共查询到20条相似文献，搜索用时 15 毫秒
1.
Almudena Fontán Manuel González Neil Wells Michael Collins Julien Mader Luis Ferrer Ganix Esnaola Adolfo Uriarte 《Continental Shelf Research》2009,29(8):998-1007
The Basque coastal area, in the southeastern Bay of Biscay, can be characterised as being more influenced by land climate and inputs, than other typically ‘open sea’ areas. The influence of coastal processes, together with the presence of irregular and steep topography, complicate greatly the water circulation patterns. Water movement along the Basque coastal area is not well understood; observations are scarce and long-term current records are lacking. The knowledge available is confined to the surface currents: the surface water circulation is controlled mainly by wind forcing, with tidal and density currents being weak. However, there is a lack of knowledge available on currents within the lower levels of the water column; likewise, on the main time-scales involved in the water circulation. This study quantifies the contribution of the tidal and wind-induced currents, to the overall water circulation; it identifies the main time-scales involved within the tidal and wind-induced flows, investigating difference in such currents, throughout the water column, within Pasaia Bay (Basque coast). Within this context, extensive oceanographic and meteorological data have been obtained, in order to describe the circulation. The present investigation reveals that the circulation, within the surface and the sub-surface waters, is controlled mainly by wind forcing fluctuations, over a wide range of meteorological frequencies: third-diurnal, semidiurnal and diurnal land–sea breezes; synoptic variability; frequencies, near fortnightly periods; and seasonal. At the lower levels of the water column, the main contribution to the water circulation arises from residual currents, followed by wind-induced currents on synoptic time-scales. In contrast, tidal currents contribute minimally to the overall circulation throughout the water column. 相似文献
2.
Two prognostic experiments taking into account real atmospheric forcing for 2006 and 2011 were carried out based on the eddy-resolving numerical model with a horizontal resolution of 1.6 km for the Black Sea. The main dynamic features such as the Rim Current, the Sevastopol, and Batumi anticyclones are reproduced in both experiments. The model results are confirmed via observation data. We accomplished the analysis of simulated circulation and energetics. The results demonstrate that both the vertical viscosity and vertical diffusion along with the energy inflow from the wind have been the main contributors to the annual and seasonal budgets of kinetic and potential energies of the Black Sea circulation. It is shown that two regimes of the Black Sea general circulation are implemented depending on a magnitude of wind contribution to the kinetic energy in winter. Intensive mesoscale eddy formation was observed along the Anatolian, Caucasian, and Crimean coasts. The analysis of the Black Sea circulation and eddy energetics allowed us to conclude that the generation and development of the mesoscale coastal eddies is associated with the barotropic instability in case of intensive coastal currents and is associated with both the barotropic and baroclinic instability in case of weak coastal currents. 相似文献
3.
A coastal prediction system as an event response tool: Particle tracking simulation of an anhydrous ammonia spill in Tampa Bay 总被引：1，自引：0，他引：1
A coastal prediction system for Tampa Bay, comprised of a numerical circulation model and Lagrangian particle transport model, rapidly produces hindcast/forecast simulations that alert authorities to high impact areas following the introduction of hazardous material into the bay. The effectiveness of the prediction system as an event response tool is evaluated during an anhydrous ammonia spill. A week-long simulation predicts the trajectory of the material due to winds and currents. Physical transport of the model particles alternates from being tidally driven to being driven both by wind action and residual circulation. A forecast simulation showing particle distribution drove field sampling that resulted in the detection of a Pseudo-nitzschia bloom likely initiated from excess ammonium in the bay. An online component of the coastal prediction system is in development to better manage response and mitigation efforts for future hazardous material spills in Tampa Bay. 相似文献
4.
This study examines main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the inner Scotian Shelf (ISS) in June and July 2006 using a nested-grid coastal ocean circulation modeling system known as the NCOPS-LB. The nested-grid system has five relocatable downscaling submodels, with the outermost submodel of a coarse horizontal resolution of (1/12)° for simulating storm surges and barotropic shelf waves over the Eastern Canadian shelf and the innermost submodel of a fine resolution of ～180 m for simulating the 3D coastal circulation and hydrography over Lunenburg Bay of Nova Scotia in the default setup. The NCOPS-LB is driven by meteorological and astronomical forcing and used to study the storm-induced circulation over the ISS during tropical storm Alberto. Model results demonstrate that the coastal circulation and hydrographic distributions over the ISS are affected significantly by tides, local wind forcing, and remotely generated coastal waves during the study period. 相似文献
5.
Wind effects on the lateral structure of density-driven circulation in Chesapeake Bay 总被引：3，自引：0，他引：3
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. 相似文献
6.
William R. Holland 《地球物理与天体物理流体动力学》2013,107(1):187-210
AbstractOne of the central unsolved theoretical problems of the large scale ocean circulation is concerned with explaining the very large transports measured in western boundary currents such as the Gulf Stream and the Kuroshio. The only theory up to now that can explain the size of these transports is that of non-linear recirculation in which the advective terms in the momentum equations became important near the western boundary. In this paper an alternative explanation is suggested. When bottom topography and baroclinic effects are included in a wind-driven ocean model it is shown that the western boundary current can have a transport larger than that predicted from the wind stress distribution even when the nonlinear advective terms are ignored. The explanation lies in the presence of pressure torques associated with bottom topography which can contribute to the vorticity balance in the same sense as the wind stress curl.Three numerical experiments have been carried out to explore the nature of this process using a three dimensional numerical model. The first calculation is done for a baroclinic ocean of constant depth, the second for a homogeneous ocean with an idealized continental slope topography, and the third for a baroclinic ocean with the same continental slope topography. The nature of the vorticity balance and of the circulation around closed paths is examined in each case, and it is shown that bottom pressure torques lead to enhanced transport in the western boundary current only for the baroclinic case with variable depth. 相似文献
7.
《Continental Shelf Research》1999,19(9):1221-1245
This paper presents some recent results of drifters released on the West Florida Shelf during 1996–1997 and compares with the numerical model results of the wind-driven circulation. Using satellite tracked surface drifters during the one year period from February 1996 to February 1997, a drifter free region, called the “forbidden zone”, is found over the southern portion of the West Florida Shelf. This finding is consistent with historical drift bottle data and with a recent numerical model study of the West Florida Shelf circulation response to climatological wind forcing. Direct drifter simulations by numerical model during March 1996 show a good agreement with both the in situ ADCP current observation and drifter observation. Three mechanisms are proposed for the observed Lagrangian features. The primarily dynamic mechanism is the along-shore wind forcing, which induces a coastal jet that tends to leave the coast and the bottom onshore and near surface offshore transports. The second one is the convergent coastal geometry and bottom topography for the southward flow in central shelf near Tampa Bay that enforces the coastal jet and the bottom and near surface transport. The last is a kinematic one, simply due to the short along-shore Lagrangian excursion, driven by the typical synoptic weather systems. Thus near surface shelf waters over the north may not reach the southern coast of the West Florida. Implication is that surface hazard such as oil spill that may occur outside of the southern West Florida shelf may not greatly impact the southern coastal region except Florida Keys. However, the biological and chemical patches over the north that may occur in the water column such as red tides still can easily reach the southern coastal region through the subsurface and bottom waters. 相似文献
8.
The response of the Chesapeake Bay to river discharge under the influence and absence of tide is simulated with a numerical model. Four numerical experiments are examined: (1) response to river discharge only; (2) response to river discharge plus an ambient coastal current along the shelf outside the bay; (3) response to river discharge and tidal forcing; and (4) response to river discharge, tidal forcing, and ambient coastal current. The general salinity distribution in the four cases is similar to observations inside the bay. Observed features, such as low salinity in the western side of the bay, are consistent in model results. Also, a typical estuarine circulation with seaward current in the upper layer and landward current in the lower layer is obtained in the four cases. The two cases without tide produce stronger subtidal currents than the cases with tide owing to greater frictional effects in the cases with tide. Differences in salinity distributions among the four cases appear mostly outside the bay in terms of the outflow plume structure. The two cases without tide produce an upstream (as in a Kelvin wave sense) or northward branch of the outflow plume, while the cases with tide produce an expected downstream or southward plume. Increased friction in the cases with tide changes the vertical structure of outflow at the entrance to the bay and induces large horizontal variations in the exchange flow. Consequently, the outflow from the bay is more influenced by the bottom than in the cases without tide. Therefore, a tendency for a bottom-advected plume appears in the cases with tide, rather than a surface-advected plume, which develops in the cases without tide. Further analysis shows that the tidal current favors a salt balance between the horizontal and vertical advection of salinity around the plume and hinders the upstream expansion of the plume outside the bay. 相似文献
9.
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. 相似文献
10.
Kyoko Ohashi Jinyu Sheng Keith R. Thompson Charles G. Hannah Harold Ritchie 《Continental Shelf Research》2009
A numerical shelf circulation model was developed for the Scotian Shelf, using a nested-grid setup consisting of a three-dimensional baroclinic inner model embedded inside a two-dimensional barotropic outer model. The shelf circulation model is based on the Princeton Ocean Model and driven by three-hourly atmospheric forcing provided by a numerical weather forecast model and by tidal forcing specified at the inner model's open boundaries based on pre-calculated tidal harmonic constants. The outer model simulates the depth-mean circulation forced by wind and atmospheric pressure fields over the northwest Atlantic Ocean with a horizontal resolution of 1/12°. The inner model simulates the three-dimensional circulation over the Gulf of St. Lawrence, the Scotian Shelf, and the adjacent slope with a horizontal resolution of 1/16°. The performance of the shelf circulation model is assessed by comparing model results with oceanographic observations made along the Atlantic coast of Nova Scotia and in the vicinity of Sable Island (on the Scotian Shelf) during two periods: October 2000–March 2001 and April–June 2002. Analysis of model results on Sable Island Bank indicates that tidal currents account for as much as ∼80% of the total variance of near-bottom currents, and currents driven by local winds account for ∼30% of the variance of the non-tidal near-bottom currents. Shelf waves generated remotely by winds and propagating into the region also play an important role in the near-bottom circulation on the bank. 相似文献
11.
We describe a numerical forecast system designed for prediction of physical and biological dynamics of a coastal inlet. It is based on a coastal ocean observatory that was located at Lunenburg Bay, Nova Scotia, Canada. Biological, chemical, optical, and physical measurements were collected from instrumented moorings, weekly sampling and detailed surveys from 2002 through 2007. Here we present a framework for calibration and evaluation of an ecosystem model using data from the summer of 2007. A three-dimensional hydrodynamic model was coupled to a simple biological (Nutrients-Phytoplankton-Detritus) model; a simple model was used so results could be compared directly to observed biological and chemical variables using skill scores as a first step toward data-assimilation modeling. As a complement to this analysis, variability of model output, e.g., the nutrient limitation term, was examined to understand the modeled biological response to the simulated physical environment. Skill scores based on variances in observed and simulated time-series of biological components were also investigated. Coastal upwelling/downwelling simulated through this model has been found to increase modeled biological activity in the bay. Also model skill in reproducing the observed patterns in nutrients and phytoplankton has been increased due to the restoring conditions for biology set up at the open ocean boundaries of the bay. 相似文献
12.
Ocean Dynamics - Response of Ganga-Brahmaputra river plume to wind forcing in the Bay of Bengal is studied using a numerical ocean circulation model. Four different wind forcing scenarios, namely,... 相似文献
13.
The transport of the Antarctic Circumpolar Current (ACC) is influenced by a variety of processes and parameters. A proper
implementation of basin geometry, ocean topography and baroclinicity is known to be a fundamental requisite for a realistic
simulation of the circulation and transport. Other, more subtle parameters are those of eddy-induced transports and diapycnal
mixing of thermohaline tracers or buoyancy, either treated by eddy resolution or by a proper parameterization. Quite a number
of realistic numerical simulations of the circulation in the Southern Ocean have recently been published. Many concepts on
relations of the ACC transport to model parameters and forcing function are in discussion, however, without much generality
and little success. We present a series of numerical simulations of circumpolar flow with a simplified numerical model, ranging
from flat-bottom wind-driven flow to baroclinic flow with realistic topography and wind and buoyancy forcing. Analysis of
the balances of momentum, vorticity, and baroclinic potential energy enables us to develop a new transport theory, which combines
the most important mechanisms driving the circulation of the ACC and determining its zonal transport. The theory is based
on the importance of the bottom vertical velocity in generating vorticity and shaping the baroclinic potential energy of the
ACC. It explains the breaking of the -constraint by baroclinicity and brings together in one equation the wind and buoyancy forcing of the current. The theory
emphasizes the role of Ekman pumping and eddy diffusion of buoyancy to determine the transport. It also demonstrates that
eddy viscosity effects are irrelevant in the barotropic vorticity balance and that friction arises via eddy diffusion of density.
In this regime, the classical Stommel model of vorticity balance is revived where the bottom friction coefficient is replaced
by (with the Gent–McWilliams coefficient and the baroclinic Rossby radius ) and a modified wind curl forcing appears. 相似文献
14.
John A. Johnson 《Continental Shelf Research》1982,1(2):143-157
Stratification is incorporated into an unsteady model of shelf currents by splitting the dynamic response of the flow into two parts, each with its own time scale. The barotropic part of the response is independent of depth and varies rapidly on a short time scale, whereas the baroclinic part depends on depth and changes slowly with time on a long time scale.The three-dimensional model has a continental shelf sloping down from an eastern boundary to the deep ocean. The equations for the barotropic component of the pressure field contain forcing by the wind stress and feedback from the baroclinic field. An integral of the heat equation over the long time scale determines the slow changes in the temperature field and hence in the baroclinic component of the velocity distribution.The temperature field is specified at the start of the numerical calculation. Its subsequent development is controlled by the numerical procedure. It is found that significant changes in the temperature field require a long period of upwelling favourable winds, whereas the longshore currents react more quickly to changes in the wind stress. 相似文献
15.
Alexander Port Klaus-Werner Gurgel Joanna Staneva Johannes Schulz-Stellenfleth Emil V. Stanev 《Ocean Dynamics》2011,61(10):1567-1585
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. 相似文献
16.
Summary With a view of understanding the various processes responsible for the deposition of sand in the vicinity of Kakinada Bay and Godavari Point, an intensive study of currents in the coastal waters has been made using floats. The circulation has high variability in both magnitude and direction related to the three current components namely wind currents, tidal currents and wave currents. The circulation pattern rapidly changes with the change in the phase of the tide and local winds of land and see breeze. The littoral currents directed up-coast during premonsoon and monsoon seasons have insignificant effect across the bay opening due to the sheltering effect of the sand bar. The study is found helpful for understanding the geomorphological changes of the shoreline in this region from time to time. 相似文献
17.
18.
Upwelling and surface cold patches in the Yellow Sea in summer: Effects of tidal mixing on the vertical circulation 总被引：5，自引：0，他引：5
A three-dimensional, prognostic, wave–tide–circulation coupled numerical model is developed to study the effects of tidal mixing on the summertime vertical circulation in the Yellow Sea (YS). The distribution and mechanisms of upwelling are investigated by numerical means. Validated by historical tide gauge data, satellite sea surface temperature (SST) data, and cruise observation data, the model shows satisfactory performances in reproducing the dominant tidal system and three-dimensional sea temperature structure. Model results suggest that strong tidal mixing plays an important role in the formation of the vertical circulation in the YS. The Yellow Sea Cold Water Mass (YSCWM) is fringed by typical tidal mixing fronts (TMFs), which separate the cold, stratified water at the offshore side from the warm, well-mixed, shallow water at the other side. Considerable baroclinic gradient across the TMF makes the frontal zone the spot where the most active vertical circulation occurs; a secondary circulation is triggered with a distinct upwelling branch occurring mainly on the mixed side of the front. The numerical model produces systematic upwelling belts surrounding the YSCWM, and the upwelling is essentially induced by the TMF over sloping topography. The relative importance of tidal mixing and wind forcing for upwelling is further examined in numerical experiments. The southerly wind enhances the upwelling off the western coasts, but its overall influences in the whole YS are less important than tidal mixing. As shown by both satellite data and numerical modeling, the summertime SST field in the YS is featured by the stable existence of several site-selective surface cold patches (SCPs), most of which scatter in the waters off convex coastlines. One of the SCPs is found off Subei Bank, and the others are located off the eastern tip of Shandong Peninsula and off the three tips of Korean Peninsula. Two processes give rise to the SCP: on the one hand, TMF-induced upwelling supplies cold water from the deep layer; on the other hand, tidal mixing itself can stir the bottom water upward and homogenize the water column vertically. In the waters around the tips of peninsula in the YS, the tidal currents are extraordinarily strong, which provides a possible explanation for the site-selectivity of the SCPs. 相似文献
19.
This paper deals with the interaction and small-scale processes occurring around the inlets that connect the Venice Lagoon
with the Northern Adriatic Sea. In a previous paper, barotropic processes have been investigated, whereas here, the focus
is on the baroclinic processes. The hydrodynamics of the area are studied by means of a 3D shallow water hydrodynamic finite-element
model, suitable to describe areas of complex morphology such as the coasts and the interaction channels. This is the first
work that models the 3D interaction between the Venice Lagoon and the Adriatic Sea. Three different sets of simulations have
been carried out to identify the physics behind the small-scale processes and the influence of the main forcings on the study
area. The first imposes different idealized forcings, such as tides, wind, and river runoff. The vorticity maps of the first
two layers show the predominance of wind forcing in the coastal area and tidal forcing in the three inlets of the Lagoon.
Bora wind acts homogeneously, increasing the littoral currents, while Sirocco wind mainly impacts near Chioggia inlet, with
a coastal current reversal, inducing its detachment offshore. Freshwater patterns are present along the coast, near the river
mouths. Rivers do not directly influence the circulation close to the coast in front of the Venice Lagoon, except for the
area near Chioggia inlet, where the Brenta river action can be seen. The second set of simulations deals with a sensitivity
analysis to define the importance of the advection and of the baroclinic pressure gradient terms in the creation of persistent
structures, such as small-scale coastal vortices seen along the littoral very close to the inlets. This analysis shows how
advection is the main physical process responsible for the persistence of the positive vorticity structures close to the coast
between the inlets, while the negative vorticity structures, also seen by the HF Radar, are due to the baroclinic-advective
interaction. Finally, a real case, year 2004, has been simulated both to validate the model with observations and to identify
the occurrence during the year of the characteristic hydrodynamic features attributable to the main forcings. The action of
Bora wind characterizes the surface current patterns of February and November 2004, while Sirocco influences the month of
May 2004. During periods of weak wind, the model reproduces the small-scale vortical structures close to the littoral. 相似文献
20.
Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia, is a shallow tidal area (average
depth = 15 m), close to the continental shelf. It shows features of an inverse estuary, due to the high evaporation rate (approx.
2 m/year), low precipitation (less than 1 m/year) and on average almost no freshwater input from rivers that drain into the
bay. The hydro- and thermodynamical structures of Hervey Bay and their variability are presented here for the first time,
using a combination of four-dimensional modelling and observations from field studies. The numerical studies are performed
with the Coupled Hydrodynamical Ecological Model for Regional Shelf Seas (COHERENS). Due to the high tidal range (>3.5 m),
the bay is considered as a vertically well-mixed system, and therefore, only horizontal fronts are likely. Recent field measurements,
but also the numerical simulations, indicate characteristic features of an inverse/hypersaline estuary with low salinity (35.5 psu)
in the open ocean and peak values (>39.0 psu) in the head water of the bay. The model further predicts a nearly persistent
mean salinity gradient of 0.5 psu across the bay (with higher salinities close to the shore). The investigation further shows
that air temperature, wind direction and tidal regime are mainly responsible for the stability of the inverse circulation
and the strength of the salinity gradient across the bay. Due to an ongoing drying trend, the occurrence of severe droughts
at the central east coast of Australia and, therefore, a reduction in freshwater supply, the salinity flux out of the bay
has increased, and the inverse circulation has also strengthened. 相似文献