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We investigate the classical problem of wind-stress-induced non-equatorial steady ocean currents, considering a three-valued piecewise-constant eddy viscosity. This extends and generalizes recent results on piecewise-uniform eddy viscosity with only two layers. The aim is to determine how variations in the relative values of the eddy viscosity at different depths may account for the deviations from the surface current deflection of 45 ∘ , predicted in the classical constant eddy viscosity case. Such variations are observed in field data, and we investigate analytically the effect the presence of a third region makes compared to the two-layer case. [ABSTRACT FROM AUTHOR]

The present numerical study builds on Ekman (1905)'s work in surface boundary layer and extends the boundary value problem to overcome some of its limitations. Previous studies addressed model's limitations by assuming that deviations from observations are usually ascribed to different eddy viscosity shapes, but seldom to the presence of baroclinic pressure gradients and shallow seas, which are the mainstays of this work. Improved solutions in the ocean boundary layer are obtained considering both depth-dependent wind-induced eddy viscosity and horizontal density gradients, ranging from well-mixed to highly-stratified conditions in a finite-depth ocean. High-order numerical solutions extend those in previous analytical and numerical works in the literature and widens the parameter space analyzed. Remarkably, the current profiles are obtained without ambiguity as a truly superposition of a geostrophic and a ageostrophic terms. Results indicate that, for a vertically-uniform eddy viscosity without density gradients and in shallow waters, currents are practically aligned with wind. As depth increases, misalignment between currents and wind increases and the complexity of the vertical structure increases. At large depths, Ekman's values are attained, i.e., deflection angles relative to wind direction, θ W , are θ S − θ W = − 4 5 ∘ at the surface, where the current is maximum, and θ T − θ W = − 90 ° for the depth-integrated transport (negative for deflections to the right in the Northern Hemisphere). These features remain regardless of the magnitude of the eddy-viscosity. For non-uniform eddy viscosity, θ S − θ W decreases from − 4 5 ∘ up to − 9 0 ∘ from low to high stratification level, respectively, whereas θ T − θ W is rather insensitive ( θ T − θ W ≈ − 9 0 ∘ ). Contrary to wind effects, the presence of the only vertically-uniform density gradient forcing, with constant eddy viscosity, deflects the surface angle θ S − θ D = + 4 5 ∘ relative to the density-gradient direction, θ D , in deep waters. Maximum currents no longer occur at the surface in this case. For non-uniform density-gradient profiles, current magnitude decreases overall while θ S − θ D ≈ + 4 5 ∘ as long as the gradient affects the entire surface boundary layer. The deflection angle θ T − θ D ∼ + 9 5 ∘ remains less sensitive to changes in density-gradient profile. • Improved Ekman solutions: variable eddy viscosity and baroclinicity in finite-depths. • Numerical solutions extend previous ones and widens the parameter space explored. • Currents are truly decoupled into geostrophic and ageostrophic terms. • Baroclinicity deflects 45 ∘ to the left from the density-gradient direction. • As stratification increases, surface current deflects 45 ∘ –90 ∘ to the right of wind. [ABSTRACT FROM AUTHOR]

The Caspian Sea water dynamics on the boundary of its northern and central basins is considered. A high-resolution numerical model (with a grid step of ~2 km) has been used to reproduce the mesoscale structure of currents. The results of two experiments are presented: a realistic reconstruction of the sea circulation in 2003 and an idealized one with an artificial forcing. The realistic calculation considers the water exchange between the two basins, which occurs primarily due to coastal jet currents near Tyub-Karagan Peninsula in the east and near the Agrakhan Peninsula in the west. The formation and evolution of these currents under various synoptic situations are analyzed, and their flow rates are quantitatively estimated. The effect of contrasting water intrusions caused by these currents on the salinity field in both basins with highly different haline regimes is estimated. In particular, the western current (WC) is shown to increase the sea surface salinity (SSS) in the Northern Caspian and decrease its value in the Middle Caspian by almost 1–2 psu/year. The water exchange in the east is asymmetric: the northern current increases salinity in the northern basin by 2–3 psu/year, while the southern current decreases the average SSS in the central basin by only around 0.5 psu/year; in this case, the southern current occurs stably only in June and July. The idealized experiment simulates the Caspian water dynamics for winds of various points: from 0° to 350° with a step of 10°. The flow rates of both western and eastern currents have a sinusoidal dependence on the wind direction: their maxima are reached with winds of 40° and 220° points for the WC and with 120° and 300° points for the eastern current (EC). This study also analyzes the establishment of quasi-steady-state sea circulation at a constant wind. [ABSTRACT FROM AUTHOR]

Although small in size, the Gulf of Trieste (GoT), a marginal coastal basin in the northern Adriatic Sea, is characterized by very complex dynamics and strong variability of its oceanographic conditions. In April–May 2012, a persistent, large-scale anticyclonic eddy was observed in the GoT. This event was captured by both High Frequency Radar (HFR) and Lagrangian drifter observations collected within the European MED TOSCA (Tracking Oil Spill and Coastal Awareness) project. The complexity of the system and the variety of forcing factors constitute major challenges from a numerical modeling perspective when it comes to simulating the observed features. In this study, we implemented a high-resolution hydrodynamic model in an attempt to reproduce and analyze the observed basin-wide eddy structure and determine its drivers. We adopted the Massachusetts Institute of Technology General Circulation Model (MITgcm), tailored for the GoT, nested into a large-scale simulation of the Adriatic Sea and driven by a tidal model, measured river freshwater discharge data and surface atmospheric forcing. Numerical results were qualitatively and quantitatively evaluated against HFR surface current maps, Lagrangian drifter trajectories and thermohaline data, showing good skills in reproducing the general circulation, but failing in accurately tracking the drifters. Model sensitivity to different forcing factors (wind, river and tides) was also assessed.

• Nine years of glider transects measure the transport across the Solomon Sea. • Seasonal and ENSO fluctuations are 25–50% of the mean. • A linear wind-driven model identifies distinct wind forcing driving the anomalies. • Interannual temperature advection through the sea influences the equatorial Pacific. The Solomon Sea carries the equatorward western boundary current of the South Pacific, a principal element of subtropical-equatorial communication. Eighty-seven glider transects across the mouth of the Sea over nine years describe the velocity structure and variability of this system. The time series spans two El Niños and two La Niñas, which produced large transport anomalies, up to 50% of the mean. While transport increased during El Niños and decreased during La Niñas, their signatures were inconsistent among the events. Separated glider tracks show the merging of two inflows, one from the tropics east of the Solomon Island chain, the other entering as a western boundary current generated by winds over the full subtropical gyre. A model of linear wind-driven dynamics, including western boundary currents, had skill in describing the variability of the two inflows, identifying the distinct wind forcing driving each. The model suggests that both the mean and low-frequency variability of flow entering the Solomon Sea are driven remotely by wind over the South Pacific, acting through long Rossby waves. The ultimate significance of in situ observations in this small sea will be to describe its role in subtropical-tropical heat exchange that is crucial to ENSO and longer-timescale climate variations along the equator. We take an initial step here, suggesting that temperature advection through the Solomon Sea is a first-order contribution to interannual temperature changes of the equatorial strip as a whole. [ABSTRACT FROM AUTHOR]

A linear coastal-trapped-wave (CTW) model is used to examine the effects of large-scale winds, with time scale ranging from a few days to a few weeks, on the West India Coastal Current (WICC), particularly on the shelf off the central west coast of India. We show that unlike the seasonal cycle of WICC, which is primarily forced by the winds along the east coast of India, the high-frequency WICC is mostly driven by the west-coast winds. Nevertheless, the influence of winds as far as Sri Lanka and east coast of India cannot be neglected. Simple numerical experiments with the CTW model show that the strong current observed at Goa (15° N) compared to Bhatkal (13° N) and Jaigarh (17° N) is due to two factors: (1) the superposition of local and remote CTWs and (2) the widening of shelf width north of Goa, which decreases the amplitude of the currents poleward of Goa. If the local winds are weak, the amplitude of current decreases poleward due to friction, and the current at the south leads the north. We also note that the observed phase difference between sea level and alongshore current at Goa could be attributed to the propagation of remotely forced higher-order modes of CTWs. [ABSTRACT FROM AUTHOR]

Abstract Surface drift of eighty-nine undrogued RAFOS floats in the California Current System (CCS) has been studied to describe patterns of flotsam drift, its seasonal variability and predictability limitations. The floats were launched in the California Undercurrent during 1992–2010 and were tracked by the ARGOS system when they surfaced at the end of their subsurface missions. The duration of surface trajectories varied from as short as 11 to as long as 280 days. The surface drift of these floats was typically equatorward in the California Current. However, some floats moved poleward into the Subpolar Gyre, and others drifted westward into the North Equatorial Current. Usually, observations of surface currents use drifters which are coupled to the surface layer by drogues located at 15 m depth. While drogued observations are useful for studies of circulation of the upper layer of the ocean, a more typical operational problem involves trying to find flotsam that has fallen off the deck of a ship or to predict the path of an abandoned vessel. To better understand the behavior of these surface drifting objects, observations of the surface drifts of RAFOS floats in the California Current system were used to compare the floats’ motions to wind-induced drift and to evaluate the drift prediction by three ocean models: Ocean Surface Current Simulator (OSCURS), Global Navy Coastal Model (gNCOM) and Hybrid Coordinate Ocean Model (HYCOM). Cross-Calibrated Multi-Platform Ocean Surface Wind Vector L3.0 First-Look Analysis wind data were used to analyze the surface drift of the RAFOS floats. The best correlation between float drift speed and wind speed was observed during summer and fall months, when the wind regime over the Northeast Pacific is dominated by the North Pacific High. The predominant winds associated with this regime are steady and contribute to the surface drift in the same direction as the large-scale geostrophic component of the California Current. Evaluation of the drift prediction by three ocean models was conducted by comparing observed drifter trajectories with model-simulated trajectories at 7-day time scales. The model-simulated trajectories were initially collocated with RAFOS positions and restarted every 15 days. The OSCURS model was the only one of three analyzed models which allowed for tuning based on the surface RAFOS trajectories. Two main parameters, Wind Angle Deflection (WAD) and Geostrophic Current Factor (GCF), were adjusted to minimize the separation between observed and modeled trajectories. At shorter time scales, from weeks to several months, the tuned OSCURS model outperformed gNCOM and HYCOM models in reproducing the observed surface drift. For seasonal and longer time scales, both gNCOM and HYCOM can reproduce the seasonal variability, flow direction, and eddy-like structures in the California Current system, which may be useful for long-term forecasts of the Northeast Pacific circulation. [ABSTRACT FROM AUTHOR]

The South China coast, especially the Pearl River Estuary (PRE) region, is prosperous and densely populated, but vulnerable to sea level changes. Sea level anomalies (SLA) during 1954–2012 from tide gauge station data and regional SLAs during 1993–2012 from satellite altimetry are analyzed and compare to the El Niño–Southern Oscillation (ENSO). Results show that sea level declines during El Niño events and rises during La Niña. Sea level in the PRE responds to ENSO with ~3–month lag. The ENSO can cause sea level in the PRE to fluctuate from −8.70 to 8.11 cm. Sea level cycles of 3 and 5 years are related to ENSO. The ENSO mechanism affecting sea level in the PRE was analyzed by identifying dominant regional and local forces. Weak/strong SLAs in most El Niño/La Niña events may be attributed to less/more seawater transport driven by anomalously weak/strong north winds and local anomalously high/low sea level pressure. Wind-driven coastal current is the predominant factor. It generated coastal seawater volume transport along a ~160 km wide cross section to decrease by 21.07% in a typical El Niño period (January 2010) and increase by 44.03% in a typical La Niña period (January 2011) as compared to an ENSO neutral situation (January 2013). Results of sea level rise and its potential mechanism provide insight for disaster protection during extreme El Niño/La Niña events. [ABSTRACT FROM AUTHOR]

Hydrodynamic conditions in Loch Linnhe, a dynamifcally wide estuary on the west coast of Scotland, are primarily influenced by wind forcing, freshwater input, and tides. Winds in the region are orographically steered along the axis of the estuary due to surrounding mountains. A large rainfall catchment area results in a large freshwater inflow into Loch Linnhe which in turn produces low salinity waters at the head of the estuary. This, combined with a connection to the open sea with coastal salinities, leads to salinity gradients in the horizontal and vertical. Even though a range of observational programmes have focussed on Loch Linnhe, the literature still lacks an evaluation of its physical dynamics. Here we present a first description of the hydrodynamics in Loch Linnhe based on observations. Wind stress predominantly influences the surface layer, especially at low frequencies and with a stronger influence than tides during neap tides. The buoyancy-driven flow due to the large river runoff influences the circulation independent of wind stress. Seasonal (spring, autumn) and interannual (2011, 2012) variability of water masses occur especially in the surface layer. Tides are dominated by the semi-diurnal constituent M 2 with tidal ellipses aligned in the along-estuary direction and a stronger influence during spring tides compared to wind. An evaluation of dimensionless numbers reveal laterally and vertically sheared exchange flows. Compared to other Scottish estuaries Loch Linnhe is wide enough to be influenced by the Earth's rotation and demonstrates an enhanced freshwater outflow along its north-western coast as the freshwater is diverted to the right in the direction of the flow. These observed patterns are important for the sustainable environmental management of this socio-economically valuable region, e.g. through their relevance to aquaculture pathogen transmission patterns. A thorough understanding of the dynamics of the system is essential for a successful evidence-based marine planning framework. [ABSTRACT FROM AUTHOR]

Large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels, currents and surface waves. In this study we apply a numerical model to simulate hydrodynamics and waves in the Albemarle-Pamlico Estuarine System, a large and shallow back-barrier basin in eastern North Carolina, over a one-month study period (September 2008) with observations from several storm wind events of differing time scales and directions. Model performance is evaluated for a spatially varying wind field from the North American Regional Reanalysis (NARR) dataset in comparison to spatially uniform forcing from wind observations at offshore, coastal and land-based sites across the region. A spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels (R = 0.88) in the estuaries than NARR (R = 0.48) after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area. The influence of a prominent bathymetric feature on hydrodynamics in Pamlico Sound is also investigated by numerically removing a 30 km long and 2–3 m deep shoal from the model grid and replacing it with an idealized depth of 6 m. The removal of the shoal increases water level setup by 14% at the estuarine shoreline, decreases current magnitudes by up to 40% in the shoal region and increases significant wave heights locally by up to 25% in the sound, indicating the importance of this relict geomorphic feature as a major control on the hydrodynamic response of the system during wind events. The results suggest that increasing the water depth over the shoal can lead to higher storm surges and wave heights with the possibility of increased inundation and erosion of the back-barrier and mainland coastal regions. The complex bathymetry and marine wind influence are critical input conditions for modeling large and shallow lagoonal estuaries like the Albemarle-Pamlico Estuarine System. [ABSTRACT FROM AUTHOR]

The wind-driven circulation and wind-induced coastal upwelling in a large shelf sea with a zonally oriented coast are examined. The Yucatan shelf is located to the north of the Yucatan peninsula in the eastern Gulf of Mexico. This area is a tropical shallow body of water with a smooth sloping bottom and is one of the largest shelves in the world. This study describes the wind-driven circulation and wind-induced coastal upwelling in the Yucatan shelf, which is forced by easterly winds throughout the year. Data obtained from hydrographic surveys, acoustic current profilers and environmental satellites are used in the analysis. Hydrographic data was analyzed and geostrophic currents were calculated in each survey. In addition an analytical model was applied to reproduce the currents. The results of a general circulation model were used with an empirical orthogonal function analysis to study the variability of the currents. The study area is divided in two regions: from the 40 m to the 200 m isobaths (outer shelf) and from the coast to the 40 m isobath (inner shelf). At the outer shelf, observations revealed upwelling events throughout the year, and a westward current with velocities of approximately 0.2 m s −1 was calculated from the numerical model output and hydrographic data. In addition, the theory developed by Pedlosky (2007) for a stratified fluid along a sloping bottom adequately explains the current’s primary characteristics. The momentum of the current comes from the wind, and the stratification is an important factor in its dynamics. At the inner shelf, observations and numerical model output show a wind-driven westward current with maximum velocities of 0.20 m s −1 . The momentum balance in this region is between local acceleration and friction. A cold-water band is developed during the period of maximum upwelling. [ABSTRACT FROM AUTHOR]

At the Gulf of Cadiz (GoC), poleward currents leaning along the coast alternate with coastal upwelling jets of opposite direction. Here the patterns of these coastal countercurrents (CCCs) are derived from ADCP data collected during 7 deployments at a single location on the inner shelf. The multiyear (2008–2014) time-series, constituting ~ 18 months of hourly records, are further analysed together with wind data from several sources representing local and basin-scale conditions. During one deployment, temperature sensors were also installed near the mooring site to examine the vertical thermal stratification associated with periods of poleward flow. These observations indicate that the coastal circulation is mainly alongshore and barotropic. However, a baroclinic flow is often observed shortly at the time of flow inversion to poleward. CCCs develop all year-round and exclusively control the occurrence of warm coastal water during the upwelling season. On average, one poleward flow lasting 3 days was observed every week, corresponding to CCCs during ~ 40% of the time without seasonal variability. Thus, the studied region is distinct from typical upwelling systems where equatorward coastal upwelling jets largely predominate. CCCs often start to develop near the bed and are frequently associated with 2-layer cross-shore flows characteristic of downwelling conditions (offshore near the bed). In general, the action of alongshore wind stress alone does not justify the development of CCCs. The coastal circulation is best correlated and shows the highest coherence with south-eastward wind in the basin that proceeds from the rotation of southward wind at the West coast of Portugal, hence suggesting a dominant control of large-scale wind conditions. In agreement, wavelet analyses indicate that CCCs are best correlated with alongshore wind occurring in a band period characteristic of the upwelling system (8–32 days). Furthermore, in the absence of wind coastal currents tend to be poleward during summer. This set of observations supports that CCCs develop in response to the unbalance of an alongshore pressure gradient during the relaxation of (system-scale) upwelling-favourable winds, oriented south-eastward in the basin. The relaxation periods defined based on this wind direction show a good correspondence with the periods of poleward flow. [ABSTRACT FROM AUTHOR]

The original method is presented for parameterization of surface wind-driven currents in the Black Sea using drifters, altimetry, and wind data. Buoys velocities for the cases with small time variability of the altimetry-derived geostrophic currents were parameterized as a function of the amplitude coefficient b and rotation angle a between wind and residual current direction at drifter drogue depth ∼ 15 m. The results show that the variability of a and b for different cases is very high: angle a changes from 10 to 90° to the right, amplitude coefficient b varies from 0.01 to 0.03. At the same time, it is shown that amplitude coefficient b and rotation angle a on 15 m depth are not independent parameters and there is a robust dependence between them. Using quasi-Ekman theory and the revealed dependence, we can determine parameterization for wind-driven currents exactly on the surface. As a result, we found that wind-driven currents at z = 0 m are directed on b = 13° to the right of wind direction with amplitudes equal to k = 2.8 % of wind velocity. It is important that these parameters did not depend on Ekman layer depth and can be used under different ocean conditions. This parameterization is used to compute the total surface currents and determine the trajectories of oil slick propagation observed on satellite images. Comparison shows that the presented method can be successfully used to predict floating objects trajectories basing on the satellite data. [ABSTRACT FROM AUTHOR]

It is shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in southeastern Australia, is situated in a region that may experience noticeable changes in longshore wind, wave and ocean currents compared to present day climate variability as a consequence of the southward shifting subtropical ridge (STR) predicted in global climate change models. These changes could modify sediment transport in the littoral zone and impact the coastline position. Thirty-year hindcasts of winds, coastal currents and waves are shown to agree well with available observations and provide a long-term dataset of the climate variability. Hindcasts of coastal ocean currents and waves indicate that while the annual net mean wave and current transport are in opposing directions, their seasonal adjusted monthly anomalies are positively correlated. Furthermore they are also correlated with the position of the STR location index. On seasonal to annual time scales a weak connection between the transport variables and Southern Oscillation Index (SOI) is found. It appears that during multiple years of positive (negative) SOI conditions the STR is located north (south) of its mean monthly position, resulting in anomalous eastward (westward) transport. The four climate models used in this study indicate a southward shift in the STR for most months under a high emission future. In summer months the shift in the STR results in both increased summer westward wind-driven currents and westward wave forcing. Changes in winter months are less related to the STR location and it is discussed that the contraction and increased intensity of the westerly storm belt linked to Southern Annular Mode could possibly influence the transport. The analysis is presented at the coastal scale to provide insights into how these changes may affect net transport across the littoral zone in more detailed numerical nearshore sediment transport modelling. [ABSTRACT FROM AUTHOR]

Contrary to many previous reports, winds do drive currents along the shelf in the central portion of the Southern California Bight (SCB). Winds off Huntington Beach CA are the dominant forcing for currents over the nearshore region of the shelf (water depths less than 20 m). Winds control about 50–70% of the energy in nearshore alongshelf surface currents. The wind-driven current amplitudes are also anomalously high. For a relatively weak 1 dyne/cm 2 wind stress, the alongshelf surface current amplitudes in this region can reach 80 cm/s or more. Mid-depth current amplitudes for the same wind stress are around 30–40 cm/s. These wind-driven surface current amplitudes are much larger than previously measured over other nearshore shelf regions, perhaps because this program is one of the few that measured currents within a meter of the surface. The near-bed cross-shelf currents over the nearshore region of the Huntington Beach shelf have an Ekman response to winds in that they upwell (downwell) for down (up) coast winds. This response disappears further offshore. Hence, there is upwelling in the SCB, but it does not occur across the entire shelf. Subthermocline water in the nearshore region that may contain nutrients and plankton move onshore when winds are southeastward, but subthermocline water over the shelf break is not transported to the beach. The currents over the outer shelf are not predominately controlled by winds, consistent with previous reports. Instead, they are mainly driven by cross-shelf pressure gradients that are independent of local wind stress. [ABSTRACT FROM AUTHOR]

Physical exchange between estuarine and continental shelf waters impacts flushing dynamics of the estuary and determines rates of ocean inputs of nutrients and plankton. To investigate the occurrence and propagation of shelf water intrusions into the Narragansett Bay estuary, we collected velocity data near the estuarine–shelf interface during three summer periods. These data were compared to environmental forcing factors, including wind velocity, tidal mixing and river discharge. Results suggest a background cyclonic flow within the two passages of the estuary based on mean inflow in the channel on the eastern side of the estuary and mean outflow on the western shoals. Within the lower estuary this background circulation was perturbed by channel-parallel winds. On the shelf outside of the estuary, winds parallel to the coast were associated with cross-shelf flow of deep water. Strong pulses in estuarine–shelf exchange flow fell into two wind-driven modes: responses to direct forcing by down-estuary wind or rebounds following relaxation or reversal of up-estuary wind. Rebound events were common, providing the most dramatic perturbations to the mean background estuarine circulation. A reduction in exchange between Narragansett Bay and shelf waters during prevailing up-estuary winds in the summertime and short-lived pulses in exchange flow under wind reversal events are expected to affect nutrient fluxes and dynamics of hypoxia in the estuary. [ABSTRACT FROM AUTHOR]

This study examines seasonal circulation, hydrography, and associated spatial variability over the inner shelf of the northern South China Sea (NSCS) using a nested-grid coastal ocean circulation model. The model external forcing consists of tides, atmospheric forcing, and open boundary conditions based on the global ocean circulation and hydrography reanalysis produced by the Hybrid Coordinate Ocean model. Five numerical experiments are conducted with different combinations of external forcing functions to examine main physical processes affecting the seasonal circulation in the study region. Model results demonstrate that the monthly mean circulation in the study region features the Guangdong Coastal Current (GCC) over coastal waters and the South China Sea Warm Current (SCSWC) in the offshore deep waters. The GCC produced by the model flows nearly southwestward in winter months and northwestward in summer months, which agrees with previous studies. The SCSWC flows roughly northeastward and is well defined in summer months. In winter months, by comparison, the SCSWC is superseded by the southwestward strong wind-driven currents. Analysis of model results in five different experiments demonstrates that the monthly mean circulation over coastal and inner shelf waters of the NSCS can be approximated by barotropic currents forced by the southwestward monsoon winds in winter months. In summer months, by comparison, the monthly mean circulation in the study region is affected significantly by baroclinic dynamics associated with freshwater runoff from the Pearl River and advection of warm and saline waters carried by the SCSWC over the NSCS. [ABSTRACT FROM AUTHOR]

The basic assumptions for the depth-dependent Ekman equations are presented. An analysis of three wind stress time series, from different geographical locations, is performed: The results lead to interpret the wind stress as a stochastic process, with components fluctuating with deterministic frequencies. The stochastic equations coupling wind stress and ocean currents are formulated; their solutions are stochastically bounded. Results of numerical simulations are given to show the main behaviors of the system. [ABSTRACT FROM AUTHOR]

Ceará shelf waters response to steady and transicnt wind forcing, from Ponta Cajuais (04°42'S, 37°19.5'W) to Ponta de Itapagé (02°50.5'S, 40000'W), was studied using a hydrodynamic numerical model. The finitc difference model was based upon the equations for a barotropic ocean in general form: advective and quadratic surface and bottom stress terms were included. Seasonal differences in the shelf waters response were characterized by simulation of summer and winter forcing. Such experiments wcre conducted for both f and equatorial beta plane domains, without significative differences in the results. Transient shelf waters response were investigated using surface winds from the Fortaleza airport , during the period extending from 14/03 to 25/03n9. Model results were compared to current data collected during the same period; modeled currents were able to roughly describe observed current pattem, but not current intensity.A resposta das águas da plataforma continental do Ceará, de Ponta Cajuais (04°42'S, 37° 19,5'W), à forçante do vento estacionária e transiente foi estudada através de um modelo numérico hidrodinâmico. O modelo, na forma de diferenças finitas, utiliza as equações do movimento e da continuidade de massa para um oceano barotr6pico no caso mais geral: estão incluídos os termos advectivos, bem como o atrito com o fundo e a tensão de cisalhamento do vento, ambos parametrizados na forma quadrática. Variações sazonais na resposta estacionária das águas da plataforma continental, da área estudada, foram caracterizadas pela simulação das condições de verão e inverno da região. Os experimentos foram realizados no plano f e no plano p equatorial sem diferenças significativas nos resultados. A resposta transiente das águas da plataforma continental, da região escolhida, foi investigada usando uma série temporal de vento de superfície do Aeroporto de Fortaleza do período de 14 à 25 de março. O período escolhido para a simulação coincide com o período em que há dados observados de corrente na região. A corrente modelada descreveu o padrão da corrente observada mas não sua intensidade.

Abstract: A three-dimensional numerical model, Estuarine, Coastal and Ocean Modeling System with Sediments (ECOMSED), is employed to study the mechanism of plume front in the Pearl River Estuary (PRE) in detail. The model is forced by winds, tides and river discharges. The modeled results of tidal elevation, current velocity and salinity are in reasonable agreement with observational data in the PRE. By analyzing momentum and saltwater transport balance equations, it is found that the wind stress term, the pressure gradient term and the local time derivative term of velocity are dominant in the momentum equation, while the local time derivative term, the horizontal advective term and the vertical mixing term of salinity are dominant in the salinity transport equation. The residual current at surface along the plume front is seaward and stronger, whilst that in the bottom layer is mainly landward. A series of sensitive experiments is also run to examine the responses of plume front to changes of river discharges at different inlets in Lingdingyang Bay and interannual variation of northeast winds in winter. The location of plume front responds differently to the change of river discharge at different inlets. An increase in the river discharge at Dahu inlet seems to affect the location of plume front most among the four river inlets, it makes the plume front move eastward and southward wholly; the variation of river discharge at Nansha or Fengmamiao inlet on the location of plume front is more local and weaker; whilst the variation of river discharge at Hengmen inlet has little effect on the plume front. The location of plume front also changes in response to the interannual variation of northeast winds in winter, the stronger or the more eastward the winds are, the more westward the plume front moves, and only in the northern PRE, the response of plume front to the variation of wind speeds is largely different from that to the variation of wind directions. [Copyright &y& Elsevier]

Simultaneous 40 h low-passed wind, current and sea level data in the Channel of São Sebastião (CSS) and atmospheric pressure and sea level data in the South Brazil Bight (SBB) during winter of 1979 were analysed and compared. Currents in the CSS were predominantly northeastward, associated with frontal southerly winds. Current reversals occurred between meteorological disturbance passages. There were significant correlation between alongchannel components of wind and current, with a time lag of 12-18 h, wind leading; and between alongchannel component of current and sea level, with a time lag of 6-12 h, current leading. Most of the variance in the CSS series is concentrated in two frequency bands: 11-16 d and 3 d. SBB series also show high variance in those two bands. Coherences in those two bands show significant values when calculated between alongchannel components of wind and current, and sea level, in the CSS. Those three last signals were almost in phase in the 11-16 d band; and there was a lead of 16 h (25 h) by wind over current (sea level) in the 3 d band. There are several indications that in die subtidal band currents in the CSS are not totally locally forced.Dados simultâneos de vento, corrente e nível do mar no Canal de São Sebastião (CSS), e de pressão atmosférica e nível do mar na Plataforma Continental Sudeste (PCS), coletados durante o inverno de 1979, foram analisados e comparados. Todas as séries de tempo foram previamente filtradas utilizando um filtro passa baixa com corte em 40 h. As correntes no CSS foram predominantemente para nordeste, em associação com ventos vindos do sul juntamente com sistemas meteorológicos frontais. Reversões de corrente ocorreram entre as passagens das perturbações atmosféricas. Foram significativas as correlações entre as componentes paralelas ao canal do vento e da corrente, havendo um deslocamento de 12-18 h, com liderança do vento; e também entre a componente paralela ao canal da corrente e o nível do mar, com deslocamento de 6-12 h, corrente liderando. A maior parte da variância nas séries de tempo para o CSS está concentrada em duas faixas de freqüência: 11-16 d e 3 d. Essas duas faixas também apresentam valores significativos quando calculadas entre as componentes paralelas ao canal do vento e da corrente, e o nível do mar no CSS. Esses três últimos sinais estavam quase em fase na faixa de 11-16 d; e havia uma liderança de 16 h (25 h) pelo vento sobre a corrente (nível do mar) na faixa de 3 d. Existem várias indicações que em baixas frequências as correntes no CSS não são forçadas localmente em sua totalidade.

Abstract: The Eastern Bering Sea shelf is divided into distinct hydrographic domains by structural fronts. Despite frontal obstructions to cross-shelf transport, each year large oceanic copepods—primarily Neocalanus spp.—are known to dominate the biomass of the outer-shelf zooplankton communities, and in some years are advected into the middle-shelf domain. Using ROMS (the Regional Ocean Modeling System), coupled with a float tracking model designed to represent ontogenetic vertical migration behavior of Neocalanus, we explored the mechanisms, timing, and location of the transport of oceanic zooplankton onto the eastern Bering Sea shelf from overwintering sources along the Gulf of Alaska and Bering Sea shelf breaks, under a variety of environmental conditions. Our float tracking experiments suggest that the timing of on-shelf transport and the distribution of oceanic zooplankton on the shelf can vary substantially between one year and another. The Bering, Pribilof, and Zhemchug Canyons and Cape Navarin were all regions of elevated on-shelf float transport. Wind direction was the primary factor controlling inter-annual variability in the timing, amount, and location of the on-shelf transport of our Neocalanus floats. Float transport across the northern and southern shelves responded in opposite directions to inter-annual differences in wind forcing: southeasterly wind enhanced on-shelf transport of the Neocalanus floats along the southern shelf but suppressed on-shelf transport over the northern shelf. Conversely, northwesterly wind suppressed on-shelf zooplankton transport onto the southern shelf but promoted enhanced transport around Cape Navarin on the northern shelf. Transport of the Neocalanus floats onto the shelf can be very episodic, reflecting the short duration of winds that promote on-shelf transport. Relatively short (days to weeks) periods of southeasterly wind between March and April significantly impacted the number of floats transported onto the shelf. The relative importance of different source areas to supplying oceanic zooplankton to the Bering Sea shelf does not appear to vary much from year to year. Our model results suggest that the Neocalanus found on the southern shelf most likely originate from overwintering sites in the Alaska Stream or the Eastern Bering Sea shelf break south of the Pribilof Islands, while Neocalanus found on the northern shelf most likely originate from sites north of the Pribilof Islands. [Copyright &y& Elsevier]

Lac d'Armor (49°27′S, 69°42′E) is a medium-sized, fjord-type lake located on the ‘Grande Terre’ island of the Kerguelen archipelago. A dense grid of high-resolution reflection seismic profiles was collected from this lake basin. The seismic stratigraphic facies reveal a last deglaciation to Holocene infill comparable to the seismic facies found in other glacigenic lakes all over the world. Remarkable features in the seismic stratigraphy are mounded structures found at the southern edge of both sub-basins. The sediment mounds can be interpreted as sediment drifts created by wind-induced bottom currents. The onset of the build-up of these drifts initiated at some point in the Holocene and indicates a strengthening of the southern Westerlies, which are currently the dominant winds on this island. [ABSTRACT FROM AUTHOR]

Prediction of mixing intensity of water masses in riverine Lake Tegel (Berlin, Germany) can be used to trace the fate of pollutants that enter the lake through several inflows. Because the contributions of each inflow have not yet been quantified and because the lake features complex bathymetry and numerous islands, a hydrodynamic circulation model with high spatial resolution and dynamic wind forcing is useful. We applied the two-dimensional version of the Princeton Ocean Model to separate the influences of wind and river discharge on the currents and mass transport in Lake Tegel. For model validation, we compared the simulation results with 1 year of electrical conductivity data, which was used as a conservative tracer to distinguish between water from the River Havel and water supplied by a smaller second inflow. Calculation of currents alone is insufficient to investigate water exchanges between rivers and lakes, especially when several islands create multiple pathways for river intrusion. Therefore, mass transport simulations are applied. Our calculations based on archetypical scenarios indicate that the proportion of (polluted) water from the River Havel in the main basin of Lake Tegel fluctuates with river discharge and wind, which either amplify or neutralize each other. [ABSTRACT FROM AUTHOR]

Abstract: A network of HF radars operated in the northeastern Adriatic Sea in the period September 2007 to August 2008. Surface currents were collected with the purpose of studying the temporal and spatial modes of surface circulation in the area. Their dependence on local wind forcing was investigated using wind records from coastal stations and the mesoscale meteorological model ALADIN/HR. EOF decomposition, spectral and tidal analyses, and time-lagged correlation extracted the dominant features in the area and their time scales. The time-averaged flow presented a cyclonic circulation pattern with relatively weak currents and standard deviations comparable to average values. Three dominant current patterns were extracted by the EOF analysis, which accounted for about 70% of total variance. In the region, wind was the major source of current variability over a wide portion of frequencies, whereas tidal forcing was weak and limited to the semidiurnal and diurnal frequencies, representing 10%–20% of the total variance. The response to wind forcing was immediate with veering angles consistent with Ekman dynamics in the majority of the area. Coherence analyses revealed strong correlation within the sub-tidal and diurnal bands, the latter related to diurnal sea-breezes variability. The seasonal variability of the inertial motions was also observed in the area. [Copyright &y& Elsevier]

Every beginning student of geophysical fluid dynamics knows that steady--state wind-driven currents are directed to the right of the wind in the northern hemisphere. In contrast, the fact that wind-induced currents may under some specific conditions be of the opposite direction is mentioned in only a few papers. Here, a succession of simple explicit solutions is used to illustrate that the wind varying at subinertial frequencies always generates currents directed to its right, whereas at superinertial frequencies the wind rotating clockwise (counterclockwise) coincides with currents directed to its left (right). The difference is related to a dynamics differing in the two frequency bands. At subinertial frequencies, friction is primarily balanced by the Coriolis acceleration, and therefore the currents vary in phase with the wind while being directed to its right. At superinertial frequencies, the primary balance is between friction and local acceleration, implying that the currents lag behind the wind that causes them while pointing down the forcing. The former dynamic regime was originally considered by Vagn Walfrid Ekman (in 1905), the latter by Karl Jakob Zöppritz (in 1878). The destiny of the two contributions, however, was completely different: Ekman's is widely appreciated today, whereas Zöppritz's is rarely mentioned. Although Zöppritz's findings were adversely influenced by his consideration of the laminar rather than turbulent viscosity, his neglect of the Coriolis acceleration was acceptable and his solution therefore formally correct at superinertial frequencies. [ABSTRACT FROM AUTHOR]

Abstract: Coastal currents in microtidal bays are assumed to be weak and random, promptly responding to variations in wind forcing. However wind effects can act at scales that vary from local to large scales. With the aim of examining the response of coastal flow to local and regional wind forcing and their relative importance as drivers of coastal circulation, current data were collected during five months during the summer 2009 in Palma Bay (western Mediterranean Sea). The data set is jointly analyzed with a primitive-equation model to characterize the circulation in the bay. Moored acoustic Doppler current profiler (ADCP) data shows that currents in the bay fluctuate widely in direction resulting in an almost negligible mean current (<1.5cm/s). This strong variability is mainly attributed to two major wind forced mechanisms interacting in the bay: island trapped waves (ITWs) propagating at an island scale and locally wind-induced mass balance. Wind forced oscillations at periods of 60 and 24h dominate current variability. The fluctuations at 60h are associated with the first radial and first azimuthal mode of ITWs generated by remote wind. Weak ITWs are associated with currents flowing parallel to the coast, whereas more intense ITWs form an anticyclonic gyre over the southeastern part of the bay due to flow separation at Enderrocat Cape. At the period of 24h, the wind has two effects: the first radial and second azimuthal mode of ITWs and a local wind-induced mass balance in response to the sea breeze. Variations in wind and consequent changes in coastal circulation are a major contributor to coastal water renewal, and hence critically influence key environmental aspects such as water quality or marine organism dispersal in Palma Bay. [Copyright &y& Elsevier]

Tidal and wind-driven surface currents in the German Bight between shallow mudflats of the North Frisian islands and the island of Helgoland are studied using coastal high-frequency radar (HFR) observations and hindcasts from a primitive equation numerical model. The setup of the observational system is described, and estimates of expected measurement errors are given. A quantitative comparison of numerical model results and observations is performed. The dominant tidal components are extracted from the two data sources using tidal harmonic analysis and the corresponding tidal ellipses are defined. Results show that the spatial patterns of different tidal ellipse parameters are consistent in the two data sets. Model sensitivity studies with constant and variable salinity and temperature distributions are used to study density-related mechanisms of circulation. Furthermore, the role of the surface wind field in driving the German Bight circulation is investigated using the complex correlation between wind and surface current vectors. The observed change of the respective correlation patterns from the coastal to open ocean is shown to be due to a combination of density effects, the coastline and topography. The overall conclusion is that HFR observations resolve the small-scale and rapidly evolving characteristics of coastal currents well in the studied area and could present an important component for regional operational oceanography when combined with numerical modelling. Some unresolved issues associated with the complex circulation and large instability of circulation in front of the Elbe River Estuary justify further considerations of this area using dedicated surveys and modelling efforts. [ABSTRACT FROM AUTHOR]

Abstract: Measurements from recently installed 5MHz high-frequency radar (CODAR) stations south of Point Arena, California, are used to describe surface current patterns during the upwelling season (June–August 2007). The systems provide hourly current maps on a 5-km grid, covering a region from approximately 10 to 150km offshore (the continental shelf into the deep ocean). These HF-radar observations provide an unprecedented view of circulation in this “coastal transition zone”, between the wind-driven circulation over the shelf and the California Current circulation offshore. Circulation patterns include: (1) bifurcation of the coastal upwelling jet downstream of Point Arena into an along-shelf (down-coast) branch and an offshore branch, and (2) a large-scale anticyclonic meander that often develops into an eddy-like recirculation south of the bifurcation. The “recirculation” feature extends well offshore, with surface currents 50–100km from the coast consistently opposing the wind stress. The spatial and temporal evolution of the surface current features during upwelling events affects surface transport from Point Arena to areas in the south, increasing the travel time of a substantial fraction of newly upwelled water from a few days to roughly two weeks. Thus, surface currents even far offshore influence coastal transport of nutrients, phytoplankton and larvae on ecologically relevant timescales, with resultant connectivity patterns very different than implied by a simple examination of the mean flow. [Copyright &y& Elsevier]

Abstract: We examine the establishment of form stress in the spinup of a rotating isopycnal wind-driven channel model, with reference to the Antarctic Circumpolar Current. Initially, the force balance resembles Ekman layer transport, where zonal surface winds are balanced by the Coriolis forces in the upper layers, while the bottom layers consist of an opposing meridional flow balanced by topographic form stress. As the meridional transport increases, the isopycnal slopes and zonal transport also increase and the flow becomes baroclinically unstable, leading to the development of interfacial form stresses due to small-scale baroclinic eddies. This form stress alters the force balance of the layers, causing the system to geostrophically readjust to new states with progressively lower meridional transports. This trend continues until the meridional transport stops and the current is balanced solely by winds and form stress. The final state is a turbulent flow consisting of a several meandering jets that are maintained by the mesoscale eddy field. Our results resemble recent observations of the Antarctic Circumpolar Current and illustrate the contribution of mesoscale eddies to the force balance of the Southern Ocean. [Copyright &y& Elsevier]

Abstract: A general ocean circulation model is used to study the dynamics of the cross-shelf circulation in the Yellow and East China Seas in winter. The model results show that the shelf circulation in winter is induced primarily by the northerly monsoonal winds. Compared with the wind-driven circulation, the Kuroshio-forced circulation over the shelf is very weak. The westward shift of the Yellow Sea Warm Current is produced by the northerly winds through the generation of a sea-level trough off the Subei coasts and a sea-level ridge along the center of the Yellow Sea topographic trough. The sea-level trough off the Subei coasts is produced because the sea level at the coast is tied to the depression in the northern Yellow Sea and is moderated by the surface Ekman transport of the northerly monsoon. The sea-level ridge along the center of the Yellow Sea topographic trough is produced because the sea level along both the east China and the west Korea coasts decreases. The structure of the sea level gives rise to a geostrophic intrusion against the wind along the western side of the Yellow Sea trough and southward movement of the Korean coastal currents along the eastern side of the trough. Under the northerly wind forcing, the currents over the East China Sea shelf flow southward in an opposite direction to the Yellow Sea Warm Current. The resulting divergence, therefore, forces the Yellow Sea Coastal Current to move offshore to form the East China Sea Current. At the head of the submarine canyon off the Changjiang mouth, a northward intrusion is produced by downwind pile-up of sea level and by the wind-curl forcing. The Yellow Sea Warm Current and the canyon intrusion then extend southward through the propagation of topographic Rossby waves to reverse the wind-driven currents over the East China Sea shelf, generating the offshore and inshore branches of the Taiwan Warm Current, both of which serve to raise the sea level over the East China Sea shelf. The final adjustment to the northerly wind forcing is a sea-level tilt to the south, which forces the East China Sea Current to flow cross the continental shelf and slope into the Okinawa Trough. The numerical experiments thus suggest that both the inshore and offshore branches of the Taiwan Warm Current are forced primarily by the northerly winds in winter. [Copyright &y& Elsevier]

Abstract: Investigations into the descriptive hydrodynamics of a semi-enclosed reefal bay showed that inner bay waters re-circled the reef and particular forcing conditions of wind and tide retarded or enhanced this circulation. Fringing reef parabola, partially enclosing bays, are generally accepted as the limit of the bay dynamics. The dynamics displayed at Wreck Bay, on the southeast coast of Jamaica, however, showed the reef as the heart of main circulation and therefore the centre of the functioning bay. Results from field measurements of the spatial and temporal variability in circulation revealed that inner bay water surging from the back-reef exited quickly through a gap in the reef (channel flow, up to 60cms−1), diverged on the fore-reef, then either re-entered the back-reef to become closed circum-reef circulation (CRC), or continued along the fore-reef as open CRC. Variation in the wind regime controlled the relative importance of wind or tides to driving circulation and bay emanation. Wind speeds above 5ms−1 were found to be the dominant forcing factor and, combined with tides, accounted for 60% of the variability in CRC when the sea-breeze developed during early summer and again when the land-breeze strengthened during the winter deployment. Open CRC was extended seawards when channel flow currents displayed occasional surges associated with strong wind-driven currents combined with similar incident wave approach. This led to change in bay dynamics by extreme expansion in bay characteristics. The opposite scenario occurred on rare occasions of low tide with wind calms, when channel flow reversed into the inner bay and flow over the emergent reef was reduced, leading to the most extreme contraction of bay characteristics. [Copyright &y& Elsevier]

Abstract: Recent studies indicated sea surface temperature (SST) cooling of 6–7 °C and a phytoplankton bloom of 3 mg chlorophyll-a m−3 during the passage of Hurricane Katrina (23–30 August 2005) in a region from 23.5° to 25.5°N and 85° to 83°W in the Gulf of Mexico (GoM). Employing a 20-layer, 1/25° horizontal resolution nested GoM HYbrid Coordinate Ocean Model (HYCOM), the evolving three-dimensional ocean response to Hurricane Katrina in the GoM was examined. During the passage of Hurricane Katrina, analysis of model surface and subsurface dynamics in this region revealed strong upwelling/downwelling of 1.5–2×10−4 m s−1, wind-driven currents dominating the surface circulation, and near-inertial oscillations following Hurricane Katrina. Associated with the storm, the 26 °C isotherm was raised by 28 m, generating SST cooling of 3–4 °C and salinity freshening of 0.1–0.2 in less than 24 h. Comparison of model-simulated SSTs with in situ buoy data and satellite observations revealed that model SSTs were cooler by 1–2 °C and had a greater spatial extent of cooling. Analysis of heat budget terms in the mixed layer (20 m) indicated that surface heat flux accounted for pre-storm temperature changes, and wind-driven mixing (−3375 W m−2) dominated net upper-ocean cooling (−2464 W m−2) during Hurricane Katrina. At 50 m depth, temperature changes were largely due to vertical advection associated with upwelling and downwelling processes. A temperature–nitrate relationship was derived to illustrate the potential contribution that nitrate influx had upon the satellite-observed phytoplankton bloom associated with Hurricane Katrina. Comparison of calculated nitrate agreed reasonably well with in situ nitrate profiles in the interest region. Nitrate concentrations of 3.7 μM were entrained from 30 m depth during hurricane passage. An approximate nitrate to chlorophyll-a ratio provided a chlorophyll-a value of 3 mg m−3, which was consistent with that derived from satellite. Thus, the elevated chlorophyll-a concentration following the passage of Katrina was greatly influenced by nitrate entrainment into the surface layer through vertical mixing and Ekman divergence. [Copyright &y& Elsevier]

Abstract: Surface patterns of the low-frequency current in a 20×30km region in front of the Venice Lagoon were analysed from a 13-month-long HF radar data set. Surface circulation was related to prevalent wind regimes in the area and to the tidal flow through the lagoon inlet. Three different categories of wind-forcing were defined: bora (NE wind), sirocco (SE wind), and finally the category containing all other wind directions and calms (winds lower than 3m/sec). Mean flow and vorticity spatial distributions were discussed for different wind conditions. The coastal area about 5km wide is characterized by a flow field with maximum vorticity. Outside the coastal boundary layer the interior flow is part of the Adriatic basin-wide cyclonic circulation. Two counter-rotating vortices of the dimension of about 4–5km were evidenced in the average flow field in front of the lagoon inlet (Malamocco inlet) in all situations except for the bora. The vortex-pair is probably associated with the tidal flow through the inlet. The bora wind induces a strong southward coastal jet detached from the coast by about 5km homogenizing the flow and eliminating the dipole. The average coastal flow pattern in calm wind conditions was also analysed as a function of the strong inflow/outflow (currents in the inlet>0.7ms−1) from the lagoon inlet. In both cases the vorticity pattern is similar, with the negative vorticity to the left of the inlet and positive to the right looking seaward. [Copyright &y& Elsevier]

Abstract: A model simulation of the circulation on the continental shelf of the Khanh Hoa province in central Vietnam during the year 2004 is presented. The model, a three-dimensional baroclinic z-coordinate model (the Hamburg Shelf Ocean Model), is implemented with a horizontal resolution of about 1 km. It is initialised with temperature and salinity fields taken from the Levitus data, and by the two main tidal constituents. The model is forced by daily fields of wind stress, air temperature, wind speed, and cloudiness taken from NCEP, and by monthly mean river runoff values. At the open boundary sea surface displacements are prescribed by the tidal variation and by the steric height determined from the density anomalies determined from climatological values of temperature and salinity. The modelled circulation reflects the monsoonal forcing fields, and reveals downwelling during winter and upwelling during summer. The modelled hydrography is compared with measured profiles, and some biases are found. The flushing times of three bays along the Khanh Hoa coast are calculated. The relative influence of river runoff, tides, and weather on the flushing times is discussed. [Copyright &y& Elsevier]

Abstract: Winter observations of shelf and slope hydrography and currents in the inner Gulf of Tehuantepec are analysed from two field studies in 1989 and 1996 to specify the variability of near-shore conditions under varying wind stress. During the winter period frequent outbursts of ‘Norte’ winds over the central Gulf result in persistent alongshore inflows along both its eastern and western coasts. Wind-induced variability on time scales of several days strongly influences the shelf currents, but has greater effect on its western coast because of the generation and separation of anticyclonic eddies there. The steadier inflow (∼0.2ms−1) on the eastern shelf is evident in a strong down-bowing of shallow isosurfaces towards the coast within 100km of shore, below a wedge of warmer, fresher and lighter water. This persistent entry of less saline (33.4–34.0), warmer water from the southeast clearly originates in buoyancy input by rivers along the Central American coast, but is augmented by a general shoreward tendency (0.2ms−1) in the southeastern Gulf. The resultant shallow tongue of anomalous water is generally swept offshore in the head of the Gulf and mixed away by the strong outflow and vertical overturning of the frequent ‘Norte’ events but during wind relaxations the warm, low-salinity coastal flow may briefly extend further west. In the head of the Gulf, flow is predominantly offshore (<0.2ms−1) as the alongshore component alternates eastward and westward in association with elevation or depression, respectively, of the pycnocline against the shore. More saline, open ocean water is introduced from the north-western side of the Gulf by the inflow along the west coast. During extended wind relaxations, the flow becomes predominantly eastward beyond the shelf while nearshore the coastally trapped buoyant inflow from the southeast penetrates across the entire head of the gulf at least as far as its western limit. On the basis of these and other recent observations, it seems that the accepted view of a broad, persistent Costa Rica Coastal Current (CRCC) is the result of averaging over many relatively sparse observations and that the instantaneous CRCC is a highly variable and convoluted flow around and between constantly changing eddies. The buoyancy-driven shelf current reported here forms a hitherto unrecognized, but major, component of this CRCC system. [Copyright &y& Elsevier]

Abstract: We present an analytical model to decompose complex along-channel and transverse residual flows into components induced by individual mechanisms. The model describes the transverse distribution of residual flows in tidally dominated estuaries. Scaling and perturbation techniques are used to obtain analytical solutions for residual flows over arbitrary across-channel bed profiles. The flows are induced by horizontal density gradients, tidal rectification processes, river discharge, wind, channel curvature and the earth''s rotation. These rectification processes induce residual flows that are up-estuary to the right and down-estuary to the left of an estuarine channel (looking up-estuary in the northern hemisphere). The tidal rectification processes fundamentally change the transverse structure of along-channel residual flows in many tidal estuaries, as these processes cause the flows to be internally asymmetric about the mid-axis of the channel for relatively large tidal velocities, steep channels or narrow estuaries. In addition, velocity scales are derived from the analytical solutions to estimate the relative importance of the various residual flow mechanisms from estuarine parameters. A case study of a transect across the Upper Chesapeake Bay showed that important features of the residual flow observed in that transect are reproduced and explained by the analytical model. The velocity scales were able to identify the relevant residual flow mechanisms as well. The tidal rectification processes considered here result from advection of along-channel tidal momentum by Coriolis-induced transverse tidal currents. [Copyright &y& Elsevier]

Abstract: The response of the density-driven circulation in the Chesapeake Bay to wind forcing was studied with numerical experiments. A model of the bay with realistic bathymetry was first applied to produce the density-driven flow under average river discharge and tidal forcing. Subsequently, four spatially uniform wind fields (northeasterly, northwesterly, southwesterly, and southeasterly) were imposed to examine the resulting cross-estuary structure of salinity and flow fields. In general, northeasterly and northwesterly winds intensified the density-driven circulation in the upper and middle reaches of the bay, whereas southeasterly and southwesterly winds weakened it. The response was different in the lower bay, where downwind flow from the upper and middle reaches of the bay competed with onshore/offshore coastal flows. Wind remote effects were dominant, over local effects, on volume transports through the bay entrance. However, local effects were more influential in establishing the sea-level slopes that drove subtidal flows and salinity fields in most of the bay. The effect of vertical stratification on wind-induced flows was also investigated by switching it off. The absence of stratification allowed development of Ekman layers that reached depths of the same order as the water depth. Consequently, bathymetric effects became influential on the homogeneous flow structure causing the wind-induced flow inside the bay to show a marked transverse structure: downwind over the shallow areas and upwind in the channels. In the presence of stratification, Ekman layers became shallower and the wind-induced currents showed weaker transverse structure than those that developed in the absence of stratification. In essence, the wind-driven flows were horizontally sheared under weak stratification and vertically sheared under stratified conditions. [Copyright &y& Elsevier]

Abstract: During 9–16 November 2001 the western Mediterranean Sea was lashed by one of the most extreme storms of the last decades. Current meter data from seven moorings in the Palamós submarine canyon (northwestern Mediterranean) are analyzed to understand the vertical propagation of near-inertial energy generated by the storm. The daily inertial rotary components are examined for evidence of free and forced near-inertial oscillations. Free near-inertial motions are increased during the storm, although they are larger outside the canyon than inside. Conversely, forced near-inertial motions are relatively large inside the canyon but are almost negligible outside. Based on the results of a three-dimensional ocean circulation model, these differences are shown to be caused by the presence of a storm-generated alongshore front. The mechanisms by which near-inertial energy propagates are distinct at each side of the front. On the onshore side of the front (inside the canyon), free near-inertial motions are rapidly carried away by normal inertial waves, and wave reflection off canyon wall is responsible for the dissipation of free near-inertial motions and enhancement of forced near-inertial motions. On the offshore side of the front (outside the canyon), on the other hand, free near-inertial motions propagates first downward with anomalously low frequency internal waves and are then advected southward and offshore by the mean flow. [Copyright &y& Elsevier]

Abstract: The baroclinic response of a stratified coastal embayment (Lunenburg Bay of Nova Scotia) to the observed wind forcing is examined using two numerical models. A linear baroclinic model based on the normal mode approach shows skill at reproducing the observed isotherm movements and sub-surface currents during a time of strong stratification in the bay. The linear model also shows that the isotherm movement in Lunenburg Bay is influenced by the wind forcing and propagation of baroclinic Kelvin waves from neighbouring Mahone Bay. The effects of nonlinearity and topography are investigated using a three-dimensional nonlinear coastal circulation model. The nonlinear model results demonstrate that the nonlinear advection terms generate a gyre circulation at the entrance of Lunenburg Bay, and the slope bottom topography at the mouth of the bay strengthens the sub-surface time-mean inflow on the southern side of the bay. A comparison of model-calculated currents in different numerical experiments clearly shows that baroclinicity plays a dominant role in the dynamics of wind-driven circulation in Lunenburg Bay. [Copyright &y& Elsevier]

Abstract: The thermal structure of two Himalayan glacial lakes, Tsho Rolpa and Imja in the eastern Nepal, was examined by observations in the pre-monsoon seasons of 1996 and 1997. Tsho Rolpa had an isothermal mixed layer at water depths of 0–20m, whereas Imja did not possess such an isothermal layer. This difference in the thermal structure is explained by the condition that diurnal valley winds, producing wind-driven currents, blow strongly near the water surface of Tsho Rolpa, but very weakly near that of Imja. The wind observations above or near the end moraine indicated that a daily wind system of strong, diurnal valley winds and weak, nocturnal mountain winds is common to the lakes. It was suggested that with respect to the valley winds, the weak winds near the surface of Imja result from topographic screening effects of the upwind dead-ice zone and end moraine 20–25m higher than the water surface. In order to ascertain the topographic effects, three-dimensional numerical simulation of airflow was carried out by making topographic models of actual size in the calculation domain, corresponding to Tsho Rolpa and Imja and their surrounding topography. The simulation revealed that, when winds blow at constant velocities of 1–5ms−1 at 2m above the points corresponding to the weather stations, the wind velocity at 2m above the water surface for Imja is 33–42% smaller than for Tsho Rolpa. With increasing heights of the end moraine and dead-ice zone, the wind velocity near the lake surface efficiently decreased by decreasing the lake length from 3.1 or 2.2km to 1.2km. [Copyright &y& Elsevier]

Abstract: As an integral part of the WEST study of the role of wind-driven transport in shelf productivity, HF radar currents are analyzed to determine typical surface flow patterns off Bodega Bay in northern California. Radar-derived surface trajectories and surface velocity divergences are used to determine the proximal origins and destinations of surface waters in the area. Surface trajectory results show a strong bimodality, with water over the entire shelf originating in the north under upwelling conditions and waters over the inner/mid-shelf originating in the south during relaxation conditions. Outer shelf waters have more variable transport patterns during relaxation conditions, with limited equatorward or onshore movements being most typical. The destinations of surface waters starting at the outer shelf are predominantly offshore, with the majority of particles exiting the radar domain west of Pt Reyes along the shelf edge in less than 2 days. Significant proportions of water from the inner/mid-shelf are exported southward and exit the radar domain inshore or within 20km of the tip of Pt Reyes, creating possibilities for either nearshore retention in the Bodega region or entrainment of water into the Gulf of Farallons. Approximately 15% of all trajectories remained in the radar domain for 6 days, suggesting that a biologically significant percentage of larvae might be retained in the area for time periods approaching typical larval durations. Calculations of surface divergence indicate where vertical flux may be significant. An extensive area of positive divergence is observed off Bodega during upwelling conditions, while weakly convergent flow is observed where upwelling flows approach Pt Reyes. Positive divergence also is observed during relaxation periods when poleward flow separates from the shore just north of Pt Reyes. Estimates of vertical flux in these divergence zones point to a significant contribution of recently upwelled waters to the observed horizontal fluxes at the surface. Determination of the ultimate source and fate of phytoplankton-rich waters requires further analysis of the detailed time dependence of phytoplankton concentration relative to the time dependence of wind-forced currents. [Copyright &y& Elsevier]

Abstract: During the 1950s and 1960s, an extensive field study and interpretive effort was made by researchers, primarily at the Scripps Institution of Oceanography, to sample and understand the physical oceanography of the eastern tropical Pacific. That work was inspired by the valuable fisheries of the region, the recent discovery of the equatorial undercurrent, and the growing realization of the importance of the El Niño phenomenon. Here we review what was learned in that effort, and integrate those findings with work published since then as well as additional diagnoses based on modern data sets. Unlike the central Pacific, where the winds are nearly zonal and the ocean properties and circulation are nearly independent of longitude, the eastern tropical Pacific is distinguished by wind forcing that is strongly influenced by the topography of the American continent. Its circulation is characterized by short zonal scales, permanent eddies and significant off-equatorial upwelling. Notably, the Costa Rica Dome and a thermocline bowl to its northwest are due to winds blowing through gaps in the Central American cordillera, which imprint their signatures on the ocean through linear Sverdrup dynamics. Strong annual modulation of the gap winds and the meridional oscillation of the Intertropical Convergence Zone generates a Rossby wave, superimposed on the direct forcing, that results in a southwestward-propagating annual thermocline signal accounting for major features of observed thermocline depth variations, including that of the Costa Rica Dome, the Tehuantepec bowl, and the ridge–trough system of the North Equatorial Countercurrent (NECC). Interannual variability of sea surface temperature (SST) and altimetric sea surface height signals suggests that the strengthening of the NECC observed in the central Pacific during El Niño events continues all the way to the coast, warming SST (by zonal advection) in a wider meridional band than the equatorially trapped thermocline anomalies, and pumping equatorial water poleward along the coast. The South Equatorial Current originates as a combination of equatorial upwelling, mixing and advection from the NECC, and Peru coastal upwelling, but its sources and their variability remain unresolved. Similarly, while much of the Equatorial Undercurrent flows southeast into the Peru Undercurrent and supplies the coastal upwelling, a quantitative assessment is lacking. We are still unable to put together the eastern interconnections among the long zonal currents of the central Pacific. [Copyright &y& Elsevier]

Abstract: Data from an Acoustic Doppler Current Profiler (ADCP) mooring maintained during the winter of 2001 in 57m of water near Senigallia, Italy are used to describe the winter conditions of the Western Adriatic Current in the northern Adriatic Sea. Wind and water temperature measurements from the Acqua Alta tower in 19m water depth off Venice and winds from a 4-km resolution reanalysis model, COAMPS™, are used to interpret the ADCP data, especially with respect to currents generated by bora winds. At the ADCP site, mean depth-average current for the winter deployment period was 10.4cm/s toward 140°, roughly aligned with local bathymetric contours. Both mean currents and fluctuations about the means were highly barotropic during the winter. Southeastward (along-shore), mean currents increased slightly (1.8cm/s) with depth between 7 and 47m following a nearly linear trend. Offshore (cross-slope), mean currents only increased (2.0cm/s) deep in the water column, between 35 and 51m. Current variability was dominated by four bursts of currents in which flow toward the southeast greatly increased. These bursts followed bora winds, the timing of which was identified by measured winds at the Acqua Alta tower. Depth-averaged, de-tided currents exceeded 30cm/s during all four events, and reached 45cm/s during one event. Correlations between these along-shore currents and simulated wind stress from the COAMPS model were calculated over the whole north Adriatic. The cross-covariance between currents and wind stress had a spatial pattern similar to the bora wind itself, reaching maxima along the northern Adriatic coast, off the southern tip of Istria, and near Ilovik Island (14.5°N, 44.4°E). Wind stress in these regions had stronger correlation with currents at the mooring than did wind stress anywhere near the mooring. Bottom water at the mooring was too warm for it to have been North Adriatic Dense Water, except perhaps for a brief pulse of cold water associated with the third current burst on April 1st. [Copyright &y& Elsevier]

Abstract: Temporal variations of the current field on the shelf of the South East Atlantic off Walvis Bay were studied during austral summer and fall by moored current profiler and temperature-salinity recorder located on the shelf 20nm off Walvis Bay, Namibia. Spatial and temporal variations of the wind field in the South East Atlantic were investigated by 3-day averaged wind fields measured by the QuikSCAT satellite. The local wind was provided by a time series of hourly wind vectors measured on a moored buoy off Swakopmund. The significant tidal motion on the shelf off Walvis Bay is composed of the anticlockwise rotating barotropic semidiurnal constituents M2 and S2. The tidal currents are described to a first order by a barotropic deep ocean Kelvin wave. The land-sea breeze forces anticlockwise rotating diurnal variations of the current in the surface mixed layer and an opposite directed current below the thermocline, which compensates the mass flux normal to the coast in the surface layer. Most of the energy of the current fluctuations were concentrated around the local inertial period of . These fluctuations consisted of at least four significant anti-clockwise rotating vertical modes with amplitudes ranging between 10 and 20cm/s. On a large scale the amplitudes of inertial motions correlate with the wind fluctuations but locally the motions consist of a superposition of locally wind forced inertial oscillations and inertial waves generated at larger distances as well near the surface as close to the bottom. The vertical structure of the inertial motion suggests that it could be a possible candidate for mixing in the bottom boundary layer by differential advection. Coastal trapped waves of horizontal mode number less that four were observed at periods of about 7 days. The mean cross shelf circulation consisted of a two cell structure. The upper cell was made of the Ekman offshore current and a compensating onshore current at intermediate depth below the thermocline. The lower cell consisted of an offshore current in the bottom layer below 80m depth and was closed by the onshore current in the intermediate depth range. The cross shelf circulation controlled the fraction of ESACW on the shelf water mass. The long shelf circulation consisted in the surface mixed layer of an equatorward coastal jet driven by the local meridional wind stress and an almost barotropic poleward counter current appearing partly as free Kelvin wave emanating from the Angola-Benguela front and as coastal counter current forced by the local negative curl of the wind stress. The longshore current controlled the fraction of the SACW on the shelf water mass, which increased continuously between austral summer and fall. [Copyright &y& Elsevier]

The results of a seismic stratigraphic analysis of a closed lake basin, Lago Cardiel, in southernmost South America are reported. Very few high-resolution, continental records spanning the Late Quaternary have been obtained from this region. Seismic sequence stratigraphic analysis allows a reconstruction of lake level variations. Two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period. Following the development of a relatively shallow lake during the late Pleistocene and a short desiccation pulse around 11 22014C yr BP, a transgression of over 135 m occurred at the beginning of the Holocene. The transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern Lago Cardiel at four different elevations. The preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level. There is no seismic evidence of a major lowering of the lake below modern level during the entire Holocene. Deposition since the mid-Holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution. Seismic reflection geometries, as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80–100 km2. As Lago Cardiel is under the influence of westerly winds, these most likely drove lake circulation. The identification of drowned beach ridges and of contourite drifts illustrates that high-resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins, but it can also provide information about the rate of lake level changes and the presence and strength of lake currents. [ABSTRACT FROM AUTHOR]

Abstract: Wind forcing and the seasonal cycles of temperature and currents were investigated on the inner shelf of the Monterey Bay area of the California coast for 460 days, from June 2001 to September 2002. Temperature measurements spanned an approximate 100km stretch of coastline from a bluff just north of Monterey Bay south to Point Sur. Inner shelf currents were measured at two sites near the bay''s northern shore. Seasonal temperature variations were consistent with previous observations from the central California shelf. During the spring, summer and fall, a seasonal mean alongshore current was observed flowing northwestward in the northern bay, in direct opposition to a southeastward wind stress. A barotropic alongshore pressure gradient, potentially driving the northwestward flow, was needed to balance the alongshore momentum equation. With the exception of the winter season, vertical profiles of mean cross-shore currents were consistent with two-dimensional upwelling and existing observations from upwelling regions with poleward subsurface flow. At periods of 15–60 days, temperature fluctuations were coherent both throughout the domain and with the regional wind field. Remote wind forcing was minimal. During the spring upwelling season, alongshore currents and temperatures in the northern bay were most coherent with winds measured at a nearby land meteorological station. This wind site showed relatively low correlations to offshore buoy wind stations, indicating localized wind effects are important to the circulation along this stretch of Monterey Bay''s inner shelf. [Copyright &y& Elsevier]

A block matrix formulation is presented for the Sinc-Galerkin technique applied to the wind-driven current problem from oceanography. The block matrix form is used to determine an approximate solution for the coupled system of differential equations describing the wind-driven current problem. The approximate solution determined by this new Sinc-Galerkin scheme is compared to the approximate solution for the original complex-valued Sinc-Galerkin approach to ocean current models. The approximate solution is also compared to exact solutions to illustrate the exponential convergence rate of the method. [Copyright &y& Elsevier]

A three-dimensional (3D) numerical model using the finite element method was used to diagnose coastal currents off Antofagasta, in the upwelling region of northern Chile. The diagnosis was emphasized in the nearshore zone off Peninsula Mejillones (23°S), a well-known upwelling site off northern Chile. Water density fields, available from seasonal climatologies of the region, were used to predict currents for the austral winter, and summer conditions. Steady-state conditions were simulated under absence of wind, with a constant southwest wind of 10 knots (5.14 m s−1), which is the dominant upwelling-favorable wind in the zone, and with a constant north wind of 10 knots. Spatial variability of winds was examined by using historical wind fields for the region. A 3D particle tracking program was further used to diagnose expected particle trajectories over a 72 h steady-state period. Coastal circulation was dominated by alongshore currents, and presence of reversal currents and coastal eddies. Wind forcing accelerated the flow of the nearsurface layer in most cases, but did not considerably alter the circulation pattern of the average water column. Simulation of passive particle drift showed that the whole nearshore zone might act as an efficient retention area. It was concluded that, as a result of the interactions among distinct water masses, upwelling plumes, and alongshore currents, physical barriers may develop and give rise to semi-enclosed habitats. Physical structuring may have important ecological implications for the upwelling ecosystem. [Copyright &y& Elsevier]