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1.
Fourteen years (September 2002 to August 2016) of high-resolution satellite observations of sea surface temperature (SST) data are used to describe the frontal pattern and frontogenesis on the southeastern continental shelf of Brazil. The daily SST fronts are obtained using an edge-detection algorithm, and the monthly frontal probability (FP) is subsequently calculated. High SST FPs are mainly distributed along the coast and decrease with distance from the coastline. The results from empirical orthogonal function (EOF) decompositions reveal strong seasonal variability of the coastal SST FP with maximum (minimum) in the astral summer (winter). Wind plays an important role in driving the frontal activities, and high FPs are accompanied by strong alongshore wind stress and wind stress curl. This is particularly true during the summer, when the total transport induced by the alongshore component of upwelling-favorable winds and the wind stress curl reaches the annual maximum. The fronts are influenced by multiple factors other than wind forcing, such as the orientation of the coastline, the seafloor topography, and the meandering of the Brazil Current. As a result, there is a slight difference between the seasonality of the SST fronts and the wind, and their relationship was varying with spatial locations. The impact of the air-sea interaction is further investigated in the frontal zone, and large coupling coefficients are found between the crosswind (downwind) SST gradients and the wind stress curl (divergence). The analysis of the SST fronts and wind leads to a better understanding of the dynamics and frontogenesis off the southeastern continental shelf of Brazil, and the results can be used to further understand the air-sea coupling process at regional level.
相似文献2.
Osmar O. Möller Jr. Alberto R. Piola Ana Cristina Freitas Edmo J.D. Campos 《Continental Shelf Research》2008
The Río de la Plata waters form a low salinity tongue that affects the circulation, stratification and the distributions of nutrients and biological species over a wide extent of the adjacent continental shelf. The plume of coastal waters presents a seasonal meridional displacement reaching lower latitudes (28°S) during austral winter and 32°S during summer. Historical data suggests that the wind causes the alongshore shift, with southwesterly (SW) winds forcing the plume to lower latitudes in winter while summer dominant northeasterly (NE) winds force its southward retreat. To establish the connection between wind and outflow variations on the distribution of the coastal waters, we conducted two quasi-synoptic surveys in the region of Plata influence on the continental shelf and slope of southeastern South America, between Mar del Plata, Argentina and the northern coast of Santa Catarina, Brazil. We observed that: (A) SW winds dominating in winter force the northward spreading of the plume to low latitudes even during low river discharge periods; (B) NE winds displace the plume southward and spread the low salinity waters offshore over the entire width of the continental shelf east of the Plata estuary. The southward retreat of the plume in summer leads to a volume decrease of low salinity waters over the shelf. This volume is compensated by an increase of Tropical waters, which dominate the northern shelf. The subsurface transition between Subantarctic and Subtropical Shelf Waters, the Subtropical Shelf Front, and the subsurface water mass distribution, however, present minor seasonal variations. Along shore winds also influence the dynamics and water mass variations along the continental shelf area. In areas under the influence of river discharge, Subtropical Shelf Waters are kept away from the coastal region. When low salinity waters retreat southward, NE winds induce a coastal upwelling system near Santa Marta Cape. In summer, solar radiation promotes the establishment of a strong thermocline that increases buoyancy and further enhances the offshore displacement of low salinity waters under the action of NE winds. 相似文献
3.
Mesoscale circulation along the Sakhalin Island eastern coast 总被引：1，自引：1，他引：0
Sergey V. Prants Andrey G. Andreev Michael Yu. Uleysky Maxim V. Budyansky 《Ocean Dynamics》2017,67(3-4):345-356
The seasonal and interannual variability of mesoscale circulation along the eastern coast of the Sakhalin Island in the Okhotsk Sea is investigated using the AVISO velocity field and oceanographic data for the period from 1993 to 2016. It is found that mesoscale cyclones with the horizontal dimension of about 100 km occur there predominantly during summer, whereas anticyclones occur predominantly during fall and winter. The cyclones are generated due to a coastal upwelling forced by northward winds and the positive wind stress curl along the Sakhalin coast. The anticyclones are formed due to an inflow of low-salinity Amur River waters from the Sakhalin Gulf intensified by southward winds and the negative wind stress curl in the cold season. The mesoscale cyclones support the high biological productivity at the eastern Sakhalin shelf in July– August. 相似文献
4.
Ocean–atmosphere coupling in the Humboldt Current System (HCS) of the Southeast Pacific is studied using the Scripps Coupled Ocean–atmosphere Regional (SCOAR) model, which is used to downscale the National Center for Environmental Prediction (NCEP) Reanalysis-2 (RA2) product for the period 2000–2007 at 20-km resolution. An interactive 2-D spatial smoother within the sea-surface temperature (SST)–flux coupler is invoked in a separate run to isolate the impact of the mesoscale (～50–200 km, in the oceanic sense) SST field felt by the atmosphere in the fully coupled run. For the HCS, SCOAR produces seasonal wind stress and wind stress curl patterns that agree better with QuikSCAT winds than those from RA2. The SCOAR downscaled wind stress distribution has substantially different impacts on the magnitude and structure of wind-driven upwelling processes along the coast compared to RA2. Along coastal locations such as Arica and Taltal, SCOAR and RA2 produce seasonally opposite signs in the total wind-driven upwelling transport. At San Juan, SCOAR shows that upwelling is mainly due to coastal Ekman upwelling transport, while in RA2 upwelling is mostly attributed to Ekman pumping. Fully coupled SCOAR shows significant SST–wind stress coupling during fall and winter, while smoothed SCOAR shows insignificant coupling throughout, indicating the important role of ocean mesoscale eddies on air–sea coupling in HCS. Coupling between SST, wind speed, and latent heat flux is incoherent in large-scale coupling and full coupling mode. In contrast, coupling between these three variables is clearly identified for oceanic mesoscales, which suggests that mesoscale SST affects latent heat directly through the bulk formulation, as well as indirectly through stability changes on the overlying atmosphere, which affects surface wind speeds. The SST–wind stress and SST–heat-flux couplings, however, fail to produce a strong change in the ocean eddy statistics. No rectified effects of ocean–atmosphere coupling were identified for either the atmospheric or oceanic mean conditions, suggesting that mesoscale coupling is too weak in this region to strongly alter the basic climate state. 相似文献
5.
Abstract In this unsteady barotropic model of the circulation over an oceanic continental shelf and shelf break, account is taken of variations in the surface wind stress along the coast. It is found that the position of maximum onshore flow is very sensitive to the alongshore variation of the wind stress, and that the longshore current becomes more influenced by the shelf break as the wind stress decreases. The relation between the shelf break secondary upwelling and the surface wind stress is investigated. The secondary upwelling is greatest when the wind is increasing most rapidly. 相似文献
6.
Jorge Zavala-Hidalgo Artemio Gallegos-García Benjamín Martínez-López Steven L. Morey James J. O’Brien 《Ocean Dynamics》2006,56(3-4):333-338
An 8-year database of sea surface temperature (SST), 7 years of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color images, wind fields, and numerical model results are analyzed to identify regions and periods of coastal upwelling on the western and southern shelves of the Gulf of Mexico. On the seasonal scale, it is found that on the Tamaulipas, Veracruz, and southwestern Texas–Louisiana shelves there are upwelling favorable winds from April to August, when southeasterly winds are dominant and cold SST anomalies associated with upwelling are observed along their coasts. However, during summer, values of chlorophyll-a concentration are lower than those in autumn and winter, which are high due to advection of old bloom biological material from upstream. During winter, there is a cold front on the Tamaulipas shelf produced by advection of cold water from the Texas–Louisiana shelf and not due to upwelling. On the eastern Campeche Bank, persistent upwelling is observed due to favorable winds throughout the year with cold SST and large chlorophyll-a content along the inner shelf from May to September. On the Tamaulipas shelf, the summer upwelling delays the annual SST peak until September, while in most of the Gulf SST peaks in August. This difference is due to the end of the upwelling favorable wind conditions and the September seasonal current reversal. 相似文献
7.
A two-dimensional numerical model is applied to a coastal ocean wherein alongshore elevation and density gradients, normally calculated by a three-dimensional model, are instead supplied by climatologically averaged data for the California Current System between 25 and 40°N. Surface wind stress is also obtained from climatological data. Both surface and bottom boundary layers are resolved in the model calculations; a second moment turbulence closure submodel supplies vertical diffusivities. Near steady state solutions are possible when surface buoyancy flux is imposed at the surface.Model results are as follows: Southward wind stress produces a broad equatorward current with an embedded coastal jet in accordance with previous studies. Positive wind stress curl reduces the jet current and produces a poleward undercurrent which then surfaces as the curl is increased. The jet currents are reduced and poleward flow increases as bottom steepness increases; to a lesser extent, inclusion of the beta effect has a similar effect. The existence of near bottom, poleward or equatorward flow is explained rather simply in terms of the bottom stress resulting from the alongshore balance of surface wind stress and vertically integrated pressure gradient, the latter involving the alongshore surface elevation and density gradient. A further finding is that the upwelling circulation associated with wind stress is confined to the top 200 to 300 m of the ocean along the California coast. 相似文献
8.
《Marine pollution bulletin》2011,62(7-12):432-448
An outstanding characteristic of New Caledonia upwelling is that most events appear limited to the southern half of the western barrier reef. This north–south difference cannot be explained by alongshore variability of the projected wind stress and no strong evidence for alternative explanations has been proposed. A major objective of this paper is to provide the first dynamical analysis of New Caledonia upwelling and its regional environment, based on numerical simulations. Coastal upwelling around New Caledonia is shown to be modulated by a system of geostrophic currents interacting with the island mass. Upwelling velocities are weaker than expected from the two-dimensional Ekman theory, as Ekman divergence is balanced by “coastal geostrophic convergence”. The cooling effect of upwelling is also attenuated by alongshore transport of warm water by the Alis current, reminiscent of the Leeuwin current off Western Australia. Nevertheless, coastal upwelling can locally modify the large-scale surface water heat budget, dominated by meridional advection warming and surface cooling. The upwelled waters appear to be mostly of western origin and are transported below the surface by the Subtropical Counter Current before upwelling off New Caledonia. This appears in sharp contrast with the eastern barrier reef where the general warming by meridional advection of tropical surface waters is accentuated by the vigorous western boundary type Vauban current. 相似文献
9.
The response of a barotropic coastal ocean on a step-shaped continental shelf to a traveling sinusoidal wind stress forcing is predicted theoretically using a frictional force proportional to the alongshore current velocity. This theory is compared to a small set of observations from the northeast coast of Australia where a sudden widening of the continental shelf provides a geographical origin. The comparison is accomplished by means of frequency response functions relating alongshore wind stress with alongshore velocity. Amplitudes of the response functions are predicted to increase with alongshore distance equatorward and also to decrease with frequency at any location. These predictions are verified by the measurements. Predicted phase lags are generally less than about 30°, with observations agreeing with theory to within about 20°C. In general, the measurements provide reasonable evidence to support the theory of wind-forced continental shelf waves from a geographical origin. 相似文献
10.
The Northern Mediterranean Current is the return branch of the cyclonic circulation of the northwestern Mediterranean Sea. Because of geostrophic constraints, this warm and oligotrophic current is forced to flow westward along the continental slope of the Gulf of Lion. But, occasionally, it penetrates on the shelf and strongly impacts the local biogeochemistry and in turn the primary production. By combining in situ observations and high-resolution modelling, it is shown that intrusions on the eastern part of the gulf are mainly forced by easterly or northwesterly wind events, through physical mechanisms that are very different in nature. Easterlies induce a piling of water along the Gulf of Lion coast that drives, through geostrophy, an alongshore shelf-intruding current. This intrusive current occurs independently of the stratification and is concomitant with the wind forcing. On the other hand, intrusions due to northwesterlies only occur during stratified conditions and are related to the development of upwellings along the Gulf of Lion coasts. When the upwelling develops, a northwestward alongshore pressure force balances the Coriolis force associated with the onshore flow at depth. When the winds drop, the upwelling relaxes and the onshore flow weakens. Consequently, the Coriolis force no longer counterbalances the pressure force that ultimately dominates the momentum balance, causing the displacement of the Northern Current on the Gulf of Lion shelf approximately 1 day after the wind relaxation. This time lag between the northwesterlies decrease and the intrusions permits to anticipate possible changes in the biogeochemistry of the Gulf of Lion. 相似文献
11.
The influence of meteorological variation, i.e., typhoon and precipitation events, on the coastal upwelling off the eastern
Hainan Island was studied based on observations taken during two upwelling seasons. The observations were made in August 2007
and July 2008, respectively. We found that, in principle, similar structure of sea surface temperature and bottom temperature
prevailed in both observational periods, providing evidence that upwelling events occur frequently during the summer monsoon
along the eastern Hainan shelf. Based on a simple momentum balance theory, we studied the balances between momentum fluxes,
wind stress, and bottom stress. The results showed that the Burger number is S ≈ 1, indicating that the cross-shelf momentum flux divergence was balanced by the wind stress and the onshore return flow
occurred in the interior of the water column. Hence, a conceptual model of the upwelling structure was built for further understanding
of upwelling events. In addition, it was also observed that variations in the strength of upwelling are controlled by storm
events, i.e., strong northerly winds change the structure of the thermocline on the shelf significantly. The strong mixing
caused by wind reduces the strength of the thermocline, in particular in coastal seas. Based on our conceptual model, a frontal
zone between mixed coastal water and offshore water develops which destabilizing the water column and hence decreases the
upwelling strength. Freshwaters from the two main rivers in the Wenchang Bay are confined to the coastal area less than 20–30
m deep, as confirmed by our water mass analysis. Freshwater discharge stabilized the water column, inhibiting the upwelling
as shown by the potential energy calculation. Consequently, estuarine water only inhibits the upwelling in the near coastal
area. Therefore, it can be concluded that estuarine water does not have a significant impact on upwelling strength on the
shelf. 相似文献
12.
Numerical simulations with the Regional Ocean Modeling System (ROMS) are used to study the initial spin-up and the evolution of a mesoscale, topographically linked eddy under steady and variable wind conditions. The development of a pool of dense water on the southern Vancouver Island shelf allows cyclonic eddies formed by coastal upwelling off Cape Flattery to spread westward, ultimately contributing to the shelf-wide circulation known as the Juan de Fuca Eddy. This dense water arises through upwelling of water present in the underlying canyon system and tidal mixing over several shallow banks to the north. Tidal mixing is critical to the separation of the eddy from the coast. Although steady upwelling winds with a seasonal mean magnitude (combined with estuarine flow and tides) produce an eddy, only fluctuating winds with timescales and magnitudes typical of the region result in an eddy with a westward extent similar to seasonal observations. With each period of upwelling-favorable winds, newly upwelled water from the coast is entrained into the eddy which grows in size and moves westward. Wind events also significantly affect the baroclinic structure of the eddy. Specifically, during typical summer wind reversals, model surface drifters continue to move cyclonically within the eddy for several days after each downwelling wind event. Under upwelling-favorable wind conditions, model drifters exit the eddy to the southeast as the eddy and coastal upwelling fronts merge into a continuous southeastward shelf break jet. 相似文献
13.
N. Ospina-Alvarez R. Prego I. Álvarez M. deCastro M.T. Álvarez-Ossorio Y. Pazos M.J. Campos P. Bernárdez C. Garcia-Soto M. Gómez-Gesteira M. Varela 《Continental Shelf Research》2010
Summer upwelling and downwelling processes were characterized in the Northern Galician Rias during July and August 2008 by means of sampling carried out onboard R/V Mytilus (CSIC) and R/V Lura (IEO). Thermohaline variables, dissolved oxygen, nutrients, chlorophyll, phytoplankton, ciliates and zooplankton abundances were measured at sections located in the Rias of Viveiro, Barqueiro and Ortigueira and their adjacent shelves. Ekman transport was calculated from QuikSCAT satellite, upwelling intensity estimated with upwelling index from the average daily geostrophic winds, and SST maps obtained from NASA GHRSST satellite. Ekman transport and SST behaviour showed two different patterns: (i) offshore and upwelling favourable conditions on 13–22nd of July; (ii) onshore and downwelling favourable conditions from 23rd July to 19th August. During upwelling, TS diagram showed an intrusion of Eastern North Atlantic Central Water affecting the continental shelf but not the rias. Nutrient salt concentrations increased with depth, reaching their maximum values near the mouth of Ortigueira Ria. During downwelling, coastal water increased its temperature (18.5–19.8 °C) and was retained inside rias; nutrients were nearly depleted, except for the innermost ria (estuarine zone) due to fluvial nutrient inputs. In this inner area, the maximum of chlorophyll-a (Barqueiro Ria) was observed. Low phytoplankton abundances were measured in both cases, even though a short increase in the plankton biomass was observed inside rias during upwelling, while under downwelling a small red tide of Lingulodinium polyedrum was detected. During the upwelling period Northern Rias tend to be mesotrophic systems as revealed by nutrient concentrations, chlorophyll levels and plankton abundances. On the contrary, in similar situations, the Western Rias behaves as eutrophics. 相似文献
14.
E.D. Barton 《Continental Shelf Research》1985,4(4):425-443
Currents, coastal winds, coastal sea level, and coastal ocean temperatures were observed at a number of northern Baja California Pacific sites between October 1978 and October 1979. Coastal winds were weakly southward on average and fluctuated north-south throughout the year. Fluctuations were uncorrelated over alongshore separations of 200 km. Coastal winds differed considerably from the large-scale offshore wind estimate (Bakun's Index) both in strength and in variability. At 30°50′N the mean currents were weakly equatorward at 25 m depth and weakly poleward at 42 and 60 m in a water depth of 75 m. The seasonal mean flow was equatorward from October to April and poleward from April to October at the shallower level but poleward all year near bottom. The fluctuations on a time scale of days to weeks were about an order of magnitude stronger than the seasonal variation, were oriented predominantly alongshore, and were quasi-barotropic in nature. Empirical orthogonal analyses showed that almost 90% of the variability could be represented by a single empirical mode. The alongshore fluctuations were significantly correlated with coastal sea level from October to July but during the rest of the year correlation was insignificant, possibly as a result of offshore eddies approaching the shelf.Observations at 25- and 60-m depth at a second mooring 100 km south of the first indicated a mean alongshore divergence from April to July 1979, consistent with long-term mean geostrophic flow patterns for the area. In general, currents were correlated alongshore but a two-week event in May, which manifested itself differently at the two sites, was suggestive of the impingement of an eddy onto the continental shelf. Currents and winds were poorly correlated in general.Temperature variation at sites along 700 km of coast showed a strong seasonal variation with the winter cool period extended by spring upwelling. Days-to-weeks scale fluctuations were similar at the five northernmost sites and correlations alongshore were significant for separations of up to 400 km. No evidence of propagating events was found in coastal temperatures or in currents. 相似文献
15.
Through a set of observations including satellite, cruise and mooring data during May-July 1997 the transition between the downwelling and upwelling regimes off Galicia has been characterized. The poleward flow, typical of downwelling, was associated with a series of mesoscale eddies and interacted with coastal freshwater inputs. The poleward flow along the continental slope was separated into an offshore branch and a nearshore branch by a well-defined equatorward flow and both associated with a prominent salinity maximum. With the onset of upwelling-favorable winds, equatorward flow was established over the entire shelf. At the same time, a buoyant, warm surface layer spread out over the shelf from the Rías as water previously forced in by southerly winds was flushed out by the upwelling winds. The completed transition to summertime coastal upwelling took place after the cruise but was evident in satellite images. A conceptual model is used to demonstrate that the coastal orientation with respect to the upwelling winds enhances offshore flow outside the Rías and displaces the poleward flow offshore after several days of upwelling. 相似文献
16.
Christopher M. Aiken Manuel I. Castillo Sergio A. Navarrete 《Continental Shelf Research》2008,28(17):2371-2381
A 4-year simulation of the surface circulation driven by the local wind on a section of the central Chilean coast is presented. The model is shown to reproduce the major observed features of the circulation. Comparison to observations of sea-surface temperature (SST) taken within the study area suggests that the model captures well coastal upwelling processes in the region. The circulation is shown to have two distinct modes corresponding to spring/summer and autumn/winter. During spring/summer sustained strong south-westerly wind forcing drives an equatorward coastal jet consistent with the Chile Coastal Current (CCC) and coastal upwelling at previously identified locations of intense upwelling at Topocalma Point and Curaumilla Point. Weaker winds during autumn/winter produce a slower CCC and a more homogenous SST field. Upwelling/relaxation and topographic eddies provide the main sources of variability on sub-seasonal time-scales in the model. The mechanisms responsible for each of these are discussed. Upwelling at Topocalma and Curaumilla Points is shown to be produced through generation of an upwelling Ekman bottom boundary layer following acceleration of the CCC close to the coast, reinforced by secondary circulation due to flow curvature around the headlands. Additional upwelling occurs north of Curaumilla Point due to development of shallow wind-driven overturning flow. Wind-sheltering is shown to be an important factor for explaining the fact that Valparaíso Bay is typically an upwelling shadow. Flow separation and eddy formation within Valparaíso Bay is seen to occur on the order of 10 times per year during relaxation after strong wind events and may persist for a number of weeks. Shorter lived topographic eddies are also seen to occur commonly at Topocalma and Toro Points. These eddies are shown to form in response to the surface elevation minima produced at each of these locations during upwelling. 相似文献
17.
Tara A. Kniskern Jonathan A. Warrick Katherine L. Farnsworth Robert A. Wheatcroft Miguel A. Goñi 《Continental Shelf Research》2011,31(7-8):789-805
The majority of water and sediment discharge from the small, mountainous watersheds of the US West Coast occurs during and immediately following winter storms. The physical conditions (waves, currents, and winds) within and acting upon the proximal coastal ocean during these winter storms strongly influence dispersal patterns. We examined this river–ocean temporal coherence for four coastal river–shelf systems of the US West Coast (Umpqua, Eel, Salinas, and Santa Clara) to evaluate whether specific ocean conditions occur during floods that may influence coastal dispersal of sediment. Eleven years of corresponding river discharge, wind, and wave data were obtained for each river–shelf system from USGS and NOAA historical records, and each record was evaluated for seasonal and event-based patterns. Because near-bed shear stresses due to waves influence sediment resuspension and transport, we used spectral wave data to compute and evaluate wave-generated bottom-orbital velocities. The highest values of wave energy and discharge for all four systems were consistently observed between October 15 and March 15, and there were strong latitudinal patterns observed in these data with lower discharge and wave energies in the southernmost systems. During floods we observed patterns of river–ocean coherence that differed from the overall seasonal patterns. For example, downwelling winds generally prevailed during floods in the northern two systems (Umpqua and Eel), whereas winds in the southern systems (Salinas and Santa Clara) were generally downwelling before peak discharge and upwelling after peak discharge. Winds not associated with floods were generally upwelling on all four river–shelf systems. Although there are seasonal variations in river–ocean coherence, waves generally led floods in the three northern systems, while they lagged floods in the Santa Clara. Combined, these observations suggest that there are consistent river–ocean coherence patterns along the US West Coast during winter storms and that these patterns vary substantially with latitude. These results should assist with future evaluations of flood plume formation and sediment fate along this coast. 相似文献
18.
The sea level and the barotropic, frictional circulation response for the New York Bight are used to demonstrate the effects of external sea-level forcing, bathymetry, and variable friction. The governing equation is the steady, integrated vorticity equation and is computed by finite differencing over a curvilinear grid conforming to the 10- and 100-m isobaths and extending for 250 km alongshore. The boundary conditions are based on the hypothesis that the dynamics of the shelf are driven by the external sea-level gradient and the coastal no-flux condition; and consequently the conditions at the lateral boundaries are dependent thereon. Therefore, the external sea-level slope must be independently specified, and the lateral boundary conditions must be dependently generated. The diabathic component of the external sea slope forces the calm wind circulation by its effect on the transport through the upstream boundary; and the parabathic component has also an important modifying effect by forcing a shelf convergent transport. The parabathic sea slope at the coast is independent of its offshore value, being instead a direct product of the coastal boundary condition.The bottom friction is expressed as related to the sea level through a bottom length parameter and a veer angle, both of which are taken to increase shoreward. An additional bottom stress component, related to the surface stress, is determined for bottom depths less than the Ekman depth. Such bottom stress variability produces significant alterations in the nearshore flow field, over the constant bottom stress formulation, by reducing it and causing it to veer downgradient and downwind in the nearshore.The model is forced by different wind directions and the results are discussed. The circulations generally conform to the observed mean flow patterns, but with several smaller-scale features. The strong bathymetric feature of the Hudson Shelf Valley causes a polarized up- and downvalley flow for winds with an eastward or westward component, respectively. Under mean westerly winds, there is a divergence in the shelf valley flow at about the 60-m isobath. The Apex gyre existing off the western tip of Long Island becomes more extensive for winds changing from northeast to southwest. Mean flow reversals (to the northeast) occur off both Long Island and New Jersey for wind directions changing counterclockwise from northwest to southeast and from west to east, respectively. Southeastward transport over the outer New Jersey shelf tends to be enhanced by wind and external sea-level conditions; and the transport over the New Jersey midshelf, particularly in the lee of the shelf valley, tends to be weak and variable also under these mean conditions. 相似文献
19.
Inertia theory and the finite element method are used to investigate the effect of marginal seas on coastal upwelling. In contrast to much previous research on wind-driven upwelling, this paper does not consider localized wind effects, but focuses instead on temperature stratification, the slope of the continental shelf, and the background flow field. Finite element method, which is both faster and more robust than finite difference method in solving problems with complex boundary conditions, was developed to solve the partial differential equations that govern coastal upwelling. Our results demonstrate that the environment of the marginal sea plays an important role in coastal upwelling. First, the background flow at the outer boundary is the main driving force of upwelling. As the background flow strengthens, the overall velocity of cross-shelf flow increases and the horizontal scale of the upwelling front widens, and this is accompanied by the movement of the upwelling front further offshore. Second, temperature stratification determines the direction of cross-shelf flows, with strong stratification favoring a narrow and intense upwelling zone. Third, the slope of the continental shelf plays an important role in controlling the intensity of upwelling and the height that upwelling may reach: the steeper the slope, the lower height of the upwelling. An additional phenomenon that should be noted is upwelling separation, which occurs even without a local wind force in the nonlinear model. 相似文献