Coastal Jet Research Articles

Wind-driven surface circulation in the Cape Blanc region

We analyze the short-term transition, on time scales of the order of days and weeks, of the surface fields in the coastal transition zone off Northwest Africa, between 15°N and 25°N, during winter and spring 2005 and 2006. This is a complex region characterized by the baroclinic coastal jet north of Cape Blanc, along-shore convergence and water export at the Cape Blanc giant filament, and substantial mesoscale variability between Capes Verde and Blanc. We use the anomalies of the wind impulse and two different coastal upwelling indexes, evaluated off 17°N, 20°N and 23°N, in order to assess the importance of wind forcing in this short-term variability. We also employ daily and weekly surface maps of wind, temperature, surface height and currents to investigate which are the mechanisms that lead to the relatively fast changes in the flow patterns. The coastal baroclinic jet and the Cape Blanc giant filament are ubiquitous features, the two being intrinsically related through the intensity of upwelling off Cape Blanc. Therefore, the strength of both features responds, to a large extent, to the fluctuations of the northeasterly winds; their intensity is greater in spring than winter but during both seasons they experience relatively fast oscillations related to the intermittency of the wind field. The mesoscalar features are visible in the entire domain, with time scales typically of the order of two weeks, but become prominent in the southern region during spring, apparently related to an intense northward coastal jet south of Cape Blanc.

Dynamics of the Leeuwin Current: Part 1. Coastal flows in an inviscid, variable-density, layer model

In this paper, we investigate basic dynamics of the Leeuwin Current (LC) using a dynamically “minimal” model, one that lies at the bottom of a planned hierarchy of LC models. The model is a steady-state, inviscid, 2-layer system, in which the upper-layer density is fixed to ρ1(y), all mixing and advection are ignored, and β≠0. As a result, solutions can be obtained analytically. Our model both simplifies and extends prior models of this sort, which include bottom drag in a fundamental way and adopt the f-plane.Solutions are obtained in a semi-infinite domain, x≤xe, y≤yn, in the southern hemisphere (yn<0), and there is a continental slope along the eastern boundary with the depth profile D(x). Generally, the interface beneath layer 1 intersects the continental slope along a “grounding” line, x=xg(y)≤xe, in which case the basin is divided into offshore and coastal regimes, and the model reduces to a 1-layer system in the latter. Solutions are forced by the density gradient ∂ρ1/∂y, by alongshore winds τy, and by the thermocline depth along the northern boundary H1, where H1 simulates the impact of the Indonesian Throughflow on the density structure in the northeastern basin. The flow field can be divided into depth-integrated and shear (thermal-wind) parts, and, because density advection is neglected, the former is independent of the latter. The depth-integrated equations are hyperbolic, their solution determined by the offshore propagation of boundary values along Rossby-wave characteristics.Even though there is no Rossby-wave damping, a coastal jet is trapped over the slope. Both the coastal jet and the offshore flow field are completely determined by the offshore propagation of signals from the coast; moreover, the offshore circulation depends only on the depth of the continental shelf at the coast, D(xe), and is independent of the slope profile farther offshore. For density-driven solutions, the grounding line shifts offshore and hence the LC deepens poleward; there is downwelling over the shelf, as well as westward flow at the bottom of the upper layer, both associated with the thermal-wind circulation and existing only when β≠0; the speed of the coastal jet is proportional to ∂D/∂x; and its transport is proportional to H12, so that it is strongest farther offshore and is very sensitive to the specified thermocline thickness in the northern basin. When equatorward wind stress is included, an equatorward jet can develop very nearshore provided that the wind stress is strong enough to overcome the density forcing.

Nonlinear hydrodynamics in a Mediterranean lagoon

Abstract. The paper addresses the application of the nonlinear hydrodynamics model (RANS (Reynolds-averaged Navier–Stokes) equations) in a wide semi-enclosed Mediterranean lagoon (Berre lagoon), considering three natural forcing functions, i.e., sea tide propagating through a long narrow channel, wind and runoff. Main attention is focused to characteristic velocities (at free surface and bottom) and to free surface elevation associated to each of these three mechanisms, with special attention to the nearshore areas (i.e., in shallow water). The most interesting result concerns wind effects which, due to Berre lagoon bathymetry, give rise to downwind coastal jets, alongshore, in shallow water areas. Such coastal jets were never mentioned before in Berre lagoon literature.

Coastal hydrodynamics in a windy lagoon

The nonlinear hydrodynamics (3D RANS model) in a wide semi-enclosed windy lagoonal ecosystem is accurately investigated in the context of analyzing the limiting conditions of the recovery of submerged aquatic vegetation (SAV). Among the main natural hydrodynamical forcings, we consider the wind effect. We mainly focus attention to characteristic velocities (free surface and bottom) and to free surface elevation in the nearshore regions (with shallow water) where SAV were severely damaged in the past decades. Our main result relates to wind effects that form downwind coastal jets, alongshore, in shallow water areas, due to Berre bathymetry. Such coastal jets, which were never described previously in Berre lagoon literature, give rise to substantial bottom currents in the shallower areas which could be responsible of changing the composition of mud-sand sediments; such changes are recognized in the literature to be a limiting factor for SAV recovery.

福島第一原発からの放射性核種の初期分散に及ぼす沿岸ジェットとメソスケール渦の影響

A detailed oceanic downscaling model (Uchiyama et al., 2012) is utilized to better understand the oceanic initial dispersion of the leaked radionuclides during the accident at the Fukushima Daiichi Nuclear Power Plant (1F). Particular attention is paid to the influences of northward geostrophic coastal jet associated with an alongshore high SSH belt peaked at 50 km offshore, and mesoscale eddies shed by the jet in Sendai Bay and by the Kuroshio near the separation point. A spectral coherence analysis exhibits that alongshore wind stress is highly correlated with alongshore current on the shelf over the periods around 168 hours, suggesting that coastally trapped shelf waves are also responsible for the dispersion of the nuclide.

Winter and spring surface velocity fields in the Cape Blanc region as deduced with the maximum cross-correlation technique

The ocean surface velocity field in the Cape Blanc region, off Northwest Africa, is investigated with the maximum cross-correlation (MCC) method applied to channel-4 Advanced Very High Resolution Radiometer satellite images. An initial sensitivity analysis allows us to select the four parameters that provide maximum area coverage and the best velocity resolution, while limiting the standard deviation for each velocity component within reasonable values. These are (m, n, MV, CT) = (22, 32, 50, 0.6), where m and n are the number of pixels of the search window (SW) and reference window (RW), respectively, MV is the maximum possible velocity (in cm s−1), and CT is a correlation threshold for a feature to be tracked. A total of 489 images, for years 2005 and 2006, are analysed, and 106 velocity maps are generated with good coverage of the coastal transition zone (CTZ), most of them for the winter (34) and spring (59) seasons. We remove spurious data using the method's own filters (MV, CT, and a neighbour-vector comparison), requesting the velocity components to have Gaussian distributions and smoothing the resulting velocity fields with a median-vector filter. The instantaneous velocity maps illustrate the response of the alongshore coastal jet north of Cape Blanc (and its extension along the Cape Verde frontal region) to wind forcing, as well as the presence of numerous mesoscalar features (100–300 km wide) superposed on a westward offshore transport south of Cape Blanc. We also produce mean and standard deviation winter and spring velocity maps, which are compared with the corresponding mean sea surface temperature fields. The along-shore and offshore flow is better defined and is more intense in spring than in winter, in concordance with cross-slope sharper temperature gradients during this season, and brings about a cooling of the whole region. We identify five different ubiquitous currents: a southwestward jet north of Cape Blanc, a northwestward jet off Banc d'Argin, an offshore convergent jet, a spring jet-like feature at 18° N, and a southward flow in the southwestern CTZ.

Fate of river Tiber discharge investigated through numerical simulation and satellite monitoring

Abstract. The aim of this study was to determine the dispersion of passive pollutants associated with the Tiber discharge into the Tyrrhenian Sea using numerical marine dispersion models and satellite data. Numerical results obtained in the simulation of realistic discharge episodes were compared with the corresponding evolution of the spatial distributions of MODIS diffuse light attenuation coefficient at 490 nm (K490), and the results were discussed with reference to the local climate and the seasonal sub-regional circulation regime. The numerical model used for the simulation of the sub-tidal circulation was a Mediterranean sub-regional scale implementation of the Princeton Ocean Model (POM), nested in the large-scale Mediterranean Forecasting System. The nesting method enabled the model to be applied to almost every area in the Mediterranean Sea and also to be used in seasons for which imposing climatological boundary conditions would have been questionable. Dynamical effects on coastal circulation and on water density due to the Tiber discharge were additionally accounted for in the oceanographic model by implementing the river estuary as a point source of a buoyant jet. A Lagrangian particle dispersion model fed with the POM current fields was then run in order to reproduce the effect of the turbulent transport of passive tracers mixed in the plume with the coastal flow. Two significant episodes of river discharge in both winter and summer conditions were discussed in this paper. It was found that the winter regime was characterized by the presence of a strong coastal jet flowing with the ambient current. In summer the prevailing wind regime induced coastal downwelling conditions, which tended to confine the riverine waters close to the shore. In such conditions sudden wind reversals due to local weather perturbations, causing moderate local upwelling, proved to be the only effective way to disperse the tracers offshore, moving the plume from the coast and detaching large pools of freshwater.

Eastern boundary drainage of the North Atlantic subtropical gyre

The eastern boundary of the North Atlantic subtropical gyre (NASG) is an upwelling favorable region characterized by a mean southward flow. The Canary Upwelling Current (CUC) feeds from the interior ocean and flows south along the continental slope off NW Africa, effectively providing the eastern boundary condition for the NASG. We follow a joint approach using slope and deep-ocean data together with process-oriented modeling to investigate the characteristics and seasonal variability of the interior–coastal ocean connection, focusing on how much NASG interior water drains along the continental slope. First, the compiled sets of data show that interior central waters flow permanently between Madeira and the Iberian Peninsula at a rate of 2.5 ± 0.6 Sv (1 Sv = 106 m3 s-1 109 km s-1), with most of it reaching the slope and shelf regions north of the Canary Islands (1.5 ± 0.7 Sv). Most of the water entering the African slope and shelf regions escapes south between the easternmost Canary Islands and the African coast: In 18 out of 22 monthly realizations, the flow was southward (−0.9 ± 0.4 Sv) although an intense flow reversal occurred usually around November (1.7 ± 0.9 Sv), probably as the result of a late fall intensification of the CUC north of the Canary Islands followed by instability and offshore flow diversion. Secondly, we explore how the eastern boundary drainage may be specified in a process-oriented one-layer quasigeostrophic numerical model. Non-zero normal flow and constant potential vorticity are alternative eastern boundary conditions, consistent with the idea of anticyclonic vorticity induced at the boundary by coastal jets. These boundary conditions cause interior water to exit the domain at the boundary, as if recirculating through the coastal ocean, and induce substantial modifications to the shape of the eastern NASG. The best model estimate for the annual mean eastward flow north of Madeira is 3.9 Sv and at the boundary is 3.3 Sv. The water exiting at the boundary splits with 1 Sv flowing into the Strait of Gibraltar and the remaining 2.3 Sv continuing south along the coastal ocean until the latitude of Cape Ghir. The model also displays significant wind-induced seasonal variability, with a maximum connection between the interior and coastal oceans taking place in autumn and winter, in qualitative agreement with the observations.

A northerly winter monsoon surge over the South China Sea studied by remote sensing and a numerical model

A northerly winter monsoon surge, which occurred on 15 December 2009 over the South China Sea (SCS), is studied by using satellite-based and ground-based remote-sensing data and an atmospheric numerical model. The remote-sensing data are from the advanced synthetic aperture radar (ASAR) onboard the Environmental Satellite (Envisat), the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Terra satellite, the imager onboard the geostationary satellite MTSAT-1R (Multi-Functional Transport Satellite-1R) and the weather radar of the Hong Kong Observatory (HKO). A northerly winter monsoon surge is a cold air outbreak associated with a northerly wind, the passage of a cold front from north to south and a strong drop in air temperature. The analyses of the weather radar and the MTSAR-1R images of 15 December show that the surge of 15 December was associated with a rain band and a cloud front travelling over the SCS in a southeastward direction. Due to the interaction of the cold air (13°C) with the warm water (19°C), they dissolved when they had reached an offshore distance of approximately 160 km. The high-resolution (150 m) ASAR image reveals fine-scale features of the wind field, in particular details of the wind front, such as embedded rain cells and atmospheric gravity waves. Quantitative information on the near-surface wind field is retrieved from the ASAR, and it is shown that the wind field associated with the surge is quite variable and that speeds up to 15 m s–1 are encountered in coastal wind jets. Finally, the remote-sensing data are compared with the simulation results of the pre-operational version of the Atmospheric Integrated Rapid-cycle (AIR) forecast model of the HKO. It is shown that, in general, the AIR model reproduces quite well the observational data.

Response of the Benguela upwelling systems to spatial variations in the wind stress

In this paper we combine field observations, numerical modeling and an idealized analytical theory to study some features of the Benguela upwelling system. The current system can be established through a combination of observations and realistic simulations with an advanced numerical model. The poleward undercurrent below the equator-ward coastal jet is often found as a countercurrent that reaches the sea surface seaward of the coastal jet. The coastal band of cold upwelled water appears to broaden from south to north and at the northern edge of the wind band an offshore flow is often detected, which deflects the coastal Angola current to the west. These features can be explained and understood with an idealized analytical model forced by a spatially variable wind.A crucial role is played by the wind stress curl, which shapes the oceanic response through Ekman-pumping. The interplay of the curl driven effects and the coastal Ekman upwelling together with the coastal jet, Kelvin waves, and the undercurrent is the key to understand the formation of the three-dimensional circulation patterns in the Benguela system. While the numerical model is based on the full set of primitive equations, realistic topography and forcing, the analytic model uses a linear, flat-bottomed f-plane ocean, where the coast is a straight wall and the forcing is represented by an alongshore band of dome-shaped wind stress. Although the analytical model is highly idealized it is very useful to grasp the basic mechanisms leading to the response patterns.

Poleward coastal jets induced by westerlies in the Bay of Biscay

Two hydrodynamic surveys based on acoustic Doppler current profiler (ADCP) and drift buoys measurements taken in summer 2008 and 2009 revealed poleward coastal jets of up to 32 cm s−1 that lasted up to 22 d along the Aquitaine shelf in the southeastern area of the Bay of Biscay. A strong increase in bottom temperature was associated with these currents, up to 4°C in 5 d at 54 m depth. These observations occurred after a few days of westerlies, cross‐shore winds which were thought to have only a limited impact on longshore circulation. Here, the MARS3D hydrodynamic model was used with a schematic bathymetry of the southeastern area of the Bay of Biscay to reproduce and analyze these coastal jets. Simulations revealed that the triggering mechanism of the poleward currents is unequivocally due to downwelling circulation induced along the Spanish coast. This downwelling induces an external longshore pressure gradient which generates a high‐speed coastal‐trapped wave that propagates along the French coast with a phase velocity of about 3 to 4 m s−1 and an internal baroclinic Kelvin wave with a phase velocity of about 1 m s−1. A sensitivity study of the role of stratification conditions, wind strength and duration was then carried out to determine the periods that are the most sensitive to this wind‐induced circulation.

Upwelling response to atmospheric coastal jets off central Chile: A modeling study of the October 2000 event

The spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes. In this study, regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central Chile. The event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern Pacific region during October 2000. A robust feature of the simulation is a sharp coastal wind dropoff, which is insensitive to model resolution. As expected, the simulated oceanic response is a significant sea surface cooling. A surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection. Sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation. This is because total upwelling, i.e., the sum of coastal upwelling and Ekman pumping, depends on the scale of wind dropoff. Because the latter is much larger than the upwelling scale, coastal wind dropoff has only a weak positive effect on vertical velocities driven by Ekman pumping but has a strong negative effect on coastal upwelling. Interestingly though, the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection, with both effects contributing to a reduction of cooling.

Trapped instability and vortex formation by an unstable coastal current

This paper addresses the instability of a two-layer coastal current in a quasigeostrophic model; the potential vorticity (PV) structure of this current consists in two uniform cores, located at different depths, with finite width and horizontally shifted. This shift allows both barotropic and baroclinic instability for this current. The PV cores can be like-signed or opposite-signed, leading to their vertical alignment or to their hetonic coupling. These two aspects are novel compared to previous studies. For narrow vorticity cores, short waves dominate, associated with barotropic instability; for wider cores, longer waves are more unstable and are associated with baroclinic processes. Numerical experiments were performed on the f-plane with a finite-difference model. When both cores have like-signed PV, trapped instability develops during the nonlinear evolution: vertical alignment of the structures is observed. For narrow cores, short wave breaking occurs close to the coast; for wider cores, substantial turbulence results from the entrainment of ambient fluid into the coastal jet. When the two cores have opposite-signed PV, the nonlinear regimes range from short wave breaking to the ejection of dipoles or tripoles, via a regime of dipole oscillation near the wall. The Fourier analysis of the perturbed flow is appropriate to distinguish the regimes of short wave breaking, of dipole formation, and of turbulence, but not the differences between regimes involving only vortex pairs. To explain more precisely the regimes where two vortices (and their wall images) interact, a point vortex model is appropriate.

Scales characterising a high density thin layer of Dinophysis acuta Ehrenberg and its transport within a coastal jet

An investigation into the distribution of Dinophysis spp. in coastal waters off the south coast of Ireland was carried out in July 2007. Dinophysis acuta was present as a sub surface layer containing up to 55,000cellsL−1. The population had a high percentage of viable cells (mean: 89%; median: 94%; n=24) with a high specific division rate (∼0.55d−1). The layer, of approximately 5m thickness, did not coincide with the fluorescence maximum and was present as a patch of horizontal dimension less than 10km×7km. Both conventional and towed undulating CTD used in conjunction with high vertical resolution sampling methods showed the patch of Dinophysis to move with a similar speed and direction as the coastal flow, which ran parallel to the coast in the form of a coastal jet with speed of the order of 6.5–7kmday−1. The implications of the alongshore transport of populations of harmful species in coastal jets for monitoring programmes and predictive models are discussed.

The Low-Level Atmospheric Circulation near Tongoy Bay–Point Lengua de Vaca (Chilean Coast, 30°S)

Abstract Strong southerly, terrain parallel winds often occur along the coast of north-central Chile (25°–35°S) embedded in the marine atmospheric boundary layer and the lower part of the capping temperature inversion. Their offshore structure and variability have received considerable attention because of the effect on open-ocean processes and connection with the southeast Pacific cloud layer. Mesoscale low-level circulations linked to the coastal topography (e.g., coastal jets and sea breeze) are less studied in Chile, but are particularly relevant as they alter the upper-ocean circulation and the cloud pattern in the nearshore strip. Surface, radiosonde, and airborne meteorological observations near point Lengua de Vaca (LdV)–Tongoy Bay (TB) at 30°S are used alongside numerical modeling to understand the local circulation near a prominent upwelling center. Most observations were gathered during the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Chilean Upwelling Experiment (VOCALS-CUpEx) during two weeks in late spring 2009. The regional topography resembles other major capes, but south of TB and east of LdV there is a low (100–300 m), dry marine terrace bounded by high elevation at the coast (~600 m) and farther inland. Coastal soundings 25 km upstream of LdV revealed a southerly wind maximum near the surface and another at 900 m separated by a destabilized layer, deviating from the two-layer model often applied to coastal flow. In the morning a shallow sea breeze penetrates from TB to the marine terrace, but is overridden by southerly flow in the afternoon. Furthermore, between 400 and 900 m, warm continental air is advected from over the marine terrace creating a residual boundary layer over TB. Concurrent with slower changes offshore, the low-level warming over TB leads to a marked cross-shore pressure gradient enhancing the coastal jet just north of LdV.

Sensitivity of the Humboldt Current system to global warming: a downscaling experiment of the IPSL-CM4 model

The impact of climate warming on the seasonal variability of the Humboldt Current system ocean dynam- ics is investigated. The IPSL-CM4 large scale ocean cir- culation resulting from two contrasted climate scenarios, the so-called Preindustrial and quadrupling CO2, are downscaled using an eddy-resolving regional ocean circu- lation model. The intense surface heating by the atmo- sphere in the quadrupling CO2 scenario leads to a strong increase of the surface density stratification, a thinner coastal jet, an enhanced Peru-Chile undercurrent, and an intensification of nearshore turbulence. Upwelling rates respond quasi-linearly to the change in wind stress asso- ciated with anthropogenic forcing, and show a moderate decrease in summer off Peru and a strong increase off Chile. Results from sensitivity experiments show that a 50% wind stress increase does not compensate for the surface warming resulting from heat flux forcing and that the associated mesoscale turbulence increase is a robust feature.

Assessment of a NEMO-based downscaling experiment for the North-Western Mediterranean region: Impacts on the Northern Current and comparison with ADCP data and altimetry products

The aim of this paper is to assess the impact of numerical resolution on the simulation of the circulation in the North-Western Mediterranean Sea by comparing two realistic model configurations of 1/64° and 1/16°, the low resolution configuration (LRC) being also used at the high resolution configuration (HRC) open boundaries. The study mainly focuses on the Northern Current (NC), the major feature of the regional circulation in the area, influencing important processes such as meanders giving birth to eddies and NC intrusions on the shelf, strongly conditioning the interactions between coastal and off-shore waters. Both configurations use the NEMO code with the LRC covering the entire Mediterranean basin and the HRC being restricted to the North-Western Mediterranean Sea. The two numerical configurations are assessed by using hull-mounted ADCP data and geostrophic velocities derived from AVISO altimetry at key locations along the NC path. The two configurations develop a different solution regarding the current dynamics but both indicate an important variability of the NC position along its general path. The LRC simulations systematically exhibit a NC shifted too far off the coast and also spuriously displaced seaward along the Gulf of Lions shelf edge while high resolution simulations better fit the remote and in situ observations. In addition, the HRC is able to simulate more realistic coastal features such as a confined coastal jet in good agreement with the ADCP measurements. As satisfactory agreement is reached with the various observations used at different space and time scales, the development of this NEMO high resolution configuration stands as a promising experiment for various process studies or operational oriented applications.

Restructuring of a zooplankton community by perturbation from a wind-forced coastal jet

The impact of transient wind events on an established zooplankton community was observed during a, field survey in a, coastal region off northern Norway in May 2002. A transient wind event induced a coastal jet/filament intrusion of warm, saline water into our survey area where a semi-permanent eddy was present. There was an abrupt change in zooplankton community structure within 4-7 days of the wind event, with a change in the size structure, an increase in lower size classes less than 1 mm in equivalent spherical diameter (ESD) and a decrease in larger size classes greater than 1.5 mm in ESD. The slope of zooplankton biovolume spectra changed from -0.6 to -0.8, consistent with the size shifting towards smaller size classes. This study shows that even well established zooplankton communities are susceptible to restructuring during transient wind events, and in particular when wind forcing induces horizontal currents or filaments.

On the role of the mesoscale circulation on an idealized coastal upwelling ecosystem

An idealized circulation model of coastal upwelling coupled to an ecosystem model has been built to address the impact of features such as eddies and filaments emerging from mesoscale dynamics on a marine ecosystem. The model mimics coastal upwelling along an infinite straight coast with north–south cyclic boundary conditions. Thanks to the parametrization of the geostrophic onshore flow in the thermocline, the circulation captures the typical characteristics of a coastal upwelling region: an equatorward coastal jet, a poleward undercurrent along the continental slope and mesoscale eddies and filaments. This eddying three‐dimensional simulation is compared to a two‐dimensional simulation using the averaged velocity field of the first simulation as velocity field. This approach allows us to compare simulations having similar upwelling and nutrient input but differing in the nature of the flow. An offshore spreading of the phytoplankton bloom is found in the eddying simulation. The width of the productive coastal band is increased from 80 km to 200 km by the mesoscale activity. A biogeochemical budget carried out in a 300 km‐wide coastal band provides evidence that mesoscale activity decreases the total phytoplankton content mainly by exporting a significant part of the surface phytoplankton below the euphotic layer. In presence of mesoscale activity, the downward and offshore export of phytoplankton, zooplankton and detritus significantly contributes to total export of organic matter out of the surface coastal ocean, whereas their contribution to export is weak in the two‐dimensional case.

Some Insights into the Characteristics and Dynamics of the Chilean Low-Level Coastal Jet

Abstract The characteristics and dynamics of the Chilean low-level coastal jet (CLLCJ) are examined here through diagnosing real-time mesoscale model forecasts in support of the Variability of the American Monsoon System (VAMOS) Ocean–Cloud–Atmosphere Land Study (VOCALS) and additional sensitivity simulations. The forecasted surface winds over the southeast Pacific compare favorably with available observations. According to the forecasts and sensitivity simulations, the Southeast Pacific high pressure system (SEPH) plays a primary role in driving the CLLCJ. The Andes significantly intensify the CLLCJ mainly through interacting with the SEPH and anchoring a baroclinic zone along the Chilean coast. The land–sea differential heating also enhances the CLLCJ by strengthening the coastal baroclinic zone. Based on the location of the SEPH center, the CLLCJ can be separated into two types: a strong-forcing jet, with the SEPH close to the central Chilean coastline; and a weak-forcing jet, with the SEPH centered far away from the coastline. The former is much more intense and associated with stronger interaction between the SEPH and the Andes. The CLLCJ is slightly supergeostrophic within the marine boundary layer top inversion, where weak easterlies develop, and subgeostrophic in the turbulent boundary layer below, where westerlies are present. The inversion easterlies induce strong subsidence along the coast, which contributes to the formation of the coastal low and the coastal baroclinic zone.