrated the need for accurate in-situ measurement of air-sea interaction processes and the importance they play in governing intensity estimation, as well as the need for in-situ surface wind observations near the point of hurricane landfall. A long-lasting cold pool in the North Atlantic SSTs, generated by a stationary Hurricane Felix, may have contributed to the weakening of Hurricane Luis, as Luis' cold wake may, in turn, have contributed to the weakening of Hurricane Marilyn. Hurricane Opal's rapid intensification occurred over a warm Loop Current eddy and its rapid weakening was accompanied by SST decreases along the coast ahead of the storm. A nearly-stationary Hurricane Roxanne gradually weakened in the Bay of Campeche in response to strong self-induced SST cooling. Strong air-sea stability offshore from Opal's landfall, together with a single strong eyewall convective cell, produced surface winds that were difficult to estimate from 700 mb reconnaissance data. To address this need, the first operational test of an air-deployed drifting buoy array was carried out during the 1995 season in Hurricanes Luis and Marilyn for the purpose of (1) testing the logistical feasibility of deploying buoy surface sensors in the path of a hurricane, (2) relaying data via satellite in real time to National Hurricane Center (NHC) forecasters and the National Meteorological Center (NMC) data base, and (3) testing their survivability. On 8 September 1995 from 20-21 UTC, three wind speed/direction (WSD) buoys and seven mini-drifting buoys (CLODS) were deployed 300 nmi ahead of Hurricane Luis. The deployment was conducted by the Air Force Reserve 53rd Weather Reconnaissance Squadron from a WC-130 aircraft. One WSD wind sensor failed and three CLODS failed on deployment. Seven buoys measured pressure, air, and sea temperature at hourly intervals, surviving 50 ft seas. The eye crossed the line near 12 UTC, 9 September, passing over one WSD and one CLOD, which reported minimum pressures within 1 mb of that reported by AFRES dropsonde observations. The highest 10-m, sustained wind estimated from the 1-m buoy data was 80 kt with a peak gust of 110 kt. Hurricane forecasters used the data to estimate the radius of gale force and 50 kt winds, which impacted warnings for Bermuda. Information on the extent of surface winds was also passed on to Canadian forecasters concerned about the subsequent landfall in Newfoundland. The data were coded and processed by NMC, appearing on most surface charts. Some coding errors occurred, which are now being remedied. The buoys also observed a 3.5°C drop in SSTs to the right of the storm. The experiment was repeated in Hurricane Marilyn on 18 September 1995 from 1430 to 1530 UTC, with AFRES aircraft deploying three additional WSD buoys and eight CLODs approximately 250 nmi ahead of the storm in a region just south of the Luis buoy locations. A WSD wind vane was damaged on deployment and five of the eight CLODs failed. This still provided NHC forecasters with an unprecedented array of six WSD buoys (four with working anemometers) and seven CLODs for a total of 13 platforms. Of these, three WSD and three CLODs passed through the eye. The lowest measured pressure was about 5 mb higher than reported by NOAA and AFRES aircraft. These data allowed forecasters to discern the surface hurricane, storm, and gale force wind distribution with great precision. It also showed that the cold wake left by Luis a week earlier was strong and covering the eastern semi-circle of Marilyn as it traveled parallel to Luis' track, a factor which may have been responsible for the storm weakening on 19 September. A NOAA WP-3D flight was flown on 19 September to correspond with the time that the storm was over the buoy array. Three additional CLODs equipped with acoustic sensors for wind speed and rain rate detection were deployed along with 35 AXBTs to sample SST and mixed layer depth at fine spatial resolution. These two experiments showed that drifting buoys can be successfully deployed ahead of a hurricane with sufficient accuracy to provide detailed surface wind fields, estimate the surface pressure distribution, and monitor the SST field for possible effects on storm intensity in a real time mode that can enhance forecaster confidence in estimating wind distribution radii. As such, it appears to be a useful tool in critical landfall or strong air-sea interaction situations.
Blackwelder, P., T. Hood, C. Alvarez-Zarikian, T.A. Nelsen, and B. McKee. Benthic foraminifera from the NECOP study area impacted by the Mississippi River plume and seasonal hypoxia. Quaternary International, 31:19-36 (1996).
Benthic foraminifera influenced by the Mississippi River plume and seasonal hypoxia were assessed from Louisiana inner-continental shelf sediment samples. Surface foraminifera assemblages were representative of in-situ populations as established by staining techniques. Community diversity and richness/evenness analyses indicate three regimes: high stress (sediment dominated), intermediate stress (hypoxia dominated), and low stress (low sediment accumulation/high oxygen). Epistominella vitrea and Buliminella morgani are useful tracers of rapid sediment accumulation rate and hypoxia. A bottom-water productivity signal west of the Mississippi River plume is indicated by benthic and planktic foraminifera abundance peaks. Surface benthic foraminifera trends are utilized to interpret changes in historical community structure from hypoxic-area sediments deposited since the turn of the century. The hypoxia-tolerant species Buliminella morgani increases markedly upcore, while hypoxia-intolerant species decrease or disappear. Diversity and dominance trends temporally correspond to a dramatic increase in U.S. fertilizer application. The results of this study have application to paleoenvironmental research spanning longer geologic timescales. The documented relationships between population structure and stressors in river-dominated marine systems may provide a useful analog for recognition of these conditions in the fossil record.
Bufkin, J.M., and U. Rivero. Real-time digital data communication system for a remotely operated ADCP. Proceedings, Ocean 96 MTS/IEEE, Ft. Lauderdale, Florida, September 23-26, 1996. Marine Technological Society, Vol. 1, 72-75 (1996).
An acoustic Doppler current profiler (ADCP) is moored adjacent to the Miami Offshore Dredged Material Disposal Site to monitor in real-time ocean currents during dredge disposal operations. The mooring site is an active shipping channel which would present a low survivability rate for surface radio communications buoys. There are also environmentally sensitive areas which prevent the direct cabling of the ADCP into shore. By combining hardwired cable and radio transmission techniques, a remote telemetry system was designed and installed at a fixed navigational marker that provides system reliability and a stable platform to work from. Most ADCP systems that provide real-time data are cabled back to a recording site which also supplies power to the ADCP down the cable. A self-powered ADCP was utilized since cabling to shore was not a viable option. This presented problems in powering the interface to the data cable and had to be overcome. Powering down the cable was limited since the telemetry unit at the other end of the cable also had to be battery powered. From the ADCP a cable was laid to the closest fixed workable point, which happened to be a navigation marker at the entrance to the Port of Miami. This cable extends approximately three miles, and proper cable drivers had to be located that would deal with this distance. At the navigation marker, a telemetry unit was designed that buffers the received data from the ADCP cable by using a micro controller, and then transmits this data by a UHF radio modem. The data is received and stored by computer at our laboratory approximately five miles away. Power consumption proved to be a major concern, since there are no available power sources at the navigation marker. The ADCP operates from its own internal battery pack, and the telemetry unit was designed to operate from batteries with solar panels to supplement the power. It is able to operate for months unattended. The system was installed in June of 1995, and has since proved to be an extremely reliable system. The design of the telemetry system has proven to be robust, and lends itself to future experiments where data must be transmitted from a remote site.
Burpee, R.W., J.L. Franklin, S.J. Lord, R.E. Tuleya, and S.D. Aberson. The impact of Omega dropwindsondes on operational hurricane track forecast models. Bulletin of the American Meteorological Society, 77(5):925-933 (1996).
Since 1982, the Hurricane Research Division (HRD) has conducted a series of experiments with research aircraft to enhance the number of observations in the environment and the core of hurricanes threatening the United States. During these experiments, the National Oceanic and Atmospheric Administration WP-3D aircraft crews release Omega dropwindsondes (ODWs) at 15-20 min intervals along the flight track to obtain profiles of wind, temperature, and humidity between flight level and the sea surface. Data from the ODWs are transmitted back to the aircraft and then sent via satellite to the Tropical Prediction Center and the National Centers for Environmental Prediction (NCEP), where the observations become part of the operational database. This paper tests the hypothesis that additional observations improve the objective track forecast models that provide operational guidance to the hurricane forecasters. The testing evaluates differences in forecast tracks from models run with and without the ODW data in a research mode at HRD, NCEP, and the Geophysical Fluid Dynamics Laboratory. The middle- and lower-tropospheric ODW data produce statistically significant reductions in 12-60 h mean forecast errors. The error reductions, which range from 16% to 30%, are at least as large as the accumulated improvement in operational forecasts achieved over the last 20-25 years. This breakthrough provides strong experimental evidence that more comprehensive observations in the hurricane environment and core will lead to immediate improvements in operational forecast guidance.
Carsey, T.P., and M.L. Farmer. Nitrogen oxides in the Pacific MBL During ACE-1. 1996 AGU Fall Meeting, San Francisco, CA, December 15-19, 1996. Supplement to EOS, Transactions, American Geophysical Union, 77(46):F76, A12A-16 (1996).
Nitric oxide, nitrogen dioxide, NOy, and PAN (peroxyacetyl nitrate) were measured in the Pacific Ocean boundary layer aboard the R/V Discoverer during the Pacific transit cruise, October 11-November 10, 1995, Seattle to Hobart, Tasmania, and during the ACE-1 cruise, November 15-December 13, 1995, south and east of Tasmania. NO, NO2, and NOy measurements employed a chemiluminescent NO detector with appropriate conversion; calibration employed standard gases (NO) or calibrated permeation devices (NO2, NOy). PAN measurements were made with an automated gas chromatograph utilizing a packed column and electron capture detection; calibration was performed using PAN generated by photolytic reaction of acetone with O2 and NO2, molybdenum catalyst conversion and chemiluminescent analysis. Mixing ratios of measured nitrogen species will be discussed in relation to meteorological conditions and concentrations of other relevant chemical species.
Carsey, T.P., M.L. Farmer, C.J. Fischer, A. Mendez, V.B. Ross, M. Springer-Young, and M.P. Zetwo. Atmospheric chemistry measurements during Leg 4, 1993 North Atlantic cruise, R/V Malcolm Baldrige. NOAA Data Report, ERL AOML-28(PB96-162581), 137 pp. (1996).
During September 1993, AOML conducted a multi-leg cruise aboard the Malcolm Baldrige in the North Atlantic from Iceland to Miami, Florida. The objective was to evaluate the distribution and transport of tropospheric ozone and ozone precursors in the North Atlantic. The investigation was associated with the North Atlantic Regional Experiment (NARE), a component of the International Global Atmospheric Chemistry (IGAC) project. The cruise track traversed three diverse wind and chemical regimes: pristine polar westerlies, polluted westerlies, and marine southeasterlies. Along this cruise track a large suite of chemical and meteorological data were measured. These included ozone, carbon monoxide in air and surface water, NO, NO2, Noy, peroxyacetyl nitrate, SO2, non-methane hydrocarbons (NMHC), and aerosols. The measurements and instrumentation are described in this data report.
Cione, J.J., and S. Raman. Surface cyclone intensity forecasting within the mid-Atlantic Gulf Stream locale using pre-storm low level baroclinic indices. Preprints, AMS Conference on Coastal Oceanic and Atmospheric Prediction, Atlanta, Georgia, January 28-February 2, 1996. American Meteorological Society, Boston (1996).
No abstract.
Cione, J.J., and S. Raman. The impact of storm track on low level mesocyclonic intensification and storm structure within the Gulf Stream locale. Preprints, AMS Conference on Coastal Oceanic and Atmospheric Prediction, Atlanta, Georgia, January 28-February 2, 1996. American Meteorological Society, Boston (1996).
No abstract.
Clark, J.F., P. Schlosser, H.J. Simpson, M. Stute, R.H. Wanninkhof, and D.T. Ho. Relationship between gas transfer velocities and wind speeds in the tidal Hudson River determined by the dual tracer technique. Proceedings, Third International Symposium on Air-Water-Gas Transfer, Heidelberg, Germany, July 24-27, 1995. Aeon Verlag and Studio, 785-799 (1996).
Gas transfer velocities were determined using the dual tracer technique (3He and SF6) for two 40-60 km reaches of the tidal Hudson River. The experiments were performed near Poughkeepsie, New York in 1993 and near Catskill, New York in 1994. During both experiments wind speeds were measured above the river. The shape of daily axial SF6 distributions and the evolution of peak concentrations followed patterns predicted by the one-dimensional advection-diffusion equation. Mean gas transfer velocities calculated from the 1994 data using the temporal change in SF6 inventory (4.6 ± 0.4 cm hr-1) and the tracer ration (5.3 ± 0.2 cm hr-1) are in good agreement, suggesting that the dual tracer technique yields reasonable results. The relationships between gas transfer velocity and wind speeds found during these experiments are very similar to those observed previously for lakes, suggesting that wind is the primary source of surface turbulence in these reaches of the tidal Hudson River. The results of the 1993 and 1994 experiments agree very well, indicating that the local geometry of the river is of secondary importance.
Claud, C., K.B. Katsaros, N.M. Mognard, and N.A. Scott. Comparative satellite study of mesoscale disturbances in polar regions. Global Atmosphere and Ocean System, 4(2-4):233-273 (1996).
Mesoscale disturbances in cold air outbreaks (polar lows) occur quite often in high latitude areas of both hemispheres. The lack of conventional meteorological observations over these areas implies heavy reliance on satellite remotely-sensed information. Six lows which formed at different places around the world have been examined in order to derive their dominant features and environments. For this purpose, the combination of a vertical atmospheric sounder (TOVS), a microwave imager (SSM/I) and an altimeter (Geosat) has been used. While most retrieved atmospheric parameters are quite variable from case to case, a number of general statements about polar lows can be made: they all occur in areas of cold and dry air outbreaks; in agreement with the low integrated water vapor content values, the amount of liquid precipitation is very light, and the cloud liquid water content moderate; both SSM/I and Geosat indicate that surface wind speeds in the cloud bands forming the developed systems are of strong to gale force, while the cloud-free center is characterized by low values. Strongest winds and largest wave heights occur on the southwestern flank of the lows in the northern hemisphere and on the north flank in the southern hemisphere.
Dagg, M.J., E.P. Green, B.A. McKee, and P.B. Ortner. Biological removal of fine grain lithogenic particles from a large river plume. Journal of Marine Research, 54:149-160 (1996).
The pelagic tunicate, Oikopleura dioica, feeds by non-selectively filtering particles in the size range of 0.1-10 µm. On the continental shelf of the northern Gulf of Mexico, dominated by the Mississippi River, particulate matter in this size range contains not only microplankton but also numerous lithogenic particles. When O. dioica is abundant it dominates total zooplankton grazing. By ingesting small (<2 µm) lithogenics that effectively do not sink as separate particles, and repackaging them into larger, more rapidly sinking particles, it also significantly alters the fates of these materials and the properties of the surface waters in and around the discharge plume of the Mississippi River.
Dammann, W.P., J.M. Bufkin, U. Rivero, S.J. Stamates, and J.R. Proni. Near real-time observations of offshore current profiles and their application to dredge material disposal activities. Proceedings, Eco-Informa '96: Global Networks for Environmental Information, Lake Buena Vista, FL, November 4-7, 1996. Environmental Research Institute of Michigan, Vol. 11, 563-568 (1996).
An acoustic Doppler current profiler (ADCP) is presently located approximately 7 km east of the Miami Harbor entrance at approximately 130 m depth. This device measures profiles of the current speed and direction in the upper 50 m of the water column directly above the instrument and transmits its data to a computer on shore. These data, sent at 20-minute intervals, are utilized to determine suitability of conditions for disposal of dredge materials. The computer performs a running one-hour average of the current vectors over the 50 m interval and transmits the east- west component to a watchstander hourly via telephone pager. If the westerly component of the current vector exceeds 12 cm per second, disposal operations are suspended. As of the date of this presentation, processed profiles of the data will be available via connection to the world wide web.
Daneshzadeh, Y.-H., J.F. Festa, and R.L. Molinari. Quality control of XBT data collected in the Atlantic Ocean: 1990-1991. NOAA Data Report, ERL AOML-29, 77 pp. (1996).
Delayed mode and real-time XBT data collected in the Atlantic Ocean during 1990 and 1991 were scientifically quality controlled at NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML) and the results of the quality control are presented in detail as tables and figures.
DeCosmo, J., K.B. Katsaros, S.D. Smith, R.J. Anderson, W.A. Cost, K. Bumke, and H. Chadwick. Air-sea exchange of water vapor and sensible heat: The Humidity Exchange Over the Sea (HEXOS) results. Journal of Geophysical Research, 101(C5):12,001-12,016 (1996).
Surface layer fluxes of sensible heat and water vapor were measured from a fixed platform in the North Sea during the Humidity Exchange Over the Sea (HEXOS) Main Experiment (HEXMAX). Eddy wind stress and other relevant atmospheric and oceanic parameters were measured simultaneously and are used to interpret the heat and water vapor flux results. One of the main goals of the HEXOS program was to find accurate empirical heat and water vapor flux parameterization formulas for high wind conditions over the sea. It had been postulated that breaking waves and sea spray, which dominate the air-sea interface at high wind speeds, would significantly affect the air-sea heat and water vapor exchange for wind speeds above 15 m/s. Water vapor flux has been measured at wind speeds up to 18 m/s, sufficient to test these predictions, and sensible heat flux was measured at wind speeds up to 23 m/s. Within experimental error, the HEXMAX data do not show significant variation of the flux exchange coefficients with wind speed, indicating that modification of the models is needed.
DeMaria, M., and J. Kaplan. Performance of the SHIPS intensity forecast model during the 1995 Atlantic hurricane season. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.25 (1996).
After the 1994 hurricane season, the statistical hurricane intensity prediction scheme (SHIPS) was modified to include 200 mb temperature as a predictor. This predictor increased the skill of the developmental sample (1989-1994) by 5%-10%. Results from independent cases during the 1995 season showed that this additional variable degrades the SHIPS forecasts. This increase in error appears to be related to modifications in the global model physics that were implemented in early 1995. The revised version of the global model has a temperature bias relative to the earlier version. A method was devised to correct for the temperature bias in the SHIPS forecasts. Results from forecasts with and without the bias correction will be compared.
Dickerson, R.R., P. Kelley, K.P. Rhodes, T.P. Carsey, M.L. Farmer, and P. Crutzen. Measurement of reactive nitrogen compounds over the Indian Ocean. Chemical Engineering News, 74:84 (1996).
No abstract.
Dietrich, D.E., M.J. Bowman, C.A. Lin, and A.M. Mestas-Nunez. Numerical studies of small island wakes in the ocean. Geophysical and Astrophysical Fluid Dynamics, 83:195-231 (1996).
Two and three-dimensional oceanic flows around small islands patterned after Barbados, West Indies (13 deg10 min N latitude: 59 deg 30 min W longitude) were modeled numerically to investigate island wake effects. The two-dimensional simulations closely agreed with laboratory flows, for both attached and shedding wake regimes. As expected, results for a flat bottom confirmed that the Coriolis terms strongly affect pressure but not the flow. For idealized, yet typical incident flow speeds, water column stratification, island topography, and appropriate Coriolis terms, three-dimensional simulations readily produced elongated wake patterns, dominated by surface intensified von Karman-like vortices. Effects of grid resolution, viscosity, bathymetry, and Coriolis forces on wake characteristics were studied. For islands with typical bottom slopes, realistically small horizontal eddy diffusivity has a minor effect compared to bottom drag in generating vorticity. Near-shore bathymetry (viz., the absence or presence of a continental shelf surrounding the island) plays a major role in determining the scale, intensity, and shedding period of vortices. The addition of a 15 km wide continental shelf around the island increased the shedding period by 67%, while reducing the Coriolis force by 50% reduced the shedding period by only 14%. Although observational data is sparse, inferred flow patterns do show von Karman-like structures near Barbados, even if eddies are not located exactly as expected. The numerical computations demonstrate that shedding eddy wakes are easily generated, and lend encouragement to the further search for organized wakes downstream of the island.
Dodge, P.P., S.H. Houston, and C. McAdie. Combined airborne and NEXRAD Doppler radar analyses of the inner core of Hurricane Erin. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.10-A.11 (1996).
An accurate real-time description of the tropical cyclone surface wind field near landfall is important for warning, preparedness, and recovery efforts. Research has helped reduce uncertainties in track and landfall forecasts, but now there is an opportunity to improve the accuracy of the surface wind fields in tropical cyclones, especially near landfall. Scientists at the Hurricane Research Division (HRD) designed the Tropical Cyclone Windfields Near Landfall experiment, part of the Hurricane Field Program, to gather flight-level wind data and make surface wind estimates to improve real-time and post-storm surface wind analyses in tropical storms and hurricanes. One of the objectives of this experiment is to collect airborne Doppler radar to combine with WSR-88D radar data in post-storm three-dimensional wind analyses. In the experiment, a time series of dual-Doppler data sets is collected by flying a single NOAA WP-3D toward or away from a WSR-88D Doppler radar. The aircraft Doppler radar rays are approximately orthogonal to the ground-based Doppler radar rays in that pattern, yielding true dual-Doppler coverage. By 1997, the Atlantic and Gulf coasts will be covered by the network of WSR-88D Doppler radars deployed by the National Weather Service (NWS), Department of Defense, and Federal Aviation Administration. The NWS will equip each radar with a digital recorder to store the base data. The WSR-88D will collect volume scans every 5-6 min. The flight pattern for this experiment is designed to obtain dual-Doppler analyses at intervals of 10-20 min in the inner core. On 1 August 1995, an Aircraft Operations Center WP-3D flew an HRD research mission to record airborne Doppler radar data in Hurricane Erin near the time of landfall on the east coast of Florida. From 2235 UTC to 0204 UTC on 2 August, the aircraft made several penetrations through the eye when the storm was within Doppler range of the Melbourne WSR-88D. The aircraft track was aligned along a radial from the WSR-88D. At the conference we will present preliminary analyses of Erin's wind field derived from airborne and WSR-88D Doppler data collected at 0150 UTC, when the center of circulation was ~170 km from the Melbourne radar.
Drennan, W.M., M.A. Donelan, E.A. Terray, and K.B. Katsaros. Oceanic turbulence dissipation measurements in SWADE. Journal of Physical Oceanography, 26(5):808-815 (1996).
Recent experiments measuring turbulence dissipation rates in the upper ocean can be divided into two types: those supporting an analogy between the upper ocean and lower atmosphere, with dissipation rates following wall layer behavior, and those finding oceanic dissipation rates to be much higher than wall layer predictions. In an attempt to reconcile these two diverse sets of observations, Terray et al. proposed a wave-dependent scaling of the dissipation rate based on the significant wave height and the rate of energy input from the wind to the waves. Their parameterization was derived from observations of strongly forced, fetch-limited waves, although they conjectured that it would apply in typical oceanic conditions as well. This paper reports new measurements of turbulent kinetic energy dissipation made in the North Atlantic Ocean from a SWATH ship during the recent Surface Waves Dynamics Experiment (SWADE). These data support the scaling of Terray et al., verifying its validity when applied to the more fully developed waves typical of the ocean.
Duncombe Rae, C.M., S.L. Garzoli, and A.L. Gordon. The eddy field of the southeast Atlantic Ocean: A statistical census from the Benguela Sources and Transports (BEST) project. Journal of Geophysical Research-Oceans, 101(C5):11,949-11,964 (1996).
Data collected during the Benguela Sources and Transports project were examined to determine some statistical properties of the eddy field observed in the Cape Basin. Seven anticyclonic eddies were encountered during the hydrographic surveys. Two of these were shown to be of Brazil Current origin (this paper and Smythe-Wright et al., 1996). Inverted echo sounder (IES) records of acoustic travel time were scaled to the depth of the thermocline, represented in the Cape Basin by the 10°C isotherm. These records indicate that a minimum of four to six eddies, assumed to be of Agulhas origin, entered the Cape Basin per year during the sampling period. They were associated with depressions in the 10°C isotherm records ranging from 100 to 400 m and of a duration between 30 and 100 days. The thermocline appears to shallow appreciably after the passage of an eddy before relaxing to the local mean. Estimates of the heat and salt contents of the hydrographically surveyed eddies indicated that the mean available heat and salt anomalies of the eddies were 0.55 × 1020 J and 3.5 × 1012 kg, respectively. Extrapolating the hydrographic data to the eddies detected in the IES record shows the eddy field responsible for the transfer of 2.2 to 3.3 × 1020 J y-1 (0.007 PW), 14 to 21 × 1012 kg salt yr-1, and 2 .6 to 3.8 × 106 m3 s-1.
Enfield, D.B. Relationships of inter-American rainfall to tropical Atlantic and Pacific SST variability. Geophysical Research Letters, 23(23):3305-3308 (1996).
Area-averaged anomalies of sea surface temperature (SSTA) and rainfall, developed from large-scale data sets, have been used to explore the relative importance of Pacific versus Atlantic SST variability for inter-American (50°S-50°N) climate variability at interannual time scales. SSTA in the tropical Pacific and tropical North Atlantic are comparably related to rainfall north of 15°S, with clear associations distributed between the southeastern United States (US) in the north and northern South America in the south. Although NINO3 explains 25% of the variance of the North Atlantic SSTA index, the rainfall correlations with North Atlantic SSTA are for the most part opposite in sign to those with NINO3. Hence, a significant part of the Atlantic SSTA probably has a direct association with rainfall, rather than being merely an indirect proxy for Pacific ENSO linkages. In contrast to the North Atlantic, South Atlantic SSTA appear to be only related to rainfall in northeast (NE) Brazil. The entire region between Venezuela and NE Brazil appears to be sensitive to both the ITCZ and to antisymmetric configurations of SSTA across the ITCZ, in a manner consistent with the relationships between SST, surface wind and surface wind divergence fields, and with previous studies.
Ffield, A., W.D. Wilson, J.M. Toole, and H.L. Bryden. The impact of eddies on the southwestern Indian Ocean. 1996 AGU Fall Meeting, San Francisco, CA, December 15-19, 1996. Supplement to EOS, Transactions, American Geophysical Union, 77(46):F406, OS21C-09 (1996).
In the Indian Ocean, the Agulhas Current advects warm water southward, balancing slower northward interior flow and input of Indonesian throughflow water. The net transfer of properties through the southwestern Indian Ocean provides the primary link of Indian Ocean water masses to the global ocean. Mesoscale eddies in this region complicate determination of volume transports and associated fluxes of heat and freshwater. While an eddy may contribute nearly zero mass flux across a section when viewed synoptically, over time it can transfer significant heat and freshwater. As part of NOAA/AOML's contribution to the international Indian Ocean WOCE effort, temperature, salinity, and oxygen measurements, along with hull-mounted and lowered ADCP measurements, were obtained along 33°S near the east African coast during March 1995. The characteristics of several energetic eddies revealed in the March 1995 data are presented and compared to other hydrographic observations obtained along the same section. Drifter and altimetry data from the NASA Ocean Altimeter Pathfinder Data Project are used to monitor the spatial and temporal variability of eddies in the southwestern Indian Ocean as well. Together, these data are used to assess the importance of eddy fluxes to the net mass, heat, and freshwater budgets of the Indian Ocean.
Franklin, J.L., S.E. Feuer, J. Kaplan, and S.D. Aberson. Tropical cyclone motion and surrounding flow relationships: Searching for beta gyres in Omega dropwindsonde datasets. Monthly Weather Review, 124(1):64-84 (1996).
In 1982, the National Oceanic and Atmospheric Admininstration's Hurricane Research Division began a series of experiments to collect Omega dropwindsonde (ODW) observations within about 1000 km of the center of tropical cyclones. By 1992, 16 ODW datasets had been collected in ten Atlantic basin hurricanes and tropical storms. Objective wind analyses for each dataset, at ten levels from 100 mb to the surface, have been produced using a consistent set of analysis parameters. The objective analyses, which resolve synoptic-scale features in the storm environment with an accuracy and confidence unattainable from routine operational analyses, have been used to examine relationships between a tropical cyclone's motion and its surrounding synoptic-scale flow. Tropical cyclone motion is found to be consistent with barotropic steering of the vortex by the surrounding flow within 3° latitude (333 km) of the cyclone center. At this radius, the surrounding deep-layer mean flow explains over 90% of the variance in vortex motion. The analyses show vorticity asymmetries that strongly resemble the beta gyres common to barotropic models, although other synoptic features in the environment make isolation of these gyres from the wind fields difficult. A reasonably strong relationship is found between the motion of the vortex (relative to its large scale surrounding flow) and the absolute vorticity gradient of the vortex environment.
Gamache, J.F., and F.D. Marks. Analysis of airborne Doppler observations of the weakening of eastern Pacific Hurricane Olivia on 25 September 1994. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.9 (1996).
The two NOAA WP-3D aircraft observed Hurricane Olivia on 25 September 1994 as its minimum pressure increased by approximately 10 mb in 2.5 hours, and its mean upper-level eyewall winds decreased by more than 10 m s-1. Winds at all levels became much more asymmetrical. Both aircraft carried vertically scanning Doppler radars in their tails, and a coordinated pattern was flown that provided full coverage of the inner core every 30 minutes. Our analysis extends out to 30 km from storm center. As the aircraft arrived around 2000 UTC, the radar presentation was highly symmetrical, and the first Doppler analysis shows that the tangential wind structure was also highly symmetrical. Three hours later, the reflectivity to the south of the center had weakened, and a highly convective region with reflectivities over 55 dBZ had developed to the north. During the same period, the mean wind shear (difference between 1 km and 9 km levels) in the eyewall increased from approximately 10 m s-1 to over 20 m s-1. The storm had already recurved at the beginning of the on-station time, so the rapid changes over the next 3 hours in minimum pressure, upper-level winds, and symmetry may have resulted from a destructive interaction with the larger-scale flow. The three-dimensional structures of reflectivity, tangential wind, and radar reflectivity will be shown at the conference.
Garzoli, S.L. SACC: South Atlantic Climate Change. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, 27 pp. (1996).
No abstract.
Garzoli, S.L., and A.L. Gordon. Origins and variability of the Benguela Current. Journal of Geophysical Research-Oceans, 101(C1):879-906 (1996).
A subset of the Benguela Sources and Transports (BEST) 1992-1993 data is analyzed to study the magnitude and variability of the large-scale transports in the area. The data consist of inverted echo sounder series and CTD stations. The mean 16-month transport values for the upper 1000 m indicate that of the 13 Sv northward transport within the Benguela Current, 50% is derived from the central Atlantic (which from geometry may be chiefly South Atlantic water), 25% comes from the Indian Ocean (which may be chiefly Agulhas water), and the remaining 25% may be a blend of Agulhas and tropical Atlantic water. A simple schematic of the transport pattern in which a somewhat restricted corridor for Agulhas eddies translation is envisioned. To the west of the eddy corridor flows the South Atlantic source for the Benguela Current; to the east is the Agulhas (Indian Ocean) source. The corridor is breached by South Atlantic and Indian Ocean water as the transient eddy field stirs these water masses.
Garzoli, S.L., A.L. Gordon, V.M. Kamenkovich, D. Pillsbury, and C.M. Duncombe Rae. Variability and sources of the southeastern Atlantic circulation. Journal of Marine Research, 54(6):1039-1071 (1996).
The 1992-1993 Benguela Sources and Transport (BEST) time series provides a quantitative view of Benguela Current transport and the eddy field across 30°S, as well as an estimate of the relation between its barotropic and baroclinic components. This is done by a simultaneous analysis of all the different data sets: inverted echo sounders, pressure sensors, CTD, current meter moorings, and ADCP. The analysis of the time series indicate that the annual mean baroclinic transport of the Benguela Current is approximately 13 Sv. The total transport is 16 Sv. The stationary flow associated with the Benguela Current is mostly confined along the African Continent while a transient flow, composed by large eddies shed from the Agulhas retroflection, composes the western portion of the flow. In the stationary part of the Benguela Current, both barotropic and baroclinic components are equally important while in the transient part, the barotropic is more substantial. Several eddies were observed during the experiment that translates to the west. They start with a speed of 12 km/day and close to the Walvis Ridge it has already diminished to 6-7 km/day. It can be assumed that after crossing the Walvis Ridge, due to their strong barotropic component (they feel the bottom), the speed decreases to that estimate previously obtained in the middle of the basin. The sources of the Benguela Current may include Indian and South Atlantic subtropical thermocline water; the relatively saline, low oxygen tropical Atlantic water and the cooler, fresher subantarctic water. The South Atlantic thermocline and subantarctic inflow is derived from the eastward flowing South Atlantic Current. The Indian Ocean water is injected into the Benguela Current through the Agulhas retroflection eddy and filament processes. A complex stirring effect of contrasting water types is envisioned. The changes in thermocline salinity correlate with transport: in general, when the northward transport is increasing the thermocline salinity also increases. This indicates that the Benguela Current increases in strength by bringing in more subtropical water. As the Agulhas input is most effective in boosting the salinity of the upper thermocline (the South Atlantic Current water being deficient in salinity relative to the Indian Ocean source), we suggest that the spatial variations in transport are tied to Agulhas water influx, presumably within and associated with the eddy field.
Goldenberg, S.B., and L.J. Shapiro. Physical mechanisms for the association of El Niño and west African rainfall with Atlantic major hurricane activity. Journal of Climate, 9(6):1169-1187 (1996).
Physical mechanisms responsible for the contemporaneous association, shown in earlier studies, of North Atlantic basin major hurricane (MH) activity with western Sahelian monsoon rainfall and an equatorial eastern Pacific sea surface temperature index of El Niño are examined, using correlations with 200- and 700-mb level wind data for the period 1968-1992. The use of partial correlations isolates some of the relationships associated with the various parameters. The results support previous suggestions that the upper- and lower-level winds over the region in the basin between ~10°N and 20°N where most MHs begin developing and critical determinants of the MH activity in each hurricane season. In particular, interannual fluctuations in the winds that produce changes in the magnitude of vertical shear are one of the most important factors, with reduced shear being associated with increased activity and stronger shear with decreased activity. The results show that most of these critical wind fluctuations are explained by their relationship to the SST and rainfall fluctuations. Results confirm previous findings that positive (warm) eastern Pacific SST and negative (drought) Sahelian rainfall anomalies are associated with suppressed Atlantic basin tropical cyclone activity through an equatorially confined near-zonal circulation with upper-level westerlies and lower-level easterlies that act to increase the climatological westerly vertical shear in the main development region. SST and rainfall anomalies of the opposite sense are related to MH activity through a zonal circulation with upper-level easterly and lower-level westerly wind anomalies that act to cancel out some of the climatological westerly vertical shear. The results also show that changes in vertical shear to the north of the main development region are unrelated to, or possibly even out of phase with, changes in the development region, providing a possible physical explanation for the observations from recent studies of the out-of-phase relationship of interannual fluctuations in MH activity in the region poleward of ~25°N with fluctuations in activity to the south. The interannual variability of MH activity explained by Sahel rainfall is almost three times that explained by the eastern Pacific SSTs. It is demonstrated that a likely reason for this result is that SST-associated vertical shears are more equatorially confined, so that the changes in shear in the main development region have a stronger association with the rainfall than with the SSTs.
Goldenberg, S.B., L.J. Shapiro, and C.W. Landsea. The hyperactive 1995 Atlantic hurricane season, Part II: Just a "spike" or a harbinger of things to come? Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.35 (1996).
After a relative lull in overall activity during the preceding four years, in 1995 the Atlantic hurricane basin experienced one of the most active seasons on record, with almost every measure of activity over twice the long-term mean. Of particular note was that the season produced five major hurricanes (maximum sustained surface winds >50 m/s) for the first time since 1964. Most of the major hurricanes in the North Atlantic basin form from easterly (African) wave disturbances and are especially sensitive to fluctuations in the tropical climate on the interannual and interdecadal time scales. The fluctuations on these scales that resulted in the "hyperactive" 1995 season and the implications of these fluctuations for the years ahead will be discussed. The chief issue that will be addressed is whether or not the activity of the 1995 season was simply an anomalous "spike" or a harbinger of long-term climate shifts signaling the probability of greater activity in the years to come.
Goni, G.J., S. Kamholz, S.L. Garzoli, and D.B. Olson. Dynamics of the Brazil/Malvinas Confluence based on inverted echo sounders and altimetry. Journal of Geophysical Research-Oceans, 101(C7):16,273-16,289 (1996).
We use data from the GEOSAT altimeter and from ten inverted echo sounder (IES) moorings deployed in the southwest Atlantic Ocean off the Argentine continental shelf to investigate several aspects of the dynamics of the upper layer in the Brazil/Malvinas Confluence region. We use the altimeter data to estimate the sea-height anomalies at each IES location, and the IES data to compute the upper-layer thickness, taken in this work to go to the depth of the 8°C isotherm. We first discuss the sea height and upper-layer thickness variations caused by the passage of the Brazil Current, Malvinas Current, and warm anticyclonic and cold cyclonic eddies. We introduce a two-layer model in which we decompose the sea height into its baroclinic and barotropic contributions. We then propose a method to monitor the thickness of the upper layer and the barotropic and baroclinic transports as a function of the sea-height anomalies and the statistics of the upper-layer thickness and reduced gravity for the region. We compute the reduced gravity values from the slope of a linear fit between the sea-height anomalies and the upper-layer thicknesses. We estimate the reduced gravity values for this region to range from 0.005 to 0.011 m s-2. We also estimate the mean barotropic sea-height difference using two methods: conservation of mass and conservation of potential vorticity. Finally, we compute the time series for the baroclinic and barotropic transports during the GEOSAT Exact Repeat Mission (ERM) time period. Our results suggest that the mean baroclinic transport in the upper layer decreases from 12 Sv at around 35°S to 7 Sv at 37°S. Our results also indicate that there is a significant barotropic contribution to the upper-layer transport in the Confluence region.
Goni, G.J., S.L. Garzoli, A.J. Mariano, D.B. Olson, and O.B. Brown. Monitoring the upper layer southeastern Atlantic transports and eddy field using altimeter data. 1996 AGU Fall Meeting, San Francisco, CA, December 15-19, 1996. Supplement to EOS, Transactions, American Geophysical Union, 77(46):F16, U11C-08 (1996).
Sea height anomaly data derived from TOPEX/POSEIDON and thermocline depth and dynamic height derived from a set of five inverted echosounders and four moored current meters are used in conjunction in the southeastern Atlantic Ocean to monitor the thermocline depth and transports of the Agulhas/Benguela system. Comparisons between TOPEX/POSEIDON altimeter observations and data from the moored instruments show that the sea surface height anomaly is significantly correlated to the thermocline depth and the sea surface dynamic height. A two-layer approximation with thermocline deviations and a reduced gravity is used to describe the vertical structure of the ocean. The reduced gravity is estimated from the slope of the linear fit of the thermocline depth and sea height anomaly data. The thermocline depth and baroclinic and geostrophic transports are then computed using simple expressions derived from the two-layer model. Analysis of three years of geostrophic transport estimates obtained from TOPEX/POSEIDON data indicate that the Benguela Current may undergo interannual variability up to 20%. However, the primary variability derives from the source waters that form the Benguela Current, i.e., waters from the South Atlantic, Indian Ocean, and tropical Atlantic. The analysis of the depth of the altimeter-derived thermocline field is used to study the formation of rings in the Agulhas retroflection region, to monitor their trajectories, and to estimate their kinetic and available potential energy.
Hacker, P., E. Firing, W.D. Wilson, and R.L. Molinari. Direct observations of the current structure east of the Bahamas. Geophysical Research Letters, 23(10):1127-1130 (1996).
Quasisynoptic absolute velocity sections were obtained in the western North Atlantic to the east of the Bahamas on five cruises from 1992 to 1994, showing complex spatial and temporal variability of the currents throughout the water column. Lowered acoustic Doppler current profilers were used on all cruises; for comparison, an acoustically-tracked free-fall profiler was used on the August 1992 and June 1993 cruises. Where simultaneous profiles from both methods are available, depth-averaged differences are less than 0.01 m s-1 in the ensemble mean and standard deviation. Though small, the mean difference appears to be statistically non-zero for one of the two Doppler profilers used; no cause has been found. The individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth-averaged components extending over the full sampling domain. Two sections show a picture of the southward-flowing Deep Western Boundary Current (DWBC) differing from previous observations. During August 1992 and June 1993 the mean DWBC core was located more than 100 km offshore; in observations prior to 1990 it was usually near 50 km offshore. Net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 Sv with a mean of about 40 Sv (1 Sv = 1 × 106 m3 s-1). Our mean is consistent with previous estimates; our sections add new evidence that the transport is highly variable to at least 400 km offshore.
Halliwell, G.R., and D.A. Mayer. Frequency response properties of forced climatic SST anomaly variability in the North Atlantic. Journal of Climate, 9(12):3575-3587 (1996).
Frequency response properties of North Atlantic (5-57°N) sea surface temperature anomaly (Tsa) variability over periods of several months to 20 years are characterized using the Cooperative Ocean Atmosphere Data Set (COADS). Significant direct forcing of Tsa variability by the anomalous wind field (primarily through the resulting anomalous surface turbulent heat flux) is observed in the Western Wind and Trade Wind belts, but not between these belts within the interior of the oceanic subtropical gyre. To analyze the response to this forcing, it is necessary to separate the total anomalous surface turbulent heat flux into a component representing the wind forcing and a component predominantly representing the negative linear feedback (Newtonian relaxation) that is the dominant damping mechanism of large-scale climatic Tsa variability. At frequencies where wind forcing is important, good agreement exists between frequency response properties estimated from data and properties theoretically predicted by a simple linearized slab mixed layer temperature balance. In particular, this balance quantifies the influence of negative feedback damping on the amplitude and phase lag of the response. In the Westerlies, wind forcing is effective over periods from several months to 8 yr, primarily 2-4 yr, and is ineffective at periods of 8-20 yr where forcing by variable oceanic flow has been demonstrated to be important. In the Trades, wind forcing is effective over periods from 8 mo to 13.3 yr, primarily 2-3 yr and 7-13.3 yr. Wind forcing in the Trades is less effective at periods of 3-6 yr where ENSO variability is significant. At frequencies where wind forcing in the Westerlies is significant, forcing and feedback have an equally large influence on Tsa, indicating that the wind-forced response is damped primarily by the negative feedback contained in the anomalous surface turbulent heat flux. In the Trades, feedback by anomalous surface turbulent heat flux is not large enough to balance the wind forcing; other processes must contribute significantly to the damping there. At frequencies where wind forcing is important, Tsa in the Westerlies is not coherent with Tsa in the Trades. The anomalous wind fluctuations driving Tsa in the Westerlies (Trades) are associated with anomalous surface pressure variability in the Icelandic low (subtropical high). Response to a coherent North Atlantic Oscillation (Icelandic Low varying out-of-phase with the subtropical high) is, therefore, not observed. The large Tsa fluctuations observed in the western basin within the Westerly Wind belt propagate to the east and northeast across the Atlantic at a characteristic speed of 6 km day-1.
Hansen, D.V., and H.F. Bezdek. On the nature of decadal anomalies in North Atlantic sea surface temperature. Journal of Geophysical Research, 101(C4):8749-8758 (1996).
North Atlantic sea surface temperature data from the Comprehensive Ocean-Atmosphere Data Set (COADS) were used to investigate the behavior of temperature anomalies on multiple-year time scales during the period 1948-1992. Monthly anomaly time series for each 2° square from the equator to 70°N were low-pass filtered at four years and normalized by the local standard deviation. Attention is focused on the extreme events, the upper and lower deciles, of the anomaly time series. A 45-year sequence of January maps shows the already familiar phenomena of generally cold conditions prior to 1951, a long warm interval from 1951 through 1967, and again a cold period from 1968 through 1977. The years 1978 through 1982 were largely devoid of persistent strong anomalies, but moderate cold conditions returned during 1983-1986. Warm cnoditions dominated the North Atlantic from 1987 onward. Within these thermal epochs, however, a total of five cold anomaly features and nine warm anomaly features have been identified. These features have individual lifetimes of three to ten years. A typical size is 20° of latitude or longitude, but they range from barely detectable to spanning the width of the basin, the latter especially in lower latitudes. Most of the anomalies move long distances along certain preferred paths. These paths generally follow the routes of the subarctic and subtropical gyres. Anomalies originating off North America along the boundary between the gyres move northeastward toward the Norwegian Sea along the approximate route of the North Atlantic Current. Midlatitude anomalies originating at the eastern boundary tend to spread both northward and southward along the coast. The speed of these movements (1-3 km d-1) is generally less than the expected speed of the near-surfce ocean circulation. Simple ideas about the effects of beta dynamics and air-sea heat exchanges are briefly considered but do not provide a satisfactory explanation for the movements of the anomalies. The long time scale of these extreme events and the continuity of their movements suggest a useful degree of predictability of sea surface temperature based on persistence and propagation of features.
Hansen, D.V., and P.M. Poulain. Quality control and interpolations of WOCE/TOGA drifter data. Journal of Atmospheric and Oceanic Technology, 13(4):900-909 (1996).
Satellite-tracked drifting buoy data are being collected by numerous investigators and agencies in several countries for the WOCE/TOGA Surface Velocity Program. By the end of the century and thereafter this global data set will provide the definitive climatology and chronology of the surface currents of the world ocean. To expedite completion of research quality data sets for archival and dissemination, a data acquisition activity is being conducted at NOAA/AOML, Miami, Florida. At AOML data from drifting buoys of cooperating operators are quality controlled and optimally interpolated to uniform six-hour interval trajectories for archival at the Marine Environmental Data Service (Canada). This report describes in detail the procedures used in preparing these data for the benefit of second or third party users, or future buoy operators who may wish to process data in a consistent way. Particular attention is given to provide quantitative estimates for uncertainty of interpolation.
Hansen, D.V., and M.S. Swenson. Mixed layer circulation during EqPac and some thermochemical implications for the equatorial cold tongue. Deep Sea Research II, 43(4-6):707-724 (1996).
Surface currents inferred from satellite-tracked drifting buoys were used to develop a chronology of surface currents in the central Pacific for the year encompassing the EqPac field program. Salient features of the chronology are the early months of the program witnessed anomalous eastward current surges near the equator within the moderate El Niño event, followed by a period of anomalously strong westward flow near the equator and eastward flow in the North Equatorial Countercurrent that led, in mid-summer, to an eruption of tropical instability waves that continued until the end of the field program. None of these events was particularly unusual, but they were departures from climatology that influence the interpretation of the biochemical measurements made for EqPac. Results from a semi-quantitative conceptual model indicate that tropical instability waves have more important long-term, as well as short-term, consequences for thermochemical properties of the cold tongue than previously recognized.
Hendee, J.C. Object-oriented analysis of a near real-time marine environmental data acquisition and reporting system. NOAA Technical Memorandum, ERL AOML-90 (PB97-114573), 64 pp. (1996).
The National Oceanic and Atmospheric Administration's Coral Health and Monitoring Program has cooperated with the Florida Institute of Oceanography in developing a near real-time marine environmental monitoring and reporting system. Using the latest in object-oriented analysis techniques, this report describes how data are retrieved from satellite data and archiving facilities, then reformatted for presentation via a remote bulletin board system and facsimile.
Hendee, J.C. Object-oriented design of a near real-time marine environmental data acquisition and reporting system. NOAA Technical Memorandum, ERL AOML-89 (PB97-114581), 29 pp. (1996).
The National Oceanic and Atmospheric Administration's Coral Health and Monitoring Program in Miami, Florida has for the last several years worked cooperatively with the Florida Institute of Oceanography in monitoring meteorological and oceanographic events at selected Coastal-Marine Automated Network sites in the Florida Straits. In a previous report, an object-oriented analysis (OOA) was conducted of the existing system with an eye toward redesigning the system. This report builds on the OOA results from the previous study and utilizes the latest in object-oriented design techniques to design a new system.
Houston, S.H., and M.D. Powell. Real-time surface wind analyses during the 1995 hurricane season. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.29 (1996).
During the 1995 hurricane season, HRD personnel conducted experimental analyses of surface wind distribution in real time and made the analyses available to duty hurricane forecasters and storm surge forecast specialists. More than 80 analyses were conducted. The analyses are based on compositing all available observations from Air Force reconnaissance aircraft, ships, buoys, C-MAN platforms, and surface aviation reports. All data are quality controlled and then processed to conform to a common framework for height (10 m), exposure (marine or open terrain over land), and averaging period (maximum sustained 1 min wind speed). Several hours of observations are usually required to provide sufficient data density and coverage for an analysis, and an analysis domain consists of three or more nested meshes within which the scale of resolvable features can be controlled. The resulting objective analysis is representative of the mean state of the storm during the chosen time period, and a typical 10 hour reconnaissance mission will yield two to three analyses. The analysis product is a streamline and isotach contour plot for a given mesh and is designed to convey the location and strength of the maximum wind, as well as the extent of hurricane force, 50 kt, and/or tropical storm force winds. Analyses conducted in Hurricanes Erin, Felix, Luis, Marilyn, and Opal will be compared to dependent and independent surface wind observations. In some situations there is wide-spread agreement (e.g., Felix, Marilyn, Erin). In other cases (e.g., Luis, Opal), where there is incomplete or questionable surface information or where single level aircraft observations do not adequately convey the level that most influences the surface, there is mixed agreement.
Houston, S.H., W.A. Schaffer, M.D. Powell, and J. Chen. Incorporating HRD surface wind fields into the SLOSH model. Preprints, Conference on Coastal Oceanic and Atmospheric Prediction, Atlanta, GA, January 28-February 2, 1996. American Meteorological Society, Boston, 265-267 (1996).
NOAA's Hurricane Research Division (HRD) has developed new methods to analyze surface winds in tropical cyclones based on all available surface wind observations, including aircraft flight-level observations adjusted to the surface. As part of NOAA's Coastal Ocean Program research on coastal hazards, HRD and the Techniques Development Laboratory (TDL) have evaluated the parametric wind model used as input to the National Weather Service's (NWS) Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model through comparisons with HRD's surface wind analyses in recent hurricanes (Hugo of 1989, Bob of 1991, Andrew of 1992, and Emily of 1993). These comparisons indicated that the SLOSH parametric wind model adequately represented the wind fields in most cases. However, in the case of Emily's closest approach to North Carolina, there were significant underestimates in portions of the SLOSH model wind profile. These reduced winds input to the SLOSH model resulted in an underestimate of storm surge along some sections of the North Carolina coastline. The HRD surface wind fields would likely improve the storm surge calculations for this tropical cyclone if they could be input to the SLOSH model. Techniques are presented here which allow the use of the HRD surface wind fields as input for hindcasting the storm surge in the SLOSH model. Examples are shown for applying these techniques to some recent hurricanes which affected the United States coastline.
Huang, H., R.E. Fergen, J.R. Proni, and J.J. Tsai. Probabilistic analysis of ocean outfall mixing zones. Journal of Environmental Engineering, 122:359-367 (1996).
A methodology for ocean outfall mixing zone analysis is presented. It is based on a combination of four deterministic models for predicting hydrodynamic mixing behaviors of the discharged effluent, a continuous time domain simulation method, and an exceedance probability field concept. The approach provides a framework for evaluating mixing zones in compliance with receiving water criteria that are set in statistical terms. The approach was applied to the Hollywood outfall located off the east coast of south Florida. An exceedance probability field for effluent at a specified relative concentration of 0.021 was created. This field was applicable for determining the exceedance probability-based concentrations of any conservative pollutant at the regulatory mixing zone edge. A comparison of the probabilistic approach with the worst-case approach was made. The use of the worst-case approach was found to be too conservative for the subject outfall.
Huber, M., M. DeMaria, and J. Kaplan. Evaluation of an empirical inland wind decay model for the landfall of Hurricane Opal. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.28-A.29 (1996).
Surface wind observations in the southeast U.S. during the landfall of Hurricane Opal are used to evaluate an empirical inland wind decay model. The model applies a simple two-parameter decay equation to the hurricane wind field at landfall to estimate the maximum sustained surface wind as a storm moves inland. The hurricane wind field at landfall is modeled as a symmetric vortex plus a wave number one asymmetry that is proportional to the storm motion. The model was run using operational information to estimate the landfall storm structure. The model was also run where a post-storm wind analysis prepared by Mark Powell and Sam Houston of the Hurricane Research Division was used to estimate the landfall storm structure. Results from these two runs will be compared with the observed wind field.
Johns, E., W.D. Wilson, and R.L. Molinari. Transport balance of the Intra-Americas Sea: Results from NOAA's Subtropical Atlantic Climate Study. EOS, Transactions, American Geophysical Union, 76(3), OS117 (1996).
No abstract.
Kaplan, J., M. DeMaria, and M. Huber. A preliminary evaluation of forecasts from an empirical inland wind decay model for Hurricane Erin (1995). Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.28 (1996).
In early August of 1995, Hurricane Erin made landfall along both the east coast and panhandle of Florida before eventually becoming extratropical and dissipating near the Virginia/Maryland border. Erin's track across the data-rich Florida peninsula make it a good candidate for evaluating an Empirical Inland Wind Decay Model (IWDM) developed recently at the Hurricane Research Division (HRD) and employed by the National Hurricane Center (NHC) during the 1995 hurricane season for the first time. The IWDM is a simple, two-parameter model developed based upon the assumption that tropical cyclone wind speeds decay exponentially with time after landfall. The decay model has several potential applications including the capability of providing an estimate of the swath of inland wind speeds produced by a landfalling tropical cyclone. This particular model application will be evaluated for landfalling Hurricane Erin by comparing the IWDM predicted wind speeds to the winds at all available inland surface observing stations. Erin's structure and intensity at landfall required to produce the forecast wind swath were determined from information contained in operational NHC hurricane advisories, as well as from detailed near real-time wind analyses produced by Sam Houston and Mark Powell of HRD. The accuracy of the forecast wind swaths produced using both techniques will be discussed.
Landsea, C.W., S.B. Goldenberg, W.M. Gray, and G.D. Bell. The hyperactive 1995 Atlantic hurricane season, Part I: A juxtaposition of favorable conditions. Minutes, 50th Interdepartmental Hurricane Conference, Miami, FL, March 26-29, 1996. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, D.C., A.34-A.35 (1996).
The 1995 Atlantic hurricane season was a year of near-record hurricane activity: a total of 19 named storms (average is 9.3 for the base period 1950-1990) and 11 hurricanes (average is 5.8) which persisted for a total of 121 named storm days (average is 46.6) and 62 hurricane days (average is 23.9), respectively. There were five intense (or major) hurricanes of Saffir/Simpson category 3, 4, or 5 (average is 2.3 intense hurricanes) with 11.5 intense hurricane days (average is 4.7). The net tropical cyclone activity, based upon the combined values of named storms, hurricanes, intense hurricanes, and their days present, was 229% of the average. This unusually active hurricane season was the result of the juxtaposition of nearly all the physical factors known to enhance seasonal hurricane activity. This convergence of favorable factors has occurred about ten times during the last century. These environmental factors included extremely low vertical wind shear, below-normal sea level pressure and above-normal SST throughout the Caribbean and tropical North Atlantic, as well as a strong west phase of the stratospheric quasi-biennial oscillation. The low vertical wind shear partially resulted from cool phase conditions of the El Niño-Southern Oscillation. Significantly, these anomalies were present in the pre-season environmental fields, as far back as February, and thus preceded the development of any hurricanes. Seasonal hurricane forecasts for 1995 issued at Colorado State University on 30 November 1994, 5 June 1995, and 4 August 1995 were able to anticipate an above-average season, but underforecast the extent of the extreme hurricane activity. The 1996 seasonal forecast will be briefly discussed.
Landsea, C.W., N. Nicholls, W.M. Gray, and L.A. Avila. Downward trends in the frequency of intense Atlantic hurricanes during the past five decades. Geophysical Research Letters, 23:1697-1700 (1996).
There is concern that the enhanced greenhouse effect may be affecting extreme weather events such as tropical cyclones. The North Atlantic basin offers a reliable, long-term record of tropical cyclone activity, though it may not be representative of tropical cyclones throughout the rest of the tropics. The most recent years of 1991 through 1994 have experienced the quietest cyclone activity on record in terms of frequency of tropical storms, hurricanes, and intense hurricanes. This was followed by the 1995 hurricane season, one of the busiest in the past 50 years. Despite 1995's activity, a long-term (five decade) downward trend continues to be evident primarily in the frequency of intense hurricanes. In addition, the mean maximum intensity (i.e., averaged over all cyclones in a season) has decreased, while the maximum intensity attained by the strongest hurricane each year has not shown a significant change.
Lobert, J.M., J.H. Butler, L.S. Geller, S.A. Yvon, S.A. Montzka, R.C. Myers, A.D. Clarke, and J.W. Elkins. BLAST94: Bromine latitudinal air/sea transect 1994 - Report on oceanic measurements of methyl bromide and other compounds. NOAA Technical Memorandum, ERL CMDL-10 (PB96-154471), 45 pp. (1996).
No abstract.
Marks, F.D., and H.A. Friedman. 1996 Hurricane Field Program Plan. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida (published for limited distribution), 138 pp. (1996).
The basic objective of NOAA's hurricane research field program is the collection of descriptive data that are required to support analytical and theoretical hurricane studies. These studies are designed to improve the understanding of the structure and behavior of hurricanes. The ultimate purpose is to develop improved methods for hurricane prediction. Nine major experiments have been planned, primarily by principal investigators at the Hurricane Research Division (HRD)/Atlantic Oceanographic and Meteorological Laboratory (AOML) of NOAA, for the 1996 Hurricane Field Program. These experiments will be conducted with the NOAA/Aircraft Operations Center (AOC) WP-3D and Gulfstream IV-SP aircraft.
Maul, G.A., M.H. Bushnell, N.J. Bravo, and D.V. Hansen. Observed sea surface height and modeled dynamic height anomaly departures in the tropical Pacific Ocean: 1986-1989. Oceanologica Acta, 20(4):569-584 (1996).
No abstract.
McCartney, M.S., R.G. Curry, and H.F. Bezdek. North Atlantic's transformation pipeline. Oceanus, 39(2):19-23 (1996).
No abstract.
Mielke, P.W., K.J. Berry, C.W. Landsea, and W.M. Gray. Artificial skill and validation in weather forecasting. Weather and Forecasting, 11(2):153-169 (1996).
The results of a simulation study of multiple regression prediction models for meteorological forecasting are reported. The effects of sample size, amount, and severity of nonrepresentative data in the population, inclusion of noninformative predictors, and least (sum of) absolute deviations (LAD) and least (sum of) squared deviations (LSD) regression models are examined on five populations constructed from meteorological data. Artificial skill is shown to be a product of small sample size, LSD regression, and nonrepresentative data. Validation of sample results is examined, and LAD regression is found to be superior to LSD regression when sample size is small and nonrepresentative data are present.
Napp, J.M., L.S. Inzce, P.B. Ortner, D. Siefert, and S. Britt. The plankton of Shelikof Strait as predators, prey, and competitors of larval pollock. Fisheries Oceanography, 5:19-38 (1996).
The vertical distribution of walleye pollock eggs and larvae in Shelikof Strait, Gulf of Alaska, was investigated using data from 36 Multiple Opening-Closing Net and Environmental Sensing System (MOCNESS) tows taken in April and May 1986-1988. Most eggs were found from below 150 m to near bottom, ~300 m, but were progressively shallower later in the season. Eggs in middle stages of development were shallower than younger or older eggs. The vertical distribution of eggs was positively related to observed differences in seawater temperature but showed no relationship to density. Larvae hatch at incubation depth and quickly rise to the upper 50 m of the water column where they remain during larval development. Larger larvae(~7-10 mm standard length) undergo limited diel vertical migration within the upper 50 m. They are deepest during the day, shallowest at dusk, slightly deeper at night, and even deeper at dawn. Their mean depths of occurrence were between 21 and 37 m at all times. At these depths, prey (copepod nauplii) generally were at densities sufficient for larval pollock growth in laboratory studies. Pronounced thermoclines and pycnoclines were present in the part of the water column inhabited by the larvae in late May. Larvae appear to remain below the upper mixed layer during periods of increased turbulence, but at depths during daytime where light was sufficient for feeding, and where prey densities were adequate.
Nelsen, T.A. Chapter 14: Coastal ocean water resources: Linkages with terrestrial freshwater resources, anthropogenic influences, and climate change. In Diachronic Climatic Impacts on Water Resources, A.N. Angelakis and A.S. Issar (eds.). NATO ASI Series, Vol. I36, Springer-Verlag, Berlin Heidelberg, 319-347 (1996).
No abstract.
Nelsen, T.A., M.P. Zetwo, H. Wanless, P. Blackwelder, P. Swart, T. Hood, C. Alvarez-Zarikian, J. Trefry, S. Metz, W.-J. Kang, R. Trocine, L. Tedesco, M. Capps, and M. O'Neal. The sediment record as a monitor of natural and anthropogenic changes in the lower Everglades/Florida Bay ecosystem: A high resolution study. 1996 Florida Bay Science Conference, Miami, Florida, June 1996. Florida Sea Grant/University of Florida Publication, 62-65 (1996).
No abstract.
Nystuen, J.A., J.R. Proni, P.G. Black, and J.C. Wilkerson. A comparison of automatic rain gauges. Journal of Atmospheric and Oceanic Technology, 13(1):62-73 (1996).
Automatic rain gauge systems are required to collect rainfall data at remote locations, especially oceanic sites where logistics prevent regular visits. Rainfall data from six different types of automatic rain gauge systems have been collected for a set of summertime subtropical rain events and for a set of wintertime rain events at Miami, Florida. The rain gauge systems include three types of collection gauges: weighing, capacitance, and tippin