Atlantic Oceanographic and Meteorological Laboratory

FY-1997 Publications

AO-001
ABERSON, S.D. Adaptive observations in a hurricane environment. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 308-309 (1997).
No abstract.
AO-002
ABERSON, S.D. Five-day statistical hurricane track forecasts. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A-3 (1997).
A dimensional analysis of five-day hurricane tracks is presented to calculate the number of predictors necessary to accurately predict tracks. While the dimensions of the hurricane tracks are large, statistical analyses can still be used as a benchmark by which other methods can be assessed. A new version of CLIPER is developed which eliminates problems with the original dependent data sets and extends the forecasts to five days. The new version updates the original CLIPER, which used data from 1930 through 1970, a time during which many tracks are conjecture and many are missed completely. The new version eliminates the Gulf of Mexico tropical cyclones from the Atlantic basin, and corrects for problems in the original Gulf of Mexico data. The new version also eliminates non-physical cross-terms in the multiple linear regression. Independent forecasts are made for the 1996 hurricane season and compared to the older version of the model. Model biases of the two versions are compared.
AO-003
ABERSON, S.D. The prediction of the performance of a nested barotropic hurricane track forecast model. Weather and Forecasting, 12(1):24-30 (1997).
Linear multiple regression and discriminant analyses provide estimates of the errors of track forecasts from a nested barotropic hurricane track forecast model (VICBAR), which was run in the North Atlantic Basin during the 1989-1994 hurricane seasons. Predictors are determined from the synoptic situation, the magnitude of atmospheric changes in the environment of the tropical cyclone, the consistency between current and past predictions, and the past performance of the model for each particular storm. This technique distinguishes cases in which VICBAR performs well from those for which it performs poorly and can provide skillful operational predictions of model performance to forecasts.
AO-004
ACERO-SCHERTZER, C.E., D.V. HANSEN, and M.S. SWENSON. Evaluation and diagnosis of surface currents in the NCEP ocean analyses. Journal of Geophysical Research, 102(C9):21,037-21,048 (1997).
Ensemble average currents from the 15 m depth level of the NCEP analyses of the tropical Pacific Ocean are evaluated against surface mixed layer current observations obtained from an extensive set of satellite-tracked drifting buoys. These averages display many climatological characteristics of the region, but are not intended to serve as a climatology because the data from the analyses are trimmed to match the time-space distribution of the observations. Substantial discrepancies between the analyses and the observations are revealed. First, the near-equatorial meridional currents and divergence have approximately twice the magnitude in the analyses as in the observations. This discrepancy is largely independent of whether temperature profile data are assimilated or not, and is attributed to the parameterization of vertical viscosity. Second, the zonal flow in both the NECC and the SEC is much stronger in the analyses than in the observations, especially in the western Pacific. This discrepancy is associated with assimilation of temperature profile data. It arises because salinity is an active variable in the underlying analysis model, but is not controlled by boundary fluxes or other observations. Under the uncontrolled influence of advection and strong horizontal diffusion, the salinity distribution becomes nearly homogeneous. Consequently, the analyses do not account for observed temperature-salinity correlations when density is computed following assimilation of temperature profile data. This leads to erroneous pressure gradients that drive excessively strong geostrophic currents and force large accelerations near the western boundary. Our results indicate that it is important to consider the consequences on the density structure of neglecting salinity during the assimilation of temperature data. We recommend that surface salinity observations from drifting buoys and volunteer observing ships be initiated to improve the ocean analyses.
AO-00
5 BARINGER, M.O., and J.F. Price. Mixing and spreading of the Mediterranean Outflow. Journal of Physical Oceanography, 27(8):1654-1677 (1997).
Hydrographic and expendable current profiler (XCP) data taken during the Gulf of Cadiz Expedition on September 21-27, 1988 were analyzed to diagnose the mixing, spreading, and descent of the Mediterranean Outflow. The q/S properties and the thickness and width of the outflow were very similar to that seen in earlier surveys (for example, by Heezen and Johnson, 1969). The transport of pure Mediterranean water (S = 38.4) was estimated to be about half a Sv, which is considerably lower than historical estimates, most of which were indirect, but comparable to other recent estimates made from direct velocity observations. The total outflow transport was about 0.7 Sv at the west end of the Strait of Gibraltar, and increased to about 1.9 Sv within the western Gulf of Cadiz. This increase in transport occurred by entrainment of fresher North Atlantic Central Water (NACW), and the salinity anomaly of the outflow was rapidly eroded. The velocity-weighted salinity decreased to 36.7 within 60 km of the Strait, during the initial descent of the continental slope, and decreased by about another 0.1 before the deeper portion of the outflow began to float off of the bottom near Cape St. Vincent. Entrainment appears to have been correlated with the occurrence of bulk Froude numbers slightly greater than 1. In the western Gulf of Cadiz, where entrainment was much weaker, Froude numbers were well below 1. The outflow began in the eastern Strait of Gibraltar as a narrow (10 km wide) current having a very narrow range of q/S properties (q varies by < 0.5°C). The outflow broadened as it descended the continental slope of the northern Gulf of Cadiz, and reached a maximum width of 90 km in the western Gulf of Cadiz. The descent of the outflow was very asymmetric: the offshore and downslope edge of the flow descends rapidly, while the onshore and shallower edge of the outflow descends slowly. The northern, nearshore side remained considerably higher in the water column and thus entrained relatively warm and salty NACW. This caused the outflow to develop horizontal q/S variability and, by about 100 km downstream, the across-stream variation in temperature on an isopycnal was more than 2°C. Much of the volume transport in the western Gulf of Cadiz was contained in two preferred modes, often called cores, apparently because of topographic steering effects. The deeper, offshore core had a central sq = 27.8, and the shallower nearshore core, which was still in contact with the bottom in the Gulf of Cadiz, had a central sq = 27.5.
AO-006
BARINGER, M.O., and J.F. Price. Momentum and energy balance of the Mediterranean Outflow. Journal of Physical Oceanography, 27(8):1678-1692 (1997).
Hydrographic and expendable current profiler (XCP) data taken during the Gulf of Cadiz Expedition in September 1988 were analyzed to describe some aspects of the dynamics of the Mediterranean Outflow. During the initial descent of the continental slope, the outflow current executes a 90 degrees right turn that appears to be approximately inertial. The estimated geostrophic velocity greatly underestimated the actual current, and the estimated curvature Rossby number is about 0.5. A form of the Bernoulli function was evaluated to infer the total stress (entrainment stress and bottom drag) acting on the outflow. Total stress was as large as 5 Pa where the outflow begins to descend the continental slope and where currents were in excess of 1 m/s. The entrainment stress, estimated independently from property fluxes, reached a maximum of only about 1 Pa, which was less than the inferred bottom stress. By about 100 km downstream, the current was aligned approximately along the topography. The current amplitude and the estimated stress were much less, about 0.3 m/s and less than 0.5 Pa. The entrainment stress was very small in the region well downstream of the Strait. Bottom stress thus appears to be the crucial element in the dynamics of the Mediterranean Outflow, allowing or causing the outflow to descend some 1000 m into the North Atlantic. In the regions of strongest bottom stress the inferred drag coefficient was about 3 ´ 10-3. Entrainment stress was much smaller by comparison, but the entrainment effect upon the density anomaly was crucial in eroding the density anomaly of the outflow.
AO-007
BLACK, M.L., and J.R. Parrish. The structure of the hurricane eyewall at altitudes reached by the NOAA Gulfstream-IV aircraft. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A-16 (1997).
Starting with the 1997 Atlantic hurricane season, the recently acquired and specially instrumented NOAA Gulfstream-IV (G-IV) jet aircraft will conduct synoptic reconnaissance missions in the periphery of tropical cyclones. The missions are designed to sample, via dropsondes, vertical profiles of the environmental air from flight altitudes of 40,000 to 45,000 ft. The flights are intended to avoid the convectively active eyewall and rainband regions of the storms. In future seasons, however, research and reconnaissance needs may warrant high altitude penetrations of the hurricane core. Before conducting flights directly into tropical cyclones, the structure of the deep convection, especially in the eyewall, needs to be assessed to determine the types of flight conditions the G-IV might experience. The purpose of this report is to use the remote-sensing capabilities of the NOAA WP-3D aircraft to document and describe the structure of the hurricane eyewall at high altitudes. Vertically-pointing Doppler radials from the tail radars on the NOAA P-3 aircraft yield estimates of the two-dimensional (radius-height plane) reflectivity and vertical velocity structure. Observations from more than 200 radial legs through the eyewalls of tropical cyclones have shown that vertical velocity extrema with magnitudes >10 m/s can occur at heights up to 15 km, well above the maximum attainable altitude of the G-IV. These extrema occur infrequently (<10% chance) but can contain steep vertical velocity gradients that may produce moderate to severe turbulence, similar to that experienced by the P-3 aircraft at lower altitudes. Examples of the various types of vertical velocity structures that the G-IV may encounter in eyewall penetrations will be presented.
AO-008
BLACK, M.L., R.W. Burpee, and F.D. MARKS, JR. The asymmetric distribution of vertical motions and precipitation in the hurricane eyewall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 100-101 (1997).
No abstract.
AO-009
BLACK, M.L., J.F. GAMACHE, H.E. WILLOUGHBY, C.E. SAMSURY, F.D. MARKS, JR., and R.W. Burpee. Airborne radar observations of shear-induced asymmetries in the convective structure of Hurricane Olivia (1994). Proceedings, 28th Conference on Radar Meteorology, Austin, TX, September 9-12,1997. American Meteorological Society, 577-578 (1997).
The Hurricane Research Division of NOAA conducted dual aircraft experiments on successive days in eastern Pacific Hurricane Olivia. The flights occurred on 24 September 1994 while Olivia was intensifying and 25 September when the hurricane was initially at maximum intensity followed by a period of rapid filling. The data collected from the flights into Hurricane Olivia provide a unique opportunity to investigate and describe the interplay between environmental wind shear, eyewall convection, and intensity changes. Radar systems on the WP-3D research aircraft recorded radar reflectivity from the horizontally-scanning, lower-fuselage (LF) radar (5 cm), and reflectivity and Doppler radials from the tail radar (3 cm) which scans in a plane perpendicular to the aircraft track. On September 24th, the hurricane was embedded in weak easterly shear and observations from the LF radar showed that the convection in Olivia's eyewall was highly asymmetric. The deepest convection and highest reflectivities were concentrated in the south and southeast portions of the eyewall, while the northern portions contained a stratiform-like precipitation structure. Vertical profiles of reflectivity and vertical velocity derived from vertically-pointing radials from the tail Doppler radar further describe the nature of these asymmetries. Large and strong updrafts were located just upwind of the heaviest precipitation while downward motion dominated in the eyewall region slightly downwind of the precipitation maximum. Much weaker and smaller up- and downdrafts existed in the low-reflectivity region of the northern eyewall. Olivia intensified during the 24-hour period between flights while the environmental shear was weak ahead of a mid-tropospheric trough. On September 25th, when the aircraft first arrived near the center, Olivia's eyewall appeared on LF radar images as a highly symmetric, nearly continuous ring of high reflectivities (>40 dBZ). Doppler radar observations of the vertical velocity structure, however, still showed an asymmetric structure, albeit not as pronounced as the previous day. During the flight, westerly shear increased dramatically, Olivia's central pressure rose, and large asymmetries in the eyewall reflectivity field developed in an apparent response to the changing vertical wind shear. Olivia's weakening may also have been partially due to the storm moving over a region of cooler sea-surface temperatures. Convective cells with strong updrafts formed in the eastern eyewall (downshear), and advected around to the high-reflectivity region of the northern eyewall. Strong downdrafts appeared to form at high altitudes, adjacent to and slightly downwind of the large and strong updrafts, and rotated around the eyewall to the weak-reflectivity region of the western eyewall (upshear). Near the end of the flight, the magnitude of the updrafts decreased and the convective tops were lower in altitude, conditions that are consistent with a weakening hurricane.
AO-010
BLACK, P.G., J.R. PRONI, J.C. Wilkerson, and C.E. SAMSURY. Oceanic rainfall detection and classification in tropical and subtropical mesoscale convective systems using underwater acoustic methods. Monthly Weather Review, 125(9):2014-2042 (1996).
Measurements of the underwater sound produced by rain were made at three U.S. coastal sites in a study to determine the feasibility and limitations of the acoustic detection and classification of rainfall over water. In the analysis of the rain sound spectra, concurrent radar reflectivity observations were used to identify convective and stratiform regions of the precipitating clouds overhead. It was found that acoustic classifications of rainfall as to type, based on information in the 4-30 kHz frequency band, were in general agreement with radar-derived classifications. The classification technique is based on use of an acoustic discriminant, DR, defined as the difference in average spectral levels between the 10-30 kHz and 4-10 kHz bands. A high correlation was found between sound spectrum levels (in dB) in the 4-10 kHz frequency band and radar reflectivity, dBZ, suggesting the possible use of the 4-10 kHz band sound spectral level as a classification tool in the same way that radar reflectivity is used in classifying precipitation. Our results demonstrate the feasibility of the acoustic method for detecting and classifying rainfall at sea.
AO-011
BLACK, R.A. Giant raindrops observed from large aircraft. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 494-495 (1997).
No abstract.
AO-012
Bringi, V.N., K. Knupp, A. Detwiler, L. Liu, I.J. Caylor, and R.A. BLACK. Evolution of a Florida thunderstorm during the Convection and Precipitation Experiment: The case of 9 August 1991. Monthly Weather Review, 125(9):2131-2160 (1997).
The relationships among kinematic, microphysical, and electric field properties within a multicell Florida thunderstorm are investigated using observations from three Doppler radar (one with multiple wavelength and polarization diversity capabilities), four instrumented penetrating aircraft, a surface-based electric field mill network, and other observation facilities. The storm was convectively active for about 1 h and at least five primary cells developed within the storm during this time, one of which went through three consecutive development cycles. The updrafts in this storm were 2-4 km wide, exhibited bubble-like evolution, and had lifetimes of 10-20 min. The maximum updraft determined by the multiple Doppler analysis was about 20 m s-1. A differential reflectivity (ZDR) "column," indicating regions containing millimeter-size raindrops, extending above the freezing level, was associated with each cell during its developing stages. This column reached altitudes exceeding 6 km (-8°C) in the stronger updrafts. As the ZDR columns reached maximum altitude, a "cap" of enhanced linear depolarization ratio (LDR) and enhanced 3-cm wavelength attenuation (A3) formed, overlapping the upper regions of the ZDR column. These parameters indicate rapid development of mixed-phase conditions initiated by freezing of supercooled raindrops. Lightning was observed only in the central and strongest convective cell. Electric fields exceeding 10 k V m-1 were noted during aircraft penetrations in this as well as several other cells that did not produce lightning . Fields exceeding 1 k V m-1 were noted by the instrumented aircraft at midcloud levels within a few minutes of development of mixed-phase conditions at these levels or aloft. The first intracloud lightning was detected by the surface field mill network within 5 min of development of mixed-phase conditions aloft in the first cycle of development in the central cell, and the first cloud-to-ground event was noted within 9 min of this development. Lightning continued through two additional cycles of updraft growth in this central region and diminished as the convection subsided after about 30 min. Aircraft-measured electric fields and lightning retrievals from the surface field meter network are consistent with a tendency for negative charge to accumulate above the 6.5 km (-12°C) level within regions of radar reflectivity maxima and for positive charge to accumulate in the anvil region well above 9 km (-30°C).
AO-013
BUSHNELL, M.H. Location accuracy of global Lagrangian drifters. WMO/DBCP Technical Document No. 10, 135-137 (1996).
No abstract.
AO-014
BUSHNELL, M.H. Low-cost drifting buoys soon to include wind sensors. NOAA Legislative Informer, No. 21, 11 (1997).
No abstract.
AO-015
BUSHNELL, M.H. Preliminary results from global Lagrangian drifters using GPS receivers. WMO/DBCP Technical Document No. 10, 23-26 (1996).
No abstract.
AO-016
BUSHNELL, M.H. Staying current with GPS. GPS World, 41 (1997).
No abstract.
AO-017
BUSHNELL, M.H. Value and application of drifting buoy data. Final Report, 4th WMO/DBCP International South Atlantic Buoy Program Meeting, Port-of-Spain, Trinidad and Tobago, September 8, 1997. South African Weather Bureau, Annex 4 (1997).
No abstract.
AO-018
BUSHNELL, M.H., and W.S. KRUG. Global Drifter Center support for the International Buoy Program in the Indian Ocean. Final Report, 2nd WMO/DBCP International Indian Ocean Buoy Program Meeting, Perth, Australia, July 1997. Australian Bureau of Meteorology, Annex V, 15-20 (1997).
No abstract.
AO-019
Butler, J.H., and S.A. YVON-LEWIS. Estimating lifetimes of atmospheric trace gases with respect to oceanic loss: Two approaches. EOS, Transactions, American Geophysical Union, 78(17):S90 (1997).
The flux of a gas across the air-sea interface typically is estimated as the product of the air-sea, gas-transfer coefficient and the difference in the partial pressure of the gas between the water and the air. Although there is some uncertainty in the value and mechanism selected for the transfer coefficient, this approach is generally considered a reasonable way to evaluate the rate at which a gas passes between the ocean and the atmosphere. Problems can arise, however, when one tries to compute the partial lifetime of this gas in the atmosphere with respect to its loss in the ocean. So long as the gas is not produced in the ocean, this calculated flux can be used to derive a partial lifetime. However, if the gas is simultaneously produced and consumed in the ocean, the lifetime estimate calculated in this way will be too long. This can be accounted for if one considers that the calculated flux from the atmosphere to the ocean is a net flux and that it will change in opposition to changes in the atmospheric burden of the gas. In this sense, the ocean acts as a "buffer" for the gas in the atmosphere, yet the effect is calculable. An alternative approach, involving the separation of inward and outward fluxes, gets past the lifetime and emission problem and allows for an accurate calculation of the partial atmospheric lifetime. This approach also provides for the computation of emissions from undersaturated waters or uptake by supersaturated waters. Each approach is internally consistent and both can be used, along with information on other non-oceanic fluxes, to describe the budgets of atmospheric trace gases. However, each carries with it certain caveats and limitations that must be considered in constructing these budgets. This talk will address these issues, with specific emphasis on methyl bromide and other trace gases of interest in ozone depletion and global warming.
AO-020
CARSEY, T.P., M.L. FARMER, C.J. FISCHER, A. Mendez, V.B. Ross, M. Springer-Young, and M.P. ZETWO. Atmospheric chemistry measurements during Leg 4, 1993 North Atlantic cruise, R/V Malcolm Baldrige. NOAA Data Report, ERL AOML-28 (PB96-162581), 137 pp. (1996).
During September 1993, AOML conducted a multi-leg cruise aboard the Malcolm Baldrige in the North Atlantic from Iceland to Miami, Florida. The objective was to evaluate the distribution and transport of tropospheric ozone and ozone precursors in the North Atlantic. The investigation was associated with the North Atlantic Regional Experiment (NARE), a component of the International Global Atmospheric Chemistry (IGAC) project. The cruise track traversed three diverse wind and chemical regimes: pristine polar westerlies, polluted westerlies, and marine southeasterlies. Along this cruise track a large suite of chemical and meteorological data were measured. These included ozone, carbon monoxide in air and surface water, NO, NO2, Noy, peroxyacetyl nitrate, SO2, non-methane hydrocarbons (NMHC), and aerosols. The measurements and instrumentation are described in this data report.
AO-021
CARSEY, T.P., D.D. Churchill, M.L. FARMER, C.J. FISCHER, A.A. Pszenny, V.B. Ross, E.S. Saltzman, M. Springer-Young, and B. Bonsang. Nitrogen oxides and ozone production in the North Atlantic marine boundary layer. Journal of Geophysical Research, 102(D9):10,653-10,665 (1997).
Measurements of reactive nitrogen gases (NO, NO2, NOy), as well as related chem--ical (O3, CO, aerosol black carbon, radon, selected nonmethane hydrocarbons) and meteo-rological parameters, were made on board the R/V Malcolm Baldridge prior to and subsequent to the 1992 ASTEX (Atlantic Stratocumulus Transition Experiment) in the North Atlantic Ocean during June and July 1992. Results showed indications of well-defined plumes from North America and Europe from both chemistry and back trajectory data. Elevated ozone concentrations were also observed in airmasses from uninhabited continental regions. Chemical and meteorological data were incorporated into a simple photochemical model in which ozone destruction predominated over generation. The principal reaction leading to ozone destruction was O(1D) + H2O ® 2OH.
AO-022
Checkley, D.M., P.B. ORTNER, L.R. Settle, and S.R. CUMMINGS. A continuous, underway fish egg sampler (CUFES). Fisheries Oceanography, 6:58-73 (1997).
We describe a method to sample the highly contagious distribution of pelagic fish eggs. CUFES, the continuous, underway fish egg sampler, consists of a submersible pump, concentrator, electronics, and sample collector. This system operates continuously and under nearly all sea conditions, providing a real-time estimate of the volumetric abundance of pelagic fish eggs at pump depth, usually 3 m. CUFES-derived estimates of volumetric abundance agree well with those from nets towed at pump depth and with a real abundance estimated from vertically-integrated plankton tows. CUFES has been used successfully to sample the eggs of menhaden, pinfish, sardine, and anchovy off the coasts of the eastern and western United States and South Africa. Two large patches of eggs of the Atlantic menhaden were sampled off North Carolina in winter 1993-1994, had a linear scale of 5-10 km, and were found in waters between the Gulf Stream and mid-shelf front. Spawning location may be related to bathymetry. CUFES is now being used to estimate spawner biomass by the Daily Egg Production Method. An optical plankton counter provided accurate estimates of the number of Atlantic menhaden eggs sampled by CUFES. Automation of egg counting in CUFES is under development.
AO-023
CIONE, J.J., and S. Raman. The impact of SST gradients on propagating low-level mesovortices near the Gulf Stream. Preprints, Conference on Coastal Oceanic and Atmospheric Prediction, Atlanta, GA, January 28-February 2, 1996. American Meteorological Society, 204-211 (1997).
No abstract.
AO-024
DAMMANN, W.P., J.M. BUFKIN, U. RIVERO, S.J. STAMATES, and J.R. PRONI. Near real-time observations of offshore current profiles and their application to dredge material disposal activities. Proceedings, Eco-Informa '96: Global Networks for Environmental Information, Lake Buena Vista, FL, November 4-7, 1996. Environmental Research Institute of Michigan, Vol. 11, pp. 563-568 (1996).
An acoustic Doppler current profiler (ADCP) is presently located approximately 7 km east of the Miami Harbor entrance at approximately 130 m depth. This device measures profiles of the current speed and direction in the upper 50 m of the water column directly above the instrument and transmits its data to a computer on shore. These data, sent at 20-minute intervals, are utilized to determine suitability of conditions for disposal of dredge materials. The computer performs a running one-hour average of the current vectors over the 50 m interval and transmits the east-west component to a watchstander hourly via telephone pager. If the westerly component of the current vector exceeds 12 cm per second, disposal operations are suspended. As of the date of this presentation, processed profiles of the data will be available via connection to the world wide web.
AO-025
DANESHZADEH, Y.-H., J.F. FESTA, and R.L. MOLINARI. Quality control of XBT data collected in the Atlantic Ocean: 1990-1991. NOAA Data Report, ERL AOML-29 (PB97-135446), 77 pp. (1996).
Delayed mode and real-time XBT data collected in the Atlantic Ocean during 1990 and 1991 were scientifically quality controlled at NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML) and the results of the quality control are presented in detail as tables and figures.
AO-026
DeMaria, M., and J. KAPLAN. An operational evaluation of a statistical hurricane intensity prediction Scheme (SHIPS). Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 280-281 (1997).
No abstract.
AO-027
Dickerson, R.R., P. Kelley, K.P. Rhodes, T.P. CARSEY, M.L. FARMER, and P. Crutzen. Measurement of reactive nitrogen compounds over the Indian Ocean. Chemical Engineering News, 74:84 (1996).
No abstract.
AO-028
DODGE, P.P., S.H. HOUSTON, and J.F. GAMACHE. Three-dimensional windfields in Hurricane Fran (1996) at landfall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 115-116 (1997).
No abstract.
AO-029
DODGE, P.P., S.H. HOUSTON, and J.F. GAMACHE. Windfields in Hurricane Fran (1996) at landfall from combined WSR-88D and airborne Doppler radar data. Proceedings, 28th Conference on Radar Meteorology, Austin, TX, September 7-12, 1997. American Meteorological Society, 575-576 (1997).
The Hurricane Research Division's (HRD) Tropical Cyclone Windfields at Landfall Experiment collects data in landfalling tropical cyclones from NOAA aircraft to improve real-time and post-storm surface wind analyses that are prepared by HRD. The real-time analyses are provided to forecasters at the Tropical Prediction Center. Airborne Doppler radar data are combined with National Weather Service WSR-88D radar data in three-dimensional analyses to document the evolution of tropical cyclones at landfall, and to provide corroborating data for testing WSR-88D tropical cyclone algorithms. From 2056 UTC, 5 September 1996, to 0348, 6 September 1996, the NOAA research aircraft RF42 flew in Hurricane Fran as it moved ashore in North Carolina. A "figure 4" pattern at 5,000 ft, overflights of marine and coastal surface platforms, and several passes along radials from the Wilmington and Morehead City WSR-88D radars in North Carolina provided flight-level wind data that were included in HRD's surface wind analyses. The research flight concluded with an overland "figure 4" pattern at 14,000 ft that passed near the Raleigh WSR-88D, and then through Fran's center when it was 70 km north-northwest of the Wilmington WSR-88D. The portable Doppler radar on wheels from the University of Oklahoma also recorded data at the Wilmington airport during the landfall, so there is a rich data set to describe convective and mesoscale features in Hurricane Fran. At the conference, we will present windfields synthesized from the airborne and WSR-88D radars that describe the kinematic structure as Fran moved over the coast. The comparison of vertical structure of the wind fields near the coast and 200 km inland should be particularly interesting. We will also discuss the problems of combining airborne and ground-based Doppler radar data.
AO-030>
ENFIELD, D.B. Relationships of inter-American rainfall to tropical Atlantic and Pacific SST variability. Geophysical Research Letters, 23:3505-3508 (1996).
Area-averaged anomalies of sea surface temperature (SSTA) and rainfall, developed from large-scale data sets, have been used to explore the relative importance of the Pacific El Niño-Southern Oscillation (ENSO) versus Atlantic SST variability for inter-American (50°S-50°N) climate variability at interannual time scales. Except for a lack of correlation south of 15°S, SSTA in the tropical Pacific and tropical North Atlantic are comparably related to rainfall, with clear associations distributed between the southeastern United States (US) in the north and northern South America in the south. Although NINO3 explains 25% of the variance of the North Atlantic SSTA index, the rainfall correlations with North Atlantic SSTA are for the most part opposite in sign to those with NINO3. Hence, a significant part of the Atlantic SSTA probably has a direct association with rainfall, rather than being merely an indirect proxy for Pacific ENSO linkages. In contrast to the North Atlantic, South Atlantic SSTA appear to be only related to rainfall in northeast Brazil. The entire region between Venezuela and northeast Brazil appears to be sensitive to both the ITCZ and to antisymmetric configurations of SSTA across the ITCZ, in a manner consistent with the relationships between SST, surface wind, and surface wind divergence fields.
AO-031
ENFIELD, D.B., and D.A. MAYER. Relationships of western hemisphere rainfall to tropical Atlantic and Pacific SST variability. Preprint Volume, 8th Conference on Air-Sea Interaction and Symposium on the Global Ocean-Atmosphere-Land System (GOALS), Atlanta, GA, January 28-February 2, 1996. American Meteorological Society, 390-394 (1996).
No abstract.
AO-032
ENFIELD, D.B., and D.A. MAYER. Tropical Atlantic sea surface temperature variability and its relation to El Niño-Southern Oscillation. Journal of Geophysical Research, 102(C1):929-945 (1997).
Past analyses of tropical Atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics, across the Intertropical Convergence Zone (ITCZ). By analyzing an improved 43-year (1950-1992) record of SST (Smith et al., 1996) and other data derived from the Comprehensive Ocean-Atmosphere Data Set (COADS), it is shown that the regions north and south of the ITCZ are statistically independent of each other at the seasonal to interannual time scales dominating the data, confirming the conclusions of Houghton and Tourre (1992). Some dipole behavior does develop weakly during the boreal spring season, when there is a tendency for SST anomaly west of Angola to be opposite of that in the tropical North Atlantic. It is further shown that tropical Atlantic SST variability is correlated with Pacific El Niño-Southern Oscillation (ENSO) variability in several regions. The major region affected is the North Atlantic area of northeast trades west of 40°W along 10°N-20°N and extending into the Caribbean. There, about 50-80% of the anomalous SST variability is associated with the Pacific ENSO, with Atlantic warmings occurring four to five months after the mature phases of Pacific warm events. An analysis of local surface flux fields derived from COADS data show that the ENSO-related Atlantic warmings occur as a result of reductions in the surface northeast trade wind speeds, which in turn reduce latent and sensible heat losses over the region in question, as well as cooling due to entrainment. This ENSO connection is best developed during the boreal spring following the most frequent season of maximum ENSO anomalies in the Pacific. A region of secondary covariability with ENSO occurs along the northern edge of the mean ITCZ position and appears to be associated with northward migrations of the ITCZ when the North Atlantic warmings occur. Although easterly winds are intensified in the western equatorial Atlantic in response to Pacific warm events, they do not produce strong local changes in SST. Contrary to expectations from studies based on equatorial dynamics, these teleconnected wind anomalies do not give rise to significant correlations of SST in the Gulf of Guinea with the Pacific ENSO. As the teleconnection sequence matures, strong southeast trades at low southern latitudes follow the development of the North Atlantic SST anomaly and precede by several months the appearance of weak negative SST anomalies off Angola and stronger positive anomalies extending eastward from southern Brazil along 15°-30°S.
AO-033
Faber, T., L.K. Shay, S.D. Jacob, S.H. HOUSTON, and P.G. BLACK. Observed air-sea interactions during Hurricane Emily. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 433-434 (1997).
No abstract.
AO-034
FESTA, J.F., and R.L. MOLINARI. Comparison of thermal statistics derived from observational data sets in the tropical Atlantic and Pacific Oceans. NOAA Technical Memorandum, ERL AOML-91 (PB97-208177), 78 pp. (1997).
Statistical analysis of surface and subsurface temperature data in the tropical Atlantic and Pacific Oceans is presented. The statistics were estimated from the Comprehensive Ocean-Atmospheric Data Set (COADS) and the historical expendable bathythermograph (XBT) observations. Spatial structure functions (semivariograms) for the anomaly fields of sea surface temperature and the temperature at 200 m and 400 m were estimated for a 2 degree by 2 degree grid in the tropical oceans. Dominant scales of spatial variability are identified and compared with other investigations.
AO-035
FRANKLIN, J.L. Status of GPS dropwindsondes. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A-19 (1997).
NOAA WP-3D aircraft have been equipped with dropwindsondes that rely on the Omega navigational network for windfinding (ODWs). The Omega network is being phased out, with funding scheduled to terminate in September 1997. NOAA has purchased a new jet aircraft for hurricane reconnaissance, the Gulfstream-IV (G-IV), that will begin operational missions in 1997. The primary mission of the G-IV will be to release dropwindsondes in the hurricane environment to improve operational forecasts of the hurricane track. With the anticipated demise of the Omega network, a new design of dropwindsonde is under development by the National Center for Atmospheric Research (NCAR). The new sonde uses the Global Positioning System (GPS) rather than Omega for windfinding. The thermodynamic sensors on this dropwindsonde are also new. Field testing of the GPS dropwindsonde began in August 1996 from one of the NOAA WP-3D aircraft, with installation and testing on the G-IV in September. Data from the new dropwindsondes have been compared to flight-level data from the G-IV and the WP-3D aircraft, simultaneous releases of ODWs, nearby rawinsondes, and buoys. Through the end of November, 85 GPS sondes had been released from the G-IV and the P-3. About half of this total was in connection with HRD's annual hurricane field program. Several biases in the thermodynamic data from the earliest drops were noted, including a cold temperature bias of 1-2 degrees, and a dry humidity bias of about 10%. Sonde splash pressures also appeared to be consistently low by 1-2 mb. NCAR was able to determine that the pressure bias, as well as much of the temperature bias, was a dynamic effect caused by the fast fall rate of the sonde (about 12 m/s at the surface) that could be corrected in software. The humidity bias is believed to be a contamination of the sensor by outgassing from the resin-impregnated cardboard tube that forms the body of the dropwindsonde. This problem has not yet been fully resolved. Early problems with GPS firmware have also been resolved, producing wind accuracies usually better than 0.5 m/s. At the time of this writing, typical measurement accuracies are believed to be about 0.5 mb, 0.5°C, 5-10%, and 0.3 m/s for pressure, temperature, relative humidity, and wind, respectively.
AO-036
FRANKLIN, J.L., H.L. Cole, T.F. Hock, D.K. Lauritsen, K.D. Norris, and E.F. Chamberlain. GPS dropwindsondes and the NOAA G-IV jet aircraft: New opportunities for forecasting and research. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 135-136 (1997).
No abstract.
AO-037
GAMACHE, J.F. Evaluation of a fully three-dimensional variational Doppler analysis technique. Proceedings, 28th Conference on Radar Meteorology, Austin, TX, September 9-12, 1997. American Meteorological Society, 422-423 (1997).
A method is described that deduces the three-dimensional wind field from two or more independent Doppler observations and from the continuity equation, using a simultaneous three-dimensional variational solution of the Doppler projection equations and the continuity equation. The solution minimizes a cost function that includes (1) the difference between observed Doppler radial velocities (corrected for precipitation fall speed) and the projection of the analysis velocities upon the observed Doppler pointing angles, (2) the error in the discretized continuity equation, and (3) and the difference between a velocity component and the surrounding six grid points. The third part of the cost function is included to quiet noise in the solution. A much higher weight is given to the second term since it represents the solution to the continuity equation at only one grid cell. Otherwise, when all grid cells are combined there would be substantial "leakage" in the continuity equation. Errors in the discretized continuity equation are less than 10-6 s-1 at individual grid points. Analytical wind fields will be resampled and the ability of the variational analysis to repeat the analytical field will be discussed at the conference. The technique has already been applied to the core of several hurricanes, convection within a developing tropical storm, and several cases in TOGA COARE. By the time of the conference it may also have been applied to a VORTEX case. Bubble-like features have been seen in several of these cases, and the bubble locations are very consistent with the radar reflectivity presentation. Several of these examples will be shown at the conference.
AO-038
GAMACHE, J.F. Wind shear and sea surface temperature in hurricanes observed by airborne Doppler radar. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A17-A18 (1997).
The relationships between sea surface temperature (SST), vertical wind shear, and hurricane structure and intensity change are described for two eastern Pacific hurricanes. Two NOAA WP-3D Doppler-equipped aircraft observed Hurricane Jimena on 23 September 1991 and Hurricane Olivia on 24 and 25 September 1994. Aircraft flight tracks were coordinated for optimum Doppler wind analysis of inner core (radius < 30 km) winds. Hurricane Jimena maintained virtually steady intensity for 24 hours, while Hurricane Olivia deepened 1-2 mb/hr during the mission on the 24th and filled at 3 mb/hr during the mission on the 25th. The missions yielded four wind analyses in Hurricane Jimena and seven for each of the two days in Olivia. The average interval between analyses is about 35 minutes. At the time of the mission, Jimena was located at 13.3°N, 109.6°W over warm tropical waters. The shear between 1 and 10 km was southeast at 15 m/s, and the hurricane remained at a nearly constant intensity. Hurricane Olivia intensified into a hurricane early on 24 September 1994. As the aircraft first reached Olivia, it was located near 15.2°N, 118.0°W. During three hours on station the central pressure decreased by about 6 mb. The hurricane had a mean shear during the mission of east at 7 m/s between 1 and 9 km, and the asymmetric distribution of greater precipitation to the south was sustained throughout the mission. During the 24th the hurricane travelled west-northwestward and was over warm tropical water (28.2°C). As the aircraft began their penetrations on 25 September, Olivia was near its maximum intensity. The radar presentation was highly symmetric, and the shear between 1 and 9 km was 3 m/s from the west. In three hours the shear had increased to 15 m/s from west-northwest, and a highly asymmetric precipitation pattern had developed with dBZ greater than 50 seen to the north of center and nothing above 40 dBZ to the south of center. Mean winds at the 9-km level decreased by 15 m/s. The role of shear in producing this change may be confused by Olivia passing the SST front as it travelled nearly northward at 5 m/s, so the SST by the end of the mission was 27°C. Another interesting feature that may be described at the Interdepartmental Conference is a highly convective feature in the northeast eyewall late on 25 September in Olivia that had an elevated echo maximum and apparently a low-reflectivity vault where the strongest updrafts were. Analysis has just begun of this feature. Hopefully, it will be described at the next conference.
AO-039
GAMACHE, J.F., H.E. WILLOUGHBY, M.L. BLACK, and C.E. SAMSURY. Wind shear, sea surface temperature, and convection in hurricanes observed by airborne Doppler radar. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 121-122 (1997).
No abstract.
AO-040
GARZOLI, S.L. SACC: South Atlantic Climate Change. U.S. Department of Commerce, NOAA/Atlantic Oceano-graphic and Meteorological Laboratory, Miami, Florida, 27 pp. (1996).
No abstract.
AO-041
GARZOLI, S.L., G.J. GOÑI, A.J. Mariano, and D.B. Olson. Monitoring the upper southeastern Atlantic transports using altimeter data. Journal of Marine Research, 55(3):453-481 (1997).
A large in-situ data set, collected in the southeastern Atlantic Ocean, is merged with the TOPEX/POSEIDON altimeter observations in order to verify the use of altimeter data in monitoring the transports of the Agulhas/Benguela system. Comparisons between altimeter observations and either moored current meters or inverted echo sounder measurements shows that the sea surface elevation anomaly is significantly correlated with the thermocline depth and the surface dynamic height, respectively. Knowing the least-squares regression parameters, it is possible to calculate the transports by using geostrophy and either a two-layer or a continuously-stratified model. The transports obtained from fits of dynamic height to altimeter sea surface height are similar to the ones calculated with the moored instruments. In the southern part of the area under analysis, around 35°S, close to the Agulhas retroflection, the transports obtained from the two-layer model are overestimated. Across the Benguela Current, at 30°S, transports are still overestimated but of the same order as the measured ones. In this part of the region, the two-layer model can be successfully used to calculate the total and barotropic transports of the Benguela Current. Analysis of the three years of geostrophic transport obtained from the altimeter data indicate that the mean Benguela Current transport does not change interannually more than 20%. However, the primary interannual variability derives from the source water that forms the Benguela Current.
AO-042
GARZOLI, S.L., A.L. Gordon, V.M. Kamenkovich, D. Pillsbury, and C.M. Duncombe Rae. Variability and sources of the southeastern Atlantic circulation. Journal of Marine Research, 54(6):1039-1071 (1996).
The 1992-1993 Benguela Sources and Transport (BEST) time series provides a quantitative view of Benguela Current transport and the eddy field across 30°S, as well as an estimate of the relation between its barotropic and baroclinic components. This is done by a simultaneous analysis of all the different data sets: inverted echo sounders, pressure sensors, CTD, current meter moorings, and ADCP. The analysis of the time series indicate that the annual mean baroclinic transport of the Benguela Current is approximately 13 Sv. The total transport is 16 Sv. The stationary flow associated with the Benguela Current is mostly confined along the African Continent while a transient flow, composed by large eddies shed from the Agulhas retroflection, composes the western portion of the flow. In the stationary part of the Benguela Current, both barotropic and baroclinic components are equally important while in the transient part, the barotropic is more substantial. Several eddies were observed during the experiment that translates to the west. They start with a speed of 12 km/day and close to the Walvis Ridge it has already diminished to 6-7 km/day. It can be assumed that after crossing the Walvis Ridge, due to their strong barotropic component (they feel the bottom), the speed decreases to that estimate previously obtained in the middle of the basin. The sources of the Benguela Current may include Indian and South Atlantic subtropical thermocline water; the relatively saline, low oxygen tropical Atlantic water and the cooler, fresher subantarctic water. The South Atlantic thermocline and subantarctic inflow is derived from the eastward flowing South Atlantic Current. The Indian Ocean water is injected into the Benguela Current through the Agulhas Retroflection eddy and filament processes. A complex stirring effect of contrasting water types is envisioned. The changes in thermocline salinity correlate with transport: in general, when the northward transport is increasing the thermocline salinity also increases. This indicates that the Benguela Current increases in strength by bringing in more subtropical water. As the Agulhas input is most effective in boosting the salinity of the upper thermocline (the South Atlantic Current water being deficient in salinity relative to the Indian Ocean source), we suggest that the spatial variations in transport are tied to Agulhas water influx, presumably within and associated with the eddy field.
AO-043
GOLDENBERG, S.B. Where we are at in forecasting seasonal Atlantic basin tropical cyclone activity. Final Report, Expert Meeting on Public Weather Services and Hurricane Disaster Preparedness, Port-of-Spain, Trinidad and Tobago, December 11-15, 1995. South African Weather Bureau, 5 pp. (1996).
Most of the tropical cyclones in the North Atlantic basin (including the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico) form from easterly (African) wave disturbances. Although the number of easterly waves in the tropical Atlantic tends to be fairly steady from year to year, the fraction of these that develop into tropical cyclones exhibits substantial interannual variability. Not only the number, but also the strength and location of the Atlantic basin tropical cyclones vary greatly from year to year. The Atlantic basin, unlike the east and west Pacific basins, in the mean, is not particularly favorable for tropical cyclone development. Year-to-year changes in the large-scale environment have a substantial influence on the overall activity of each Atlantic hurricane season. The search for conditions that result in the development or nondevelopment of the waves into tropical cyclones has been the subject of numerous studies, some of which have attempted to relate the variability to fluctuations in the tropical and global climate. Some of the climatic indicators that have been associated with fluctuations in Atlantic basin hurricane activity include sea-surface temperature (SST) anomalies for the equatorial central and eastern Pacific (i.e., El Niño activity), SSTs for the tropical Atlantic, rainfall variations over west Africa, the stratospheric Quasi-Biennial Oscillation (QBO), and vertical wind shear over the tropical Atlantic. Various studies have examined some of these indicators in an attempt to establish the actual physical mechanisms responsible for the associations with tropical cyclone activity. Other work has used selected parameters to predict Atlantic basin activity as much as 6-11 months in advance. Information will be presented describing the various parameters and their possible physical association with Atlantic hurricane activity. Current methodology used by other investigators to make seasonal predictions of activity and a discussion of their past performance will be presented with a special emphasis on implications for the Caribbean. The extended-range forecast for the 1996 Atlantic seasonal hurricane activity and verifications for the 1995 seasonal forecast will be discussed. The strengths and weaknesses of the current state of seasonal forecasting will be presented. The implications of fluctuations in hurricane activity on the multi-decadal scale will also be discussed.
AO-044
GOLDENBERG, S.B., C.W. LANDSEA, and L.J. SHAPIRO. Are we seeing the beginning of a long-term upturn in Atlantic basin major hurricane activity? Tropical Cyclone Symposium, Melbourne, Australia, December 9-13, 1996. U.S. Office of Naval Research, 10 pp. (1997).
No abstract.
AO-045
GOLDENBERG, S.B., L.J. SHAPIRO, and C.W. LANDSEA. Are we seeing a long-term upturn in Atlantic basin major hurricane activity related to decadal-scale SST fluctuations? Preprints, 7th Conference on Climate Variations, Long Beach, CA, February 2-6, 1997. American Meteorological Society, 305-310 (1997).
No abstract.
AO-046
GOLDENBERG. S.B., L.J. SHAPIRO, and C.W. LANDSEA. Mounting evidence for a decadal-scale upturn in Atlantic basin tropical cyclone activity. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 507-508 (1997).
No abstract.
AO-047
GOLDENBERG, S.B., L.J. SHAPIRO, and C.W. LANDSEA. The hyperactive 1995 Atlantic hurricane season: Just a spike or a harbinger of things to come? Proceedings, 21st Climate Diagnostics and Prediction Workshop, Huntsville, AL, October 28-November 1, 1996. American Meteorological Society, 9-12 (1997).
For over 25 years the North Atlantic hurricane basin has experienced a relative lull in tropical cyclone activity, in particular, in major hurricane (maximum sustained surface winds of at least 50 m/s) activity and in overall activity in the deep tropics. After the experience of renewed "normal" activity in 1988 and 1989, it was suggested that the Atlantic basin was returning to a long-term period of higher activity such as what was experienced back in the decades of the 1950s and 1960s and some earlier periods. The renewed activity in 1988 and 1989 was followed, however, by a marked downturn in activity from 1991 to 1994. In fact, the inhabitants of the regions surrounding the Caribbean experienced no hurricanes from 1990-1994. As a result of the resumption of the below-normal activity, primarily attributed to the highly anomalous, long-lasting warm event (El Niño) in the tropical Pacific, the notion that the Atlantic basin had entered a high-activity decade was pretty much discarded. The warm event in the Pacific finally ended in early 1995 and was followed by one of the most active hurricane seasons in the Atlantic on record, including renewed activity in the Caribbean, and with almost every measure of activity over twice the long-term mean. Of particular note was that the season produced five major hurricanes for the first time since 1964. Most of the major hurricanes in the North Atlantic basin form from easterly (African) wave disturbances and are especially sensitive to fluctuations in the tropical climate on the interannual and interdecadal time scales. The chief issue that will be addressed in the current study is whether or not the activity of the 1995 season was simply an anomalous "spike" or a harbinger of longer-term climate shifts signaling the probability of greater activity over the next decade or so.
AO-048
GOLDENBERG, S.B., L.J. SHAPIRO, and C.W. LANDSEA. The hyperactive 1995 Atlantic hurricane season: A spike or a harbinger of things to Come? Workshop Proceedings, Climate Change and Climate Variability in the Atlantic, Halifax, Nova Scotia, December 3-6, 1996. American Meteorological Society, 113-119 (1997).
No abstract.
AO-049
GOÑI, G.J., S.L. GARZOLI, A.J. Mariano, D.B. Olson, and O.B. Brown. Monitoring the upper layer southeastern Atlantic transports and eddy field using altimeter data. EOS, Transactions, American Geophysical Union, 77(46):F16 (1997).
Sea height anomaly data derived from TOPEX/POSEIDON and thermocline depth and dynamic height derived from a set of five inverted echosounders and four moored current meters are used in conjunction in the southeastern Atlantic Ocean to monitor the thermocline depth and transports of the Agulhas/Benguela system. Comparisons between TOPEX/POSEIDON altimeter observations and data from the moored instruments show that the sea surface height anomaly is significantly correlated to the thermocline depth and the sea surface dynamic height. A two-layer approximation with thermocline deviations and a reduced gravity is used to describe the vertical structure of the ocean. The reduced gravity is estimated from the slope of the linear fit of the thermocline depth and sea height anomaly data. The thermocline depth and baroclinic and geostrophic transports are then computed using simple expressions derived from the two-layer model. Analysis of three years of geostrophic transport estimates obtained from TOPEX/POSEIDON data indicate that the Benguela Current may undergo interannual variability up to 20%. However, the primary variability derives from the source waters that form the Benguela Current, i.e., waters from the South Atlantic, Indian Ocean, and tropical Atlantic. The analysis of the depth of the altimeter-derived thermocline field is used to study the formation of rings in the Agulhas retroflection region, to monitor their trajectories, and to estimate their kinetic and available potential energy.
AO-050
GOÑI, G.J., S.L. GARZOLI, A.J. ROUBICEK, D.B. Olson, and O.B. Brown. Agulhas ring dynamics from TOPEX/POSEIDON satellite altimeter data. Journal of Marine Research, 55(5):861-883 (1997).
The transfer of warm water from the Indian Ocean into the South Atlantic subtropical gyre takes place in the form of rings and filaments formed when the Agulhas Current retroflects south of Africa between 15°E and 25°E. A survey of the rings formed from September 1992 until December 1995 in the retroflection region was carried out using TOPEX/POSEIDON altimeter data. A two-layer model was used to estimate the upper layer thickness from the altimeter-derived sea surface height anomaly data. An objective analysis scheme was used to construct a map of upper layer thickness every ten days. Seventeen rings and their trajectories were identified using these maps. The shedding of rings from the Agulhas Current was neither continuous nor periodic, and for long periods there is no formation of rings. Several rings remained in the region for more than a year and, at any given time, two to six rings coexisted in the region east of the Walvis Ridge. The results showed that the number of rings translating simultaneously in this region is larger during the first half of each year. The upper layer transport of the Agulhas Current in the retroflection region was computed and a close association between high variations in transport and ring shedding was found. Rings translated west-northwest at translation speeds ranging from 5 to 16 km day-1 following formation. The values of available potential energy computed for the rings place them among the most energetic rings observed in the world oceans, with values of up to 70 ´ 1015 J. Transport computations indicate that each ring contributes in the average approximately 1 Sv of Agulhas Current waters to the Benguela Current.
AO-051
Gordon, A.L., M. Shubin, D.B. Olson, P. Hacker, A. Ffield, L.D. Talley, W.D. WILSON, and M.O. BARINGER. Advection and diffusion of Indonesian Throughflow within the Indian Ocean South Equatorial Current. Geophysical Research Letters, 24(21):2573-2576 (1997).
No abstract.
AO-052
Gray, W.M., J.D. Sheaffer, and C.W. LANDSEA. Climate trends associated with multi-decadal variability of Atlantic hurricane activity. In Hurricanes, Climate, and Socioeconomic Impacts, H.F. Diaz and R.S. Pulwarty (eds.). Springer, Berlin, 15-53 (1997).
No abstract.
AO-053
Haddad, Z.S., D.A. Short, S.L. Durden, E. Im, S. Hensley, M.B. Grable, and R.A. BLACK. A new parameterization of the rain drop size distribution. IEEE, Transactions on Geoscience and Remote Sensing, 35(3):532-539 (1997).
This paper revisits the problem of finding a parametric form for rain drop size distribution (DSD) which (1) is an appropriate model for tropical rainfall, and (2) involves statistically-independent parameters. Using TOGA/COARE data, we derive a parameterization which meets these criteria. This new parameterization is an improvement on the one that was derived in [3], using TRMM ground truth data from Darwin, Australia. The new COARE data allows us to verify that the spatial variability of the two "shape" parameters is relatively small, thus confirming that this parameterization should be particularly useful for remote sensing applications. We also derive new DSD-based radar-reflectivity-rain-rate power laws, whose coefficients are directly related to the shape parameters of the DSD. Perhaps most important, since the coefficients are independent of the rain-rate itself, and very little spatially, the relations are ideally suited for rain retrieval algorithms. It should also prove straightforward to extend this method to the problems of estimating cloud hydrometeors from remote-sensing measurements.
AO-054
Halliwell, G.R., and D.A. MAYER. Frequency response properties of forced climatic SST anomaly variability in the North Atlantic. Journal of Climate, 9:3575-3587 (1996).
Frequency response properties of North Atlantic (5-57°N) sea surface temperature anomaly (Tsa) variability over periods of several months to 20 years are characterized using the Cooperative Ocean Atmosphere Data Set (COADS). Significant direct forcing of Tsa variability by the anomalous wind field (primarily through the resulting anomalous surface turbulent heat flux) is observed in the Western Wind and Trade Wind belts, but not between these belts within the interior of the oceanic subtropical gyre. To analyze the response to this forcing, it is necessary to separate the total anomalous surface turbulent heat flux into a component representing the wind forcing and a component predominantly representing the negative linear feedback (Newtonian relaxation) that is the dominant damping mechanism of large-scale climatic Tsa variability. At frequencies where wind forcing is important, good agreement exists between frequency response properties estimated from data and properties theoretically predicted by a simple linearized slab mixed layer temperature balance. In particular, this balance quantifies the influence of negative feedback damping on the amplitude and phase lag of the response. In the Westerlies, wind forcing is effective over periods from several months to 8 yr, primarily 2-4 yr, and is ineffective at periods of 8-20 yr where forcing by variable oceanic flow has been demonstrated to be important. In the Trades, wind forcing is effective over periods from 8 mo to 13.3 yr, primarily 2-3 yr and 7-13.3 yr. Wind forcing in the Trades is less effective at periods of 3-6 yr where ENSO variability is significant. At frequencies where wind forcing in the Westerlies is significant, forcing and feedback have an equally large influence on Tsa, indicating that the wind-forced response is damped primarily by the negative feedback contained in the anomalous surface turbulent heat flux. In the Trades, feedback by anomalous surface turbulent heat flux is not large enough to balance the wind forcing; other processes must contribute significantly to the damping there. At frequencies where wind forcing is important, Tsa in the Westerlies is not coherent with Tsa in the Trades. The anomalous wind fluctuations driving Tsa in the Westerlies (Trades) are associated with anomalous surface pressure variability in the Icelandic low (subtropical high). Response to a coherent North Atlantic Oscillation (Icelandic Low varying out-of-phase with the subtropical high) is, therefore, not observed. The large Tsa fluctuations observed in the western basin within the Westerly Wind belt propagate to the east and northeast across the Atlantic at a characteristic speed of 6 km day-1.
AO-055
HARRIS, J.E., D.B. ENFIELD, and N. BRAVO. Altimetric assessment of the NMC ocean model. AVISO Newsletter, 4:18-20 (1996).
No abstract.
AO-056
Hasler, A.F., P.G. BLACK, V.M. Karyampudy, M. Jentoft-Nilsen, K. Palaniappan, and D. Chesters. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 201-202 (1997).
No abstract.
AO-057
HENDEE, J.C. Object-oriented analysis and design of a near real-time marine environmental data acquisition and reporting system. Proceedings, 8th International Coral Reef Symposium, Panama City, Panama, June 24-28, 1996. Smithsonian Tropical Research Institute, 2:1569-1574 (1997).
The National Oceanic and Atmospheric Administration's Coral Health and Monitoring Program has cooperated with the Florida Institute of Oceanography in developing a near real-time marine environmental monitoring and reporting system. Using an object-oriented analysis technique, this report describes how data are retrieved from satellite data and archiving facilities, then reformatted for presentation via a Remote Bulletin Board system and facsimile. Using an object-oriented design technique, a new system is designed using a requirements analysis of the original system.
AO-058
Hitchcock, G.L., W.J. Wiseman, W.C. Boicourt, A.J. Mariano, N. Walker, T.A. NELSEN, and E. Ryan. Property fields in an effluent plume of the Mississippi River. Journal of Marine Systems, 12:109-126 (1997).
Surface property distributions were mapped in the Mississippi River plume during May and August 1993 while following surface drifters. Prevailing winds were the primary factor controlling the orientation of the plume. In May, under typical southeasterly winds, the plume turned anticyclonically towards the coast, while in August, under anomalous westerly winds, the plume turned east. Remote imagery of sea surface temperature and suspended sediments confirmed the direction of the plume. Optimally interpolated maps of surface salinity, temperature, chlorophyll a fluorescence, and transmissivity from underway sampling, and periodic nutrient samples, reveal the plume structure. In May, concentrations of nitrate, silicate, and phosphate decreased linearly with increasing salinity. Chlorophyll a increased to peak concentrations of 10 mg 1-1 in the plume, although higher pigment biomass was observed near the coast. In August, nitrate and silicate concentrations decreased conservatively near the mouth of Southwest Pass, except where pigment biomass was enhanced in a convergent surface front. Surface nutrient concentrations in the plume also decreased with increasing salinity. The observations provide the first Lagrangian view of surface property distributions in the Mississippi River plume, and indicate that significant temporal variability exists in physical and biological properties within a day after waters are discharged from the river delta.
AO-059
Ho, D.T., L.F. Bliven, R.H. WANNINKHOF, and P. Schlosser. The effect of rain on air-water gas exchange. Tellus, 49B:149-158 (1997).
The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF6 evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with 18 different rain rates (7 to 110 mm h-1) and 1 of 2 dropsizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and dropsize. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.
AO-060
Ho, D.T., R.H. WANNINKHOF, J.C. MASTERS, R.A. Feely, and C.E. Cosca. Measurements of underway fCO2 in the eastern equatorial Pacific on NOAA ships Malcolm Baldrige and Discoverer from February to September 1994. NOAA Data Report, ERL AOML-30 (PB97-169056), 58 pp. (1997).
From February through September 1994, underway measurements of the fugacity (partial pressure) of carbon dioxide (fCO2) were performed in the eastern equatorial Pacific as part of the Ocean Atmosphere Carbon Exchange Study (OACES) of the National Oceanic and Atmospheric Administration (NOAA). The measurements were performed with semi-autonomous instruments which measured the fugacity in the air and in the headspace of an equilibrator drawing water from the bow of the ship, from which the fCO2 of the surface water is calculated. From the difference in fugacity in air and water, the CO2 flux from the equatorial Pacific can be estimated. On the NOAA ship Malcolm Baldrige, the system measured three reference standards, three air values, and eight water values per hour. The system on the Discoverer measured three standards, one 19-minute average air sample, and one 20-minute average water sample per hour. This report contains a description of the methodology and reduction of the fCO2 and ancillary measurements. The results from the cruises of the Malcolm Baldrige in the equatorial Pacific in the (boreal) spring and fall of 1994 and from the Discoverer along nominally 110°W in the spring of 1994 are shown in a series of graphs with fCO2 air and water versus latitude as top panel and temperature and salinity versus latitude as bottom panel.
AO-061
Hopkins, M., M. DeMaria, and J. KAPLAN. Evaluation of an empirical inland wind model for the landfall of Hurricane Fran (1996). Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A-22 (1997).
A simple empirical model for predicting the winds from landfalling hurricanes has been developed for the Gulf and east coasts of the United States. This model was originally developed to estimate the maximum sustained surface winds near the center of landfalling storms, but was generalized to predict the two-dimensional field of maximum winds (wind swath). The performance of the model during the landfall of Hurricane Fran will be evaluated by comparing the predicted winds with all available surface observations. Plans for improving the swath part of the model using a combined wind data set from several recent landfalling storms will also be described.
AO-062
HOUSTON, S.H., M.D. POWELL, and P.P. DODGE. Surface wind fields for Hurricanes Bertha and Fran (1996). Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A-23 (1997).
Hurricanes Bertha and Fran made landfall near Wilmington, North Carolina within two months of each other in 1996. These tropical cyclones contained maximum sustained surface winds (marine exposure at 10 m) estimated to be 46 m s-1 and 50 m s-1, respectively, at the time of landfall. Fran caused more loss of life and greater estimated U.S. property damage (34 deaths and $3.2 billion) than Bertha (8 deaths and $250 million). In both storms, the property losses were primarily due to storm surge and waves along the coast rather than directly from the wind. Fran also caused considerable damage due to inland flooding resulting from heavy rainfall across a large swath of the eastern U.S. as it moved northward after landfall. The Hurricane Research Division (HRD) has been providing real-time tropical cyclone surface wind fields to forecasters at the National Hurricane Center (NHC) since 1993; there were 134 of these analyses made in 1996. The analysis system contains adjustment techniques for exposure and interactive data quality control that produce a field of input observations conforming to a common framework for exposure, height, and averaging period. In Hurricane Bertha, HRD transmitted 14 real-time surface wind fields to NHC. The real-time and post-storm surface wind analyses indicate that the peak sustained surface winds in Bertha were primarily over the Atlantic Ocean at the time of landfall. The storm rapidly weakened after landfall and, based on the HRD wind fields, it is very unlikely that the peak sustained surface winds were observed at any point along the coastline of North Carolina. During Hurricane Fran, HRD produced 28 real-time surface wind fields for NHC. These, together with post-storm analyses, indicated that Fran's surface winds at landfall were stronger and spread over a larger area north and east of the center than Bertha. Unlike Bertha, the coastal areas were affected by Fran's strongest winds, especially in advance of landfall. Real-time and post-storm surface wind analyses in Hurricanes Bertha and Fran will be discussed, along with their utility for NHC's marine forecasts, emergency management, and storm surge forecasting.
AO-063
HOUSTON, S.H., M.D. POWELL, and P.P. DODGE. Surface wind fields in 1996 Hurricanes Bertha and Fran at landfall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 92-93 (1997).
No abstract.
AO-064
JONES, R.W., and H.E. WILLOUGHBY. Sensitivity of a spectral shallow-water barotropic vortex to variations of domain size and spectral truncation. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 577-578 (1997).
Recent studies by Willoughby (1992, 1994, 1995) discuss the motion of a vortex on a beta plane for various environmental flows with a linear and non-linear version of the model. The domain size was 3000 km. Experiments for a 6000 km domain show small 50-km track differences by 10 days for an all cyclonic vortex with no environmental flow. Experiments with environmental flows will also be reported. The spectral truncation is wave number 3 for the non-linear model. Spectral truncations at wave numbers 2 and 4 will be reported. The purpose of these calculations is to show that highly truncated models are good enough to describe the dynamics of vortex motion on a beta plane with environmental flows. In the future, a baroclinic model will be developed for theoretical studies and for application to real-time hurricane tracking.
AO-065
KAPLAN, J., C.W. LANDSEA, M. DeMaria, and J.J. CIONE. The differing roles of the large- scale environment in the intensity changes of three 1996 Atlantic hurricanes. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 358- 359 (1997).
No abstract.
AO-066
Lamb, M.F., J.F. Bullister, R.A. Feely, G.C. Johnson, D.P. Wisegarver, B. Taft, R.H. WANNINKOF, K.E. McTaggart, K.A. Krogslund, C.W. Mordy, K. Hargreaves, D. Greeley, T. Lantry, H. Chen, B.E. HUSS, F.J. Millero, R.H. Byrne, D.A. Hansell, F.P. Chavez, P.D. Quay, P.R. Guenther, J.-Z. ZHANG, W. Gardner, M.J. Richardson, and T.-H. PENG. Chemical and hydrograph measurements in the eastern Pacific during the CGC94 expedition (WOCE section P18). NOAA Data Report, ERL PMEL-61 (PB97-158075), 235 pp. (1997).
No abstract.
AO-067
LANDSEA, C.W. Comments on "Will greenhouse gas-induced warming over the next 50 years lead to higher frequency and greater intensity of hurricanes?" Tellus, 49A:622-623 (1997).
No abstract.
AO-068
LANDSEA, C.W. Indices of global tropical cyclone activity. CLIVAR/GCOS/WMO Workshop on Indices and Indicators for Climate Extremes, Asheville, North Carolina, 10 pp. (1997).
No abstract.
AO-069
LANDSEA, C.W., G.D. Bell, W.M. Gray, and S.B. GOLDENBERG. The hyperactive 1995 Atlantic hurricane season: A juxtaposition of favorable conditions. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 505-506 (1997).
No abstract.
AO-070
LANDSEA, C.W., W.M. Gray, P.W. Mielke, K.J. Berry, and J.A. Knaff. A seasonal hurricane forecast for 1997. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, B-183 (1997).
The forecast for the 1997 Atlantic hurricane season issued by Dr. Bill Gray and collaborators (including myself) will be discussed. This prediction was issued in early December 1996 and will be updated in early April, early June, and early August. Uncertainties in the predictors, especially in El Niño and Sahel rainfall, will be discussed in how they may impact the number and intensity of tropical cyclones this year. I will also briefly discuss the performance of the 1996 forecasts.
AO-071
LANDSEA, C.W., N. Nicholls, W.M. Gray, and L.A. Avila. Reply. Geophysical Research Letters, 24(17):2205 (1997).
No abstract.
AO-072
LEE, K., F.J. Millero, and R.H. WANNINKHOF. The carbon dioxide system in the Atlantic Ocean. Journal of Geophysical Research, 102(C7):15,693-15,708 (1997).
During the National Oceanic and Atmospheric Administration's Ocean Atmosphere Carbon Exchange Study expedition in the eastern North Atlantic in summer 1993, measurements of four CO2 parameters, along with hydrographic properties, were made: fugacity of CO2, fCO2 (measured at 20°C and in situ); pH (measured at 20°C); total inorganic carbon, TCO2; and total alkalinity, TA. The major objective of this cruise was to establish a benchmark against which future measurements of the transient invasion of CO2 can be made. The large-scale distributions of surface water CO2 parameters were related to temperature and salinity in this region. The subsurface TA and TCO2 measurements were fitted to multiple linear functions of salinity, in situ temperature, apparent oxygen utilization, and silicate. The measurements of the inorganic carbon system were also used to examine the internal consistency of the carbonate system in this area. The measurements were internally consistent to ±1.3% in fCO2, ±0.006 in pH, ±3 mmol kg-1 in TCO2, and ±3 mmol kg-1 in TA if proper carbonic acid dissociation constants are used for different input combinations. The thermodynamic constants of Goyet and Poisson (1989), Roy et al. (1993), Millero (1995), and Lee and Millero (1995) were most consistent with the measurements of pH (at 20°C), TCO2, and TA. However, if fCO2 (at 20°C) is used in thermodynamic calculations, the constants of Mehrbach et al. (1973) gave the best representation of measurements. The constants of Lee and Millero (1995) were also in reasonable agreement with these measurements.
AO-073
Lobert, J.M., S.A. YVON-LEWIS, J.H. Butler, S.A. Montzka, and R.C. Myers. Undersaturations of CH3Br in the Southern Ocean. Geophysical Research Letters, 24(2):171-172 (1997).
Dry mole fractions of methyl bromide (CH3Br) in marine boundary layer air and air equilibrated with surface seawater were measured in the Southern Ocean. Saturation anomalies were consistently negative at -36±7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH3Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at -21 (-11 to -32) Gg y-1.
AO-074
MARKS, F.D., JR., and P.P. DODGE. Hurricane concentric eyewall characteristics as revealed by airborne Doppler radar analyses. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 102-103 (1997).
No abstract.
AO-075
MARKS, F.D., JR., and H.A. FRIEDMAN. 1997 Hurricane Field Program Plan. U.S. Department of Commerce, NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, FL (published for limited distribution), 132 pp. (1997).
The objectives of the National Oceanic and Atmospheric Administration (NOAA) hurricane research field program is the collection of descriptive data that are required to support analytical and theoretical hurricane studies. These studies are designed to improve the understanding of the structure and behavior of hurricanes. The ultimate purpose is to develop improved methods for hurricane prediction. Ten major experiments have been planned, primarily by principal investigators at the Hurricane Research Division (HRD)/Atlantic Oceanographic and Meteorological Laboratory (AOML) of NOAA, for the 1997 hurricane field program. These experiments will be conducted with the NOAA/Aircraft Operations Center (AOC) WP-3D and Gulfstream IV-SP aircraft.
AO-076
MARKS, F.D., JR., and L.N. Shay. Landfalling tropical cyclones: Forecast problems and associated research opportunities: Report of the Fifth Prospectus Development Team of the U.S. Weather Research Program. Minutes, 51st Interdepartmental Hurricane Conference, Miami, FL, March 24-28, 1997. Research Committee Meeting, A-26 (1997).
The Fifth Prospectus Development Team (PDT-5) of the U.S. Weather Research Program was charged to identify and delineate emerging research opportunities relevant to the prediction of local weather, flooding, and coastal ocean currents associated with landfalling U.S. hurricanes, specifically, and tropical cyclones, in general. Central to this theme are fundamental and applied issues including: rapid intensity change; initialization of and parameterization in dynamical models; coupling of atmospheric and oceanic models; quantitative use of satellite information; and optimal adaptive observing strategies to validate predictive models. To acquire the necessary understanding and provide the initial conditions for improved prediction, a focused, comprehensive observing system in a translating storm-coordinate system is required. With the development of proven instrumentation and improvement of existing systems, three-dimensional wind and thermodynamic data sets can be obtained whenever major hurricanes threaten the United States. Satellites, aircraft, expendable probes released from aircraft, and coastal, moored, and drifting surface platforms are needed to estimate the upper-ocean temperatures and currents, air-sea interactions, the distribution of storm surge, boundary layer winds, rainfall, and potential damage. In the hurricane core, airborne Doppler radar, supplemented by a suite of other instruments, would measure tropospheric winds including critical areas of the boundary layer and outflow region. Microwave systems would determine surface winds, ocean waves, and storm surge. On the hurricane periphery, dropsondes would be released from turboprop and jet aircraft to map the atmospheric temperature, humidity, and wind structure. Satellites would acquire both storm-scale and surrounding environmental data. To take full advantage of these new observations, techniques need to be developed to objectively analyze these observations, and initialize models aimed at improving prediction of hurricane track and intensity from global-scale and mesoscale dynamical models. Multi-nested models allow prediction of all scales from the global, which determine long-term hurricane motion, to the convective-scale, which affect intensity. Development of an integrated analysis and model forecast system optimizing the use of observations and providing the necessary forecast skill on all relevant spatial scales is required. Detailed diagnostic analyses of these data sets will lead to improved understanding of the physical processes of hurricane motion, intensity change, the atmospheric boundary layer, and air-sea coupling. Ultimately, the aim is on development of real-time analyses of storm surge, winds, and rain, before and during landfall, to improve warnings and provide local officials with the information needed to focus recovery efforts in the hardest hit areas as quickly as possible.
AO-077
Martin, D., M. Tsivou, B. Bonsang, C. Abonnel, T.P. CARSEY, M. Springer-Young, and A.A. Pszenny. Hydrogen peroxide in the marine atmospheric boundary layer during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) experiment in the eastern subtropical North Atlantic. Journal of Geophysical Research, 102(D5):6003-6015 (1997).
Gas phase hydrogen peroxide (H2O2) was measured in surface air on the NOAA ship Malcolm Baldrige from June 8-27, 1992 (Julian days 160-179), during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic region. Average H2O2 mixing ratios observed were 0.63 ± 0.28 ppbv, ranging between detection limit and 1.5 ppbv. For the entire experiment, only weak or no correlation was found between H2O2 mixing ratio and meteorological parameters (pressure, temperature, humidity, or UV radiation flux), as well as with tracers of continental air masses (CO, black carbon, radon). The average daily H2O2 cycle for the entire period exhibits a maximum of 0.8 ± 0.3 ppbv near sunset and a minimum of 0.4 ± 0.2 ppbv 4-5 hours after sunrise. Several clear H2O2 diurnal variations have been observed, from which a first-order removal rate of about 1 ´ 10-5 s-1 for H2O2 can be inferred from nighttime measurements. This rate compares well with those deduced from measurements taken at Cape Grim (Tasmania, 41°S) and during the Soviet-American Gas and Aerosol III experiment (equatorial Pacific Ocean).
AO-078
Maul, G.A., M.H. BUSHNELL, N.J. BRAVO, and D.V. HANSEN. Observed sea surface height and modeled dynamic height anomaly departures in the tropical Pacific Ocean: 1986-1989. Oceanologica Acta 20(4):569-584 (1996).
Observations of sea surface height variations (SSH¢) from November 1986 through September 1989 in the tropical Pacific from the improved (T2) GEOSAT data set (Cheney et al., 1991) are compared with monthly mean dynamic height anomaly departure (DD¢) from the "second reanalysis" using the NOAA ocean analysis system (Ji et al., 1994, 1995). For comparisons, DD¢ is calculated by removing north-south tilt and bias as in SSH orbit error removal, giving standard deviation fields sSSH¢ and sDD¢ that quantitatively reproduce variability of the North Equatorial Current (NEC)/North Equatorial Countercurrent (NECC)/South Equatorial Current (SEC) system between El Niño and non-El Niño years. Hovmöller diagrams of SSH¢ and DD¢ variability at 110°W, 140°W, 170°W, and 165°E between 20°S and 20°N, and along the equator from 120°E to 80°W, display the amplitude and phase of the 1986-1987 El Niño-Southern Oscillation (ENSO) event as distin-guished from the years following, with the NECC significantly weakened in 1987 as compared to 1988. Cross correlations (r) between DD¢ and SSH¢ are highest near the equator in the vicinity of the TOGA-TAO (Hayes et al., 1991; McPhaden, 1993) in situ mooring arrays, with values above r = 0.7 in much of the region ±7° of the equator across about half of the Pacific basin. Differences between DD¢ and SSH¢ are typically less than ±5 cm RMS in this same equatorial band, but there are two regions of differences in excess of ±15 cm RMS: off Central America and east of New Guinea. The reason for these large RMS differences is uncertain, but it is advanced from Lagrangian buoy data that intense eddy activity is unresolved in the model as compared to GEOSAT. For the 35 monthly realizations, the ensemble cross-correlation r = 0.5 has ±7 cm RMS within ±15° of the equator, and peaks in 1988 with decay towards the end of the GEOSAT Exact Repeat Mission (ERM) in September 1989. Seasonally, both SSH¢ and DD¢ show that the boreal winter (DJF) of 1987 is dominated by the ENSO-related sea level maximum in mid-basin, which is absent in the following two winters; spring (MAM) and summer (JJA) of all three years have little resemblance to each other, with 1987 and 1989 being more similar than 1988; autumn (SON) of 1988 shows a well developed NECC across of the eastern Pacific centered at ~7°N. The ERM altimeter data and the model calculations of the annual cycle both show east-west height amplitude maxima along 5°N and 10°N that explain more than 50% of the variance for a substantial portion of the central Pacific Ocean. Concurrent drogued buoy tracks show more eddies along ~5°N in the eastern Pacific in 1988 as compared to 1987 or 1989, but DD¢ is unable to resolve these features.
AO-079
McCarthy, M.C., L.D. Talley, and M.O. BARINGER. Deep upwelling and diffusivity in the southern Central Indian Basin. Geophysical Research Letters, 24(22):2801-2804 (1997).
Transport of the deepest water westward through a gap at 28°S in the NinetyEast Ridge between the Central Indian Basin and the West Australia Basin is calculated from hydrographic data collected as part of the WOCE Hydrographic Program section I8N. Zero reference velocity levels at mid-depth were chosen through consideration of water masses. The small transport of 1.0 Sv westward through the gap of water denser than s4 = 45.92 kg/m3 must all upwell in the southern Central Indian Basin. Of this, 0.7 Sv upwells between the central and western sill sections, that is, close to the sill itself. Using the areas covered by the isopycnal, we calculate an average vertical velocity of 3.3 ´ 10-3 cm/s close to the sill and of 4.2 ´ 10-4 cm/s west of the sill. Associated average vertical diffusivities are 105 cm2/s close to the sill and 13 cm2/s west of the sill, in this very near bottom layer.
AO-080
McCartney, M.S., R.G. Curry, and H.F. BEZDEK. North Atlantic's transformation pipeline. Oceanus, 39(2):19-23 (1996).
No abstract.
AO-081
McCartney, M.S., R.G. Curry, and H.F. BEZDEK. The interdecadal warming and cooling of Labrador Sea Water. ACCP Notes, 1-10 (1997).
No abstract.
AO-082
MOLINARI, R.L., D.A. MAYER, J.F. FESTA, and H.F. BEZDEK. Multi-year variability in the near surface temperature structure of the midlatitude western North Atlantic Ocean. Journal of Geophysical Research, 102(C2):3267-3278 (1997).
Between 1966 and 1995, subsurface temperature data have been collected in the western North Atlantic Ocean using expendable bathythermographs. Data coverage is sparse in both time and space, but evidence for decadal variability in the upper 400 m of the water column is found. The data were averaged by month onto a 2 degree of latitude by 4 degree of longitude grid. Thirty-one quadrangles in the region bounded by 17°N and 43°N and 78°W and 66°W have sufficient data to provide consistent results. Anomaly time series at 0, 100, 200, 300, and 400 m were estimated by subtracting a mean monthly climatology. The individual records were detrended and filtered to highlight the longer period signals. The analysis resulted in 25-year records (1969-1993) for study. Within the thermocline of the subtropical gyre and the Gulf Stream at 100 and 200 m, periods of predominately positive temperature anomaly end in 1971, 1982, and 1990, while periods of negative anomaly end in 1976 and 1985. Only the events ending in 1971, 1976, and 1990 are in the majority of the records at 300 and 400 m. Most of the events also appear in the sea surface temperature (SST) records, but are somewhat masked by significant noise at the surface. Meridional-vertical temperature sections through the subtropical gyre show that transitions from negative to positive anomaly events are characterized by a deepening of the isotherms throughout the section and transitions from positive to negative events by a rising of the isotherms. Significant lateral migration of the axis of the Gulf Stream, although possibly masked by the 2 degree averaging, is not necessary to explain either type of event. The transitions in the SST and 100 m temperature time series occur at essentially the same time as the transitions in an index of the North Atlantic Oscillation (NAO) that has also been detrended (i.e., 1971, 1976, 1980, 1984, 1988). The 1971, 1976, and 1988 NAO events are also observed at 300 and 400 m as described earlier. Periods of positive (negative) subsurface temperature anomaly are coincidental with periods of positive (negative) NAO index. Thus, earlier results showing connections between the NAO and western Atlantic SST at decadal time scales are now extended to at least 400 m in the water column. Trends were computed from the individual 25-year records. The trends at all depths are predominately negative (positive) north (south) of 38°N. Inferences from the horizontal distribution of the trends and results from earlier studies suggest that the 1969-1993 period may be a phase of a 30- to 50-year signal observed in the northern Atlantic since the beginning of the century.
AO-083
MURILLO, S., S.H. HOUSTON, and M.D.POWELL. Composites of surface marine observations for hurricanes during 1975-1996. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 78-79 (1997).
No abstract.
AO-084
NELSEN, T.A., M.P. ZETWO, H. Wanless, P. Blackwelder, P. Swart, T. Hood, C. Alvarez-Zarikian, J. Trefry, S. Metz, W.-J. Kang, R. Trocine, L. Tedesco, M. Capps, and M. O'Neal. The sediment record as a monitor of natural and anthropogenic changes in the lower Everglades/Florida Bay ecosystem: A high resolution study. 1996 Florida Bay Science Conference, Miami, Florida, June 1996. Florida Sea Grant/University of Florida Publication, 62-65 (1996). No abstract.
AO-085
OOYAMA, K.V. Footnotes to "conceptual evolution." Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 13-18 (1997). No abstract.
AO-086
OOYAMA, K.V. The semi-implicit integration of a nested spectral model and the result of tests in squall-line simulation. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 531-532 (1997).
No abstract.
AO-087
Parrish, J.R., and M.L. BLACK. The NOAA G-IV and the tropical cyclone environment. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 123-124 (1997).
No abstract.
AO-088
POWELL, M.D., and S.H. HOUSTON. Surface wind fields of 1995 hurricanes Erin, Opal, Luis, Marilyn, and Roxanne at landfall. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 90-91 (1997). No abstract.
AO-089
PRONI, J.R., and T.A. NELSEN. Final Report: Deep Ocean Relocation Project, Phase II: Application of acoustical and tracer methodologies to the deep ocean relocation of dredge material. Contract Report ARPAC 558.AOO, Naval Research Laboratory, Washington, D.C., 37 pp. (1997).
One of the major challenges facing the United States today is disposal of contaminated dredged material. Inexorable economic and population pressures assure that this challenge will exist for the foreseeable future. One concept for dealing with this material is deep ocean disposal or deep ocean relocation (DOR). A key component of DOR concepts is monitoring of the geosynthetic fabric containers (GFCs), which will be used to contain the dredged material, during descent through the oceanic water column to the ocean bottom. The present report deals with the use of acoustical and tracer methodologies for monitoring DOR-associated plumes. Discussed herein is the feasibility of utilizing active acoustical systems to monitor both GFCs and any escaping plumes. A discussion of nepheloid layer characteristics of relevance to GFC detection is presented.
AO-090
PRONI, J.R., and R.G. Williams. Acoustic measurements of currents and effluent plume dilutions in the western edge of the Florida Current. In Acoustic Remote Sensing Applications, S.P. Singal (ed.). Narosa Publishing House, New Delhi, India, 537-550 (1997). The Southeast Florida Outfall Experiment (SEFLOE), carried out in the western boundary of the Florida Current off southeast Florida, USA, between 1988 and 1993, was the most extensive application of acoustics to wastewater effluent studies performed in the United States. The objective was to provide a scientific basis for managerial regulations for effluent discharges. This article describes the acoustical measurements to map effluent plume distributions, and the three-dimensional current regime. Current meters were installed near each outfall near the top and bottom of the water column. An acoustic Doppler current profiler (ADCP) was deployed on the bottom in the vicinity of the outfalls. Research ships towed active acoustical systems over the diffusers. Examples are given of the outfall plume distribution and the principal current regimes. A conceptual three-dimensional model is developed to compare with observed data. The acoustical measurements are shown to serve as a surrogate for the effluent constituent distributions.
AO-091
Rhoads, K.P., P. Kelley, R.R. Dickerson, T.P. CARSEY, and M.L. FARMER. Composition of the troposphere over the Indian Ocean during the monsoonal transition. Journal of Geophysical Research, 102(D15):18,981-18,996 (1997).
The atmosphere over the equatorial Indian Ocean is a unique environment in which to study the chemical and radiative effects of an intense source of anthropogenic emissions from the northern hemisphere directly coupled to the relatively pristine background conditions present in the southern hemisphere. As an initial investigation into the role of the intertropical convergence zone (ITCZ) on interhemispheric transport of pollutants, a number of trace atmospheric species were measured aboard the National Oceanic and Atmospheric Administration (NOAA) R/V Malcolm Baldrige between Durban, South Africa, and Colombo, Sri Lanka, from March 12 to April 22, 1995. Sharp increases in the concentrations of carbon monoxide (CO), carbon dioxide (CO2), and aerosols were associated with four distinct meteorological regimes transected by the cruise track from 33°S to 9°N. Across the ITCZ, aerosol concentrations, including non-sea-salt sulfate, nitrate, and ammonium, increased by a factor of 4. Surface zone measurements showed a latitudinal gradient with a minimum near the equator and a strong diurnal variation in the equatorial regions. The latitudinal profile of gas-phase reactive nitrogen paralleled ozone and was higher in the remote southern hemisphere than in the remote northern hemisphere. Evidence of direct anthropogenic impact on the region was observed more than 1500 km from the southern tip of India. Back trajectories, calculated with NOAA's medium range forecast data using the Hybrid Single Particle Lagrangian Integrated Trajectory (HY-SPLIT) program, identified the origin of the air mass regimes characterized by the trace gas and aerosol data. Continental emissions in the northern hemisphere were shown to have a major impact on the radiative properties and oxidizing capacity of the marine atmosphere.
AO-092
SAMSURY, C.E., M.L. BLACK, P.P. DODGE, and R.E. Orville. Utilization of airborne and NEXRAD data in the analysis of cloud-to-ground lightning in 1995 and 1996 tropical cyclones. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 125-126 (1997).
No abstract.
AO-093
Severinghaus, J.P., W.S. Broecker, T.-H. PENG, and G. Bonani. Transect along 24°N latitude of 14C in dissolved inorganic carbon in the subtropical North Atlantic Ocean. Radiocarbon, 38(3):407-414 (1996).
The distribution of bomb-produced 14C in the ocean provides a powerful constraint for circulation models of upper ocean mixing. We report 14C measurements from an east-west section of the main thermocline at 24°N latitude in the subtropical North Atlantic Ocean in summer 1992, and one profile from the Gulf of Mexico in 1993. Observed gradients reflect the transient invasion of bomb 14C into the thermocline via mixing along-isopycnals from the poleward outcrop, with progressively more sluggish mixing at greater depths. A slight deepening of the profile is observed over the 20-year period since the GEOSECS survey at one location where the comparison is possible.
AO-094
SHAPIRO, L.J. The motion of Hurricane Gloria: A potential vorticity diagnosis. Monthly Weather Review, 124(11):2497-2508 (1996).
Multilevel, multinested analyses of Hurricane Gloria of 1985 are the most comprehensive kinematic data set yet developed for a single hurricane. A piecewise inversion technique is used with these analyses and the nonlinear balance equation to deduce the three-dimensional distribution of potential vorticity (PV) that contributed to the deep-layer mean (DLM) flow that steered Hurricane Gloria toward the northwest. The background state is taken to be the azimuthally averaged winds in balance with a geopotential distribution on an f plane. Advantage is taken of the near-linearity of the weak asymmetries near the hurricane's core and of PV in the environment. Thus, ad hoc aspects of the linearization required by other investigators are effectively eliminated. Removal of the hurricane vortex and the use of a climatological mean background state are avoided as well. The insensitivity of the results to the imposed lateral boundary condition is also demonstrated. Wind anomalies attributable to pieces of anomalous PV restricted to cylinders of different radii centered on the hurricane are evaluated. The DLM wind that steered Gloria to the northwest is primarily attributable to PV anomalies confined within a cylinder of radius 1000 km and levels 500 mb and above, including positive anomalies associated with a cold low over Cuba. The vector difference between the hurricane's observed motion and the DLM wind at Gloria's center attributable to these PV anomalies is 1.0 m s-1, explaining more than five-sixths of the hurricane's 6.2 m s-1 motion. Implications for measurements required to establish short-term changes of the environmental steering flow are considered. Difficulties in the interpretation of results are discussed for PV anomalies that are confined to noncircular regions; the implication for other studies is considered as well.
AO-095
SHAPIRO, L.J., and J.L. FRANKLIN. Potential vorticity and hurricane motion. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 156- 157 (1997).
No abstract.
AO-096
Sirkes, Z., E. Tziperman, and W.C. THACKER. Combining data and a global primitive equation ocean general circulation model using the adjoint method. In Modern Approaches to Data Assimilation in Ocean Modeling, P. Malanotte-Rizzoli (ed.). Elsevier, Amsterdam, 119-145 (1996).
A Primitive Equation Ocean General Circulation Model (PE OGCM) in a global configuration similar to that used in coupled ocean-atmosphere models is fitted to climatological data using the adjoint method. The ultimate objective is the use of data assimilation for the improvement of the ocean component of coupled models, and for the calculation of initial conditions for initializing coupled model integrations. It is argued that oceanic models that are used for coupled climate studies are an especially appropriate target for data assimilation using the adjoint method. It is demonstrated that a successful assimilating of data into a fully complex PE OGCM critically depends on a very careful choice of the surface boundary condition formulation, on the optimization problem formulation, and on the initial guess for the optimization solution. The use of restoring rather than fixed surface-flux boundary conditions for the temperature seems to result in significantly improved model results as compared with previous studies using fixed surface-flux boundary conditions. The convergence of the optimization seems very sensitive to the cost formulation in a PE model, and a successful cost formulation is discussed and demonstrated. Finally, the use of simple, suboptimal, assimilation schemes for obtaining an initial guess for the adjoint optimization is advocated and demonstrated.
AO-097
Slansky, C.M., R.A. Feely, and R.H. WANNINKHOF. The stepwise linear regression method for calculating anthropogenic CO2 invasion into the North Pacific Ocean. In Biogeochemical Processes in the North Pacific, S. Tsunogai (ed.). Japan Marine Science Foundation, 70-79 (1997).
No abstract.
AO-098 Approximately 250,000 measurements made for the pCO2 difference between surface water and the marine atmosphere, DpCO2, have been assembled for the global oceans. Observations made in the equatorial Pacific during El Niño events have been excluded from the data set. These observations are mapped on the global 4° ´ 5° grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Niño year. Monthly global distributions of DpCO2 have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO2 across the sea surface has been computed using DpCO2 distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C × yr-1 depending on different formulations used for wind speed dependence on the gas transfer coefficient. These estimates are subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of DpCO2 over the global oceans. Temperate and polar oceans of both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans. The Indian and Southern Oceans take up about 20% each.
AO-099
Talley, L.D., and M.O. BARINGER. Preliminary results from WHP Sections I8N/I5E in the central Indian Ocean. Geophysical Research Letters, 24(22):2789-2792 (1997).
The R/V Knorr departed Colombo, Sri Lanka on March 10, 1995 and arrived in Fremantle, Australia on April 15, 1995 to carry out its third WOCE hydrographic leg in the Indian Ocean. Basic technical support was provided by Scripps Institution of Oceanography's Oceanographic Data Facility. Acoustic Doppler current profiler (ADCP) operations were carried out by the University of Hawaii (Firing). The basic sampling program was accomplished very smoothly. The full cruise report can be obtained from the author. The cruise track is shown in the overview figure for this newsletter, labeled I8N and I5E. The latter portion was a nominal repeat of the 1987 section (Toole and Warren, 1993). The goals of the sampling were to obtain a section through the center of the Central Indian Basin, and to repeat the crossing of the northward flow of deep water just to the west of Australia. Particular attention was paid to a potential source of deep water for the Central Indian Basin, through a sill in the NinetyEast Ridge, located at about 28°S. It was also possible to deviate from the 32°S section, and sample in the deep water south of Broken Ridge instead of along the top of the ridge. Between Broken Ridge and Australia we chose to move the section slightly north of the original position of I5E in order to resolve whether the deep flow splits around Dirck Hartog Ridge. All stations were to within 10 m of the bottom and included a 36-bottle rosette/CTD cast with lowered ADCP. A ship-mounted ADCP was operated throughout. Basic station spacing was 30 nmi, and was reduced at the equator, Sri Lankan, and Australian coasts and crossings of the NinetyEast and Broken Ridges. The CTD data stream consisted of elapsed time, pressure, two temperature channels, conductivity, oxygen, altimeter, and transmissometer signals. Water samples were collected for analyses of salt, oxygen, silica, phosphate, nitrate, and nitrite on all stations and of CFC-11, CFC-12, carbon tetrachloride, helium-3, helium-4, tritium, AMS C14, pCO2, total dissolved inorganic carbon, alkalinity, and barium on selected stations. Water sample results were compared with preliminary data acquired on prior WOCE legs and with earlier data. The comparisons are available in the cruise report and show that the WOCE data collected on legs 1 through 3 are a uniform data set; they also show significant differences from Geosecs salinity and phosphate which are attributable to measurement precision.
AO-100
THACKER, W.C. Climatic fingerprints, patterns, and indices. Journal of Climate, 9:2259-2261 (1996).
The purpose of this note is to point out that Hasselmann's optimal fingerprints for detecting climatic change follow from the geometrical interpretation of covariance as an inner product.
AO-101
THACKER, W.C. Metric-based principal components: Data uncertainties. Tellus, 48A:584-592 (1996).
Seeking an index characterizing the best-determined mode of variability leads to a natural generalization of principal-component analysis with an explicit metric characterizing the uncertainties of the data. This formalism, which distinguishes between state-space patterns and patterns of coefficients defining principal components, allows the more accurate data to exert a greater influence on the definition of the indices than they do in conventional principal-component analysis; in all other aspects, the new formalism is the same as the old. Within the context of the simple example of Bretherton and collaborators, metric-based principal-component analysis is shown to be capable of finding correlated patterns of variability in two different data sets.
AO-102
THACKER, W.C., and R. LEWANDOWICZ. A comparison of low-dimensional representations of sea-surface temperature anomalies in the North Atlantic. International Journal of Climatology, 17:953-967 (1997).
Correlation-matrix principal components of North Atlantic sea-surface temperature anomalies for the interval 1950-1970 account for the anomalous variability observed during the interval 1972-1992 better than do similar numbers of covariance-matrix principal components, regional averages, or carefully selected local anomalies. When drift in the seasonal cycle is taken into account, local anomalies for the 127 6° ´ 4° longitude-by-latitude North Atlantic cells could be recovered with an average skill as high as 0.79. Surprisingly, skill increased monotonically with increasing numbers of principal components, and the maximum value was not obtained until 62 were used to characterize the field. Clearly, far more principal components carry useful information about local details than has been previously suspected.
AO-103
THACKER, W.C., and R. LEWANDOWICZ. Climatic indices, principal components, and the Gauss-Markov theorem. Journal of Climate, 9:1942-1958 (1996).
If indices are to be used as the variables predicted by linear statistical models, it is important to be able to recover as much local information as possible from the values forecast for the indices. Here it is shown that the indices that encapsulate the most information about the local climatic state are determined by a generalized (two-matrix) eigenvalue problem that is equivalent to the usual (one-matrix) eigenvalue problem involving the sample correlation matrix. Thus, the best indices in the sense of providing the most location-specific information are familiar principal-component indices. Regarding the indices as predictors in linear statistical models similar to those routinely used for estimating meteorological fields from observations, reveals the role of the Gauss-Markov theorem in EOF analyses. From this perspective each index can be characterized by two EOF-like maps: the first illustrating the linear combinations of the data used to define the index, and the second displaying the Gauss-Markov weights for the index to predict local variables, both of which are related to the eigenvectors of the sample correlation matrix. Other maps can be used to display information about sampling errors: one to characterize the uncertainty of the weights; another to display the skill with which the index accounts for the training data; and a third to show how well it explains independent data. Such maps are illustrated within the context of 43 years of North Atlantic seasonal sea-surface temperature anomalies. The analysis presented here underlines two additional points. First, any linear combination of the indices would result in an equivalent model yielding exactly the same forecast. Consequently, it may be desirable to use indices that are easier to interpret physically. Second, when indices are regarded as being variables of a linear statistical model, the analysis of sampling error can be formulated in terms of the uncertainty of the Gauss-Markov weights inferred from a limited training set rather than in terms of the sample-to-sample variability of eigenvalues and eigenvectors.
AO-104
THACKER, W.C., and R. LEWANDOWICZ. Partitioning the North Atlantic into regions of similar seasonal sea-surface temperature anomalies. International Journal of Climatology, 17:3-23 (1997).
Mean sea-surface temperatures were computed within 127 6° ´ 4° longitude-by-latitude cells comprising most of the North Atlantic for 171 three-month seasons from 1950 through 1992, the mean seasonal cycle was removed, and cells with correlated seasonal anomalies were clustered into regions of coherent thermal behavior. Clustering algorithms consistently produced smaller thermal regions in the vicinity of the Gulf Stream, and while the regions were generally contiguous, a disjoint region was consistently found near the Grand Banks. Examining within-region variability as a function of the number of regions revealed no obvious "best" number of regions. For 26 regions, correlations between pairs of cells within a common region were typically 0.7; for 13 regions, a sizeable fraction were less than 0.5; and for only seven regions, within-region correlations were distributed fairly uniformly between 0.2 and 0.8.
AO-105
Vaughan, S.L., and R.L. MOLINARI. Temperature and salinity variability in the Deep Western Boundary Current. Journal of Physical Oceanography, 27:749-761 (1997).
A ten-year time series (1984-1993) of repeat hydrographic sections from offshore Abaco Island, the Bahamas (26.5°N), is used to define the mean and time dependent characteristics of the Deep Western Boundary Current (DWBC). The DWBC flow is divided into four vertical layers based on chlorofluorocarbon (CFC) concentration and formations regions (upper layer, CFC core, q ~3.9-5.0°C; second layer, classical Labrador Sea Water, q ~3.2-3.9°C; third layer, CFC minimum, q ~2.4-3.2°C; deepest layer, CFC core, q ~1.85-2.4°C). Time series analysis of mean layer properties and their anomalies showed that the temperature and salinity of each layer did not increase or decrease monotonically with time. Variations in temperature and salinity were characterized by two to three-year period oscillations. Variability between years is illustrated by subtracting repeat sections of temperature and salinity along levels of both constant pressure and constant potential density. To determine an original water mass modification that could be responsible for the observed variability in the section differences, an analytical method, which uses both types of differencing schemes, was applied to the DWBC data. Variability in the upper layer between 1987 and 1993 was shown to originate primarily from an increased salinity of the source waters for this layer. Variability in the second layer was shown to arise from a combination of cooling and salinification. Variability in the two deepest layers seemed to be almost entirely due to vertical movement of the isopycnals. Increases in potential temperature and salinity observed in a sublayer of the second layer defined by s1.5 ~34.68-34.74 (classical Labrador Sea Water) from 1991 to 1993 was shown to be mainly the result of cooling. It is suggested that this cooling may have originally occurred in the central Labrador Sea during the period of active deep water renewal in the early 1970s.
AO-106
WANNINKHOF, R.H., G. Hitchcock, W.J. Wiseman, G. Vargo, P.B. ORTNER, W. Asher, D.T. Ho, P. Schlosser, M.-L. Dickson, R. Masserini, K. Fanning, and J.-Z. ZHANG. Gas exchange, dispersion, and biological productivity on the west Florida shelf: Results from a Lagrangian tracer study. Geophysical Research Letters, 24:1767-1770 (1997).
A Lagrangian tracer study was performed on the west Florida shelf in April 1996 using deliberately injected trace gases. Although such studies have been performed previously, this work is the first where the deliberate tracers, in conjunction with carbon system parameters, are used to quantify changes in water column carbon inventories due to air-sea exchange and net community metabolism. The horizontal dispersion and the gas transfer velocity were determined over a period of 2 weeks from the change in both the concentrations and the concentra-tion ratio of the two injected trace gases, sulfur hexafluoride (SF6) and helium-3 (3He). Horizontal diffusion estimates were about an order of magnitude greater than calculated from empirical equations, and the differ-ence is attributed to vertical shear. The second moment of the patch grew to 1.6 ´ 103 km2 over a period of 11 days. The gas transfer velocity, normalized to CO2 exchange at 20°C, was 8.4 cm hr-1 at an average wind speed, U10, of 4.4 m s-1 for the duration of the experiment, which is in good agreement with empirical estimates. Reminer-ali-zation rates exceeded productivity, causing an increase in dissolved inorganic carbon of about 1 mmol kg-1 day-1 in the water column. During this period of senescence, 80% of the increase in inorganic carbon is attributed to community remineralization and 20% due to invasion of atmospheric CO2. This net remineralization is in accordance with in situ and on-deck incuba-tion experiments.
AO-107
WILLIS, P.T., P.P. DODGE, F.D. MARKS, JR., D. Smith, and D. Churchill. Evaluation of the accuracy of the NEXRAD radar rainfall estimates in tropical summer convective rainfall over the Everglades/Florida Bay. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 679-680 (1997).
No abstract.
AO-108
WILLOUGHBY, H.E. More about hurricane eye thermodynamics. Preprints, 22nd Conference on Hurricanes and Tropical Meteorology, Ft. Collins, CO, May 19-23, 1997. American Meteorological Society, 96-97 (1997).
No abstract.
AO-109
YVON-LEWIS, S.A., and J.H. Butler. The oceanic lifetime and budget of atmospheric methyl bromide. EOS, Transactions, American Geophysical Union, 78(17):S90 (1997).
Methyl bromide (CH3Br) has become of interest recently because of its involvement in the depletion of stratospheric ozone. However, unlike the chlorofluorocarbons, which are entirely anthropogenic, methyl bromide has both natural and anthropogenic sources. At ~10 parts per trillion in the troposphere, methyl bromide is believed to be the single largest contributor of stratospheric Br. Once in the stratosphere, Br is estimated to be 40 to 100 times more effective in depleting stratospheric ozone than chlorine. Known sinks for atmospheric methyl bromide include photolysis at high altitudes and reaction with OH, uptake by the oceans and loss to soils. In the ocean, dissolved methyl bromide is degraded via hydrolysis and chloride substitution. Recently, it has been shown that methyl bromide also undergoes biological degradation, which may be due to bacterial uptake. Results from field studies, showing large undersaturations in polar and sub-polar waters, also suggest an additional, perhaps biological, sink mechanism. Previous calculations of the partial atmospheric lifetime of methyl bromide with respect to oceanic degradation have only considered the chemical degradation mechanisms. We use a global, coupled ocean-atmosphere box model to examine the potential effect that biological degradation and its distribution can have on the lifetime of atmospheric methyl bromide. The results of this study show that both the value of the oceanic degradation rate constant and its global distribution are important in determining the calculated atmospheric lifetime. The "best" estimate of the partial lifetime of atmospheric methyl bromide with respect to oceanic loss now comes to 1.7-1.8 y with a full possible range of 0.85-3.7 y, which, together with other non-oceanic losses, yields a total atmospheric lifetime of 0.7 y with a range of 0.5-0.9 y due only to uncertainty in the oceanic lifetime. A subsequent revision of the budget for atmospheric methyl bromide indicates that a source or sources of methyl bromide totaling 90 to Gg/y (1/2 of the total sink strength) has not yet been identified.
AO-110
YVON-LEWIS, S.A., and J.H. Butler. The potential effect of oceanic biological degradation on the lifetime of atmospheric CH3Br. Geophysical Research Letters, 24(10):1227-1230 (1997).
We use a global, coupled ocean-atmosphere box model to examine the potential effect that biological degradation and its distribution can have on the lifetime of atmospheric CH3Br. The results of this study show that both the value of the oceanic degradation rate constant and its global distribution are important in determining the calculated atmospheric lifetime. The "best" estimate of the partial lifetime of atmospheric CH3Br with respect to oceanic loss now comes to 1.7-1.8 y with a full possible range of 0.85-3.7 y, which, together with other, non-oceanic losses, yields a total atmospheric lifetime of 0.7 y (0.5-0.9 y). A subsequent revision of the budget for atmospheric CH3Br indicates that estimated sinks of CH3Br today exceed estimated sources by about 90 Gg y-1.