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1.
The intensification of upwelling front and two-cell circulation is studied numerically in a two dimensional level model. Upwelling front is set initially with longshore geostrophic flow. The uniform wind stress forces the ocean which has an infinite north-south coast line. Two-cell circulation, downwelling just inshore-side of the front and upwelling offshore-side, is induced, and the front is intensified. It is found that the intensification is occurred in the inshore-side of the front, and the intensification is basically due to the deviation from the thermal-wind balance, as is shown bySuginohara (1977). It is found that the inshore-side cell intrudes under the pycnocline. It seems to reproduce the observed two-cell circulation. 相似文献
2.
Nobuo Suginohara 《Journal of Oceanography》1974,30(1):23-33
On the assumption that motions of the barotropic mode are horizontally nondivergent, action of the wind stress with longshore variation on a two-layer ocean adjacent to the meridional east coast is studied. Only the equatorward wind stress is considered. Along the east coast, upwelling is induced by the direct effect of the coast and is confined in a narrow strip with the width of the order of the internal radius of deformation. The upwelling propagates poleward with the internal gravity wave speed. Coastal upwelling induced by the wind stress with longshore variation may be interpreted as the generation and propagation of internal Kelvin waves. Associated with the coastal upwelling, the equatorward flow in the upper layer and the poleward flow in the lower layer are formed as an internal mode of motions. When the bottom topography with the continental shelf and slope is taken into account, occurrence of the poleward undercurrent is delayed by a few days because of the generation of continental shelf waves. And, after the forcing is stopped, the shelf waves propagate poleward away from the upwelling region and the poleward undercurrent fully develops. At the margin of the continental shelf, another upwelling region is induced and propagates poleward. 相似文献
3.
Masahiro Endoh 《Journal of Oceanography》1977,33(1):30-37
Simple numerical experiments on two-dimensional coastal upwelling are made with emphasis on the role of non-geostrophic solenoidal field of density in the formation of double-celled circulation and multi-celled density front. Geometry of shelf and slope is not taken into account. Existence of poleward undercurrent presumably caused by the longshore variation of the large scale pressure field is also suppressed for the sake of simplicity.The results are, (1) double-celled circulation revealed in the present experiment is closely related with the internal frictional layer, where the horizontal density gradient balances with the vertical gradient of the longshore velocity and the vertical diffusion of the vorticity. (2) density front formed by the emergence of the pycnocline to the sea surface is successively advected offshoreward by the Ekman transport. (3) the pycnocline intersecting the sea surface forms the density front which is nearly vertical on account of the small scale convection. The surface currents converge at the front and construct an anti-clockwise circulation (viewed from the lee side). (4) small coefficient of eddy viscosity and strong wind stress lead the Ekman transport unstable and form a multi-celled structure in the frontal region. 相似文献
4.
In this paper, the authors study the influence of the wind on the dynamics of the continental shelf and margin, in particular the formation of a secondary upwelling (or downwelling) front along the shelf break.Observations during the MOUTON2007 campaign at sea along the Portuguese coast in summer 2007 reveal the presence of several upwelling fronts, one being located near the shelf break. All upwellings are characterized by deep cold waters close to or reaching the surface and with high chlorophyll concentrations. Simplified numerical models are built in order to study a possible physical mechanism behind this observation. First, a simple shallow water model with three distinct layers is used to study the formation of secondary upwelling fronts. We show that the physical mechanism behind this process is associated with onshore transport of high potential vorticity anomalies of the shelf for upwelling favorable conditions. Sensitivity studies to bottom friction, shelf width, continental slope steepness, shelf “length” are analysed in terms of potential vorticity dynamics. In particular bottom friction is analyzed in detail and we find that, even though bottom friction limits the barotropic velocity field, it enhances the cross-shore circulation, so that no steady state is possible when stratification is taken into account. Bottom friction accelerates the onshore advection of high potential vorticity, but also drastically reduces its amplitude because of diabatic effects. The net effect of bottom friction is to reduce the secondary upwelling development. Based on similar mechanisms, previous results are then extended to downwelling favorable conditions. Finally a more realistic configuration, with bottom topography, wind forcing and stratification set up from observations, is then developed and the results confronted to the observations. Simulations overestimate the velocity amplitude but exhibit good agreement in terms of density ranges brought over the shelf and general isopycnal patterns.The application and extension of the results to more general oceanic regions is discussed and we conclude on the influence of such process on the dynamics of wind driven circulation over a shelf. 相似文献
5.
A two-dimensional numerical model is constructed to study the interaction between the coastal upwelling and the coastal front off Zhejiang coast in summer. In the f-plane model, the shelf topography, continuous stratification, and Richardson number-dependent eddy coefficients are considered. The results show that the coastal up-welling off Zhejiang in summer can be divided into two regions, the nearshore one (Region A) and the offshore one (Region B). In Region A, the alongshore wind stress has more important effect on the coastal upwelling while in Region B, the upwelling is mainly induced by the Taiwan Warm Current. The results also suggest that the formation of coastal front off Zhejiang in summer is closely related to the strength of the coastal upwelling in Region A. 相似文献
6.
2006年夏季琼东、粤西沿岸上升流研究 总被引：3，自引：1，他引：2
利用2006年夏季广东、海南、广西近海的海洋水文调查资料和卫星遥感QuikSCAT风场资料分析琼东、粤西沿岸上升流的空间结构特征, 探讨风场、风应力旋度对上升流的影响以及上升流区水温、海流、海平面对上升流的响应。结果表明:琼东、粤西沿岸上升流区并非相互独立, 从10 m层以下已经连成一片。琼东沿岸上升流主要由夏季西南季风驱动而产生, 风应力旋度也有一定贡献。琼东沿岸上升流的强度比粤西强。琼东沿岸海域的上层海水(18 m以浅)以离岸运动为主, 中下层海水以向岸运动为主。上层的离岸流速大于中下层的向岸流速。琼东沿岸的上升流现象是间歇性的, 与沿岸风速强弱有关。琼东沿岸海域海平面的升降与上升流的强弱有良好的关系, 上升流的强弱滞后于海平面的升降约1～2 d。 相似文献
7.
The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized. 相似文献
8.
The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized. 相似文献
9.
Kozo Yoshida 《Progress in Oceanography》1980,9(2):83-131
A simple three-dimensional model of a time-dependent coastal upwelling is discussed for time scales of several days to a week, with the linear, two-layer, flat-bottom and approximation. Emphasis is placed on the effects of longshore scales determined by the longshore variabilities in the wind stress distributions. The responses of the inshore motions are shown to depend critically on the longshore scales. For a certain wide range of the scales, the system reveals dominantly baroclinic responses and a full development of the poleward coastal undercurrent without β effect. Somewhat detailed discussions are given on the coastal upwelling, the coastal jet and the poleward undercurrent, which are interpreted simply as the orbital velocities of the forced Kelvin-type waves. 相似文献
10.
A three-dimensional numerical model is developed and used to study the coastal upwelling processes and corresponding seasonal changes in the sea level along the west coast of India. The upwelling and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. The model is designed to represent coastal ocean physics by resolving surface and bottom Ekman layers as realistically as possible. The prognostic variables are the three components of the velocity field, temperature, salinity and turbulent energy. The governing equations together with their boundary conditions are solved by finite-difference techniques. Experiments are performed to investigate sea level fluctuations associated with the thermal response and alongshore currents of the coastal waters. The model is forced with mean monthly wind stress forcing of January, May, July and September representing northeast monsoon and different phases of the southwest monsoon. It is known from the observational study that the upwelling process reaches to the surface waters by May along the coastal waters of the extreme southwest peninsular region. The process is more intense in July compared to May and September and its strength decreases from south to north. However, during the northeast monsoon season, which is represented by January wind stress forcing in the model, downwelling is simulated along the coast. The model simulations of the coastal response are compared with the observations and are found to be in good agreement. The maximum computed vertical velocity of about 2.0 ×10 -3 cm s -1 is predicted in July in the southern region off the coast. 相似文献
11.
Masahiro Endoh 《Journal of Oceanography》1980,36(2):134-140
Summarized is the author's study of the ocean circulation dynamics with numerical models, for which he was honored by the
Okada Prize (1979). Cited topics are formation of the western boundary current and its variation associated with imposed wind
stress, some effects of a marine ridge on the boundary current, coastal upwelling circulation and coastal thermohaline front
formation. Recent modelling efforts in Japan, specifically on numerical study of ocean circulation dynamics are also reviewed. 相似文献
12.
Yoshihiko Sekine 《Journal of Oceanography》1988,44(2):60-67
In recent years, anomalous southward intrusions of the Oyashio have been observed frequently from winter to late spring. A barotropic model is used to see the occurrence of the Oyashio intrusion, with special reference to a short time lag between the change in the wind stress in midwinter and the occurrence of the Oyashio intrusion generally in spring of the same year. It is shown that the barotropic response of the ocean to the change in wind stress is fast, and its representative time scale is about 50 days at most. The southward shift of the Oyashio and the subarctic circulation are simulated quantitatively, when the imposed wind stress is changed from the mean wind stress prior to no Oyashio intrusion to that prior to the Oyashio intrusion. It is suggested that the southward intrusion of the Oyashio is a phenomenon connected with the global change in atmospheric circulation. 相似文献
13.
A three-dimensional numerical model is developed and used to study the coastal upwelling processes and corresponding seasonal changes in the sea level along the west coast of India. The upwelling and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. The model is designed to represent coastal ocean physics by resolving surface and bottom Ekman layers as realistically as possible. The prognostic variables are the three components of the velocity field, temperature, salinity and turbulent energy. The governing equations together with their boundary conditions are solved by finite-difference techniques. Experiments are performed to investigate sea level fluctuations associated with the thermal response and alongshore currents of the coastal waters. The model is forced with mean monthly wind stress forcing of January, May, July and September representing northeast monsoon and different phases of the southwest monsoon. It is known from the observational study that the upwelling process reaches to the surface waters by May along the coastal waters of the extreme southwest peninsular region. The process is more intense in July compared to May and September and its strength decreases from south to north. However, during the northeast monsoon season, which is represented by January wind stress forcing in the model, downwelling is simulated along the coast. The model simulations of the coastal response are compared with the observations and are found to be in good agreement. The maximum computed vertical velocity of about 2.0 2 10 -3 cm s -1 is predicted in July in the southern region off the coast. 相似文献
14.
《Ocean Modelling》2011,36(4):277-303
We investigate the influence of bottom topography on the formation and trapping of long upwelling filaments using a 2-layer shallow water model on the f-plane. A wind forced along-shore current, associated with coastal upwelling along a vertical wall, encounters a promontory of finite width and length, perpendicular to the coast.In the lower layer, topographic eddies form, which are shown to drive the formation of a filament on the front. Indeed, as the upwelling current and front develop along the coast, the along shore flow crosses the promontory, re-arranging the potential vorticity structure and generating intense vortical structures: water columns with high potential vorticity initially localized upon the promontory are advected into the deep ocean, forming cyclonic eddies, while water columns from the deep ocean with low potential vorticity climb on the topography forming a trapped anticyclonic circulation. These topographic eddies interact with the upper layer upwelling front and form an elongated, trapped and narrow filament.Sensitivity tests are then carried out and it is shown that:
- •baroclinic instability of the front does not play a major role on the formation of long trapped filaments;
- •increasing the duration of the wind forcing increases the upwelling current and limits the offshore growth of the filament;
- •modifying the promontory characteristics (width, length, height and slopes) has strong impact on the filament evolution, sometimes leading to a multipolarisation of the potential vorticity anomaly structure which results in much more complicated patterns in the upper layer (numerous shorter and less coherent filaments). This shows that only specific promontory shapes can lead to the formation of well defined filaments;
- •adding bottom friction introduces a slight generation of potential vorticity in the bottom layer over the promontory, but does not significantly alter significantly the formation of the filament along the outcropped front in the present configuration;
- •modifying the stratification characteristics, in particular the density jump between the layers, has only a weak influence on the dynamics of topographic eddies and on filament formation;
- •the influence of capes is also modest in our simulations, showing that topography plays the major role in the formation of long and trapped upwelling filaments.
15.
16.
We the discuss the results of modelling wind currents in the system of Sevastopol bays. Numerical calculations are carried
out according to the model of Felzenbaum. It is shown that the decisive role in the formation of distinctive features of circulation
of waters and the essentially three-dimenstional character of currents in this part of the sea is played by the bottom topography
and the direction of winds. These distinctive features are demonstrated for the cases where the motion is induced by the northeast
and northwest winds. In the Sevastopol bays, we discovered the existence of jet longshore currents, vortex character of integral
circulation, and intense processes of upwelling and downwelling.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
17.
Seasonal variability of the Antarctic Coastal Current and its driving mechanisms in the Weddell Sea 总被引：2，自引：0，他引：2
Ismael Núez-Riboni Eberhard Fahrbach 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):1927-1941
Insight into the dynamics of the Antarctic Coastal Current (ACoC) is achieved by quantifying the contributions of its driving mechanisms to the seasonal variability of its barotropic and baroclinic components. These mechanisms are sought out in the local wind, the sea-ice concentration, wind curl of the Weddell Gyre (Sverdrup transport) and the thermohaline forcing related to warming/cooling and ice melting and freezing. These driving mechanisms induce most of the seasonal variability of both the barotropic and baroclinic components of the ACoC by deepening the pycnocline towards the coast and sharpening the baroclinic profile following thermal wind balance. The resulting coastal current has mainly a barotropic transport (82%) and a major annual cycle, which explains 37% of this component's variability (tides and other high-frequency events generate 40%). The wind contributes with 58% of the seasonal variability of the barotropic component and 23% of the baroclinic; the sea-ice concentration contributes with 8% and 18%, respectively; Sverdrup transport with 4% and 30% and the thermohaline forcing with 30% and 29%. The results of this study are obtained with analysis of fifteen CTD sections (potential density and geostrophic velocities) of RV-Polarstern obtained between 1992 and 2005, as well as composite, spectral and harmonic analyses of 9 years of time series from moored instruments (current speed and temperature), wind speed, atmospheric pressure and sea-ice concentration of satellite imagery. 相似文献
18.
The paper analyses results of the numerical simulation of upwelling events in the north-western part of the Black Sea, mostly
near the South Crimea. The calculations were performed using a numerical model based on primitive hydrodynamics equations.
Emphasis is laid on the case when a salinity front simulating the Black Sea rim current is prescribed in the initial conditions.
The interaction of the Black Sea rim current's stream with the coastline and bottom topography leads to the development of
an upwelling near the Crimea's coast, even in the absence of wind forcing. The paper discusses the structure of the three-dimensional
circulation of waters in the shelf area of the NW Black Sea. Numerical modelling results are matched up with the satellite
data obtained by the HRPT receiving station.
Translated by Vladimir A. Puchkin. 相似文献
19.
冬季婆罗洲岛西北沿岸上升流的时空特征及机理研究 总被引：1，自引：0，他引：1
Winter coastal upwelling off northwest Borneo in the South China Sea(SCS) is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in December, matures in January, starts to decay in February and almost disappears in March. Both Ekman transport induced by the alongshore winter monsoon and Ekman pumping due to orographic wind stress curl are favorable for the upwelling. Transport estimates demonstrate that the month-to-month variability of Ekman transport and Ekman pumping are both consistent with that of winter coastal upwelling, but Ekman transport is two times larger than Ekman pumping in January and February. Under the influence of El Ni?o-Southern Oscillation(ENSO), the upwelling shows remarkable interannual variability: during winter of El Ni?o(La Ni?a) years, an anticyclonic(a cyclonic) wind anomaly is established in the SCS, which behaves a northeasterly(southwesterly) anomaly and a positive(negative) wind stress curl anomaly off the northwest Borneo coast, enhancing(reducing) the upwelling and causing anomalous surface cooling(warming) and higher(lower) chlorophyll concentration. The sea surface temperature anomaly(SSTA) associated with ENSO off the northwest Borneo coast has an opposite phase to that off southeast Vietnam, resulting in a SSTA seesaw pattern in the southern SCS in winter. 相似文献
20.
A proxy named “upwelling age”, defined as the ratio of wind time scale to “advection time”, was developed to quantify the
local tendency for coastal upwelling. The formulation of the “advection time” was derived from Ekman theory. A 3D numerical
model was used to validate and refine the theoretical formula by simulating a total of 30 cases of different bottom topographies
and wind stresses. The results agree reasonably well with the theoretical formulation although some modifications are necessary.
The final formulation of the “advection time” was parameterized as a function of pycnocline depth, bottom slope, and wind
stress. 相似文献