bluuebunny/crossref_metadata_2025 huggingface dataset:
Geographically correlated errors observed from a laser‐based short‐arc technique
Authors: Bonnefond P. , Exertier P. , Barlier F.
Published: December 2003

The laser‐based short‐arc technique has been developed in order to avoid local errors which affect the dynamical orbit computation, such as those due to mismodeling in the geopotential. It is based on a geometric method and consists in fitting short arcs (about 4000 km), issued from a global orbit, with satellite laser ranging tracking measurements from a ground station network. Ninety‐two TOPEX/Poseidon (T/P) cycles of laser‐based short‐arc orbits have then been compared to JGM‐2 and JGM‐3 T/P orbits computed by the Precise Orbit Determination (POD) teams (Service d'Orbitographie Doris/Centre National d'Etudes Spatiales and Goddard Space Flight Center/NASA) over two areas: (1) the Mediterranean area and (2) a part of the Pacific (including California and Hawaii) called hereafter the U.S. area. Geographically correlated orbit errors in these areas are clearly evidenced: for example, −2.6 cm and +0.7 cm for the Mediterranean and U.S. areas, respectively, relative to JGM‐3 orbits. However, geographically correlated errors (GCE) which are commonly linked to errors in the gravity model, can also be due to systematic errors in the reference frame and/or to biases in the tracking measurements. The short‐arc technique being very sensitive to such error sources, our analysis however demonstrates that the induced geographical systematic effects are at the level of 1–2 cm on the radial orbit component. Results are also compared with those obtained with the GPS‐based reduced dynamic technique. The time‐dependent part of GCE has also been studied. Over 6 years of T/P data, coherent signals in the radial component of T/P Precise Orbit Ephemeris (POE) are clearly evidenced with a time period of about 6 months. In addition, impact of time varying‐error sources coming from the reference frame and the tracking data accuracy has been analyzed, showing a possible linear trend of about 0.5–1 mm/yr in the radial component of T/P POE.
On the dynamics of the Zapiola Anticyclone
Authors: de Miranda Anne P. , Barnier Bernard , Dewar William K.
Published: December 2003

Recent observations obtained in the South Atlantic suggest the existence of a strong anticyclonic flow positioned over a major bottom topographic feature known as the Zapiola Drift. Here a numerical simulation of the South Atlantic is described in which this anticyclone is reproduced, and the model is used to diagnose the dynamics maintaining this flow. With a mean barotropic transport of 140 Sv and bottom velocities of 10 cm s−1, the simulated Zapiola Anticyclone compares well with in situ observations. Furthermore, the model surface eddy kinetic energy shows a local minimum over the drift, in agreement with observations from TOPEX/POSEIDON. Numerical experiments show that the circulation feature is sensitive to the intensity of the eddy field and to the particular value of the bottom friction. Both of these tendencies are in agreement with a theoretical explanation of the Zapiola Anticyclone that has recently appeared elsewhere. Thus we argue that the anticyclone is maintained by eddy‐driven potential vorticity fluxes accelerating flow within topographically closed, ambient potential vorticity contours. As far as we know, this is the first South Atlantic simulation to reproduce the Zapiola Anticyclone in a realistic fashion. The quantitative success of this experiment is attributed to the use of a topography following (sigma) coordinate in a spatially well resolved model.
Ocean circulation beneath Filchner‐Ronne Ice Shelf from three‐dimensional model results
Authors: Gerdes Rüdiger , Determann Jürgen , Grosfeld Klaus
Published: December 2003

A high‐resolution three‐dimensional ocean circulation model is applied to the cavity beneath Filchner‐Ronne Ice Shelf (FRIS). The model predicts predominantly barotropic currents which form a series of cyclonic gyres in the deep basins and anticyclonic circulations around the islands. The surface circulation can be such that the water moves in the direction of decreasing or increasing ice thicknesses, in the former case leading to freezing, while melting at the ice shelf base results in the latter case. The pattern of melting and freezing is consistent with known distributions of marine ice and melting areas beneath FRIS. An anticyclonic circulation around the Korff and Henry Ice Rises with melting west of Korff Ice Rise and freezing on the eastern side and north of Henry Ice Rise is the main source for an ice‐pumping mechanism that produces the observed large marine ice body in the central Filchner‐Ronne Ice Shelf. The estimates for net melting for realistic conditions at the open ocean boundary are 40–50 km3 yr−1, indicating that ice shelf‐ocean interaction is an important contribution to the mass balance of the ice shelf.
Carbon, alkalinity and nutrient budgets on the East China Sea continental shelf
Authors: Chen Chen‐Tung Arthur , Wang Shu‐Lun
Published: December 2003

The western part of the Kuroshio Intermediate Water originates from the nutrient‐rich South China Sea intermediate water which upwells onto the East China Sea (ECS) continental shelf and contributes a large amount of nutrients to the ECS. This contribution, especially for phosphorus, is far more than the inputs from the phosphorus‐deficient Yangtze and Yellow Rivers. Mass balance calculations reveal that the net denitrification rate in the ECS shelf is 95 ± 50 × 109 mol N yr−1, which is more than the total riverine supply of nitrogen. The nutrient supply allows the ECS to produce 1030 ± 310 × 109 moles dissolved organic carbon and 709 ± 280 × 109 mol particulate organic carbon for a total of 1739 ± 870 × 109 mol organic carbon per year, which translates to a new production rate of phytoplankton as 64 ± 32 mg C m−2 d−1 or 15% of the average primary production rate. The downslope transport of modern particulate carbon is 2547 ± 1250 × 109 mol yr−1, of which 695 ± 350 × 109 mol yr−1 is organic. This value is only 12% of the offshore dissolved organic carbon transport of 5563 ± 1700 × 109 mol yr−1. The alkalinity budget, never attempted before, indicates that there is a substantial amount of alkalinity generation in the sediments (3.9 ± 3.9 mmol m−2 d−1) due to anaerobic respiration such as by iron and sulfate reductions.
Volume transport of the Malvinas Current: Can the flow be monitored by TOPEX/POSEIDON?
Authors: Vivier Frédéric , Provost Christine
Published: December 2003

Current meter measurements were collected between 40° and 41°S in the Malvinas (Falkland) Current from December 1993 to June 1995. Owing to the premature failure of a mooring, a reliable volume transport time series could only be calculated for 254 days, leading to a mean transport of about 41.5 Sv with a standard deviation of 12.2 Sv. This time series is tentatively extended to 386 days. It is also shown that the TOPEX/POSEIDON altimeter, combined with the statistical information on the vertical structure of the current provided by the current meters, can be used to sensitively monitor the flow. A 3‐year‐long time series of transport is derived, which is well correlated (0.8) to the transport estimated from current meters, including about 60% of the variance of the flow at periods beyond 20 days; this series makes it possible to consider a relatively broad spectral range. Dominant periods are 50–80 days and close to 180 days. Interannual variations are large. Comparatively, little energy is found at the annual period, suggesting that the Malvinas Current has only little impact on the annual migrations of the confluence. The predominance of a semiannual cycle is compatible with a remote forcing of the flow suggested by previous numerical studies.
On the circulation in the upper layer of the western equatorial Atlantic
Authors: Bourlès B. , Gouriou Y. , Chuchla R.
Published: December 2003

Hydrographic observations of pressure, temperature, salinity, dissolved oxygen, and shipboard acoustic Doppler current profiler measurements are used to study the upper layer circulation in the western equatorial Atlantic Ocean, limited to the region bounded by the 10°S and 14°N latitudes between the longitudes 30°W and 52°W. Data were obtained during four World Ocean Circulation Experiment cruises, carried out in January‐March 1993, January‐March 1994, September‐October 1995, and April‐May 1996. In the upper layer, the continuity of the northwestward flowing North Brazil Current along the American continent toward the Caribbean Sea is confirmed in boreal spring. Furthermore, part of the North Brazil Current also continues northwestward in the subthermocline layer during short periods in boreal spring, contrary to previous estimates. The North Equatorial Countercurrent (NECC) is present in boreal spring west of 40°W, fed with water of Northern Hemisphere origin only. The southeastward flowing current observed at 3°N–44°W is fed by the North Brazil Current retroflection and by a cyclonic recirculation of the southern edge of the North Equatorial Current. The upper layer of this current, at 3°N–44°W, feeds the Equatorial Undercurrent (EUC) and the NECC, when its subthermocline layer feeds the EUC and the North Equatorial Undercurrent. Near‐surface eastward flow is present above the EUC during all cruises, yielding to a strong increase of the eastward warm water transport.
Intermediate water in the Brazil‐Malvinas Confluence Zone: A Lagrangian view
Authors: Boebel Olaf , Schmid Claudia , Podestá Guillermo , Zenk Walter
Published: December 2003

The subsurface flow within the subantarctic and subtropical regions around the Brazil‐Malvinas (Falkland) Confluence Zone is studied, using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the South American shelf. The float trajectories are mapped against sea surface flow patterns as visible in concurrent satellite sea surface temperature (SST) images, with focus on the November 1994 and October/November 1995 periods. The unprecedented employment of Lagrangian θ‐S diagrams enables us to trace the advection of patches of fresh Antarctic Intermediate Water (AAIW) from the Confluence Zone into the subtropical region. The fresh AAIW consists of a mixture of subtropical AAIW and Malvinas Current core water. Within the subtropical gyre, these patches are discernible for extended periods and drift over long distances, reaching north to 34°S and east to 40°W. The cross‐frontal migration of quasi‐isobaric floats across the Confluence Zone from the subtropical to the subantarctic environment is observed on three occasions. The reverse process, float migration from a subpolar to a subtropical environment was observed once. These events were located near 40°S, 50°W, the site of a reoccurring cold core feature. Subsurface float and SST data comparison reveals similarities with analogous observations made in the Gulf Stream [Rossby, 1996] where cross‐frontal processes were observed close to meander crests. The limited number of floats of this study and the complex structure of the Brazil‐Malvinas Confluence Zone, however, restricts the analysis to a description of two events.
Three Agulhas rings observed during the Benguela Current Experiment
Authors: Garzoli Silvia L. , Richardson Philip L. , Duncombe Rae Christopher M. , Fratantoni David M. , Goñi Gustavo J. , Roubicek Andreas J.
Published: December 2003

A field program to study the circulation of the Benguela Current and its extension into the southeastern Atlantic Ocean has completed the survey and instrument deployment phase. We report here new observations of three Agulhas rings north and west of Cape Town, South Africa. Three mesoscale anticyclonic rings initially identified by means of TOPEX/POSEIDON altimetry were surveyed with expendable bathythermographs, conductivity‐temperature‐depth‐oxygen profiles, direct current measurements from a lowered acoustic Doppler current profiler, a hull‐mounted acoustic Doppler current profiler, and satellite‐tracked surface drifters. Characteristics of the rings are presented, and their origins are discussed. Two are typical Agulhas rings surveyed at different times after their generation; the third Agulhas ring has an anomalous water mass structure whose most likely origin is the Subtropical Front.
Dimensions and dynamics of megaplumes
Authors: Woods Andrew W. , Bush John W. M.
Published: December 2003

We investigate the generation of megaplumes by the release of buoyant hydrothermal fluid from the seafloor. We show that megaplumes may be generated from various modes of venting, including both the instantaneous and continuous release of hydrothermal effluent from either a point or line source. The hydrothermal effluent forms a buoyant plume, which rises through the water column to its neutral buoyancy height and then intrudes laterally to form a neutral cloud. Owing to the influence of the Earth's rotation ƒ, whose magnitude is Ω = ƒ/2, the neutral cloud eventually becomes unstable, giving rise to geostrophic vortices that propagate away from the source. By combining the scaling laws governing turbulent plumes and geostrophic vortices, we establish new relationships between the megaplume geometry and the source conditions. We find that megaplumes whose radius greatly exceeds their height of rise are formed from sources that persist for at least several days, since, in the deep ocean, the radii of eddies produced by short‐lived releases of buoyant fluid are comparable to their rise height. Our model predicts the total buoyancy B of the hydrothermal effluent released in forming such megaplume structures. We also calculate the total megaplume heat content in terms of the total buoyancy release and the thermal anomaly of the megaplume, by considering the effects of the ambient stratification in both temperature and salinity on plume properties. Finally, we apply the model to data from three historic megaplume events at the Juan de Fuca ridge.
Rapid water exchange between the lagoon and the open ocean at Majuro Atoll due to wind, waves, and tide
Authors: Kraines Steven B. , Suzuki Atsushi , Yanagi Tetsuo , Isobe Masahiko , Guo Xinyu , Komiyama Hiroshi
Published: December 2003

Current measurements and conductivity‐temperature‐depth surveys of the lagoon and ocean at Majuro Atoll, the Republic of the Marshall Islands, were made from January 10 to 24, 1997. A vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements by Fourier transform. A three‐dimensional, robust diagnostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles. We used the diagnostic model to examine the effects of wind stress, radiation stress, density gradients, and tidal stress on the exchange of water between the lagoon and the ocean. Wind effectively mixes the lagoon water in approximately 2 weeks. Tidal flushing appears to be restricted to a small area near the main channels connecting the lagoon to the ocean. Cross‐reef‐flat currents induced by radiation stress and flowing to the deep channels in the center of the northern boundary form the dominant mechanism for exchange between the lagoon and the open ocean, causing water to exchange completely with the ocean in about 15 days. Computer‐generated particles tracked through the lagoon showed that radiation stress is also the main forcing mechanism for particle export from the lagoon. However, the coupling of tidal exchange through the Calalin Channel and wind‐stress‐induced mixing in the lagoon could also provide a significant export mechanism, particularly for particles originating uniformly inside the lagoon.
Internal tides resulting from the passage of surface tides through an eddy field
Authors: Krauss W.
Published: December 2003

If a surface (barotropic) tide passes through a baroclinic eddy field, the nonlinear terms produce, among others, internal waves having near‐tidal frequency but wavelength and vertical mode structure as given by the eddy field. Stationary eddy fields yield stationary internal tides, whereas moving eddy fields yield modulated, progressive internal tides. These internal tidal currents have amplitudes in the range of observations, 1–3 cm s−1.
Wind influence on the mesoscale activity along the Gulf Stream and the North Atlantic currents
Authors: Garnier Valérie , Schopp Richard
Published: December 2003

Two independent data sets are used to diagnose the wind effect on the mesoscale activity in the North Atlantic Ocean. The oceanic surface variability is described with TOPEX/Poseidon sea surface height measurements from October 1992 to September 1997. Spatial extensions and temporal variations of high mesoscale activity are compared with the zonal and meridional components of the ERS‐1 wind stress, the Ekman pumping, and the zonal Sverdrupian velocity. Regions with high mesoscale surface variability seem to be correlated to regions with eastward Sverdrupian velocities. When the Sverdrupian velocity is eastward and increases with time, the mesoscale activity is intensified, indicating a growth of instability rates. Theoretical and numerical results based on the interplay of barotropic eastward Sverdrup flows and westward propagation of long Rossby waves suggest that the wind controls western regions where baroclinic instability is favored. Interactions between the eddy field and the mean circulation are therefore analyzed to try to extract the instability mechanism responsible for the growth of the mesoscale activity along the Gulf Stream and the North Atlantic Current. Our results seem to suggest that the seasonal changes of mesoscale activity, associated with eastward currents, are linked to seasonal changes of the eastward Sverdrupian velocity.
The pattern and variability of Antarctic sea‐ice drift in the Indian Ocean and western Pacific sectors
Authors: Heil Petra , Allison Ian
Published: December 2003

Sea‐ice drift physically redistributes pack ice and changes ice extent, concentration, and, through deformation, the ice‐thickness distribution. In this paper, data are presented from 39 satellite‐tracked buoys, deployed during various seasons from 1985 to 1996 in the sea ice of the Southern Ocean off East Antarctica between 20° and 160°E longitude. The dominant features of the ice motion in the region are a westward drift parallel to the bathymetry near the Antarctic continent, a cyclonic circulation cell in Prydz Bay, and eastward drift of the ice to the north of the zonal shear zone. The oceanic circulation along the coast is generally barotropic and the ice drift is well correlated with bottom topography. Northward outflows, the locations of which are determined by both bottom topography and the seasonally varying position of the zonal shear zone, allow the discharge of sea ice from the westward drift in the south into the northerly belt of eastward flow, but with considerable variability in the net northward ice transport. The ice translation monitored by the buoys is used to derive the spatial pattern of the ice‐velocity field. The daily average ice‐drift speed in the westward flow is 0.23 m s−1 (19.8 km d−1), with considerable spatial and temporal variability, and in the eastward flow the average is 0.17 m s−1 (15.1 km d−1). Seasonal and interannual ice‐drift variabilities are analyzed. The results are compared with satellite data of sea‐ice extent and concentration over the same time, as well as with hydrographic observation of the position of the Antarctic Divergence.
Results from an ECMWF‐SSM/I forced mixed layer model of the Southern Ocean
Authors: Markus Thorsten
Published: December 2003

A bulk mixed layer model of the entire Southern Ocean forced by European Centre for Medium‐Range Weather Forecasts (ECMWF) near‐surface air temperatures and winds is presented. In addition, the Southern Ocean sea ice concentration determined from daily Defense Meteorological Satellite Program special sensor microwave imager (SSM/I) observations obviates the need for a dynamic‐thermodynamic sea ice model. The oceanic mixed layer serves as the interface between the deep ocean and the atmosphere or sea ice. Measurements have shown that in the Southern Ocean entrainment of relatively warm deep water into the mixed layer has a significant impact on the oceanic stability and is the primary reason for the thinness of its sea ice cover. The use of satellite‐derived ice concentrations reduces greatly the required accuracy in air temperature and wind needed by the model compared to the accuracy needed by coupled sea ice ocean models because these data are only needed here in the calculation of salt and heat fluxes and not to derive ice cover or ice dynamics. The results show that the seasonal cycle and the spatial distribution of mixed layer temperature, salinity, and depth can be reproduced and are in good agreement with in situ observations. Limitations in accuracy result predominantly still from uncertainties in air temperature, cloud cover, and wind speed during the summer months for areas with no or little ice coverage, ice concentration, and snow depth during the winter months as well as ocean currents.
Deriving long‐term time series of sea ice cover from satellite passive‐microwave multisensor data sets
Authors: Cavalieri D. J. , Parkinson C. L. , Gloersen P. , Comiso J. C. , Zwally H. J.
Published: December 2003

We have generated consistent sea ice extent and area data records spanning 18.2 years from passive‐microwave radiances obtained with the Nimbus 7 scanning multichannel microwave radiometer and with the Defense Meteorological Satellite Program F8, F11, and F13 special sensor microwave/imagers. The goal in the creation of these data was to produce a long‐term, consistent set of sea ice extents and areas that provides the means for reliably determining sea ice variability over the 18.2‐year period and also serves as a baseline for future measurements. We describe the method used to match the sea ice extents and areas from these four multichannel sensors and summarize the problems encountered when working with radiances from sensors having different frequencies, different footprint sizes, different visit times, and different calibrations. A major obstacle to adjusting for these differences is the lack of a complete year of overlapping data from sequential sensors. Nonetheless, our procedure reduced ice extent differences during periods of sensor overlap to less than 0.05% and ice area differences to 0.6% or less.
Arctic sea ice extents, areas, and trends, 1978–1996
Authors: Parkinson Claire L. , Cavalieri Donald J. , Gloersen Per , Zwally H. Jay , Comiso Josefino C.
Published: December 2003

Satellite passive‐microwave data for November 1978 through December 1996 reveal marked seasonal, regional, and interannual variabilities, with an overall decreasing trend of −34,300±3700 km2/yr (−2.8%/decade) in Arctic sea ice extents over the 18.2‐year period. Decreases occur in all seasons and on a yearly average basis, although they are largest in spring and smallest in autumn. Regionally, the Kara and Barents Seas have the largest decreases, at −15,200±1900 km2/yr (−10.5%/decade), followed by the Seas of Okhotsk and Japan, the Arctic Ocean, Greenland Sea, Hudson Bay, and Canadian Archipelago. The yearly average trends for the total, the Kara and Barents Seas, and the Seas of Okhotsk and Japan all have high statistical significance, with the null hypothesis of a 0 slope being rejected at a 99% confidence level. Regions showing increasing yearly average ice extents are Baffin Bay/Labrador Sea, the Gulf of St. Lawrence, and the Bering Sea, with only the increases in the Gulf of St. Lawrence being statistically significant at the 99% level. Hemispheric results for sea ice areas exhibit the same −2.8%/decade decrease as for ice extents and hence a lower absolute decrease (−29,500±3800 km2/yr), with the ice‐free area within the ice pack correspondingly decreasing at −4800±1600 km2/yr. Confidence levels for the trends in ice areas and ice‐free water areas exceed 99% and 95%, respectively. Nonetheless, interannual variability is high, and, for instance, the Arctic Ocean ice extents have a positive trend 1990–1996, in spite of their negative trend for the time period as a whole.
Near‐surface trajectories off central and southern California
Authors: Winant C. D. , Alden D. J. , Dever E. P. , Edwards K. A. , Hendershott M. C.
Published: December 2003

The near‐surface circulation in the Santa Barbara Channel and off the coast of central and southern California is described based on 20 releases of drifters drogued 1 m beneath the surface from 12 sites within the channel at bimonthly intervals. This description includes small‐scale features of the circulation which are not part of descriptions based on moored observations or of the statistics of the drifter releases. The eventual fate of drifters at long time intervals compared to the residence time in the channel (about 7 days) is also included. In the channel the trajectories document a persistent cyclonic circulation with a typical recirculation period between 3 and 5 days. In the spring, currents near the mainland are weaker than near the Channel Islands, and the overall flow is toward the southeast. Trajectories document the possibility for water parcels to leave the channel through the interisland passes. In the late fall and winter a poleward flow with velocities often exceeding 0.5 m s−1 is confined within 20 km of the mainland. Between these two seasons the cyclonic tendency is enhanced, although most of the drifters eventually migrate westward. The trajectories of drifters released at the same time from sites only 20 km apart can be remarkably different. Once the drifters migrate out of the channel, their trajectories can be grouped into a few patterns. In spring and summer, drifters tend to remain in the Southern California Bight. Their trajectories often remain close over extended periods, as if they were caught in convergence zones. In fall the drifters often are caught in a poleward current.
Simulation of the nitrate seasonal cycle in the equatorial Atlantic Ocean during 1983 and 1984
Authors: Loukos Harilaos , Mémery Laurent
Published: December 2003

We use a three‐dimensional, off‐line geochemical model to simulate the nitrate cycle in the equatorial Atlantic during the years 1983–1984 corresponding to the Français Océan et Climat dans l'Atlantique Equatorial (FOCAL) and Seasonal Response of the Equatorial Atlantic programs. After comparing our simulations with FOCAL data, we investigate interactions between equatorial circulation and biological activity on both seasonal and interannual timescales. Our results suggest that the upwelling of nitrate in the surface layer is strongly dependent on the behavior of both the nitracline and Equatorial Undercurrent (EUC). In the western basin, the equatorial upwelling partly feeds the EUC and has a low signature on surface nitrate. On the contrary, in the eastern basin, where the upwelling core and the nitracline are closer to the surface, vertical advection is the driving mechanism causing seasonal variations of nitrate concentration. Above the EUC, nitrate is transferred to the very surface by vertical diffusion, whereas the contribution by vertical advection is negligible. While slightly cold oceanic conditions prevailed in 1983, a warm anomaly produced by a decrease in trade winds and upwelling was observed in 1984. In our simulations, the significant changes in circulation do not notably alter the seasonal cycle of new production. Consequently, variations of annual primary production between 1983 and 1984 are small (9% decrease in the 2°S–2°N band) compared to the amplitude of the seasonal cycle (twofold variations). Contrary to the Pacific Ocean, where the interannual signal dominates, our results suggests that seasonal variability is the most significant large‐scale signal on primary production in the equatorial Atlantic.
A simulation of biological processes in the equatorial Pacific Warm Pool at 165°E
Authors: McClain Charles R. , Murtugudde Ragu , Signorini Sergio
Published: December 2003

A 9‐year simulation (1984–1992) of biological processes in the equatorial Pacific Warm Pool is presented. A modified version of the four‐component (phytoplankton, zooplankton, nitrate, and ammonium) ecosystem model by McClain et al. [1996] is used. Modifications include use of a spectral model for computation of photosynthetically available radiation and inclusion of fecal pellet remineralization and ammonium nitrification. The physical parameters (horizontal and vertical velocities and temperature) required by the ecosystem model were derived from an improved version of the Gent and Cane [1990] ocean general circulation model [Murtugudde and Busalacchi, 1998]. Surface downwelling spectral irradiance was estimated using the clear‐sky models of Frouin et al. [1989] and Gregg and Carder [1990] and cloud cover information from the International Satellite Cloud Climatology Project. The simulations indicate considerable variability on interannual timescales in all four ecosystem components. In particular, surface chlorophyll concentrations varied by an order of magnitude with maximum values exceeding 0.30 mg m−3 in 1988, 1989, and 1990 and pronounced minima during 1987 and 1992. The deep chlorophyll maximum (DCM) ranged between 75 and 125 m with values occasionally exceeding 0.40 mg m−3. With the exception of periods during 1984 and 1988, surface nitrate was always near depletion. Ammonium exhibited a subsurface maximum just below the DCM with concentrations as high as 0.5 mg‐atN m−3, where “at” is atoms. Total integrated annual primary production varied between 40 and 250 gC m−2 yr−1 with an annual average of 140 gC m−2 yr−1. Finally, the model is used to estimate the mean irradiance at the base of the mixed layer, i.e., the penetration irradiance, which was 18 W m−2 over the 9‐year period or about 8% of the incident total irradiance. The average mixed layer depth was 42 m.
Internal tide generation at a shelf break by an oblique barotropic tide: Observations and analytical modeling
Authors: Guizien Katell , Barthélemy Eric , Inall Mark E.
Published: December 2003

An analytical model has been developed to describe the generation of a linear interfacial wave over a steep ocean margin by a barotropic tide propagating toward the shelf break with a variable angle of incidence. The stratification is reduced to a two‐layer system, and the model uses step‐like shelf geometry. In both shallow and deep regions an open boundary is assumed (this implies particularly that there is no reflection at the coast). The model is forced with the amplitude and direction of an incident barotropic Poincaré wave propagating toward the shelf break. With this forcing, the model gives the amplitude, direction of propagation, and wavenumber of both barotropic and baroclinic Poincaré waves transmitted onto the shelf and reflected into the deep region in the vicinity of the shelf break. After comparison with Baines' [1973] model, our model is compared with internal tide observations made in July 1996 on the Malin Shelf within the U.K. Land Ocean Interaction Study‐Shelf Edge Study program. The observations are from moored thermistor chains and acoustic Doppler current profilers sited at two locations, one near the shelf break and the other 47.5 km onto the shelf. Observations at this latter mooring are not described by the generation model because of nonlinear changes and damping as the internal wave propagates through shallow water. Baroclinic displacements of the thermocline of 8 m amplitude were observed close to the shelf break, and total baroclinic energy was estimated at 2.4 J/m3 during neap tide and 3 J/m3 during spring tide. Both amplitude and energy of the shoreward propagating internal tide waves are compared with the model. Using a barotropic forcing taken from bibliographical data, good agreement with observations is found during neap tide (when the density structure is close to being two‐layer) for an incident barotropic tide of 1 m amplitude and propagation direction on a bearing of 23°T (T means from True North in a clockwise sense).
Production rates of sea‐spray droplets
Authors: Pattison Martin J. , Belcher Stephen E.
Published: December 2003

The question of whether sea‐spray droplets make a significant contribution to the transfer of heat and water vapor between the air and sea has been addressed by many researchers over the last few decades. Quantification of the effect is difficult owing to a number of factors; in particular, the available data on droplet concentrations over the sea are limited and the airflow over rough seas is not well known. In the work described in this paper, a model for simulating droplet trajectories over the sea was developed, taking into account the droplet evaporation and the effects of turbulence on the motion. This model was used to simulate the behavior of droplets under conditions for which field data on droplet concentrations were available, and the rates at which droplets are generated were calculated. Estimates of the spray contribution to the heat and mass transfer made using these results suggest that droplets are likely to make only a small contribution to the overall fluxes, except under storm conditions, when they could be a major source of water vapor.
Circulation of the Pacific Ocean seen in a global ocean model: Ocean Circulation and Climate Advanced Modelling project (OCCAM)
Authors: Saunders Peter M. , Coward Andrew C. , de Cuevas Beverly A.
Published: December 2003

This paper compares observations made in the Pacific Ocean and the 8–12 year climatology of a global numerical model. Meridional mass and heat transports and their divergences are calculated, and zonal averages compared with the air‐sea exchange values of Doney et al. [1998] with mixed success. The large scale distribution of sea surface height and near‐surface currents are shown to be well reproduced by the model, but their variance is underestimated, severely so in areas of weak variability. Synoptic wind forcing enhances the latter, though only slightly, while higher model resolution improves agreement in areas of strong variability. Model mean transports in the East Australian Current, in the Vitiaz Strait and in the Kuroshio exceed measurements by 10, 0, 18 Sv, respectively, and variability is underestimated by factors between 2 and 4. Near 1000 m and in strong currents the flow is overestimated, but over most of the ocean, model output does not match either the magnitude or the spatial variability of the observations. In contrast, the inflow of bottom water and its spreading path throughout both South and North Pacific is well described. Good agreement is found with measured transport through the Samoan Passage, but at 32°S, east of the Tonga‐Kermadec Ridge, the model yields only 60% of the observed value. The Sverdrup balance is shown to hold widely in the model interior. Utilizing the complete depth‐integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents.
Equatorial currents and transports in the upper central Indian Ocean: Annual cycle and interannual variability
Authors: Reppin Jörg , Schott Friedrich A. , Fischer Jürgen , Quadfasel Detlef
Published: December 2003

The zonal circulation south of Sri Lanka is an important link for the exchange of water between the Bay of Bengal and the Arabian Sea. Results from a first array of three moorings along 80°30′E north of 4°10′N from January 1991 to March 1992 were used to investigate the Monsoon Current regime [Schott et al., 1994]. Measurements from a second array of six current meter moorings are presented here. This array was deployed along 80°30′E between 45′S and 5°N from July 1993 to September 1994 to investigate the annual cycle and interannual variability of the equatorial currents at this longitude. Both sets of moorings contribute to the Indian Ocean current meter array ICM8 of the World Ocean Circulation Experiment. The semiannual equatorial jet (EJ) was showing a large seasonal asymmetry, reaching a monthly mean eastward transport of 35 Sv (1 Sv = 1×106 m3 s−1) in November 1993, but just 5 Sv in May 1994. The Equatorial Undercurrent (EUC) had a maximum transport of 17 Sv in March to April 1994. Unexpectedly, compared to previous observations and model studies, the EUC was reappearing again in August 1994 at more than 10 Sv transport and was still flowing when the moorings were recovered. In addition, monthly mean ship drifts near the equator are evaluated to support the interpretation of the moored observations. Interannual variability of the EJ in our measurements and ship drift data appears to be related to the variability of the zonal winds and Southern Oscillation Index. The output of a global numerical model (Parallel Ocean Climate Model) driven by the winds for 1993/1994 is used to connect our observations to the larger scale. The model reproduces the EJ asymmetry and shows the existence of the EUC and its reappearance during summer 1994.
Tracer distributions and deep circulation in the western tropical Atlantic during CITHER 1 and ETAMBOT cruises, 1993–1996
Authors: Andrié Chantal , Ternon Jean‐François , Bourlès Bernard , Gouriou Yves , Oudot Claude
Published: December 2003

This paper presents CFC and nontransient tracer observations in the western equatorial Atlantic Ocean on repeated sections along 7°30′N, the 35°W meridian, and a transect crossing the Ceara Rise. Three World Ocean Circulation Experiment cruises have been carried out in this area, in February‐March 1993 (CITHER 1) and September‐October 1995 and April‐May 1996 (ETAMBOT 1 and 2). Together with the tracer data, the direct current measurements are used to deduce the circulation pathways. The data confirm the principal circulation features of the Upper North Atlantic Deep Water within the area. The Deep Western Boundary Current flows southward along the continental slope, while, adjacent to the DWBC, there is a northward flow corresponding to the DWBC recirculation whose origin appears variable. The largest variability is observed along the 35°W meridional section, where the DWBC bifurcates eastward north of 3°S but the eastward equatorial flow does not appear to be permanent. At the Middle North Atlantic Deep Water level, CFC distributions exhibit the most important contrast between waters of northern and southern origin. The circulation at the Lower North Atlantic Deep Water level, mainly controlled by the topography, looks more permanent because the DWBC is regularly observed during the three cruises, and there is no evidence for a northwestward recirculation along the Mid‐Atlantic Ridge. The transient behavior of CFC distributions, which is superimposed on local circulation effects, can be seen clearly through their temporal evolution within the DWBC. The variability of the deep circulation observed during the 1993–1996 interval rules out a dominant variability in response to semi annual forcing.
Contributions of wind forcing, waves, and surface heating to sea surface height observations in the Pacific Ocean
Authors: Vivier Frédéric , Kelly Kathryn A. , Thompson LuAnne
Published: December 2003

The dominant processes affecting sea surface height (SSH) variability observed by the TOPEX/Poseidon altimeter vary regionally in the Pacific; baroclinic Rossby waves, equatorially trapped Kelvin waves, steric response to seasonal heating, and the response to wind stress curl forcing are all important. The steric response to surface heating dominates seasonal SSH variability in the subpolar gyre and the eastern subtropical gyre. South of the Kuroshio Extension and south of 20°N in the eastern Pacific, the dominant contribution to SSH is from near‐annual period Rossby waves. To quantify the wave energy, observed SSH was assimilated into a kinematic model of westward propagating waves. These waves account for >70% of SSH variance between 10°S and 10°N but only ∼30% between 10°N and 30°N. Although wave energy in the eastern Pacific is correlated with SSH anomalies at the equator, the much larger wave energy in the western Pacific is correlated with wind stress curl, suggesting that the Rossby waves there are locally forced. In addition to these planetary waves, the ocean response to wind forcing via Ekman pumping is observed in several places, specifically in the North Equatorial Current. A quasi‐steady topographic Sverdrup balance is detectable over most of the North Pacific at latitudes as low as 10–15°N, as well as in the South Pacific, where it is seen north of 50°S. The decomposition of the SSH signal into propagating waves, an Ekman pumping response, and Sverdrup transport is consistent with the results from an isopycnal numerical model.
Daily reconstruction of water temperature from oxygen isotopic ratios of a modern Tridacna shell using a freezing microtome sampling technique
Authors: Watanabe T. , Oba T.
Published: December 2003

Daily (1–2 day interval) reconstruction of sea water temperature is calculated via a freezing microtome sampling technique for oxygen isotope analysis and by counting the daily growth lines in a modern Tridacna (Hippopus hippopus, LINNE, 1758) shell collected from Ishigaki Island, Japan. This method enables the first direct comparison between shell oxygen isotopic values and daily meteorological data. The H. hippopus shell calcifies mainly under isotopic equilibrium with surrounding sea water. The high‐resolution profile of δ18O of the H. hippopus shell was recorded monthly to seasonal sea surface temperature variations of the local coral reef environment.
An energy‐conserving thermodynamic model of sea ice
Authors: Bitz C. M. , Lipscomb William H.
Published: December 2003

We introduce an energy‐conserving sea ice model for climate study that accounts for the effect of internal brine‐pocket melting on surface ablation. Sea ice models that parameterize latent heat storage in brine pockets often fail to reduce the energy required for surface ablation in proportion to the internal melting that has already occurred. These models do not conserve energy during the summer melt season. Compared with our energy‐conserving model, a nonconserving model underestimates top‐surface ablation of multiyear ice by 12–22% and overestimates the equilibrium ice thickness by 50–124 cm. In addition, a nonconserving model is less sensitive to perturbative forcing than our energy‐conserving model is: The equilibrium thickness changes 22–44% less owing to surface albedo perturbations and 13–31% less owing to downward longwave radiation perturbations. The smaller differences are associated with a model that has a time‐independent, vertically varying salinity profile, and the larger differences are associated with a model that assumes the ice is isosaline with a salinity of 3.2‰. Simulations with a vertically varying salinity profile have low salinity at the top surface compared to isosaline cases, which leads to reduced heat conduction, less internal brine‐pocket melting, and more surface ablation.
Momentum balances on the North Carolina inner shelf
Authors: Lentz Steve , Guza R. T. , Elgar Steve , Feddersen Falk , Herbers T. H. C.
Published: December 2003

Four months of moored current, pressure, temperature, conductivity, wave, and wind observations on the North Carolina shelf indicate three dynamically distinct regions: the surf zone, the inner shelf between the surf zone and the 13‐m isobath, and the midshelf. In the surf zone the along‐shelf momentum balance is between the cross‐shelf gradient of the wave radiation stress and the bottom stress. The linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone. On the inner shelf the along‐shelf momentum balance is also frictional; the along‐shelf wind stress and pressure gradient are balanced by bottom stress. In the cross‐shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the Coriolis force (geostrophy) and wave setdown from shoaling, unbroken surface gravity waves. At midshelf the along‐shelf momentum balance is less frictional and hence flow accelerations are important. The cross‐shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown. The cross‐shelf density gradient is in thermal wind balance with the vertical shear in the along‐shelf flow in depths as shallow as 10 m. The dominant along‐shelf momentum balances provide a simple estimate of the depth‐averaged, along‐shelf current in terms of the measured forcing (i.e., wind stress, wave radiation stress divergence, and along‐shelf pressure gradient) that reproduces accurately the observed cross‐shelf variation of the depth‐averaged, along‐shelf current between the surf zone and midshelf.
On the importance of intermediate water flows for the global ocean overturning
Authors: de las Heras Miriam M. , Schlitzer Reiner
Published: December 2003

A steady state inverse global ocean model is used together with the available original, historical hydrographic database to study and quantify the large‐scale global ocean circulation. The model has a variable resolution grid with grid sizes as small as 2.5° longitude by 2° latitude along boundaries, straits or over steep topography and a default resolution of 5° by 4° in “quiet” open ocean regions. The model has 26 vertical levels with 60 m resolution near the surface. The adjoint method is applied to drive the model to the hydrographic data and to optimize horizontal flows, air‐sea heat fluxes, and mixing coefficients in an iterative way. Mass, heat, and salt budgets are satisfied exactly by the model. After assimilation, both simulated temperature and salinity fields are in good agreement with observations. Sensitivity experiments show that different circulation patterns with varying relative importance of intermediate water versus warm water transports and varying warm water inflow from the Indian Ocean into the Atlantic are consistent with the hydrographic data. However, for all solutions we find that the water mass that dominates the compensation of North Atlantic Deep Water export is Antarctic Intermediate Water. The northward transport rates of intermediate water in the South Atlantic and South Pacific in our model solutions range between 10 and 15 Sv in each ocean and are considerably larger than previously published values.
Altimetric signal and three‐dimensional structure of the sea in the Channel of Sicily
Authors: Nardelli Bruno Buongiorno , Santoleri Rosalia , Iudicone Daniele , Zoffoli Simona , Marullo Salvatore
Published: December 2003

The 1996 Altimeter/Synoptic Mesoscale Plancton Experiment (ALT/SYMPLEX) was specifically designed to perform in situ measurements simultaneous with the passage of TOPEX/POSEIDON (T/P) and ERS 2 over selected tracks in the central and eastern Sicily Channel. This experiment made it possible to have, for the first time, a validation of altimetry with in situ data over the Mediterranean, where weak dynamics results in a modest sea elevation, rarely exceeding 10 cm. Historical infrared and altimetric satellite data were first analyzed in order to study the variability of the circulation in the area. The comparative and integrative analysis of simultaneous satellite data and in situ measurements permitted investigation of the relation between the altimeter‐derived surface topography and the three‐dimensional structure of the sea. The Pearson correlation coefficients between altimeter data and dynamic heights along track resulted to be 0.72–0.89 (T/P) and 0.88 (ERS 2) when using conventional repeat track analysis. For T/P, a correlation value of 0.87 was found for time differences computed basing on a collinear analysis technique. This analysis also led to the identification of a strong barotropic component of the velocity field located near the Sicilian continental shelf, where it is responsible for approximately 60% of the signal.