bluuebunny/crossref_metadata_2025 huggingface dataset:
Equatorial wave sequence associated with warm pool displacements during the 1986–1989 El Niño‐La Niña
Authors: Picaut Joël , Delcroix Thierry
Published: February 2004

In the Pacific equatorial band the zonal displacement of the eastern edge of the warm pool, subject to insignificant seasonal variations, is dominated by strong interannual variations almost in phase with the Southern Oscillation Index. Over the 1971–1973 El Niño‐La Niña period, Gill (1983) suggested that such displacement was caused solely by horizontal advection by zonal current anomaly. Basin‐wide Geosat‐derived zonal surface current anomalies are available during the 1986–1989 period, and they agree quite well with observed equatorial currents in the western and central Pacific. Within the 4°N–4°S equatorial band the cumulative contribution of first‐baroclinic Kelvin and first‐symmetric (m = 1) Rossby modes to surface zonal equatorial current anomalies account for most of the Geosat‐derived current variability. From these Geosat‐derived currents it is demonstrated that the eastward (westward) displacement of the eastern edge of the warm pool was primarily due to horizontal advection by zonal current anomalies during the 1986–1987 El Niño (1988–1989 La Niña). As a corollary, the El Niño (La Niña) warm (cold) sea surface temperature (SST) anomaly in the central western Pacific was the result of anomalous zonal advection. The 1986–1989 displacement of the warm pool appeared as a low‐frequency movement resulting from high‐frequency forcing, i.e., a succession of local wind forcing and its remote Kelvin and m = 1 Rossby wave responses in the equatorial waveguide. In the central western Pacific a m = 1 downwelling Rossby wave, issued from the eastern Pacific, shifted the displacement from eastward to westward and therefore seems to have been the cause for El Niño to turn to La Niña in boreal fall 1987. In the eastern Pacific the simultaneous occurrence of free‐propagating downwelling (upwelling) Kelvin waves with the seasonal SST warming (cooling) appeared necessary for the development of local El Niño (La Niña) SST anomaly. Over most of the equatorial Pacific, slow migration of SST anomalies clearly showed up, distinct during El Niño and La Niña. These zonal migrations appeared to result from the delayed association of two phenomena: the zonal advection in the central western Pacific and the arrival of downwelling (upwelling) Kelvin waves into the eastern Pacific, synchronous with the seasonal SST warming (cooling). Albeit different in terms of equatorial wave action, as compared to the delayed action oscillator theory, our results suggest that zonal advection and wave dynamics were both important for the generation and migration of El Niño‐ Southern Oscillation SST anomalies in 1986–1989. Finally, our observational results about warm pool displacements, equatorial wave sequence, the shift from El Niño to La Niña, and the slow SST migrations are presented in a schematic form involving sequential ocean‐atmosphere coupling which appears continuously over the November 1986 to February 1989 period.
Rossby waves in the Southern Ocean: A comparison of TOPEX/POSEIDON altimetry with model predictions
Authors: Hughes C. W.
Published: February 2004

Results are presented from an eddy‐resolving model of the Southern Ocean which suggest that regions of moderate eddy activity are occupied by wavelike eddies with wavelengths of about 300 km and periods of 4 to 12 months. These waves travel eastward where the current (and wave amplitude) is strongest, and westward elsewhere, and it is argued that they are Rossby waves advected by the mean flow. It is shown that TOPEX/POSEIDON altimetry data should be able to resolve these waves in the Pacific sector of the Southern Ocean. A technique for wave detection is then presented which is capable of extracting useful information about the waves in this as well as other regions. Altimeter data are then presented which confirm the existence of waves in the Pacific sector and are consistent with wave presence elsewhere. An analysis of tide model errors shows that such errors are incapable of producing a signal which could mimic the modeled waves, although tide model errors may explain the difference between altimetry and model results in shallow regions of the ocean and in regions of low eddy activity.
Wind‐forced sea level variability on the southeast Brazilian shelf
Authors: Castro Belmiro M. , Lee Thomas N.
Published: February 2004

Coastal sea level data collected along the southeast coast of Brazil, from Cabo Frio to Cabo de Santa Marta, for the period August–November 1978 were examined, together with meteorological data for evidence of wind‐forced, low‐frequency fluctuations. A dominant 9‐ to 12‐day perturbation in sea level, atmospheric pressure, and wind propagated equatorward from Cananéia and appeared to propagate poleward between Cananéia and the southernmost station. A 6‐ to 7‐day perturbation in sea level and wind propagated equatorward from the southernmost station, in agreement with the movement of cold fronts through the area. Sea level fluctuations in the central and northern portions of the bight for both 9‐ to 12‐ and 6‐ to 7‐day bands were better correlated with winds located southward and earlier in time than with the local wind at the time of sea level measurement. Modeling of sea level response at Ubatuba for a period of 90 days, using the theory of barotropic continental shelf waves generated by wind forcing, presented results that were similar to the observed response.
Near‐surface mean circulation and kinetic energy in the central North Atlantic from drifter data
Authors: Brügge Bernd
Published: February 2004

An analysis of a large drifting buoy data set is presented. The objective is to obtain a self‐contained description of the properties of the near‐surface circulation (drogue depth 100 m) in the central North Atlantic Ocean, independent of hydrographic data. A necessary preanalysis step was the removal of all data from undrogued buoys from the data set. The physical parameters of the circulation were deduced by averaging the remaining data in 2°×3° boxes. The minimum amount of data which is necessary to get statistically stable results was determined by an empirical quality criterion. All important mean currents in the investigation area are reproduced by the near‐surface mean velocity field. A separation of the mean velocity field into a nondivergent and an irrational part shows that the flow field is almost nondivergent. The distribution of eddy kinetic energy is concentrated along the mean currents and provides the largest part of the total kinetic energy, but there are regional variations. Energy from inertial movements dominates the high‐frequency part of the kinetic energy. Its distribution is very patchy. The analysis of the Reynolds stress terms shows an energy transfer from the eddy field to the mean circulation in the vicinity of the North Atlantic Current.
Regional climate variability and ocean heat transport in the southwest Pacific Ocean
Authors: Sprintall Janet , Roemmich Dean , Stanton Basil , Bailey Richard
Published: February 2004

The winter of 1992 was the coldest on record in New Zealand since the 1940s. Temperatures in New Zealand were as much as 3°C below average, with heavy rain and unusual snow. The oceanic surface layer in the southwest Pacific was also anomalously cold over the same period. A World Ocean Circulation Experiment (WOCE) hydrographic section (P14C) between Auckland and Fiji during September 1992 found cold sea surface temperatures and deep mixed layers near New Zealand when compared to 8 years of high‐resolution expendable bathy thermograph (XBT) temperature measurements collected along the same transect. High nutrient and low dissolved oxygen concentrations in the surface layer indicated recent entrainment of thermocline waters. The Auckland to Fiji XBT section is one of three WOCE high‐resolution XBT survey lines in the “Tasman Box” region, whose boundaries are Auckland‐Fiji, Fiji‐Brisbane and Wellington‐Sydney transects plus the Australian coast. Geostrophic shear and transport were estimated from 10 realizations of the Tasman Box during the period 1991–1993. The time series of geostrophic transport shows that following a convergence in late 1991, early in 1992 there was a substantial divergence of mass in the upper waters, equivalent to a thinning of the warm water layer. The phase of this anomalous divergence is matched to an observed amplification of the seasonal oceanic heat storage cycle in 1991–1992. The top 200‐m average temperature was warmer in the 1992 summer than in 1991 or 1993, but the winter of 1992 was the coldest of the 8‐year record along the Auckland‐Fiji line. The divergence (thinning) of the warm water layer appears to have preconditioned the region for the exceptionally cold 1992 winter. The alternative, cool conditions from anomalous air‐sea heat exchange caused by variability in the wind field, is considered unlikely as large fluctuations in heat loss are not observed in the air‐sea flux data during this period. The severe weather conditions and anomalous ocean heat transport are most likely related to the prolonged El Niño‐Southern Oscillation episode that began in early 1991.
Ridging and strength in modeling the thickness distribution of Arctic sea ice
Authors: Flato Gregory M. , Hibler William D.
Published: February 2004

A theory describing evolution of the ice thickness distribution (the probability density of ice thickness) was proposed by Thorndike et al. (1975) and has been used in several sea ice models. The advantage of this theory over the widely used two‐level formulation is that it treats ridging explicitly as a redistribution of ice thickness, and ice strength as a function of energy losses incurred by ridge formation. However, the parameterization of these processes remains rather speculative and largely untested, and so our purpose here is to explore these parameterizations using a numerical model based on this theory. The model uses a 160‐km resolution grid of the Arctic and 7 years of observed atmospheric forcing data (1979–1985). Monthly oceanic heat flux and current fields are obtained from a 40‐km resolution coupled ice‐ocean model run separately with the same forcing. By requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift, we estimate the primary strength parameter: the ratio of total to potential energy change during ridging. This ratio depends on the value of other parameters; however, the standard case has a ratio of 17 which is within the range estimated by Hopkins (1994) in simulations of individual ridging events. The effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics. In addition, these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented: first, the process of first‐year to multiyear ridge consolidation is ignored; and second, the observed preferential melt of thick ridged ice is not reproduced.
A note on the barotropic response of sea level to time‐dependent wind forcing
Authors: Fu Lee‐Lueng , Davidson Roger A.
Published: February 2004

This study examines the extent to which sea level variations at periods between 30 days and 1 year and spatial scales greater than 1000 km can be described by the wind‐driven linear barotropic vorticity dynamics. The TOPEX/POSEIDON altimetric observations of sea level and the wind products of the National Meteorological Center are used as the database for the study. Each term of the linear barotropic vorticity equation was evaluated by averaging over regions of 10°×10°. In most of the open ocean the result of the analysis suggests that the sea level variabilities at the scales considered cannot be fully described by the equation; the apparent net vorticity change is more than what can be explained by the local wind stress curl. In the few regions where the wind stress curl is strong enough to balance the vorticity budget, predominantly in the northeast Pacific and the southeast Pacific, the balance is basically achieved in terms of the time‐dependent topographic Sverdrup relation, namely, the balance between the advection of the planetary vorticity plus the topography‐induced vorticity and the forcing by the wind stress curl.
A comparison between the TOPEX/POSEIDON data and a global ocean general circulation model during 1992–1993
Authors: Chao Yi , Fu Lee‐Lueng
Published: February 2004

The TOPEX/POSEIDON altimetric sea level observation during 1992–1993 was used to validate the simulation made by a global ocean general circulation model (OGCM) forced by the daily wind stress and heat flux derived from the National Meteorological Center operational analysis. The OGCM is a version of the modular ocean model with a horizontal resolution of 2° longitude and 1° latitude and 22 levels in the vertical. The model simulation is compared to the observation at spatial scales of the order of 500 km and larger. Only the temporal variations are examined. The variability is composed primarily of the annual cycle and intraseasonal fluctuations (periods shorter than 100 days). The basic features of the annual cycle are simulated well by the model. Major discrepancies are found in the eastern tropical Pacific, as well as the eastern North Pacific and most of the interior of the North Atlantic. The culprit is suspected to be the inadequate heat forcing and mixing parameterizations of the model. Significant intraseasonal variability is found in the central North Pacific and the Southern Ocean. The simulation is highly correlated with the observation at periods from 20 to 100 days. The spatial scales are larger than 1000 km in many places. These variabilities are apparently the barotropic response of the ocean to wind forcing. The results of the study provide a basis for future assimilation of the data into the OGCM for improved description of the large‐scale ocean variabilities.
Mapping mesoscale variability of the Azores Current using TOPEX/POSEIDON and ERS 1 altimetry, together with hydrographic and Lagrangian measurements
Authors: Hernandez Fabrice , Le Traon Pierre‐Yves , Morrow Rosemary
Published: February 2004

The SEMAPHORE mesoscale air/sea experiment was conducted in the Azores‐Madeira region from July to November 1993. TOPEX/POSEIDON (T/P) and ERS 1 were flying simultaneously at that time. The main purposes of this paper are to evaluate the estimation of the oceanic mesoscale circulation from the two different sets of altimetric data (T/P and ERS 1) and to compare the results with in situ measurements provided by the SEMAPHORE hydrographic surveys and surface drifters (three expendable bathytermograph conductivity‐temperature‐depth surveys in a 500‐km2 box and a set of 47 Lagrangian surface drifters drogued at 150 m). Comparisons are carried out through the maps obtained by objective analysis from the four data sets. The mapping accuracy of T/P, ERS 1, T/P and ERS 1 combined, and in situ data is investigated, as well as the sensitivity of the mapping to the correlation functions used. There is a good qualitative agreement between altimetric maps and corresponding drifter and hydrographic maps for the three hydrographic surveys. Correlations are about 0.8, and the regression fit is about 0.6–0.7; the lower values are due to the smooth climatology used to reference the altimetric maps. The correlation for time differences is better, with regression lines not significantly different from 1, especially when ERS 1 and T/P are combined. T/P mapping is almost as good as ERS 1 mapping, which was rather unexpected since the ERS 1 space‐time sampling is better suited for the mesoscale. This may reflect the fact that the signal mapped by the hydrography and drifters does not contain the high frequency/wavenumber components. T/P and ERS 1 combined provide better results, although the improvement is not as large as expected, probably for the same reason.
Sensitivity of the tropical Atlantic circulation to specification of wind stress climatology
Authors: Bryan F. O. , Wainer I. , Holland W. R.
Published: February 2004

This study examines the sensitivity of a simulation of the tropical Atlantic circulation to the choice of climatological wind stress forcing. Three climatological wind stress data sets, representing different classes of data products, are used to drive a high‐resolution general circulation model of the Atlantic Ocean. One set is from historical surface marine datasets compiled by Hellerman and Rosenstein. The second climatology is based on surface wind analyses from the European Centre for Medium Range Weather Forecasts. The last climatology is derived from an integration of the National Center for Atmospheric Research Community Climate Model, version 2, at T42 resolution (CCM2). The analysis of the model sensitivity to these different wind stress climatologies focuses on the mean seasonal cycle and low order statistics of the simulated upper ocean circulation in the tropics and its comparison with observations. In the North Equatorial Countercurrent (NECC) the three simulations agree with each other and with observations reasonably well. The differences that do exist in the simulation of the NECC are primarily in smaller‐meridional‐scale features and in the phase of the onset and decay. There are much larger differences among the simulations near the equator. Most of these differences in the equatorial circulation are attributable to differences in the cross‐equatorial meridional wind stress. The ECMWF climatology has relatively weak meridional stress and correspondingly weak equatorial upwelling. The CCM2 climatology has unrealistically large meridional stress and equatorial upwelling.
Satellite retrieval of the absorption coefficient of chromophoric dissolved organic matter in continental margins
Authors: Hoge Frank E. , Williams Mark E. , Swift Robert N. , Yungel James K. , Vodacek Anthony
Published: February 2004

The absorption coefficient of chromophoric dissolved organic matter at 443 nm, aCDOM(443), has been retrieved from coastal zone color scanner (CZCS) normalized water‐leaving radiances. For a wintertime, low‐chlorophyll condition in the Middle Atlantic Bight the aCDOM(443) is computed by mathematical inversion of an oceanic spectral radiance model. The CZCS aCDOM(443) retrieval is validated by a recent ship‐aircraft aCDOM(443) retrieval experiment within the same oceanographic region.
Extraction of tidal streams from a ship‐borne acoustic Doppler current profiler using a statistical‐dynamical model
Authors: Dowd Michael , Thompson Keith R.
Published: February 2004

We present a method for extracting the barotropic tide directly from the time‐space series of horizontal velocity obtained by a ship‐borne acoustic Doppler current profiler (ADCP). The method is conceptually straightforward, easy to implement, and suitable for operational use. It involves fitting a limited area tidal model, based on the linearized depth‐averaged shallow water equations, to the ADCP record. The flows across the open boundaries of the model domain are assumed periodic in time with known frequencies corresponding to the tidal constituents of interest. The unknown tidal amplitudes and phases at the boundary are estimated from interior ADCP velocities using an inverse method; the solution of the shallow water equations is posed as a boundary value problem in the frequency domain, and the estimation procedure is based on generalized least squares regression. Results obtained include tidal maps, a tidal residual series, and associated error estimates. An application of the method to ship ADCP data collected on a cruise to the Western Bank region of the Scotian Shelf off the east coast of Canada is described. The tidal estimates and the residual field obtained are verified by comparison to other data collected during the cruise. The residual circulation shows an anticyclonic gyre centered on the crest of Western Bank and a northward current to the west of this region.
Interactions between western boundary currents and shelf waters: A mechanism for coastal upwelling
Authors: Condie Scott A.
Published: February 2004

A geostrophic adjustment model has been developed to describe interactions between shelf waters and an offshore current such as a western boundary current. A simple analysis demonstrates the response of coastal waters to the gradual encroachment of a western boundary current and reveals how this can lead to strong upwelling when bottom friction is taken into account. Conditions favorable to upwelling actually occur well before the western boundary current comes into direct contact with the bottom. Some aspects of the theory have been compared with laboratory experiments on interacting currents over sloping topography. The comparisons are quite favorable for relatively stable flows. However, under other conditions, baroclinic instabilities grow into large eddies which dramatically enhance exchange between the two currents. Results from the study are used to interpret documented observations of coastal encroachment by the East Australian Current and associated phytoplankton blooms.
Oscillatory behavior in Arctic sea ice concentrations
Authors: Gloersen Per , Yu Jun , Mollo‐Christensen Erik
Published: February 2004

We have done a frequency analysis of the 9‐year record of sea ice concentrations obtained with the NASA Nimbus 7 scanning multichannel microwave radiometer (SMMR). Because of the periodic revisit time of the SMMR, we are able to examine recurrence of shorter‐period oscillations, as aliased by the revisit frequency, and longer‐period oscillations per se. A number of findings result from a sequence of two analysis schemes, as follows. We have first determined, then removed, the mean, linear trend, and seasonal cycle (the latter composed of five harmonics of the annual cycle) from the time series for each pixel of gridded SMMR ice concentration data in the Arctic, using multiple linear regression. We find that the 9‐year trends are most positive in the Beaufort and East Greenland Seas, whereas the most negative areas are in the Barents Sea and the sea ice surrounding Svalbard; this is similar to trend patterns in the lengths of the sea ice season reported earlier by Parkinson [1992]. In the residual data, the standard deviation ranges from 12% to 16% in the central Arctic basin, considerably above the estimated wintertime ice concentration accuracies of 5% in that region; this is in part due to fluctuations in the ice concentration rather than noise. Secondly, we have used Fourier analysis and multiple‐taper filtering techniques to identify tentatively some of these fluctuations as tidal components or multiyear components similar to those found in the El Niño‐Southern Oscillation Index, and we show their spatial distribution. However, there are some high‐amplitude, periodic components that we have not yet been able to identify; we show the spatial distribution of one of these components.
Bulk parameterization of air‐sea fluxes for Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response Experiment
Authors: Fairall C. W. , Bradley E. F. , Rogers D. P. , Edson J. B. , Young G. S.
Published: February 2004

This paper describes the various physical processes relating near‐surface atmospheric and oceanographic bulk variables; their relationship to the surface fluxes of momentum, sensible heat, and latent heat; and their expression in a bulk flux algorithm. The algorithm follows the standard Monin‐Obukhov similarity approach for near‐surface meteorological measurements but includes separate models for the ocean's cool skin and the diurnal warm layer, which are used to derive true skin temperature from the bulk temperature measured at some depth near the surface. The basic structure is an outgrowth of the Liu‐Katsaros‐Businger [Liu et al., 1979] method, with modifications to include a different specification of the roughness/stress relationship, a gustiness velocity to account for the additional flux induced by boundary layer scale variability, and profile functions obeying the convective limit. Additionally, we have considered the contributions of the sensible heat carried by precipitation and the requirement that the net dry mass flux be zero (the so‐called Webb correction [Webb et al., 1980]). The algorithm has been tuned to fit measurements made on the R/V Moana Wave in the three different cruise legs made during the Coupled Ocean‐Atmosphere Response Experiment. These measurements yielded 1622 fifty‐min averages of fluxes and bulk variables in the wind speed range from 0.5 to 10 m s−1. The analysis gives statistically reliable values for the Charnock [1955] constant (α = 0.011) and the gustiness parameter (β = 1.25). An overall mean value for the latent heat flux, neutral bulk‐transfer coefficient was 1.11 × 10−3, declining slightly with increasing wind speed. Mean values for the sensible and latent heat fluxes were 9.1 and 103.5 W m−2; mean values for the Webb and rain heat fluxes were 2.5 and 4.5 W m−2. Accounting for all factors, the net surface heat transfer to the ocean was 17.9 ± 10 W m−2.
Spectral modeling of wave breaking: Application to Boussinesq equations
Authors: Eldeberky Yasser , Battjes Jurjen A.
Published: February 2004

The nonlinear transformation of wave spectra in shallow water is considered, in particular the role of wave breaking and the energy transfer among spectral components due to triad interactions. Energy dissipation due to wave breaking is formulated in a spectral form, both for energy‐density models and complex‐amplitude models. The spectral breaking function distributes the total rate of random‐wave energy dissipation in proportion to the local spectral level, based on experimental results obtained for single‐peaked spectra that breaking does not appear to alter the spectral shape significantly. The spectral breaking term is incorporated in a set of coupled evolution equations for complex Fourier amplitudes, based on ideal‐fluid Boussinesq equations for wave motion. The model is used to predict the surface elevations from given complex Fourier amplitudes obtained from measured time records in laboratory experiments at the upwave boundary. The model is also used, together with the assumption of random, independent initial phases, to calculate the evolution of the energy spectrum of random waves. The results show encouraging agreement with observed surface elevations as well as spectra.
Heat budgets of the Arctic Mediterranean and sea surface heat flux parameterizations for the Nordic Seas
Authors: Simonsen Knud , Haugan Peter M.
Published: February 2004

A review is given of volume and heat budgets for the Arctic Ocean and the Nordic Seas based on oceanic transport observations. The present preferred estimates indicate a northward transport of about 300 TW through the Greenland‐Scotland passage of which 50–80 TW continues into the Arctic Ocean. The net budgets for the Nordic Seas are about 220–250 TW. Regional surface heat budgets are computed based on climatological data from the Comprehensive Ocean Atmosphere Data Set and European Centre for Medium Range Weather Forecasts in addition to monthly mean weather station temperature data from the Carbon Dioxide Information Center database. Each of the terms in the sea surface heat budget is computed with several parameterizations, which are frequently applied in heat budget calculations and in ocean and sea ice modeling. Combining all parameterizations for each term provides 90 different parameterizations of the sea surface heat budget. On the basis of identical climatological data, the surface heat budgets for the Nordic Seas vary from a heat loss of 304 TW to a heat gain of 52 TW. The heat loss from the Barents Sea is in the range from 42 to 162 TW. Twelve combinations of the parameterizations provide a heat budget for the Nordic Seas which is within the advective estimates. One is selected for use in ocean modeling of this region. The same parameterizations provide a heat loss of 129–147 TW (or 98–112 Wm−2) from the Barents Sea. Published volume transports and temperatures indicate that the heat loss from the Barents Sea is only within 28–80 TW. Our results suggest that the heat transport from the Norwegian Sea to the Barents Sea is larger than recent advective estimates, and, thus, that the Barents Sea plays a major role in renewal of the deep water and the thermohaline circulation of the Arctic Mediterranean.
Currents and transports of the Great Whirl‐Socotra Gyre system during the summer monsoon, August 1993
Authors: Fischer J. , Schott F. , Stramma L.
Published: February 2004

From August 11 to 22, 1993, a conductivity‐temperature‐depth/acoustic Doppler current profiler survey was carried out in the Somali‐Socotra region to investigate currents and transports associated with the Great Whirl and Socotra Gyre circulation during the height of the summer monsoon. The monsoon circulation was confined to the upper 300 m depth, with intense surface currents up to 2.2 m s−1 in the Great Whirl and up to 1.4 m s−1 in the Socotra Gyre. Deeper‐reaching flow was found in the northwestern part of the Somali Basin and in the passage between the shelf of Somalia and Abd al Kuri. The Great Whirl transport was 58 Sv, of which nearly 25% were due to ageostrophic flow components. The northern part of the Great Whirl thereby appeared as a closed circulation cell in which the offshore transport was balanced by a southward transport of the same magnitude. Upwelled water was advected from the cold wedge of the upwelling regime at the Somali coast along the edge of the gyre. The water in the center of the gyre had the characteristics of Indian Equatorial Water (IEW). The Socotra Gyre carried 23 Sv of modified Arabian Sea Water (ASW). With the transports in the two anticyclonic gyres nearly balanced, the exchange of water masses between the Somali Basin, west of the Carlsberg Ridge, and the Arabian Sea occurred in two areas; about 16 Sv of warm and saline surface water of southern offshore origin entered the northern Somali Basin within a 120‐km‐wide swift current between the Great Whirl and the Socotra Gyre. The other key region for the exchange of water masses was the passage between Somalia and Abd al Kuri. There, the total northward transport was 13 Sv, with contributions of IEW, of upwelled water close to the surface, and ASW underneath.
Modulation of ocean skin temperature by swell waves
Authors: Jessup A. T. , Hesany V.
Published: February 2004

Infrared measurements of sea surface temperature from R/P Flip in the deep ocean show that there is significant modulation of ocean skin temperature by swell waves and that the wind plays a dominant role in the process. The squared coherence and the magnitude of the transfer function between the skin temperature and surface displacement respond to the wind speed, while its phase is determined by the direction of the wind relative to the swell. When the swell and wind are in the same direction, the transfer function phase indicates that the maximum skin temperature occurs on the forward face, which, in this case, is also the downwind side. Remarkably, the phase changes by roughly 180° when the wind direction reverses from going with the swell to going against it, so that the maximum switches to the rear face, which is again downwind. The peak‐to‐peak modulation T0 is found to be correlated with the bulk‐skin temperature difference ΔT. Furthermore, T0 is of the same order as ΔT, suggesting that small‐scale wave breaking due to longwave/shortwave interaction may dominate the phenomenon.
Georges Bank residual circulation during weak and strong stratification periods: Prognostic numerical model results
Authors: Naimie Christopher E.
Published: February 2004

The seasonal extremes of the three‐dimensional residual circulation on Georges Bank are studied by numerically computing the circulation during weakly (March–April) and strongly (July–August) stratified periods. The computations are performed using a prognostic (i.e., including tidal‐time advection of the density field), free surface, nonlinear, finite element model on realistic Georges Bank topography. The dynamics considered result from the dominant M2 tide, baroclinic pressure gradients, wind stress, upstream boundary conditions, and advanced turbulence closure. Comparison of these solutions with earlier diagnostic model results illustrates the importance of processes which could not be included in these earlier simulations (such as density evolution and advanced turbulence closure in tidal time, inclusion of nonlinear baroclinic effects, improved treatment of other nonlinearities, etc.). During the strongly stratified July–August period, the newly modeled processes intensify the residual circulation and result in recirculating transport on Georges Bank of 0.25 Sv, which is twice the diagnostic result. The level of agreement between modeled and observed residual circulation improves very significantly for this period, with the prognostic model predicting aroundbank currents as high as 46 cm s−1 in the frontal zone on the Northeast Peak. Analysis of the tidal‐time density and current structure in the frontal zone on the Northeast Peak indicates important tidal frequency dynamics and features which are supported by observational evidence. During the weakly stratified March–April period, the dynamical impact of the newly modeled processes is small. Hence the prognostic and diagnostic models predict similar global structure (with a recirculating transport on Georges Bank of 0.05 Sv), although there are local differences which result in the prognostic simulation agreeing more closely with the observed circulation.
Variation of Indonesian throughflow and the El Niño‐Southern Oscillation
Authors: Meyers Gary
Published: February 2004

The expendable bathythermograph (XBT) line Fremantle‐Sunda Strait transects the eastern Indian Ocean between northwestern Australia and Java. It was established in 1983 with low‐density sampling and upgraded to a frequently repeated line (>18 times per year) in 1987 to monitor currents. The observations during 1983 to 1994 are described and related to the field of wind stress. Variation of thermal structure shows a rich mixture of annual, semiannual, and interannual timescales. Empirical orthogonal function (EOF) analysis of anomalies of sea surface temperature (SST), dynamic height, and depth of the 20°C isotherm D20 identifies two distinctive signals. The El Niño ‐ Southern Oscillation (ENSO) signal (EOF 1) appears throughout the region and is strongest off the coast of Australia. A modulation of the annual signal (EOF 2) appears off the coast of Java. EOF 2 has a shorter timescale than the ENSO signal, and its temporal coefficients are correlated to zonal winds over the equatorial Indian Ocean. For both EOFs, anomalously low SST and dynamic height occur at the same time as anomalously shallow D20 and vice versa for opposite anomalies. The XBT data are used with a climatological temperature‐salinity relationship to calculate net, relative (0/400 dbar) geostrophic transports T through the section. For long timescales, T is representative of Indonesian throughflow. The variations associated with ENSO show a maximum during the La Niña of 1988–1989 and minima during the El Niños of 1986–1987 and 1991–1994. The peak‐to‐trough amplitude of the ENSO signal is 5 Sv. The ENSO signal in throughflow is discussed in terms of earlier studies. For the shorter timescales, T is representative of currents from the Indian Ocean flowing in and out of the region between northwestern Australia and Indonesia, changing the volume of upper layer water stored there. Associated with EOF 2, a sharp peak in westward transport developed during May to October 1994.
On the branching of the Kuroshio west of Kyushu
Authors: Hsueh Y. , Lie Heung‐Jae , Ichikawa Hiroshi
Published: February 2004

Trajectories of satellite‐tracked surface drifters released in the continental margin area west of Kyushu indicate a separation of the inshore side of the Kuroshio that appears to form the beginning of the Tsushima Current. The trajectories also indicate an anticyclonic sense of circulation in the area between the separated branch and the eastward directed Kuroshio main stream, consistent with long‐term geomagnetic electrokinetograph measurements of surface currents, which show a broad southward flow along the west Kyushu coast. A theory is put forth that ties together these observed flow features. In the theory, the incidence is considered of an inertial current upon a step rise in topography (characterized by a step depth of H0 to simulate the west Kyushu coastal bathymetry) in an f plane, two‐layered, inviscid ocean with a quiescent lower layer. The inertial current is of a constant potential vorticity f/H, where H (>H0) is the undisturbed upper layer depth and is bounded inshore by a free streamline along which the upper layer depth is a constant hc (<H). The steady state downstream configuration of a separation branch and a deflected main stream along the step is connected to the upstream approach current through the consideration of the constancy of the Bernoulli function and the conservation of potential vorticity and mass. In the immediate neighborhood of the incidence, a complicated flow region is anticipated in which recirculation is featured and an anticyclonic gyre is expected further onto the step. The volume‐integrated balance of along‐step momentum of the constant potential‐vorticity flow allows the determination of the angle the branch current makes with the step as a function of the angle of incidence and two depth ratios, hc/H and H0/H. The bifurcation quotient, defined as the ratio of the branch current transport to that of the approach current, is found to be also such a function, except it is independent of the incidence angle. These functions yield results that are qualitatively in agreement with the observed bifurcation of the Kuroshio west of Kyushu that gives rise to the Tsushima Current.
Assimilation of Geosat altimeter data into an eddy‐resolving primitive equation model of the North Atlantic Ocean
Authors: Oschlies Andreas , Willebrand Jürgen
Published: February 2004

We present a new method for assimilating observations of sea surface height (SSH) into a high‐resolution primitive equation model. The method is based on the concept of reinitialization. First, the surface velocity increments necessary to adjust the model forecast to the observed geostrophic surface currents are projected onto deep velocity increments by a linear regression method. Second, changes in the density field required to balance the changes in the velocity field geostrophically are obtained from an inversion of the thermal wind equation. A unique partition of the density increments into corresponding temperature and salinity changes is realized by conserving the local θ‐S relation of the model forecast. In contrast to pure statistical methods that infer temperature and salinity changes from correlations with SSH anomalies, our approach explicitly conserves water mass properties on isopycnals. For the assimilation experiment we use optimally interpolated maps of Geosat SSH anomalies (the mean topography is taken from the model), which are assimilated into the World Ocean Circulation Experiment (WOCE) Community Modeling Effort (CME) model of the North Atlantic Ocean at 5‐day intervals covering the year 1987. It is shown that the assimilation significantly improves the model's representation of eddy activity, with the hydrographic structure of individual eddies agreeing well with independent hydrographic observations. The importance of a careful treatment of water mass properties in the assimilation process is discussed and further illustrated by comparing different assimilation schemes.
Changes in surface radiation caused by a scattering layer as calculated using radiative perturbation theory
Authors: Box Michael A.
Published: February 2004

The changes in surface flux (irradiance) and actinic flux (radiant energy density) caused by an elevated scattering layer have been computed using radiative perturbation theory, a technique which is well suited to addressing such questions. A range of layer elevations and solar zenith angles was considered, for wavelengths of 300 nm and 550 nm. Our results for 300 nm are in broad agreement with a recently published single‐scattering calculation, showing large enhancements when both layer elevation and solar zenith angle are high. Our results for 550 nm show a somewhat unexpected enhancement in actinic flux for small solar zenith angles.
Solubility of HBr in sulfuric acid at stratospheric temperatures
Authors: Williams Leah R. , Golden David M. , Huestis David L.
Published: February 2004

The solubility of HBr in 54 to 72 wt % sulfuric acid at low temperatures (200 to 240 K) was measured using two different experimental techniques. In the first, the time dependence of the uptake coefficient of HBr was measured in a Knudsen cell reactor and analyzed to give the effective Henry's law coefficient. In the second, equilibrium vapor pressures of HBr (gas) over solutions containing known concentrations of HBr (dissolved) were measured. The two techniques were in good agreement Typical values of the effective Henry's law coefficient at 220 K were 1.5×107 M/atm for 54 wt %, 2.2 × 106 M/atm for 60 wt %, 1.5×105 M/atm for 66 wt %, and 8.5×103 M/atm for 72 wt % sulfuric acid. The measured solubilities combined with the stratospheric gas phase concentration of HBr indicate that very little HBr will be dissolved in stratospheric sulfate aerosol particles.
Trace gas measurements and air mass classification from a ground station in Taiwan during the PEM‐West A experiment (1991)
Authors: Buhr M. P. , Hsu K.‐J. , Liu C. M. , Liu R. , Wei L. , Liu Y.‐C. , Kuo Y.‐S.
Published: February 2004

Measurements of the ambient concentrations of O3, NOx (NO + NO2), and PAN (peroxyacetyl nitrate) were collected at Kenting, a rural site near the southern end of Taiwan, during the autumn of 1991 as part of the Pacific Exploratory Mission ‐ West A (PEM‐West A) experiment. Two principal component analyses (PCAs) were performed on the data. The results of the PCA indicated that at least three different air mass types were observed at the site, including marine boundary layer, urban plume, and continental outflow (from the Asian mainland). The average concentrations determined for PAN and O3 in the marine boundary layer are 0.03 ± 0.02 and 13 ± 5 parts per billion by volume (ppbv), respectively. In the continental outflow type air masses the average concentrations of PAN and O3 were 0.33 ± 0.41 and 46 ± 7 ppbv, respectively. The data collected indicate that a minimum of 100–150 parts per trillion by volume (pptv) PAN is required in order to affect the production of ozone in the marine boundary layer.
Continental drift, runoff, and weathering feedbacks: Implications from climate model experiments
Authors: Otto‐Bliesner Bette L.
Published: February 2004

Changes in atmospheric carbon dioxide have been proposed as a major regulator of climate during the last 570 million years. Continental weathering and its variation over time are hypothesized to be important for controlling atmospheric carbon dioxide. Continental weathering is altered by changes in total runoff as well as changes in the size and elevation of the land masses to be weathered. When paleogeographic information for the Phanerozoic (570 m.y. ago to present) is used in a global climate model, the model exhibits substantial variations in precipitation, evaporation, and runoff. Even with dramatically different land‐ocean distributions, an increase in global surface temperature leads to an increase in global precipitation but not always an increase in global runoff. During the early Phanerozoic (514–342 Ma), when the continents are relatively small and widely distributed, runoff depends on continental evaporation and temperature. As the continents migrate into subtropical latitudes, global runoff decreases as global land temperatures and evaporation increase. As the continents shift to higher latitudes, global runoff increases as global land temperatures and evaporation decrease. During the middle to late Phanerozoic (306 Ma‐present), when large continental land masses predominate, runoff depends on continental precipitation. Experiments with increased atmospheric CO2 for the middle Ordovician (458 Ma), when the paleocontinent of Gondwana was centered at subtropical latitudes, and the early Silurian (425 Ma), when Gondwana had shifted to middle and high latitudes, also point to a correlation between land mass location and runoff. Global runoff increases 15% with increased CO2 at 425 Ma but remains unchanged for 458 Ma, even though global mean temperature and precipitation increase comparable amounts for the two time periods. These results imply that weathering feedback between temperature and runoff may be dependent on land‐ocean configuration.
Modeling the atmospheric dust cycle: 1. Design of a soil‐derived dust emission scheme
Authors: Marticorena B. , Bergametti G.
Published: February 2004

A soil‐derived dust emission scheme has been designed to provide an explicit representation of the desert dust sources for the atmospheric transport models dealing with the simulation of the desert dust cycle. Two major factors characterizing the erodible surface are considered: (1) the size distribution of the erodible loose particles of the soil which controls the erosion threshold and the emission strength and (2) the surface roughness which imposes the efficient wind friction velocity acting on the erodible surface. These two parameters are included in a formulation of the threshold wind friction velocity by adapting a size‐dependent parameterization proposed by Iversen and White (1982) and by applying to the rough erodible surfaces a drag partition scheme derived from Arya (1975). This parameterization of the threshold friction velocity has been included in an horizontal flux equation proposed by White (1979). This allows to attribute a specific production rate to each soil size range for each type of surface. The dust flux F is then considered as a fraction of the total horizontal flux G, the value of the ratio F/G being imposed, at this time, by the soil clay content. In summary, the computed mass fluxes depend on the soil size distribution, the roughness lengths, and the wind friction velocity. The different steps of this scheme have been independently validated by comparison with relevant experimental data. Globally, the agreement is satisfying, so that the dust fluxes could be retrieved with less uncertainties than those observed in previous simulations of the desert dust cycle.
UV absorption cross sections of methylchloroform: Temperature‐dependent gas and liquid phase measurements
Authors: Nayak Akshaya K. , Kurylo Michael J. , Fahr Askar
Published: February 2004

The absorption cross sections for methylchloroform (CH3CCl3) have been measured in the gas phase (from 160 to approximately 240 nm) and in the liquid phase (from approximately 235 to 260 nm) over the temperature range 220–330 K. The liquid phase results were converted into effective gas phase cross sections using a wavelength shift procedure described and verified in earlier work. The results are compared with other available data in the wavelength region 185–240 nm. The multiplicity of measurements in different laboratories lends increased confidence in the quantification of uncertainties in the atmospheric (photolysis and kinetic) lifetime calculations for this important chemical species.