**In Press** **2002**
Asher, W., J. Edson, W.R. McGillis, R.H. Wanninkhof, D.T. Ho, and T. Litchendorf. Fractional area whitecap coverage and air-sea gas transfer velocities measured during GasEx-98. In Gas Transfer at Water Surfaces, M.A. Donelan, W.M. Drennan, E.S. Saltzman, and R.H. Wanninkhof (eds.). AGU Geophysical Series, Volume 127 (ISBN 0-87590-986-8), 199-203 (2002).
GasEx-98 was an air-sea exchange process cruise conducted aboard the NOAA ship Ronald H. Brown in the North Atlantic during May and June of 1998. During the cruise, air-sea gas transfer velocities for carbon dioxide were measured using the direct-covariance method. Because the sampling times for the covariance method are on the same order as the time scales of changes in meteorological forcing, the GasEx-98 results provide a unique data set for investigating whether changes in different forcing mechanisms correlate with changes in gas transfer. In particular, fractional area whitecap coverage, WC, was measured during daylight hours using a dual-camera video system mounted on a bow tower. Several high wind speed events occurred during the cruise, and the resulting correlation between wind speed and WC is consistent with previous oceanic measurements. The whitecap coverage data were combined with the wind speed records and these data were used in a parameterization of whitecap-mediated gas transfer to predict transfer velocities. These predicted transfer velocities are in good agreement with the transfer velocities derived from the direct-covariance data.
Johns, W.E., T.L. Townsend, D.M. Fratantoni, and W.D. Wilson. On the Atlantic inflow to the Caribbean Sea. Deep-Sea Research, 49(2):211-243 (2002).
New observations are summarized that lead to the first comprehensive description of the mean inflow distribution in the passages connecting the Atlantic Ocean with the Caribbean Sea. The total Caribbean inflow of 28 Sv is shown to be partitioned approximately equally between the Windward Islands Passages (~10 Sv), Leeward Islands Passages (~8 Sv), and the Greater Antilles Passages (~10 Sv). These results are compared to a numerical model study using a 6-layer, 1/4° resolution Atlantic Basin version of the NRL Layered Ocean Model. Results from two simulations are described, including a purely wind-forced model driven by Hellerman and Rosenstein (J. Phys. Oceanogr., 13 (1983) 1093) monthly winds, and a model with an additional 14 Sv meridional overturning cell driven by inflow/outflow ports at the northern (65°N) and southern (20°S) model boundaries. The purely wind-driven version of the model exhibits a total Caribbean inflow of 17 Sv, consistent with expectations from steady, non-topographic Sverdrup theory. Nearly all of the wind-driven inflow occurs north of Martinique at latitude ~15°N. The net transport through the Lesser Antilles passages south of 15°N (Grenada, St. Vincent, and St. Lucia passages) is nearly zero when the model is forced by winds alone. The addition of a 14 Sv meridional cell in the model increases the net Caribbean inflow to 28 Sv, with nearly all of the additional 11 Sv of inflow entering through the southern Lesser Antilles passages. The modeled inflow distribution resulting from the combined wind and overturning forced experiment is found to compare favorably with the observations. The seasonal cycle of the total inflow in the combined forcing experiment has a mixed annual/semiannual character with maximum in spring and summer and minimum in fall, with a total range of about 4 Sv. The seasonal cycle of the Florida Current resulting from this inflow variation is in good qualitative agreement with observations. Most of the seasonal inflow variation occurs through the Windward Islands passages in the far southern Caribbean, whose annual cycle slightly leads that of the Florida and Yucatan Currents. Variability of the modeled inflow on shorter time scales shows a dramatic change in character moving northward along the Antilles arc. The southern passages exhibit large fluctuations on 30-80 day time scales, which decay to very small amplitudes north of Dominica. Much of this variability is caused by North Brazil Current Rings that propagate northwestward from the equatorial Atlantic and interact with the abrupt island arc topography. The total range of transport variability in individual passages predicted by the model is consistent with observations. However, observations are presently too limited to confirm the seasonal cycles or variability spectra in the Caribbean passages.
Katsaros, K.B., P.W. Vachon, W.T. Liu, and P.G. Black. Microwave remote sensing of tropical cyclones from space. Journal of Oceanography, 58:137-151 (2002).
This article reviews several microwave instruments employed in research and analysis of tropical cyclones (TCs), typhoons and hurricanes. The instruments discussed include scatterometers, microwave radiometers, synthetic aperture radars (SAR), and rain radar from space. Examples of the particular contribution by one or more of these instruments in analysis of several storms illustrate the comprehensive new views provided by the SeaWinds scatterometers, the detailed high-resolution wind field provided by RADARSAT SAR, particularly inside and in the vicinity of hurricane "eyes," and the presence of secondary flows in the region between rainbands in TCs. The high spatial resolution of precipitation data from the Tropical Rainfall Measuring Mission's rain radar, combined with scatterometer or SAR data, give a significant improvement in the details that can be seen from space, at the surface, and in the precipitating areas of TCs. The microwave instruments provide the penetrating view below the upper level cirrus clouds.
Rogers, R.F., S.D. Aberson, J. Kaplan, and S.B. Goldenberg. A pronounced upper-tropospheric warm anomaly encountered by the NOAA Gulfstream-IV aircraft in the vicinity of deep convection. Monthly Weather Review, 130(1):180-187 (2002).
Recent flights near deep convection by the National Oceanic and Atmospheric Administration's Gulfstream-IV surveillance aircraft have occasionally experienced significant positive temperature anomalies that sometimes impact the aircraft performance. One such event occurred over the Bahamas on 23 August 1999. During a 20-s time period, when the plane was cruising at an altitude of 175 hPa, the flight-level ambient temperature rose 15°C and returned to ambient values, concurrent with significant fluctuations in the horizontal and vertical winds. Large temperature anomalies such as that reported here can cause the avionics on the aircraft to compensate with a sudden decrease in air speed and a loss of altitude. Possible explanations for this anomaly include instrument error and convectively forced gravity waves or upper-level subsidence.
Schecter, D.A., M.T. Montgomery, and P.D. Reasor. A theory for the vertical alignment of a quasigeostrophic vortex. Journal of the Atmospheric Sciences, 59(2):150-168 (2002).
This article presents a new theory for the rate at which a quasigeostrophic vortex realigns, under conservative dynamics, after being tilted by an episode of external vertical shear. The initial tilt is viewed as the excitation of a three-dimensional "vortex Rossby mode." This mode, that is, the tilt, decays exponentially with time during its early evolution. The decay rate, gamma, is proportional to the potential vorticity gradient at a critical radius, where the fluid rotation is resonant with the mode. The decay rate gamma also depends on the internal Rossby deformation radius lR, which is proportional to the stratification strength of the atmospheric or oceanic layer containing the vortex. The change of gamma with lR is sensitive to the form of the vortex. For the case of a "Rankine-with-skirt" vortex, the magnitude of gamma increases (initially) with increasing lR. On the other hand, for the case of a "Gaussian" vortex, the magnitude of gamma decreases with increasing lR. The relevance of this theory to tropical cyclogenesis is discussed.
Wang, C. Atmospheric circulation cells associated with the El Niņo-Southern Oscillation. Journal of Climate, 15(4):399-419 (2002).
Atmospheric circulation cells associated with the El Niņo-Southern Oscillation (ENSO) are described and examined using the NCEP-NCAR reanalysis field and the NCEP sea surface temperature (SST) from January 1950 to December 1999. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. The warm phase of ENSO shows positive SST anomalies in the equatorial eastern Pacific and along the east coast of Asia and the west coast of North America, and negative SST anomalies in the off-equatorial western Pacific and in the central North Pacific. Associated with this SST anomaly distribution are variations of atmospheric zonal and meridional circulation cells over the Pacific. The equatorial zonal Walker circulation cell is weakened, consistent with previous schematic diagrams. The anomalous meridional Hadley circulation cell in the eastern Pacific shows the air rising in the Tropics, flowing poleward in the upper troposphere, sinking in the subtropics, and returning back to the Tropics in the lower troposphere. The anomalous Hadley cell in the western Pacific is opposite to that in the eastern Pacific. The divergent wind and vertical velocity also show a midlatitude zonal cell (MZC) over the North Pacific. The mean MZC is characterized by the air rising in the central North Pacific, flowing westward and eastward in the upper troposphere, descending in the east coast of Asia and the west coast of North America, then returning back to the central North Pacific in the lower troposphere. The anomalous MZC during the mature phase of El Niņo shows an opposite rotation to the mean MZC, indicating a weakening of the MZC.
**2001**
Aberson, S.D. The ensemble of tropical cyclone track forecasting models in the North Atlantic Basin (1976-2000). Bulletin of the American Meteorological Society, 82(9):1895-1904 (2001).
The suite of tropical cyclone track forecast models in the Atlantic basin from the 1976 to 2000 hurricane seasons are treated as a forecast ensemble. The 12-h ensemble mean forecast, adjusted for forecast difficulty, has improved at a rate of just under 1% per year, and the improvement rate increases to almost 2.4% per year for the 72-h forecasts. The average size of the 72-h (48-h) error in 1976 is less than the average size of the 48-h (36-h) error in 2000. The average 36-h forecast error in 2000 is comparable to the 24-h forecast error in 1976. The ensemble currently spans the true path of the tropical cyclone in the cross-track direction more than 90% of the time and in the alongtrack direction between 60% and 90% of the time depending on the forecast lead time. The ensemble spread is unable to provide estimates of individual forecast reliability, likely making probabilistic landfall forecasts from this ensemble unreliable. The reliability of the spread in the cross-track direction suggests the possibility of limiting hurricane watch and warning regions depending upon the ensemble spread at landfall.
Alvarez-Zarikian, C.A., P.L. Blackwelder, T. Hood, H.R. Wanless, T.A. Nelsen, and C. Featherstone. Impact on the sedimentary record derived from micropaleontological data. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 58-59 (2001).
Hurricanes are the strongest force causing immediate and long-term environmental changes to coastal areas in the lower Everglades and Florida Bay, and their sedimentary record. Hurricane-induced sediment erosion and deposition, and bi-directional sediment transport, can disrupt the sediment record, blending the signature of other ecological factors (i.e., salinity fluctuations) and leaving behind a complex overprint of natural and anthropogenic influences. Their frequency is also a potential mechanism for carbon storage and removal. Paleohurricane impact in the stratigraphic record is marked by abrupt changes in microfaunal abundance and community structure, as well as in quantitative and qualitative organic carbon content and sediment texture. Hurricane signatures, verifiable by offsets in 210Pb-geochronology data, are found in sediment cores recovered from Florida and Oyster Bays. Sediment core location controls the magnitude of variations in the sediment record. Semi-protected areas such as Oyster Bay exhibit the least amount of sediment disruption during and following the Labor Day Hurricane of 1935 and Hurricane Donna in 1960, whereas unprotected or less protected areas such as the First National Bank and Jimmy Key in western and central Florida Bay, respectively, experience the greatest effects.
Baringer, M.O., and J.C. Larsen. Sixteen years of Florida Current transport at 27°N. Geophysical Research Letters, 28(16):3179-3182 (2001).
Daily transports of the Florida Current have been inferred since 1982 through the use of submerged submarine telephone cables that measure the voltage difference across the Straits of Florida. Using all 16 years of data, the annual cycle ranges from a minimum of 30 Sv in January to a maximum of 33.5 Sv in July. The annual cycle is not stable throughout the entire period, however; the first eight years show a slightly larger peak-to-peak annual range of 5 Sv, while the second eight years have a semi-annual cycle with a distinct minimum in July and peak-to-peak range of 4 Sv. Filtered Florida Current transports contain a two to three year variation between 2 and 3 Sv in amplitude and a decadal variation of about ą2 Sv. The decadal changes in the Florida Current transport are significantly correlated (R = 0.75 at 95% significance) to the North Atlantic Oscillation Index.
Bentamy, A., K.B. Katsaros, A.M. Mestas-Nunez, E.B. Forde, W.M. Drennan, and H. Roquet. Latent heat fluxes over the ocean from merged satellite data. Intercomparison and Validation of Ocean-Atmosphere Flux Fields Workshop, Potomac, MD, May 21-24, 2001. WCRP-115-WMO/TD-No. 1083, 205-208 (2001).
The specific objectives of this paper emphasize estimation of global latent heat flux over the oceans with high spatial and temporal resolution using satellite radar and radiometer measurements. Consistency of the same surface parameters retrieved from several satellites is assured. The flux fields are compared to in-situ observations and atmospheric analysis fields globally and in different regions of the ocean with particular focus on the tropical oceans.
Brenner, R.J., M.J. Dagg, and P.B. Ortner. Growth, grazing, distribution, and carbon demand in the plankton of Florida Bay. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 103-104 (2001).
The zooplankton community of Florida Bay was examined over four years from September 1994 through November 1998 to determine zooplankton distribution and abundance and to allow calculation of community metabolic demands. Net zooplankton were collected at 10 sites within the Bay on a bimonthly basis using a 64 µm net, and copepod nauplii were collected from the surface at each site using a 10L bucket and 20 µm mesh. The net zooplankton were split into four functional groups: copepods, copepods nauplii, meroplanktonic larvae, and "others." The microplankton community was also investigated using the dilution technique of Landry and Hassett (1982). Microphytoplankton growth and microzooplankton grazing rates were determined fluorometrically at four sites, one in each region, from May 1997 through September 1998. Community structure within the microphytoplankton was determined using HPLC analysis. All data were used to determine if the four regions of Phlips et al. (1995), which were established based on primarily physical characteristics of the waters within each region, were applicable to the zooplankton community of Florida Bay. The copepod community was typically dominated by three genera--Acartia, Oithona, and Paracalanus--though other genera occasionally constituted >20% of the copepod stock. The "others" category was typically composed of chaetognaths, larvaceans, medusae, isopods, flatworms, and polychaetes, with distributions and abundances varying with no obvious seasonality. Copepods and their nauplii dominated the net zooplankton numerically and in terms of biomass and metabolic demands. Seasonal trends were apparent for most parameters within each group, with maxima occurring most frequently during the summer or fall and minima in the winter.
Broecker, W.S., C. Langdon, T. Takahasi, and T.-H. Peng. Factors controlling the rate of CaCO3 precipitation on Great Bahama Bank. Global Biogeochemical Cycles, 15(3):589-596 (2001).
Measurements by Langdon et al. (2000) in the man-made mesocosm coral reef at Biosphere 2's ocean reveal a strong dependence of calcification rate on the degree of supersaturation of CaCO3 in seawater. A similar trend was previously encountered on the Bahama Banks, where Halimeda and other calcifiers are likely responsible for aragonite precipitation (Broecker and Takahashi, 1966). In this paper, we compare these two sets of results and conclude that the dependence on saturation state is significant but less strong in the Bahamas. However, it must be kept in mind that to some extent, the reduction of CaCO3 precipitation on the Bahama Banks may be due to impact of higher salinity on the growth of the calcifying algae. However, if, as many sedimentologists are convinced, the precipitation of CaCO3 on the Bahama Banks is inorganic (Macintyre and Reid, 1992; Milliman et al., 1993), then the comparison of the Bahamas and Biosphere 2 results for dependence of calcification rate on saturation state is telling us something quite different.
Campos, E., A. Busalacchi, S.L. Garzoli, J. Lutjeharms, R. Matano, P. Nobre, D. Olson, A. Piola, C. Tanajura, and I. Wainer. Important aspects of the South Atlantic to the understanding of the global climate. In Observing the Oceans in the 21st Century: A Strategy for Global Ocean Observations, C.J. Koblinsky and N.R. Smith (eds.). GODAE Project Office, 19 pp. (2001).
Important aspects of the South Atlantic physical oceanography are discussed, and an attempt is made to identify 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 variability. Given the importance of the South Atlantic, it becomes crucial that variables such as sea surface temperature, currents, and surface fluxes be monitored on a continuous basis if one wishes to determine and predict the relationship between oceanic variability in the South Atlantic and global or regional climate. Thus, we understand that efforts should be concentrated in the study of the air-sea-land interactions leading to sea surface temperature variability, and the processes associated with the inter-hemispheric exchange of mass and heat by the Atlantic Meridional Overturning Cell. The knowledge of long-term variations of the Atlantic thermohaline circulation and how these variations lead to changes in SST and oceanic heat transports are key issues to be addressed. With regard to the thermohaline circulation, we identify some key locations where very important processes occur, and need to be monitored. These are the Brazil-Malvinas Confluence, the Agulhas Retroflection, the Benguela Current, and the bifurcation of the South Equatorial Current (SEC). Based on the topics discussed in this article, a sustainable observational program in the South Atlantic is proposed, based on a combination of ship-based hydrographic samplings, moored arrays of current meters and other profiling instruments, satellite-tracked drifters and ARGO floats, repeat cruises and SOOP XBT lines, acoustic measurements, surface flux measurements, and remote sensing. Contribution of the South American oceanographic community would be of great interest in the monitoring of the Brazil-Malvinas Confluence and South Equatorial Current Bifurcation regions. Cooperation with the African community would be desirable for the surveys in the Agulhas Retroflection and the Benguela Current.
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. Evolution and historical perspective of the 1997-1998 El Niņo-Southern Oscillation event. Bulletin of Marine Science, 69(1):7-25 (2001).
The ocean thermal history of the 1997-98 El Niņo 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 Niņa) 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. The magnitude of the event is also discussed in an historical context, with emphasis on comparisons to the El Niņo of 1982-83. Each of the two events, in its own way, set records. However, the two events are generally comparable in their magnitudes and the extent of their impacts, while both are top-ranked events for the period after 1950. In the centennial context, however, these events are not unprecedented, considering that they were probably enhanced by strong decadal warming during the 1980s and 1990s. An attempt is made to assess the accuracy of model forecasts of the 1997-1998 event. Two recent studies are discussed which generally agree that statistical and dynamical models under-predicted the equatorial warming prior to its onset and failed to capture the strong, early onset at all. Predictions of the late-1997 climax, with shorter lead times, improved once the data showing large mid-1997 anomalies were ingested into the models. However, the revised predictions were not in time to guide the successful atmospheric climate outlook for North America, which was issued in June 1997 on the basis of observed strong anomalies on the equator.
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., and A.M. Mestas-Nunez. The Atlantic multidecadal oscillation and its relationship to rainfall and river flows in the continental U.S. Greater Everglades Ecosystem Restoration Science Conference, Naples, FL, December 11-15, 2000. South Florida Ecosystem Restoration Task Force and Working Group, 325 (2001).
An Atlantic Multidecadal Oscillation (AMO) has recently been identified that may have had a large impact on European and American climates in the 19th and 20th centuries and may be driven by the Atlantic thermohaline circulation (Schlesinger and Ramankutty, 1994; Enfield and Mestas-Nunez, 1999; Kerr, 2000; Delworth and Mann, 2000). As an index of the oceanic expression of the AMO, we have computed the 10-year running means of North Atlantic SST anomaly (SSTA) from the Kaplan et al. (1998) SSTA analysis (1856-1999). In agreement with other studies, we find AMO maxima (positive SSTA) during 1860-1880 and 1940-1960, and minima during 1905-1925 and 1970-1990, with periods ranging from 65 to 80 years. We find a significant (95%) correlation of the AMO with monthly precipitation for many of the climate divisions of the continental U.S. (1895-1992). We use a Monte Carlo approach with frequency-domain phase randomization of the serially correlated data to judge the significance. Over much of the Mississippi River Basin the significant correlations are negative, as is the integrated rainfall over the basin. Strong negative correlations are also found in the northern Rocky Mountains. Positive correlations are limited to two small regions: south-central Florida and in the Pacific Northwest east of the Cascades. At hydrological checks, we also find a significant negative correlation with the directly measured Mississippi River outflow, and a significant positive correlation with the inflow into Lake Okeechobee (south-central Florida). To diagnose the relationships, we construct composite averages (for recent contrasting phases of the AMO) of tropospheric NCEP/NCAR reanalysis variables (1950-present). We also examine the strength of ENSO-rainfall correlations for both phases of the AMO.
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 Niņo-Southern Oscillation are also significantly changed between AMO phases.
Feely, R.A., C.L. Sabine, T. Takahashi, and R. Wanninkhof. Uptake and storage of carbon dioxide in the ocean: The global CO2 survey. Oceanography, 14(4):18-32 (2001).
No abstract.
Fine, R.A., K.A. Maillet, K.F. Sullivan, and D. Willey. Circulation and ventilation flux of the Pacific Ocean. Journal of Geophysical Research, 106(C10):22,159-22,178 (2001).
The flux of water from the mixed layer into the thermocline/intermediate layers of the Pacific Ocean is quantified using chlorofluorocarbon (CFC) and hydrographic data. The total ventilation flux of at least 123 Sv for the South Pacific (SP) only sightly exceeds that of at least 111 Sv for the North Pacific (NP). Although the overall ventilation flux (to 27.3 sigmatheta) is similar in the NP and SP, the partitioning amongst the water masses is markedly different. In the NP, the partitioning is equal between the wind-driven (< 26.5 sigmatheta) and thermohaline (>26.5-27.3 sigmatheta) layers. While in the SP, the ventilation flux of the thermohaline layers exceeds by nearly 2:1 the wind-driven layers. The wind-driven subtropical gyre thermocline ventilation flux for the NP (41 Sv) exceeds the SP (25 Sv), and both agree well with literature estimates of Sverdrup transports. The ventilated volumes and ages are related to the wind stress curl and surface buoyancy fluxes. In the thermocline ventilation of Shallow Salinity Minimum Water (22 m yr-1 in the NP, 15 m yr-1 in the SP) and Subtropical Mode Water is more effective in the NP than in the SP. In contrast, in the thermohaline layers direct air-sea exchange during convective formation of Subantarctic Mode and Antarctic Intermediate Water is more effective in ventilating the SP than processes in the NP. These same differences are also used to explain the larger volume of the shadow zone in the NP. In the subpolar regions, the ventilation fluxes can be used to infer formation rates of 8 Sv for the NP Intermediate Water and 9 Sv for the Subantarctic Mode Water. Into the tropical Pacific there is a substantial flux of 35 Sv of extratropical water for the wind-driven layers and 36 Sv for the thermohaline layers. The relatively young (5-20 years increasing with increasing density) CFC-derived ages show that a climate anomaly introduced into the subtropical thermocline could be transported into the tropics relatively quickly.
Garzoli, S.L. CLIVAR workshop on tropical Atlantic variability. CLIVAR Exchanges, 6(4):33-35 (2001).
No abstract.
Garzoli, S.L., and R.L. Molinari. Ageostrophic transport in the upper layers of the tropical Atlantic Ocean. Geophysical Research Letters, 28(24):4619-4622 (2001).
A test of the theoretical Ekman relation in the tropical Atlantic Ocean is performed by comparing estimated Ekman transport with observations collected along two transects symmetric about the equator (6°N and 6°S). Ekman transport is calculated theoretically using ship winds and climatological data. Total ageostrophic transport is obtained by subtracting the observed geostrophic transports from the measured total transports using the data collected along the two transects. Along 6°S, both the zonal mean ageostrophic transport and its variability with longitude can be accounted for by the theoretical Ekman transport. Along 6°N, the total ageostrophic and Ekman transports agree, but significant differences are found in the cumulative transport curves between the African coast and about 40°W. These departures from theory may be related to the effect of advective terms in the Ekman relation and/or other ageostrophic motion at the reference depth for the comparisons.
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.
Goni, G.J., and I. Wainer. Brazil Current front dynamics from altimeter data. Journal of Geophysical Research, 106(C12):31,117-31,128 (2001).
The southwestern Atlantic is characterized by the confluence of the Brazil and Malvinas Currents forming very strong surface and subsurface fronts which can be detected from hydrographic and remote sensing procedures. Three data sets, consisting of TOPEX/Poseidon-derived sea height anomalies, and the climatologically-derived depth of the 10°C isotherm and reduced gravity are used within a two-layer dynamical ocean model context to monitor the Brazil Current front and to investigate its variability during a six-year period (1993 through 1998). Results reveal that the fronts exhibit motions that are larger zonally than meridionally, showing strong interannual variability with annual mean amplitudes that range from 1 to 6 degrees. The annual and semiannual components account for more than 75% of the variability of the frontal oscillations. In the annual cycle, the frontal motions appear to be closely related to fluctuations in the baroclinic transport of the Brazil Current and are only influenced by the Malvinas Current when the Brazil Current transport is very small.
Goodwin, K.D., R.K. Varner, P.M. Crill, and R.S. Oremland. Consumption of tropospheric levels of methyl bromide by C1 bacteria and comparison to saturation kinetics. Applied and Environmental Microbiology, 67(12):5437-5443 (2001).
Pure cultures of methylotrophs and methanotrophs are known to oxidize methyl bromide (MeBr); however, their ability to oxidize tropospheric concentrations (parts per trillion by volume [pptv]) has not been tested. Methylotrophs and methanotrophs were able to consume MeBr provided at levels that mimicked the tropospheric mixing ratio of MeBr (12 pptv) at equilibrium with surface waters (~2 pM). Kinetic investigations using picomolar concentrations of MeBr in a continuously stirred tank reactor (CSTR) were performed using strain IMB-1 and Leisingeria methylohalidivorans strain MB2T, terrestrial and marine methylotrophs capable of halorespiration. First-order uptake of MeBr with no indication of threshold was observed for both strains. Strain MB2T displayed saturation kinetics in batch experiments using micromolar MeBr concentrations, with an apparent Ks of 2.4 µM MeBr and a Vmax of 1.6 nmol h-1 (106 cells)-1. Apparent first-order degradation rate constants measured with the CSTR were consistent with kinetic parameters determined in batch experiments, which used 35- to 1 x 107-fold higher MeBr concentrations. Ruegeria algicola (a phylogenetic relative of strain MB2T), the common heterotrophs Escherichia coli and Bacillus pumilus, and a toluene-oxidizer, Pseudomonas mendocina KR1, were also tested. These bacteria showed no significant consumption of 12 pptv MeBr; thus, the ability to consume ambient mixing ratios of MeBr was limited to C1-oxidizing bacteria in this study. Aerobic C1 bacteria may provide model organisms for the biological oxidation of tropospheric MeBr in soils and waters.
Hendee, J.C., E. Mueller, C. Humphrey, and T. Moore. A data-driven expert system for producing coral bleaching alerts at Sombrero Reef in the Florida Keys. Bulletin of Marine Science, 69(2):673-684 (2001).
A computer expert system shell was employed to provide interpretations of near real-time acquired combinations of meteorological and oceanographic parameters from a SEAKEYS (Sustained Ecological Research Related to Management of the Florida Keys Seascape) station at Sombrero Reef. When environmental conditions were conducive to coral bleaching, according to different models, alerts were automatically posted to the World-Wide Web and emailed to researchers so they could verify and study bleaching events as they might happen. The models were refined using feedback from field data on bleaching recorded after alerts from the expert system. The expert system was programmed to produce alerts when sea temperatures over 30°C occurred, or when temperatures of 30°C occurred concomitant with low winds. Alerts were produced in June 1998 when these conditions were met, but bleaching did not occur. Reconfiguration of the system, which included a point system for three models (high sea temperature only, high sea temperature plus low winds, high sea temperature plus low winds plus low tide), resulted in the transmittal of alerts which coincided with bleaching during early August 1998. Bleaching occurred after sea temperature reached an average of 31.5°C over a period of three days, with excursions over 31.8°C occurring over 15 times during those three days. High sea temperatures, low wind speeds, and a very low tide occurred coincident to the time of bleaching, but it was not possible to tell if these were factors acting synergistically.
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 (GASEX-98), 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.
Humphrey, J.C., J. Absten, S.L. Vargo, J.C. Ogden, J.C. Hendee, T.A. Nelsen, D. Danaher, C.L. Jeffris, and D. Burwell. SEAKEYS: Florida Keys monitoring initiative. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 87-88 (2001).
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 with initial funding from the John D. and Catherine T. MacArthur Foundation, and has been maintained through continuing support provided by the South Florida Ecosystem Restoration, Prediction and Monitoring program, administered by the National Oceanic and Atmospheric Administration (NOAA). The SEAKEYS environmental monitoring program was designed to provide data for a long-term database of meteorological and oceanographic data from the Florida Straits and Florida Bay. The SEAKEYS network provides wind speed, wind gust, air temperature, barometric pressure, sea temperature, and salinity for all stations; and tide level, precipitation, photosynthetically active radiation, fluorometry, and transmissometry for selected stations. These data are transmitted hourly to a GOES satellite, and from there are downloaded for data and information management purposes. SEAKEYS data have been used to characterize the dynamics of several hurricanes since 1992, and have been of great benefit to hurricane forecasters at the National Weather Service and at AOML's Hurricane Research Division in Miami, Florida. Daily data are posted to NOAA's Coral Health and Monitoring Program Web site (http://www.coral.noaa.gov), while historical data are available at http://www.neptune.noaa.gov. These data have also allowed researchers to correlate meteorological and hydrographic dynamics, e.g., El Niņo/La Niņa conditions, with environmental changes in Florida Bay and the Florida Keys National Marine Sanctuary.
Johns, E., R.H. Smith, W.D. Wilson, T.N. Lee, and E. Williams. Influence of hurricanes, tropical storms, and cold fronts on south Florida coastal waters. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 14-15 (2001).
The south Florida climate is characterized by a tropical dry season/wet season pattern, with a wet season typically beginning in June with the onset of summer rainy conditions, and much drier conditions from November to April. The regional climate is also affected in late summer by the passage of tropical cyclones, and in the winter by the passage of cold fronts. These extreme weather events are evident not only in the standard meteorological measurements such as barometric pressure, wind speed and direction, air temperature, and precipitation, but are also manifested in such oceanographic variables as sea surface temperature, sea surface height, current speed and direction, sea surface salinity, and water column turbidity. As part of a joint University of Miami/NOAA project entitled Circulation and exchange of Florida Bay and connecting waters of the Gulf of Mexico and the Florida Keys, a variety of observations have been collected beginning in December 1995. These measurements, which were expanded in scope beginning in September 1997, now include bimonthly interdisciplinary shipboard surveys of salinity, temperature, fluorescence, and nutrients, as well as satellite-tracked surface drifters and moored arrays of currents, temperature, and conductivity. The study area extends from Florida Bay north to Naples, Florida, southwest to the Dry Tortugas, east to Key West and then northeast to Miami, Florida. In addition to the bimonthly surveys, observations are obtained monthly within Florida Bay using a shallow draft catamaran equipped with a continuous flow-through thermosalinograph system. Since 1995, a number of tropical cyclones have come close enough to affect south Florida environmental conditions by means of extreme wind, rain, or both. Although none of these recent tropical cyclones have come close to matching the historically most severe events of the region (e.g., the well-known Labor Day hurricane in 1935, Hurricane Donna in 1960, and Hurricane Andrew in 1992), they still influenced the regional meteorological and oceanographic climate.
Johns, E., P.B. Ortner, R.H. Smith, W.D. Wilson, T.N. Lee, and E. Williams. Salinity variability in Florida Bay from monthly high resolution surveys. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 16-17 (2001).
As part of NOAA's South Florida Ecosystem Restoration, Prediction and Modeling (SFERPM) program, a time series of high resolution salinity maps of Florida Bay has been obtained using a shallow draft catamaran equipped with a continuous flow-through thermosalinograph system. Each survey is completed within two consecutive days. These maps, produced at an approximately monthly interval from March 1997 to the present, cover the three major subdivisions of Florida Bay, i.e., the northeast Bay, the central Bay, and the western Bay. The three Bay regions respond differently to meteorological and other forcing mechanisms due to their differing degrees of isolation from other coastal waters. For example, the northeast Bay is relatively isolated by the geometry of its coastlines and the shallow mud banks which separate it from the central Bay. The northeast Bay is subject to time-varying inputs of fresh water from the rivers and canals of the Taylor Slough and, as a result, has an extremely large salinity variability related to seasonal and interannual precipitation patterns, as well as to water management practices. On the other hand, the central region of Florida Bay, although also fairly isolated in terms of its topography (except at its southern border where exchange of water with the Atlantic occurs through a few narrow tidal channels between the Florida Keys), has few direct sources of fresh water. Thus, the salinity of the central Bay exhibits a different pattern of variability, responding to the changing balance between local evaporation and precipitation which regularly produces periods of hypersalinity interspersed with much lower salinity periods on a timescale of several months or longer. The persistence of these high or low salinity periods is indicative of long residence times for these basins. Western Florida Bay, on the other hand, has an open western boundary and thus is subject to open exchange of water with the eastern Gulf of Mexico and the southwest Florida shelf. The numerous rivers of the southwest Florida coast, such as the Shark, Broad, and Lostmans Rivers, contribute a time-varying source of fresh water from the Shark River Slough area of the Everglades which at times can flow around Cape Sable and interact with western Florida Bay, providing another source of salinity variability there. Due to the more open exchange with the surrounding Gulf of Mexico and southwest Florida shelf waters, the salinity of the western part of the Bay does not exhibit the long residence times of the northeast and central Bay, but instead can change rather rapidly when influenced by tropical storms, the passage of cold fronts, and other extreme forcing events. Determination of the rates and pathways of exchange between the interior basins of Florida Bay and with the southwest Florida shelf is a critical need for predicting the effects of modifying the fresh water supply to the Everglades as part of the Everglades restoration effort. At present, it is not understood how the proposed changes in water delivery, with increased fresh water flows to the Shark River and Taylor Slough, will affect salinity variability within Florida Bay. However, it is generally agreed that the large seasonal and longer period variations of salinity within the Bay have significant impacts on the sea grass and plankton communities within the Bay, and possibly also with adjacent marine ecosystems of the southwest Florida shelf and the Florida Keys National Marine Sanctuary due to transport processes linking the regions.
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. Basin boundaries. In Wind Stress Over the Ocean, I.S.F. Jones and Y. Toba (eds.). Cambridge University Press, 270-275 (2001).
No abstract.
Katsaros, K.B. Evaporation and humidity. In Encyclopedia of Ocean Sciences, J.H. Steele, S.A. Thorpe, and K.K. Turekian (eds.). Academic Press, London, 870-877 (2001).
No abstract.
Katsaros, K.B. Sensors for mean meteorology. In Encyclopedia of Ocean Sciences, J.H. Steele, S.A. Thorpe, and K.K. Turekian (eds.). Academic Press, London, 2744-2751 (2001).
No abstract.
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 m/s. 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.
Knaff, J.A., and C.W. Landsea. Application of the El Niņo-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 10(2):31-34 (2001).
No abstract.
Knaff, J.A., and C.W. Landsea. Application of the El Niņo-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 10(3):40-42 (2001).
No abstract.
Kollias, P., B.A. Albrecht, and F.D. Marks. Raindrop sorting induced by vertical drafts in convective clouds. Geophysical Research Letters, 28(14):2787-2790 (2001).
Evidence of raindrop sorting by a convective updraft is presented. Using a vertically pointing 94-GHz Doppler radar (lambda = 3.2 mm) and capitalizing on the resonant nature of the backscattering cross-section as a function of the raindrop size (Mie scattering), the vertical air motions to an accuracy of 0.1 m s-1, and the shape of the raindrop size distribution are retrieved from the Doppler spectra. The interaction of vertical drafts and raindrops is documented for the first time by high resolution radar data. The updraft structure clearly causes horizontal and vertical sorting of the raindrops. In the updraft core, small raindrops (D < 1.7 mm) that have terminal velocities less than the updraft velocities (6-7 m s-1) and a clear absence of drops > 3 mm are observed. Towards the updraft periphery, a gradual increase in the raindrop sizes is documented where large raindrops (D > 3 mm) are observed. The observations demonstrate the importance of updrafts in distributing the raindrops in space.
Landsea, C.W. Comment on "Changes in the rates of North Atlantic major hurricane activity during the 20th century." Geophysical Research Letters, 28(14):2871-2872 (2001).
No abstract.
Landsea, C.W., and J.A. Knaff. Application of the El Niņo-Southern Oscillation CLImatology PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 10(1):31-33 (2001).
No abstract.
Lee, T.N., E. Williams, E. Johns, W.D. Wilson, and N.P. Smith. Transport processes linking south Florida coastal ecosystems. In The Everglades, Florida Bay, and Coral Reefs of the Florida Keys: An Ecosystem Sourcebook, K.G. Porter and J.W. Porter (eds.). CRC Press, Boca Raton, 309-342 (ISBN 0849320267) (2001).
No abstract.
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.
Macdonald, A.M., M.O. Baringer, and A. Ganachaud. Heat transport and climate. In Encyclopedia of Ocean Sciences, J.H. Steele, S.A. Thorpe, and K.K. Turekian (eds), London, Academic Press, Vol. 2, 1195-1206 (2001).
No abstract.
Marks, F.D. Quantitative precipitation forecasting in hurricanes: Issues and opportunities. Preprints, Symposium on Precipitation Extremes: Prediction, Impacts, and Responses, Albuquerque, NM, January 14-19, 2001. American Meteorological Society, Boston, 293-296 (2001).
No abstract.
Mayer, D.A., R.L. Molinari, M.O. Baringer, and G.J. Goni. Transition regions and their role in the relationship between sea surface height and subsurface temperature structure in the Atlantic Ocean. Geophysical Research Letters, 28(20):3943-3946 (2001).
Expendable bathythermograph (XBT) profiles and TOPEX/Poseidon altimeter data (T/P) are compared for the years 1993 through 1997 to determine how much can be understood about water column variability from XBTs given only sea height anomalies (SHA) from T/P. Our focus is on the annual cycle along two well sampled XBT sections in the Atlantic Ocean from 10°S to 40°N. Regions of transition are identified that separate the mid-latitudes where surface buoyancy fluxes dominate the forcing of sea level, from those in the equatorial region where thermocline effects dominate. Zones of transition occur in the vicinity of troughs where small fluctuations in SHA belie the true nature of water column variability. Here, surface and thermocline variability tend to cancel each other. Thus, the character of SHA in transition regions emphasizes how important direct observations can be in interpreting satellite altimetric observations correctly when both surface and thermocline variability are important but are compensating in nature.
McGillis, W.R., J.B. Edson, J.D. Ware, J.W.H. Dacey, J.E. Hare, C.W. Fairall, and R.H. Wanninkhof. Carbon dioxide flux techniques performed during GasEx-98. Marine Chemistry, 75(4):267-280 (2001).
A comprehensive study of air-sea interactions focused on improving the quantification of CO2 fluxes and gas transfer velocities was performed within a large open ocean CO2 sink region in the North Atlantic. This study, GasEx-98, included shipboard measurements of direct covariance CO2 fluxes, atmospheric CO2 profiles, atmospheric DMS profiles, water column mass balances of CO2, and measurements of deliberate SF6-3He tracers, along with air-sea momentum, heat, and water vapor fluxes. The large air-sea differences in partial pressure of CO2 caused by a springtime algal bloom provided high signals for accurate CO2 flux measurements. Measurements were performed over a wind speed range of 1-16 m s-1 during the three-week process study. This first comparison between the novel air-side and more conventional water column measurements of air-sea gas transfer show a general agreement between independent air-sea gas flux techniques. These new advances in open ocean air-sea gas flux measurements demonstrate the progress in the ability to quantify air-sea CO2 fluxes on short time scales. This capability will help improve the understanding of processes controlling the air-sea fluxes which, in turn, will improve our ability to make regional and global CO2 flux estimates.
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 Niņo-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 1982-1983 and 1997-1998 El Niņo events were accounted for by the residual variability. The non-ENSO variability is characterized by the known shift from cold to warm in the eastern tropical Pacific in the mid to 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.
Michaels, M., M. Shepard, S.D. Aberson, H.A. Friedman, and K. Murphy. Survey results of Society membership: The face of our profession at the threshold of the new millennium. Bulletin of the American Meteorological Society, 82(7):1331-1352 (2001).
In the spring of 1999, the American Meteorological Society surveyed its membership in order to update demographic information on the Society and to gain a more detailed perspective on the workplace. The survey was sent out with the dues statement and was solicited on a separate form returned independently to protect privacy and maintain anonymity. The responses were captured in a newly employed, machine-readable format to provide an ease of statistical analysis and data compilation not available in prior survey analysis. This data collection and subsequent demographic analysis represents the first attempt to update information regarding the membership since the 1993 survey results were published by Zevin and Seitter. The format of the 1999 survey was designed to logically follow and expand upon the historical data of the membership collected at varying intervals since 1975. The 1999 survey was broken into six parts. The sections on demographics, education, and current employment closely followed the previous surveys from 1993 and 1990 to facilitate direct comparisons between historical datasets whenever possible. The last three sections were reworked to elicit more declarative responses regarding personal circumstances, workplace circumstances, and additional issues concerning career choice and AMS membership, respectively. An additional space was provided for narrative comments regarding opportunities for women and minorities in the AMS-related sciences. Some 10,000 members were sent the 1999 dues statement and enclosed survey questionnaire. A total of 4,669 members responded. The following is a detailed analysis of the data collected from the 1999 membership survey.
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 ą0.7 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. McGraw-Hill, 687 pp. (ISBN 0072190930) (2001).
No abstract.
Nelsen, T.A., G. Garte, C. Featherstone, H.R. Wanless, J.H. Trefry, W.-J. Kang, S. Metz, C. Alvarez-Zarikian, T. Hood, P. Swart, G. Ellis, P. Blackwelder, L. Tedesco, C. Slouch, J.F. Pachut, and M. O'Neal. Linkages between the south Florida peninsula and coastal zone: A sediment-based history of natural and anthropogenic influences. In The Everglades, Florida Bay, and Coral Reefs of the Florida Keys: An Ecosystem Sourcebook, K.G. Porter and J.W. Porter (eds.). CRC Press, Boca Raton, 415-449 (ISBN 0849320267) (2001).
No abstract.
Ochoa, J., J. Sheinbaum, A. Badan, J. Candela, and W.D. Wilson. Geostrophy via potential vorticity inversion in the Yucatan Channel. Journal of Marine Research, 59(5):725-747 (2001).
It has become common practice to measure ocean current velocities together with the hydrography by lowering an ADCP on typical CTD casts. The velocities and densities thus observed are considered to consist mostly of a background contribution in geostrophic balance, plus internal waves and tides. A method to infer the geostrophic component by inverting the linearized potential vorticity (PV) provides plausible geostrophic density and velocity distributions. The method extracts the geostrophic balance closest to the measurements by minimizing the energy involved in the difference, supposed to consist of PV-free anomalies. The boundary conditions and the retention of PV by the geostrophic estimates follow directly from the optimization, which is based on simple linear dynamics and avoids both the use of the thermal wind equation on the measured density, and the classical problem of a reference velocity. By construction, the transport in geostrophic balance equals the measured one. Tides are the largest source of error in the calculation. The method is applied to six ADCP/CTD surveys made across the Yucatan Channel in the springs of 1997 and 1998 and in the winter of 1998-1999. Although the time interval between sections is sometimes close to one inertial period, large variations on the order of 10% are found from one section to the next. Transports range from 20 to 31 Sv with a net average close to 25 Sv, consisting of 33 Sv of inflow into the Gulf of Mexico and 8 Sv of outflow into the Caribbean Sea. The highest velocities are 2.0 m sec-1 into the Gulf of Mexico near the surface on the western side of the channel, decreasing to 0.1 m sec-1 by 400 to 500 m depth. Beneath the core of the Yucatan Current a countercurrent, with speeds close to 0.2 m sec-1 and an average transport of 2 Sv, hugs the slopes of the channel from 500 to 1500 m depth. Our data show an additional 6 Sv of return flow within the same depth range over the abrupt slope near Cuba, which is likely to be the recirculating fraction of the Yucatan Current deep extension, unable to outflow through the Florida Straits. The most significant southerly flows do not occur in the deepest portion of the channel, but at depths around 1000 m.
Ooyama, K.V. A dynamic and thermodynamic foundation for modeling the moist atmosphere with parameterized microphyics. Journal of the Atmospheric Sciences, 58(15):2073-2102 (2001).
Moist convection is an exquisite yet powerful participant in the creation of weather on our planet. To facilitate numerical modeling of weather systems in a moist atmosphere, a direct and consistent application of dynamic and thermodynamic principles, in conjunction with parameterized microphysics, is proposed. An earlier formulation of reversible thermodynamics, in terms of the mass of air and water substance and the total entropy, is now extended to include the irreversible process of precipitation through parameterized microphysics. The dynamic equations are also formulated to account consistently for the mass and momentum of precipitation. The theoretical proposal is tested with a two-dimensional model that utilizes a versatile and accurate spectral method based on a cubic-spline representation of the spatial fields. In order to allow a wide range of scale interactions, the model is configured on multiply-nested domains of outwardly decreasing resolution, with noise-free, two-way interfaces. The semi-implicit method provides efficient time integration for the nested spectral model. The tests performed are the simulation of the growth of single-cell clouds and also the generation of self-sustaining multicell squall lines, and the effects of various resolutions on the simulations are examined. The results favorably compare with similar results found in the literature, but also offer new insights into the interplay between dynamics and precipitation.
Ortner, P.B., L.C. Hill, M.J. Dagg, J. Rabelais, and G. Thayer. Mesozooplankton abundance variability within Florida Bay (1994-2000). Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 195-196 (2001).
Since 1994, NOAA's South Florida Ecosystem Restoration Prediction and Modeling (SFERPM) program has supported regular monitoring of plankton populations in Florida Bay and adjacent coastal waters along the west Florida shelf and seaward of the Florida Keys. One reason is that the zooplankton of Florida Bay had received comparatively little attention prior to this work with not a single published report quantitatively characterizing the resident population. Another impetus for doing so was the relationship between zooplankton grazing and phytoplankton blooms. However, bloom incidence might be but one aspect of a more general phenomenon, ecosystem shift, and habitat change. A change of state in the Bay ecosystem could have enormous consequence to the commercially and recreationally significant living resources to which the Bay represents a nursery ground and was, therefore, a particularly important issue to NOAA. Initial results supported this notion. However, as additional data have accumulated, we now have little doubt that these initial hypotheses were over simplified. The ecosystem in Florida Bay does not appear to be undergoing a monotonic change to a more pelagic state. In this respect, the results appear consistent with the SERC surveys indicating that over the same time period plankton blooms have, in general, not systematically increased throughout Florida Bay. By coincidence, we may have initiated our study close to the apex of phytoplankton bloom intensity. Based on enumerations from 64 µm net tows, the abundance of copepods and other holoplanktonic macroplankton was moderate in the fall of 1994 through mid-winter 1995 but declined markedly thereafter to exceedingly low levels until ca. spring 1996 when it returned to similar levels. Thereafter to the present, it has increased markedly. Taxa vary but values more than five times higher than those present in 1994 have become common. The increase has occurred without any apparent increase in their apparent food source, the phytoplankton. This is not surprising, however. In shallow subtropical estuaries such as Florida Bay, a substantial fraction of the trophic base supporting zooplankton populations may be derived from primary production by seagrass and benthic algae rather than phytoplankton, vitiating any direct positive relationship between the abundances of zooplankton and phytoplankton. Interestingly, a similar trend was observed in the western, central, and eastern regions of the Bay despite their systematic differences in salinity, water column chlorophyll, bloom incidence, etc. In contrast, the abundance of a dominant water column planktivore, Anchovia mitchelli, the bay anchovy, varied almost inversely with the abundance of its prey. Bay anchovy abundance in the same regions was high until 1996, when it dominated the forage fish community, but has declined precipitously thereafter to levels observed during the mid-1980s. However, sampling has been insufficient to provide rigorous estimates of bay anchovy abundance. Concentrations sufficient to appreciably reduce zooplankton numbers were observed with some regularity. In short, the recent history of phytoplankton, zooplankton, and planktivorous fish abundance provides little or no support for the concept of a fundamental persistent Bay shift from a demersal benthic production-based ecosystem to a pelagic water column production-based ecosystem.
Peltola, E., K. Lee, R. Wanninkhof, R. Feely, M. Roberts, D. Greeley, M.O. Baringer, G. Johnson, J. Bullister, C. Mordy, J.-Z. Zhang, P. Quay, F. Millero, D. Hansell, and P. Minnett. Chemical and hydrographic measurements on a Climate and Global Change Cruise along 24°N in the Atlantic Ocean WOCE Section A5R (repeat) during January-February 1998. NOAA Data Report, OAR AOML-41, 199 pp. (2001).
This document contains data and metadata from a zonal cruise along nominally 24.5°N in the Atlantic Ocean from Las Palmas, Canary Islands in Spain to Miami, Florida. The cruise took place from January 23 to February 24, 1998 aboard the NOAA Ship Ronald H. Brown under auspices of the National Oceanic and Atmospheric Administration (NOAA). This report presents the analytical and quality control procedures performed during the cruise and bottle data from the cruise. The research was sponsored by the NOAA Climate and Global Change Program under: (i) The Ocean-Atmosphere Carbon Exchange Study (OACES); and (ii) the World Ocean Circulation Experiment (WOCE) repeat hydrography program. Samples were taken from up to 36 depths at 130 stations. The data presented in this report includes the analyses of water samples for: salinity, nutrients, total dissolved inorganic carbon dioxide (DIC), fugacity of carbon dioxide (fCO2), total alkalinity (TA), pH, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), chlorofluorocarbons, and stable carbon isotopic ratio of DIC (13C/12C). Basic hydrographic parameters, pressure, CTD salinity, temperature and the calculated potential temperature, and potential density are included as well.
Phoebus, P.A., D.R. Smith, P.J. Croft, H.A. Friedman, M.C. Hayes, K.A. Murphy, M.K. Ramamurthy, B. Watkins, and J.W. Zeitler. Meeting summary: Ninth AMS symposium of education. Bulletin of the American Meteorological Society, 82(2):295-303 (2001).
The American Meteorological Society held its Ninth Symposium on Education in conjunction with the 80th Annual Meeting in Long Beach, California. The theme of this year's symposium was "Atmospheric and Oceanographic Education-Expanding our Vision for the New Millennium." Thirty-five oral presentations and 53 poster presentations summarized a variety of educational programs or examined educational issues for both the precollege and university levels. There was a special session reporting on a recent survey conducted by the Board on Women and Minorities, as well as a special session on the educational applications of satellite meteorology and oceanography. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference. The program for the Ninth Symposium on Education can be viewed in the October 1999 issue of the Bulletin.
Pinker, R.T., K.B. Katsaros, and B. Zhang. Prospects for satellite estimates of net air-sea flux. Intercomparison and Validation of Ocean-Atmosphere Flux Fields Workshop, Potomac, MD, May 21-24, 2001. WCRP-115-WMO/TD-No. 1083, 223-227 (2001).
No abstract.
Powell, M.D., and S.D. Aberson. Accuracy of United States tropical cyclone landfall forecasts in the Atlantic Basin (1976-2000). Bulletin of the American Meteorological Society, 82(12):2749-2768 (2001).
About 13% of all Atlantic basin tropical cyclone forecasts issued from 1976 to 2000 are for landfalls along the United States coastline, and 2% more are for storms forecast to make landfall in the United States but that remain at sea. Landfall position and time forecasts are skillful at all forecast time periods and are more skillful than Atlantic basin track forecasts as a whole, but within 30 h of predicted landfall, timing errors demonstrate an early bias of 1.5-2.5 h. Landfall forecasts are most accurate for storms moving at oblique or normal angles to the coastline and slow-moving storms. During the last quarter century, after adjustment for forecast difficulty, no statistically significant improvement or degradation is noted for landfall position forecasts. Time of landfall forecasts indicate no degradation at any period and significant improvement for the 19-30 h period. The early bias and lack of improvement are consistent with a conservative or "least regret" forecast and warning strategy to account for possible storm accelerations. Landfall timing uncertainty is ~11 h at 24 and 36 h, which suggests that hurricane warnings could be disseminated about 12 h earlier (at 36 h, rather than 24 h, before predicted landfall) without substantial loss of lead time accuracy (although warning areas necessarily would be larger). Reconsideration of National Weather Service Strategic Plan and United States Weather Research Program track forecast goals is recommended in light of these results.
Reasor, P.D., and M.T. Montgomery. Three-dimensional alignment and corotation of weak, TC-like vortices via linear vortex Rossby waves. Journal of the Atmospheric Sciences, 58(16):2306-2330 (2001).
The vertical alignment of an initially tilted geostrophic vortex is shown here to be captured by linear vortex Rossby wave dynamics when the vortex cores at upper and lower levels overlap. The vortex beta Rossby number, defined as the ratio of nonlinear advection in the potential vorticity equation to linear radial advection, is less than unity in this case. A useful means of characterizing a tilted vortex flow in this parameter regime is through a wave-mean flow decomposition. From this perspective, the alignment mechanism is elucidated using a quasigeostrophic model in both its complete and linear equivalent barotropic forms. Attention is focused on basic-state vortices with continuous and monotonically decreasing potential vorticity profiles. For internal Rossby deformation radii larger than the horizontal scale of the tilted vortex, an azimuthal wavenumber 1 quasi mode exists. The quasi mode is characterized by its steady cyclonic propagation, long lifetime, and resistance to differential rotation, behaving much like a discrete vortex Rossby wave. The quasi mode traps disturbance energy, causing the vortex to precess, or corotate, and thus prevents alignment. For internal deformation radii smaller than the horizontal vortex scale, the quasi mode disappears into the continuous spectrum of vortex Rossby waves. Alignment then proceeds through the irreversible redistribution of potential vorticity by the sheared vortex Rossby waves. Further decreases in the internal deformation radius result in a decreased dependence of vortex evolution on initial tilt magnitude, consistent with a reduction of the vortex beta Rossby number. These results are believed to have relevance to the problem of tropical cyclone (TC) genesis. Cyclogenesis initiated through the merger and alignment of low-level convectively generated positive potential vorticity within a weak incipient vortex is captured by quasi-linear dynamics. A potential dynamical barrier to TC development in which the quasi mode frustrates vertical alignment can be identified using the linear alignment theory in this case.
Rizzoli, P., A. Busalacchi, R. Fine, J. McCreary, R.L. Molinari, and F. Schott. Meeting summary: CLIVAR workshop on shallow tropical-subtropical overturning cells (STCs) and their interaction with the atmosphere: Venice, Italy, 9-13 October 2000. Bulletin of the American Meteorological Society, 82(12):2815-2816 (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.
Schecter, D.A., M.T. Montgomery, and P.D. Reasor. The alignment of a geophysical vortex by the resonant damping of a vortex Rossby mode. AGU 2001 Spring Meeting, Boston, MA, May 29-June 2, 2001. Supplement to EOS, Transactions, American Geophysical Union, 82(20):S47, A41C-10 (2001).
During its early stages of development, a geophysical vortex such as a tropical cyclone or an ocean eddy can be destroyed by episodes of external vertical shear. However, some vortices can survive because they have a dominant tendency to stand upright. We will demonstrate that the process of vertical alignment can often be viewed as the damping of a 3-D vortex Rossby mode. This mode decays exponentially with time, by a resonant "wave-fluid" interaction. In general, the exponential decay rate gamma of the vortex Rossby mode increases with the vorticity gradient at a critical radius, where the fluid rotation is resonant with the mode. The decay rate, gamma, is also affected by the level of atmospheric/oceanic stratification, measured by the internal Rossby deformation radius lR. However, the rate of change of gamma with lR is sensitive to the form of the vortex. For the case of a "Rankine-with-skirt" vortex, the magnitude of gamma increases (initially) with lR. On the other hand, for the case of a "Gaussian" vortex, the magnitude of gamma decreases as lR increases. It has been shown that a similar resonant wave-fluid interaction can cause 2-D vortex axisymmetrization. The analogy between axisymmetrization and vertical alignment will be addressed.
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.
Schubert, W.H., S.A. Hausman, M. Garcia, K.V. Ooyama and H.-C. Kuo. Potential vorticity in a moist atmosphere. Journal of the Atmospheric Sciences, 58(21):3148-3157 (2001).
The potential vorticity principle for a nonhydrostatic, moist, precipitating atmosphere is derived. An appropriate generalization of the well-known (dry) Ertel potential vorticity is found to be P = rho-1 (2OMEGA + gradient x u) • gradient thetarho, where rho is the total density, consisting of the sum of the densities of dry air, airborne moisture (vapor and cloud condensate), and precipitation; u is the velocity of the dry air and airborne moisture; and thetarho = Trho (p0/p)Ra/CPa is the virtual potential temperature, with Trho = p/(rho Ra) the virtual temperature, p the total pressure (the sum of the partial pressures of dry air and water vapor), p0 the constant reference pressure, Ra the gas constant for dry air, and CPa the specific heat at constant pressure for dry air. Since thetarho is a function of total density and total pressure only, its use as the thermodynamic variable in P leads to the annihilation of the solenoidal term, that is, gradient thetarho • (gradientrho × gradientp) = 0. In the special case of an absolutely dry atmosphere, P reduces to the usual (dry) Ertel potential vorticity. For balanced flows, there exists an invertibility principle that determines the balanced mass and wind fields from the spatial distribution of P. It is the existence of this invertibility principle that makes P such a fundamentally important dynamical variable. In other words, P (in conjunction with the boundary conditions associated with the invertibility principle) carries all the essential dynamical information about the slowly evolving balanced part of the flow.
Smith, D.R., M.C. Hayes, M.K. Ramamurthy, J.W. Zeitler, K.A. Murphy, P.J. Croft, J.M. Nese, H.A. Friedman, H.W. Robinson, C.D. Thormeyer, P.A. Ruscher, and R.E. Pandya. Meeting summary: 10th AMS symposium on education. Bulletin of the American Meteorological Society, 82(12):2817-2824 (2001).
The American Meteorological Society held its 10th Symposium on Education in conjunction with the 82nd Annual Meeting in Albuquerque, New Mexico. The theme of 2001's symposium was "enhancing public awareness of the atmospheric and oceanic environments." Thirty-six oral presentations and 38 poster presentations summarized a variety of educational programs or examined educational issues at both the precollege and university levels. There was a special session on increasing awareness of meteorology and oceanography through popular and informal educational activities, as well as a joint session with the 17th International Conference on Interactive Information and Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology on using the World Wide Web to deliver information pertaining to the atmosphere, oceans, and coastal zone. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference. The program for the 10th Symposium on Education can be viewed in the November 2000 issue of the Bulletin.
Smith, R.H., E. Johns, W.D. Wilson, T.N. Lee, and E. Williams. Moored observations of salinity variability in Florida Bay and south Florida coastal waters on daily to interannual time scales. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 42-43 (2001).
In support of the South Florida Ecosystem Restoration, Prediction, and Modeling Program (SFERPM), a three year, physical oceanographic study of the connectivity between Florida Bay and the surrounding waters of the Gulf of Mexico, the southwest Florida shelf, and the Atlantic Ocean was conducted. The field survey included a moored array equipped with current meters, bottom pressure sensors, and conductivity/temperature sensors, satellite-tracked surface drifters, and bimonthly interdisciplinary shipboard surveys with continuous underway thermosalinograph observations of surface salinity, temperature, and fluorescence. The moored conductivity/temperature array consists of 21 sensors positioned from the Florida Keys reef tract, through western Florida Bay and around Cape Sable, extending northward off the mouths of the Shark, Broad, and Lostmans Rivers, to Indian Key just south of Marco Island, Florida. Salinity time series collected from this array are affected by the local precipitation/evaporation balance, riverine discharge from the Everglades which is, in turn, influenced by precipitation as well as anthropogenic factors, fluctuations in the Gulf of Mexico Loop Current, meteorological forcing events such as hurricanes and tropical storms in the summer and cold fronts in the winter, and interannual meteorological events such as El Niņo. Though the bulk of the array was deployed in late 1997, the effects of the 1997/1998 El Niņo on the climate patterns of south Florida can be seen throughout the salinity time series. A wet season/dry season reversal is evident in 1998 with salinity minima occurring at our moorings in April (traditionally the most saline period of the year due to dryer, winter weather) and maxima prevalent in late summer (contradictory to typical wet season conditions).
Testud, J., S. Oury, R.A. Black, P. Amayenc, and X. Dou. The concept of "normalized" distribution to describe raindrop spectra: A tool for cloud physics and cloud remote sensing. Journal of Applied Meteorology, 40(6):1118-1140 (2001).
The shape of the drop size distribution (DSD) reflects the physics of rain. The DSD is the result of the microphysical processes that transform the condensed water into rain. The question of the DSD is also central in radar meteorology, because it rules the relationships between the radar reflectivity and the rainfall rate R. Normalizing raindrop spectra is the only way to identify the shape of the distribution. The concept of normalization of DSD developed in this paper is founded upon two reference variables, the liquid water content LWC and the mean volume diameter Dm. It is shown mathematically that it is appropriate to normalize by N0* proportional to LWC/Dm4 with respect to particle concentration and by Dm with respect to drop diameter. Also, N0* may be defined as the intercept parameter that would have an exponential DSD with the same LWC and Dm as the real one. The major point of the authors' approach is that it is totally free of any assumption about the shape of the DSD. This new normalization has been applied to the airborne microphysical data of the Tropical Ocean and Global Atmosphere-Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) collected by the National Center for Atmospheric Research Electra aircraft. The classification of the TOGA-COARE raindrop spectra into four categories (one stratiform, and three convective [0-10, 10-30, and 30-100 mm h-1]) allowed the following features to be identified. (1) There is a distinct behavior of N0* between stratiform and convective rains; typical values are 2.2 × 106 m4 for stratiform and 2 × 107 m4 for convective. (2) In convective rain, there is a clear trend for Dm to increase with R, but there is no correlation between N0* and R. (3) The "average" normalized shape of the DSD is remarkably stable among the four rain categories. This normalized shape departs from the exponential, but also from all the analytical shapes considered up to now (e.g., gamma, lognormal, modified gamma). The stability of the normalized DSD shape and the physical variability of N0* and Dm are discussed in respect to the equilibrium theory of List et al. The stability of the shape implies that two parameters (and only two) are needed to describe the DSD. This stability supports the robustness of rain relations parameterized by N0*. The same TOGA-COARE dataset is used to check that the rain relations parameterized by N0* are much less dispersed than the classical ones, even after rain-type classification.
Tokarczyk, R., K.D. Goodwin, and E.S. Saltzman. Methyl bromide loss rate constants in the North Pacific Ocean. Geophysical Research Letters, 28(23):4429-4432 (2001).
The degradation rate constant of CH3Br in the North Pacific Ocean was measured in surface seawater between September and October 1999, using the stable isotope (13CH3Br) incubation technique. Total degradation rate constants ranged from 0.02-0.43 d-1, decreasing in colder waters as a result of the temperature-dependence of chemical losses. Biological rate constants ranged from 0.01-0.20 d-1. In subtropical waters (13-20°N), biological loss rate constants were small compared to chemical loss rate constants. North of Hawaii, biological processes played an increasingly significant role in CH3Br degradation. In subpolar waters (40-58°N), biological losses dominated the removal of methyl bromide. Comparison of the measured loss rate constants with surface water CH3Br concentrations suggest that the CH3Br production rate is higher in warm, low latitude waters than in cold subpolar waters at this time of year. Diel studies revealed a midday maximum in biological degradation of methyl bromide.
Wang, C. A unified oscillator model for the El Niņo-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 Niņo-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. On the ENSO mechanisms. Advances in Atmospheric Sciences, 18:674-691 (2001).
The El Niņo-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 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.
Wang, C., and R.H. Weisberg. Ocean circulation influences on sea surface temperature in the equatorial central Pacific. Journal of Geophysical Research, 106(C9):19,515-19,526 (2001).
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.
Waworuntu, J.M., S.L. Garzoli, and D.B. Olson. Dynamics of the Makassar Strait. Journal of Marine Research, 59(2):313-325 (2001).
Data collected as part of the Arlindo Project ("Arlindo" is an acronym for Arus Lintas Indonen, meaning "throughflow" in Bahasa Indonesia) from October 1996 through March 1998 are analyzed to study the characteristics of the flow through the the Makassar Strait. Analysis of inverted echo sounders (IES) and bottom pressure data (PIES), combined with TOPEX/POSEIDON satellite-derived sea height anomaly, suggest that a minimum of three-layer approximation is necessary to explain the dynamics of the flow in the Makassar Strait. The simple two-layer model used in several studies of the throughflow is rejected based on total incompatibility with the data sets. A three-layer model with significant contributions by the middle layer provides a consistent interpretataion of PIES and satellite data. Results are interpreted in the framework of the large-scale circulation.
Willoughby, H.E., and R.W. Jones. Nonlinear motion of a barotropic vortex in still air and in an environmental zonal flow. Journal of the Atmospheric Sciences, 58(14):1907-1923 (2001).
This study employs a Vortex Tracking Semispectral (VTSS) model cast in cylindrical coordinates that move with the vortex. Variables are represented spectrally in azimuth only, so that the model becomes a set of linear equations for each azimuthal wavenumber component, forced by the environmental flow and coupled by wave-wave interactions that account for all of the nonlinearity. The vortex is advected by the surrounding wind and propagates when potential vorticity (PV) gradients due to the surrounding flow or the beta effect force wavenumber one (WN1) asymmetries. Nonlinearity generally plays a dissipative role. Although propagation is faster in stronger PV gradients, nonlinear interactions cause the motions due to superposed PV gradients to be slower than the sum of their individual motions. In still air or uniform wind on a beta plane, the wave energy spectrum falls off rapidly with wavenumber. For most situations, the calculations converge for truncation at WN6 on a 4000-km domain. In an anticyclonically sheared environmental zonal flow, the spectrum of asymmetric energy narrows because the WN2 asymmetry is forced directly by the environmental deformation. The deformation-induced asymmetry interferes destructively with WN2 due to internal wave-wave interaction. In a cyclonically sheared zonal flow, the deformation-induced and nonlinearly-induced asymmetries interfere constructively, resulting in a broader spectrum. Energy cascades from WN2 to wavenumbers >2. A reverse cascade also carries energy to WN1, changing the beta gyres and the motion. Consequent perturbation of WN1 leads to slow convergence of the predicted vortex position after 10 simulated days with increasing spectral resolution. When imposed mass sources and sinks are used to supply energy directly to the asymmetries in the middle of the spectrum, similar wave-wave interactions force WN1, leading to a trochoidal vortex track.
Wright, C.W., E.J. Walsh, D. 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. Journal of Physical Oceanography, 31(8):2472-2488 (2001).
The sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane's inner core over open water. The NASA airborne Scanning Radar Altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane research aircraft at 1.5-km height acquired the open-ocean data on 24 August 1998 when Bonnie, a large hurricane with 1-min sustained surface winds of nearly 50 m s-1, was about 400 km east of Abaco Island, Bahamas. The NOAA aircraft spent more than five hours within 180 km of the eye and made five eye penetrations. Grayscale coded images of Hurricane Bonnie wave topography include individual waves as high as 19 m peak to trough. The dominant waves generally propagated at significant angles to the downwind direction. At some positions, three different wave fields of comparable energy crossed each other. Partitioning the SRA directional wave spectra enabled determination of the characteristics of the various components of the hurricane wave field and mapping of their spatial variation. A simple model was developed to predict the dominant wave propagation direction.
Yao, Q., S.L. Garzoli, R. Zantopp, and W.E. Johns. North Brazil Current Rings Experiment: Time series data report. NOAA Data Report (PB2001-106244), OAR-AOML-40, 104 pp. (2000).
This data report presents the data collected through moored instrumentation during the North Brazil Current Rings Experiment, a joint effort between the University of Miami's Rosenstiel School of Marine and Atmospheric Science, NOAA's Atlantic Oceanographic and Meteorological Laboratory, the Woods Hole Oceanographic Institution, and Columbia University's Lamont Doherty Earth Observatory. The program is funded by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). The main goal of this program is to study the contribution of the North Brazil Current (NBC) rings to inter-hemispheric exchange of heat and salt and to determine their role in climate.
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 an 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., and C.J. Fischer. The role of sediment resuspension in the phosphorus cycle in Florida Bay. Proceedings, 2001 Florida Bay and Adjacent Marine Systems Science Conference, Key Largo, FL, April 23-26, 2001. University of Florida, 98-99 (2001).
The mass mortality of sea grass and frequent algal blooms in Florida Bay are a result of eutrophication. Existing data indicate that phosphorus is the limiting nutrient, while nitrogen is abundant. Therefore, the supply of phosphorus is critical to the onset and persistence of phytoplankton blooms in Florida Bay. Biogenic calcium carbonates are major components of the sediments (>90%) in the Florida Bay. Our studies have shown that phosphorus is strongly adsorbed on the surface of calcium carbonate sediment. Sediments in Florida Bay can easily be suspended by storms and tidal mixing due to shallow water depth (~3 m). Phosphorus cycling processes such as release from adsorption to and coprecipitation with suspended sediment may play an important role in the supply phosphorus to phytoplankton bloom. Our project has been focused on the following three aspects: (1) The time scales of phosphate availability through sediment resuspension in Florida Bay water and kinetic of interaction of sedimentary phosphorus with seawater; (2) the distribution coefficients for phosphorus partitioning between sediment/seawater in Florida Bay; and (3) the reactivity and partitioning of various pools of sedimentary phosphorus in Florida Bay surface sediments.
Zhang, J.-Z., C.J. Fischer, and P.B. Ortner. Continuous flow analysis of phosphate in natural waters using hydrazine as a reductant. International Journal of Environmental Analytical Chemistry, 80(1):61-73 (2001).
The use of hydrazine to reduce 12-molybdophosphoric acid to phosphomolybdenum blue in continuous flow analysis of phosphate in natural water samples is characterized. Using hydrazine in gas-segmented continuous flow phosphate analysis minimizes coating and silicate interference in comparison with using ascorbic acid. The addition of Sb to the molybdate reagent increases sensitivity at temperatures greater than 50°C but causes severe additional coating. The degree of coating was found to be a function of pH. Minimal coatings were achieved at a final solution pH of 0.5. Silicate interference was found to increase dramatically with color development temperature. At room temperature no detectable silicate interference was found. We recommend hydrazine in preference to ascorbic acid for gas-segmented continuous flow phosphate analysis with optimal reaction conditions of room temperature color development and a final solution pH of 0.5.
Zhang, J.-Z., C.R. Kelble, and F.J. Millero. Gas-segmented continuous flow analysis of iron in water with a long liquid waveguide capillary flow cell. Analytica Chimica Acta, 438:49-57 (2001).
A long liquid waveguide capillary flow cell has been successfully adapted to a gas-segmented continuous flow auto-analyzer for trace analysis of iron in water. The flow cell was made of new material, Teflon AF-2400, which has a refractive index (1.29) lower than water (1.33). Total reflection of light can be achieved provided that the incident angle at each reflection on the water/Teflon interface is greater than the critical angle. Teflon AF-2400 is superior to currently used materials in both refractivity and mechanical stability. This allows for construction of a long liquid waveguide capillary flow cell in a helical, rather than linear shape, with compact dimensions. Since the internal volume of a 2 m-long, 550 µm ID liquid waveguide capillary flow cell is only approximately 0.5 cm3, a small sample volume is required. Utilization of this long flow cell significantly enhances the sensitivity of automated colorimetric analysis of iron by the ferrozine method, allowing for accurate determination of nanomolar concentrations of iron in natural waters. The advantages of this technique are low detection limit (0.1 nM), small sample volume (2 ml), high precision (1%), and automation for rapid analysis of a large number of samples. This technique is applicable to any gas-segmented continuous flow analysis or flow injection analysis with spectrophotometric detection.
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.
Bauer, S., and M.S. Swenson. Eddy-mean flow decomposition and eddy-diffusivity estimates in the tropical Pacific Ocean. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F739, OS21D-08 (2000).
Eddy diffusivity is a statistic that provides a quantitative measure of the diffusive transport caused by mesoscale motions. The principal objective of this work is to estimate eddy diffusivities of the surface velocity field in the tropical Pacific Ocean. The data are satellite-tracked drifting buoys from 1979 through mid-1996. The tropical Pacific surface current system is characterized by: (1) nonstationarity due to rapid response time of equatorial and near-equatorial dynamics; (2) strong meridional shear in the large-scale mean; and (3) an energetic mesoscale velocity component. Taylor (1921) defined eddy diffusivity as the integral of the autocovariance of Lagrangian eddy velocities, requiring both stationary and homogeneous statistics of the eddy field. Eddy velocities were obtained in this study by removing the splined mean field to eliminate mean shear as described in Part 1 (Bauer et al., 1998) and binned spatially to group data that have similar dispersion characteristics. Temporal partitions were made to create stationary eddy statistics. Zonal diffusivity estimates (ku) vary with latitude from about 5 ×107 to 76 × 107 cm2/s. Largest estimates are in regions of strong meridional shear and large eddy variance between 4°S and 10°N. However, meridional diffusivity estimates (kv) are nearly constant throughout the tropics, varying from 2 × 107 to 9 × 107 cm2/s. Simple autoregressive models provide the analysis with estimates of Lagrangian integral time scale (a measure of the turbulence decorrelation time scale). First order (AR(1)) and second order (AR(2)) autoregressive processes adequately describe the eddy transport statistics. All zonal eddy transport statistics and meridional statistics from low variance regions (generally poleward of 4°S and 10°N) can be modeled by AR(1) statistics modified by inertial wave oscillations. Meridional statistics of the near-equatorial regions (between 4°S and 10°N) are characterized by large meridional eddy variance associated in part with tropical instability waves (TIWs), and by low meridional diffusivity: Wave motion increases eddy variance but does not diffuse water parcels with periodic trajectory motion. Therefore, meridional eddy diffusivities are low in these regions and are modeled by AR(2) statistics. Further, an independent confirmation of the diffusivity estimates in the central and eastern Pacific was obtained by comparing tracer flux divergence computed from a parameterization using diffusivity estimates of our analysis and that from direct eddy Reynolds stress flux divergence. Thus, our results show that diffusivity can be estimated for regions that have not been considered before, either because of lack of data or because of the complexities of the velocity field.
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.
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 Niņo 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 Niņo versus non-El Niņo data sets. During non-El Niņo 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 Niņo 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 Niņo seasons. The regression line for the composite El Niņo data, which shows no significant seasonal variability, has a slope very similar to the non-El Niņo 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.
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 Airborne Field Mill Mission 2000 (ABFM 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 three-dimensional 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 Detection and Ranging (LDAR) system, 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 Global and Regional Impacts, 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 empirical orthogonal function (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).
Using an updated version of the Kaplan et al. SST dataset (1870-1998), we have constructed a global complex EOF mode of SST anomalies that reproduces the known canonical aspects of El Niņo-Southern Oscillation (ENSO), including phase propagation of SST within and between ocean basins. When the global ENSO mode is subtracted from the data, we are left with a non-ENSO residual dataset for SST anomalies that includes fluctuations from inter-seasonal to multidecadal time scales. Reconstructed for the NINO3 index region, the global ENSO mode accounts for about three-fourths of the total SST anomaly variability, while the residual, dominated by decadal time scales, accounts for the rest. Interestingly, about 40-50% of the amplitudes of the record-setting 1982-83 and 1997-98 El Niņo events is accounted for by the residual variability. Related to this, the ranking of the canonical ENSO events changes significantly with respect to the NINO3 index based on data (e.g., 1972-73 is equal to or stronger than 1982-83 and 1997-98). Based on indices of the canonical ENSO and residual (non-ENSO) variabilities in the NINO3 region, we construct the associated boreal winter (DJF) global composite maps of the tropospheric direct circulation (NCAR/NCEP reanalysis, 1950-1999): velocity potential and and irrotational flow at 850 and 200 hPa, and vertical velocity at 500 hPa. Questions we address include: (1) Does the tropospheric circulation anomaly associated with decadal-scale warming in the NINO3 region reinforce the corresponding anomaly associated with superimposed ENSO warmings? (2) If the warm/cold associations for the two time scales are significantly different, how so and where, and what are the implications for climate predictions?
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 Niņo 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 Niņo, 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 Niņo and La Niņa 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 Niņo. 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 Niņo and La Niņa temperature fluctuations into the Indian Ocean. The ENSO variability in the internal energy transport is calculated: 0.63 PW during the La Niņa months of December 1996 through February 1997, and 0.39 PW during the El Niņo months of December 1997 through February 1998.
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 (PB2001-100486), 258 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 (PB2001-101653), 276 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 (ISBN 0-444-50501-6),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.
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.
Gonzalez, N.M., F.E. Muller-Karger, S.C. Estrada, R. Perez de los Reyes, I.V. del Rio, P.C. Perez, and I.M. Arenal. Near-surface phytoplankton distribution in the western Intra-Americas Sea: The influence of El Niño and weather events. Journal of Geophysical Research, 105(C6):14,029-14,043 (2000).
The space-time variation of phytoplankton pigments in the vicinity of the island of Cuba is examined using digital images obtained with the Coastal Zone Color Scanner (CZCS) sensor, flown aboard the Nimbus-7 satellite from 1978 to 1986. The results are compared to historical in-situ hydrographic observations. A marked seasonality in pigment concentration is observed in waters around Cuba, with an average of 0.07 mg m-3 in summer (April-September) and 0.13 mg m-3 during winter (October-March). The range of variation in pigment concentration is larger in the Gulf of Mexico relative to that in the western Caribbean Sea. Four biogeographical areas are identified based on groups of pixels with similar patterns of time variability. Area I: southwest of Cuba, Yucatan Channel, and Florida Strait; Area II: central Gulf of Mexico; Area III: east of Cuba; and Area IV: central Caribbean Sea, south of Jamaica and Hispaniola. Two major factors led to anomalies in the seasonal cycle of pigment concentrations. During the 1982-1983 El Niņo-Southern Oscillation (ENSO) event, positive anomalies are observed in pigment concentration in the northwestern Caribbean and in the Gulf of Mexico. This is due to intense mixing of the water column driven by the higher frequency of cold fronts during winter and associated strong winds. The 1982-1983 El Niņo therefore had a fertilizing effect on this region. Another positive anomaly was observed during non-ENSO years, specifically during 1980-1981. This anomaly is associated with a higher frequency of hurricanes and extra-tropical low-pressure systems.
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.
Knaff, J.A., and Landsea, C.W. Application of the El Niņo-Southern Oscillation CLImatology and PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 9(3):48-50 (2000).
No abstract.
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 ą2 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. El Niņo-Southern Oscillation and the seasonal predictability of tropical cyclones. In El Niņo and the Southern Oscillation: Multiscale Variability and Global and Regional Impacts, H.F. Diaz and V. Markgraf (eds). Cambridge University Press, 149-181 (ISBN 0521621380) (2000).
Perhaps the most dramatic effect that El Niņo has upon the climate system is in changing tropical cyclone characteristics around the world. This chapter reviews how tropical cyclone frequency, intensity, and areas of occurrence are altered in all of the cyclone basins by the phases of El Niņo-Southern Oscillation (ENSO). In addition to ENSO, other global (such as the stratospheric Quasi-Biennial Oscillation) and local factors (such as sea surface temperature, monsoon intensity and rainfall, sea level pressures, and tropospheric vertical shear) can also help modulate tropical cyclone ariability. Understanding how these various factors relate to tropical cyclone activity can be challenging due to the fairly short (on the scale of only tens of years) record of reliable data. Despite this limitation, many of the factors that have been linked to tropical cyclones, the foremost of which being ENSO, have substantial lead relationships and can be utilized to provide seasonal forecasts of tropical cyclones. Details of methodologies that have been developed for the North Atlantic, northwest Pacific, south Pacific and Australian basin tropical cyclones are presented, as well as the real-time forecasting performance of Atlantic hurricanes as issued by Professor William Gray.
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. Application of the El Niņo-Southern Oscillation CLImatology PERsistence (CLIPER) forecasting scheme. Experimental Long-Lead Forecast Bulletin, 9(4):48-50 (2000).
No abstract.
Landsea, C.W., and J.A. Knaff. How much "skill" is there in forecasting El Ni Niņo? 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 Niņo? Bulletin of the American Meteorological Society, 81(9):2107-2120 (2000).
The very strong 1997-1998 El Niņo was the first major event in which numerous forecasting groups participated in its real-time prediction. A previously developed simple statistical tool, the El Niņo-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 Niņo, 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 Niņo'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 Niņo impacts were correctly anticipated by national meteorological centers one-half year in advance, because of the tendency for El Niņo events to persist into and peak during the boreal winter. Despite this, the zero to two season (0-8 month) forecasts of the El Niņo 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, and 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 Niņo-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-Nuņez 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 Niņo 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 Niņo conditions.
Peng, T.-H., and R.H. Wanninkhof. Re-evaluation of GEOSECS carbon data in the Pacific Ocean based on recent high quality measurements. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F701, OS11B-11 (2000).
Inorganic carbon data collected during the GEOSECS program in the early 1970s represent results of the first systematic geochemical survey on a global scale. These data sets have become an essential baseline for studies of temporal variations of geochemical properties since this time. This is especially true for estimating the oceanic uptake of anthropogenic CO2 by determining the increase in concentration of total dissolved inorganic carbon (DIC) since GEOSECS. It is essential that the accuracy of this historic data set is consistent with recent high quality carbon data resulting from improvements in measurement techniques and the use of reference material. Here we report the results of the re-evaluation of GEOSECS inorganic carbon data in the Pacific Ocean by examining deep water properties at crossover stations between GEOSECS and WOCE cruises. We find that DIC and total alkalinity (TA) measurements made during the GEOSECS program are systematically higher than those made during the recent global CO2 survey. We suggest that the originally reported GEOSECS DIC should be revised downward by 30.3 µmol/kg and TA by 18.1 µmol/kg. Comparison of temperature, salinity, and oxygen concentrations show that these properties are consistent with each other, although they were measured two decades apart. The corrected GEOSECS carbon data will be made available to the research community through NOAA/AOML's public web site.
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 Niņo-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 Niņo 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.
Richardson, P.L., S.L. Garzoli, C.M. Duncombe Rae, D.M. Fratantoni, and G.J. Goni. Float trajectories at 750 m in the Benguela Current (KAPEX). AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F716, OS11F-09 (2000).
Thirty RAFOS floats were launched at Intermediate Water depths (approximately 750 m) in the Benguela Current along 30°S and its extension along 7°W. The floats have surfaced after 18-24 month missions and are being tracked. Preliminary results from the overall subsurface displacements show that the floats drifted westward at typical speeds of 2-5 cm/sec. Six floats looped in three Agulhas rings for long times as they also translated westward. Eleven floats crossed over the mid-Atlantic Ridge into the western Atlantic in the latitude band 23°S-33°S. Three floats reached 25°W and one reached 30°W. Two of these farthest westward-drifting floats were in Agulhas rings, suggesting that they translate faster than the background water at 750 m. A summary of the new trajectories will be represented along with some hydrography, altimetry, and surface-drifter tracks. Intermediate Water is an important part of the northward-flowing limb of the thermohaline circulation in the Atlantic. The floats show the path of Intermediate Water as it flows westward along the northern side of the subtropical gyre, across the mid-Atlantic Ridge and into the western Atlantic.
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.
Rona, P.A., D.R. Jackson, K.G. Bemis, C.D. Jones, K. Mitsuzawa, and D.R. Palmer. Acoustic imaging of seafloor hydrothermal flow regimes at the RIDGE Endeavour Observatory, Juan de Fuca Ridge. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F629, OS52I-06 (2000).
We report preliminary results of acoustic imaging of black smoker plumes and diffuse flow in the Main Endeavour Field of the Endeavour segment of the Juan de Fuca Ridge on the VIP (Vents Imaging Pacific) 2000 cruise of the R/V Thompson (21-31 July 2000) using innovative methods developed by our group. We modified a state-of-the-art sonar system (Simrad SM 2000; 200 kHz) to perform the imaging while mounted on ROV Jason and developed specialized processing methods for acoustic remote sensing and visualization/quantification of hydrothermal flow. We carried out four types of acoustic experiments coordinated with selected in-situ measurements of hydrothermal discharge temperatures and flow rates, as follows: (1) Panoramic imaging (range 10 m to 150 m) of four vent clusters each tens of meters wide and high (Peanut-Puffer-Bastille group; Salut, S&M, and Grotto sites), which shows seafloor features, plumes (based on acoustic backscatter from suspended particulate matter), and diffuse flow (based on acoustic scintillation thermometry). The images reveal differences between the four vent clusters in intensity of venting and partitioning between black smoker discharge and diffuse flow. (2) A time series of panoramic images (hourly during 24-hour period), which shows the effect of a mixed semi-diurnal tide on intensely-venting plumes and diffuse flow (Grotto site). (3) Flow rates in black smoker plumes, which were measured using the coherent Doppler method. (4) Acoustic mapping of diffuse flow, which was conducted to test stationary and moving modes (multiple sites). The preliminary results are evaluated in terms of the applicability of our acoustic and processing methods for synoptic imaging and long-term monitoring of these hydrothermal flow regimes.
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 ą 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.
Schaefer, J.K., K.D. Goodwin, I. McDonald, J.C. Murrell, and R.S. Oremland. Methyl halide oxidation by a novel marine methylotroph, Ruegeria sp. strain MB2. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F278, B22A-05 (2000).
Strain MB2 was isolated from coastal seawater with the capacity to utilize methyl bromide as a sole carbon and energy source. Additional carbon sources included the methylotrophic substrates: methyl chloride, methionine, and glycine betaine, as well as the complex substrates casein and yeast extract. This bacterium, however, was unusual for a methylotroph in that it was unable to grow on methylated amines, dimethyl sulfide, formate, methane, acetate, or glucose. Cells were capable of complete oxidation of methyl bromide and methyl iodide with stoichiometric release of bromide and iodide, respectively. Specific growth rates were 0.07 h-1, 0.05 h-1, and 0.04 h-1 for methyl bromide, methyl chloride, and methyl iodide, respectively. Methyl bromide oxidation was readily inducible in casein-grown cells. Strain MB2 exhibited a requirement for NaCl and Mg2+ similar to that found in seawater. Analysis of the 16S rDNA gene placed this strain in the a-subgroup of the Proteobacteria with significant homology to the genus Ruegeria. We propose the identity of strain MB2 as a novel species, designated Ruegeria methylhalovorans sp. nov. Characterization of strains such as MB2 should enhance understanding of the mechanisms involved in the oxidation of methyl halides in the oceans.
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.
Schott, F., C. Boning, H. Bryden, R.L. Molinari, P. Schlosser, C. Wunsch, and L. Stramma. 2000 Report of the WOCE North Atlantic Workshop. WOCE Report No. 169/2000, 110 pp. (2000).
No abstract.
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.
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.
Tokarczyk, R., E.S. Saltzman, and K.D. Goodwin. Degradation of methyl bromide in surface waters of Atlantic and Pacific Ocean. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F277, B22A-03 (2000).
The ocean plays a complex role in the global biogeochemical cycle of methyl bromide as both a source and sink for atmospheric CH3Br. The loss of methyl bromide in seawater occurs by both chemical and biological mechanisms. This study is an effort to measure the oceanic loss rate of methyl bromide using a shipboard stable isotope (13CH3Br) incubation technique. Data are presented from two expeditions: the GASEX-98 cruise across the Atlantic and western coastal North Pacific (May-July 1998) and the KWAJEX cruise in the North Pacific ocean (11°N to 57°N, September-October 1999). The methyl bromide lifetimes measured in this study ranged from approximately 2.5 to 50 days. Chemical loss rate constants were obtained by following the first-order loss of 13CH3Br in 0.2 µm filtered seawater, and biological loss rate constants were inferred from the difference between the loss rate in unfiltered waters and the chemical loss rate. Chemical loss rate constants varied strongly with water temperature, in accordance with previous measurements of the rates of hydrolysis and chloride substitution in seawater. Biological degradation was observed in most water samples, at rates that can be significant to the lifetime of seawater CH3Br. These losses are attributed to bacterial activity on the basis of earlier filtration experiments carried out in coastal seawater. In contrast to the chemical loss rate constants, biological losses do not show a consistent correlation with water temperature but do exhibit variability between various water masses. In general, chemical losses control the lifetime of oceanic methyl bromide in warmer waters and biological losses are significant in colder waters.
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 Niņo-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 Niņo. Journal of Atmospheric Sciences, 57(22):3767-3781 (2000).
The atmospheric heating and sea surface temperature (SST) anomalies during the mature phase of El Niņo 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 Niņo. When the model heating anomaly forcing is modified to resemble the observed heating anomalies during the mature phase of El Niņo, 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 Niņo. 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 Niņo-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 Niņo evolution relative to previous Niņo events. Journal of Climate, 13(2):488-501 (2000).
The evolution of the 1997-1998 El Niņo 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 Niņo decay. The paper also compares the 1997-1998 El Niņo with previous warm events, and discusses different ENSO mechanisms relevant to the 1997-1998 El Niņo.
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. Observations through models to forecasts. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F115, A72E-04 (2000).
Isaac Cline forecast the Galveston Hurricane of 1900 based upon incomplete climatology, misleading instructions from Washington, and what he could see and feel. Since then, hurricane meteorologists have learned to use radio ship reports (1900s), upper air observations (1930s), aircraft reconnaissance and radar (1940s), statistical models (1950s), polar-orbiting satellites and barotropic models (1960s), geostationary satellites and baroclinic models (1970s), Doppler radar (1980s), and targeted observations and coupled models (1990s). These developments produced a ~1% annual decline in mean track forecast errors between 1970 and 2000. Over the same period, average hurricane mortality was 25 souls annually, compared with estimates of >200 annually if forecasting had not improved. The successful strategy has been evacuation of the storm-surge inundation zone on a length of coastline wide enough to allow for forecast error. Accelerating coastal development increases demands on the forecast system. Essential improvement of track forecasts will stem from better specification of the "steering" flow that accounts for 80% of motion. The improvement will continue as a result of assimilation of remotely-sensed data and targeted in-situ observations from piloted and autonomous aircraft. By 2050, the limit of deterministic track forecasting will be reached with 24 h error of ~100 km. Even before then, ensemble-based, probabilistic forecasting will be the key for rational decisions. The great hurricane catastrophe of the 21st century will happen through the poorly understood process of "rapid deepening," in which the sea and atmosphere combine to intensify a category 2 hurricane to category 4 in ~24 h. In the worst case, deepening begins late in the day as the storm accelerates overnight toward a poorly-prepared city. A substantial basic and applied science investment is essential to produce adequate forecasts of this potentially devastating phenomenon.
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.
Yvon-Lewis, S.A., J.H. Butler, P.A. Matrai, and E.S. Saltzman. The cycling of methyl bromide in the North Atlantic and eastern Pacific Oceans. AGU 2000 Fall Meeting, San Francisco, CA, December 15-19, 2000. Supplement to EOS, Transactions, American Geophysical Union, 81(48):F277, B22A-02 (2000).
Methyl bromide (CH3Br) saturation anomalies, degradation rates, and net production rates were measured during the 1998 Gas Exchange cruise (GasEx98) and the subsequent transit to Newport, Oregon. This cruise was conducted aboard the NOAA ship Ronald H. Brown between May 8 and July 27, 1998. Persistent CH3Br supersaturations were observed (King et al., 2000; JGR, 105 [D15], 19,763-19,769), which suggested seasonal cycling of CH3Br in temperate regions when compared to previous observations (Lobert et al., 1996; NOAA Technical Memorandum, ERL CMDL-10, Boulder, CO). King et al. (2000) demonstrated that 40-70% of the global variability in the CH3Br saturation anomaly could be explained by variations in sea-surface temperature (SST). However, in temperate North Atlantic waters, variations in SST could explain only 15% of the apparent seasonal variability in the CH3Br saturation anomaly. During this cruise, results from the first open ocean measurements of the chemical and biological degradation rate constants for CH3Br agreed with laboratory estimates of the chemical degradation rate constant and showed biological degradation was ubiquitous (Tokarczyk and Saltzman, 2000; JGR, submitted). Biological degradation accounted for up to 40% of the total degradation of CH3Br in individual water samples. Additionally, the first open ocean incubation experiments to examine the net production of CH3Br in seawater suggest that a substantial fraction of CH3Br is produced in the dissolved portion of the sample (0.2 mm filtered seawater) and that up to 50% of the variability in net CH3Br production can be explained statistically by variations in SST in the waters sampled. Here, we incorporate the data discussed above into an air-sea exchange model to examine the cycling of CH3Br and to assess the impact of the biologically-mediated processes on its uptake from and emission to the atmosphere. This well-constrained system allows us to examine the uptake fluxes, a function of the observed chemical and biological degradation rate constants, the net fluxes, determined from the observed saturation anomalies, and the observed net production rates independently.
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 Niņo 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.
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, Vol. 1, 16 pp. (1999).
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.
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 Niņo 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 Niņo-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).
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 Niņo 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 Niņo year of 1996. The total reduction of the sea-to-air CO2 flux during the 1991-1994 El Niņo 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 ą 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.
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, Vol. 1, 14 pp. (1999).
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.
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. Goņi. 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.
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, Vol. 1, 19 pp. (1999).
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.
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 incr