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1.
Sea Surface Height (SSH) variability in the Indian Ocean during 1993-1995 is studied using TOPEX/POSEIDON (T/P) altimetry data. Strong interannual variability is seen in the surface circulation of the western Arabian Sea, especially in the Somali eddy structure. During the Southwest (SW) monsoon, a weak monsoon year is characterized by a single eddy system off Somalia, a strong or normal monsoon year by several energetic eddies. The Laccadive High (LH) and Laccadive Low (LL) systems off southwest India are observed in the altimetric SSH record. The variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal, is also detected. Evidence is found for the propagation of Kelvin and Rossby waves across the northern Indian Ocean; these are examined in the context of energy transfer to the western boundary currents, and associated eddies. A simple wind-driven isopycnal model having three active layers is implemented to simulate the seasonal changes of surface and subsurface circulation in the North Indian Ocean and to examine the response to different wind forcing. The wind forcing is derived from the ERS-1 scatterometer wind stress for the same period as the T/P altimeter data, enabling the model response in different (active/weak) monsoon conditions to be tested. The model output is derived in 10-day snapshots to match the time period of the T/P altimeter cycles. Complex Principal Component Analysis (CPCA) is applied to both altimetric and model SSH data. This confirms that long Rossby waves are excited by the remotely forced Kelvin waves off the southwest coast of India and contribute substantially to the variability of the seasonal circulation in the Arabian Sea. 相似文献
2.
Sea Surface Height (SSH) variability in the Indian Ocean during 1993-1995 is studied using TOPEX/POSEIDON (T/P) altimetry data. Strong interannual variability is seen in the surface circulation of the western Arabian Sea, especially in the Somali eddy structure. During the Southwest (SW) monsoon, a weak monsoon year is characterized by a single eddy system off Somalia, a strong or normal monsoon year by several energetic eddies. The Laccadive High (LH) and Laccadive Low (LL) systems off southwest India are observed in the altimetric SSH record. The variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal, is also detected. Evidence is found for the propagation of Kelvin and Rossby waves across the northern Indian Ocean; these are examined in the context of energy transfer to the western boundary currents, and associated eddies. A simple wind-driven isopycnal model having three active layers is implemented to simulate the seasonal changes of surface and subsurface circulation in the North Indian Ocean and to examine the response to different wind forcing. The wind forcing is derived from the ERS-1 scatterometer wind stress for the same period as the T/P altimeter data, enabling the model response in different (active/weak) monsoon conditions to be tested. The model output is derived in 10-day snapshots to match the time period of the T/P altimeter cycles. Complex Principal Component Analysis (CPCA) is applied to both altimetric and model SSH data. This confirms that long Rossby waves are excited by the remotely forced Kelvin waves off the southwest coast of India and contribute substantially to the variability of the seasonal circulation in the Arabian Sea. 相似文献
3.
南海海面高度季节变化的数值模拟 总被引：8，自引：1，他引：8
比较POM模式模拟与观测(TOPEX/Poseidon高度计资料)的南海海面高度(SSH)的季节变化在空间分布上的一致性和差异.结果表明:本文使用的POM模式能较好地模拟南海SSH的季节变化;冬季与夏季,春季与秋季南海海面异常场形式完全相反,冬季Ekman输运造成在西海岸的堆积要比夏季在东海岸堆积更明显,而吕宋冷涡中心附近和吕宋海峡海面季节变化振幅最大;除春季以外,在南海绝大部分海域,海面高度的季节变化主要受风力的控制,南海海面热量通量对SSH的季节变化贡献约为20%,风应力对SSH的季节变化的贡献约为80%. 相似文献
4.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(7):917-926
Time-longitude diagrams of monthly anomalies of TOPEX/Poseidon sea surface height (SSH), Levitus steric height, COADS wind stress curl, as well as meridional surface wind averaged over the northern South China Sea (SCS) from 18° to 22°N, exhibit a coherent westward phase propagation, with a westward propagation speed of about 5 cm s−1. The consistency between oceanic and atmospheric variables indicates that there is a forced Rossby wave in the northern SCS. The horizontal patterns of monthly SSH anomalies from observations and model sensitivity experiments show that the forced Rossby wave, originating to the northwest off Luzon Island, actually propagates west-northwestward towards the Guangdong coast because of zonal migration of the meridional surface wind. The winter Luzon Cold Eddy (LCE), which has been found from field observations, can be identified as a forced Rossby wave with a negative SSH anomaly in winter. It corresponds to strong upwelling and a negative temperature anomaly. Sensitivity experiments show that the wind forcing controls the generation of the LCE, while the Kuroshio is of minor importance. 相似文献
5.
V.L. Meccia C.G. Simionato M.E. Fiore E.E. D'Onofrio W.C. Dragani 《Estuarine, Coastal and Shelf Science》2009,85(2):327-343
A long term simulation of the barotropic circulation in the Río de la Plata estuary was performed with the aim of identifying the characteristic patterns of sea surface height (SSH) variability from synoptic to inter-annual time scales and their forcing mechanisms. Hamburg Shelf Ocean Model (HamSOM), forced by tides, monthly mean runoffs and 4-daily 10 m winds and surface atmospheric pressure from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis was run. The solution was analyzed for the period 1965–2004. Inter-annual variability accounts for almost 10% of the variance. The first EOF mode of SSH variability on this time scale is associated with a mean anomaly of approximately 0.25 m at the upper estuary forced by both runoff and winds, which seems to be strongly associated with the ENSO cycles. Other two modes, with periodicities around 2.5 and 10 years were also found. Even though they are linked to weaker SSH anomalies, they are consistent with inter-annual modes of wind variability reported by other authors. Those modes are important, particularly if they act in phase, because they can provide a background for stronger surges. In contrast with the salinity field, SSH variability on seasonal time scales accounts for a very small percentage of variance and it is the combination of an annual and a semi-annual signal forced by winds and runoff, respectively. Approximately 90% of the variance is due to wind driven variability on sub-annual time scales. The most significant SSH anomalies in this band are associated with cyclogenetic events in the atmosphere, occurring either over Uruguay or over the Patagonian Shelf, whereas the strengthening or weakening of the semi-permanent South Atlantic anticyclone displays a relatively smaller influence. In agreement with previous publications, the estuary's spatial patterns in response to short-scale wind variability seem to be determined by wind direction more than by wind speed. 相似文献
6.
The mechanism governing the mean state and the seasonal variation of the transports through the straits of the Japan Sea is
studied using a newly presented, simple analytical model and a basin scale general circulation model (GCM). The GCM reproduces
the transports through the straits of the Japan Sea realistically owing to its fine horizontal resolution of about 20 km and
realistic topography. A series of experiments conducted by changing surface forcing shows that the annual mean wind-driven
circulation in the North Pacific Ocean is most responsible for the formation of the mean transports. It is also found that
the seasonal variation of the alongshore component of monsoonal wind stress over the North Pacific basin, especially that
over the Okhotsk Sea, is responsible for the seasonal variation of the transports. The simple analytical model can explain
these simulated features very well. The physical concept of this model is based on the formation of the around-island circulation
through the adjustment of coastally trapped waves and Rossby waves and geostrophic control at the narrow straits. It solves
the sea surface heights (SSHs) at the edge of each strait and the transport through it. The value of the line integral of
the SSH along the island is determined by the baroclinic Rossby waves approaching the island from the east and the alongshore
wind stress around the island. The basin scale seasonal variation of SSH along the coast induced by the variation of the alongshore
monsoonal wind stress can also be incorporated into this model by giving the SSH anomaly at the northeastern point of the
Soya Strait. Thus, it is suggested that both the mean state and the seasonal variation are caused mainly by wind stress forcing.
Minor modification by the seasonal heat flux forcing brings the amplitude and the phase of the seasonal variation closer to
the observed values. 相似文献
7.
《Ocean Modelling》2008,20(3):240-251
Using new global satellite remote sensing data, we show that ignoring the ocean current dependence in the wind stress artificially increases global wind power input to the oceanic general circulation by about 32%, and more than doubles the input in the regions of strong ocean current systems. Scatterometer-derived wind stress naturally accounts for the moving ocean that is not included in traditional wind stress products. However, forcing an ocean model with a scatterometer-derived wind stress cannot actually account for the ocean current effect on the wind power input. The difference between the real and modeled surface eddy fields can reduce the damping associated with the ocean current dependence in wind stress, leading to a positive bias in global wind power input of about 23%. Most of this spurious energy flux goes directly to the fluctuation eddy field and is several times larger than the energy flux to real ocean eddies. 相似文献
8.
利用 POM(Princeton Ocean Model)海洋数值模式建立渤、黄、东海冬季三维环流动力学区域模型。模型在海-气边界使用包括风应力、气压和热通量的大气驱动, 海洋边界使用西太平洋模式提供的环流和潮位驱动, 综合模拟潮波运动、温度、盐度、环流变化和水位低频波动。 模拟了 2001 年 1 月寒潮过境时黄、 渤海水位低频波动及流场变化, 分析了其对大风过程、 气压、降温的响应, 发现冬季强劲的北风和西北风都可以通过抽吸振荡在渤、 黄海诱发水位的低频波动, 东北风则由于地形影响不能诱发渤、黄海的低频波动。气压和降温只是在波动幅度上有一定的影响。波动发源于渤海和北黄海, 最大波幅可以达到 0.6 m。波动进入南黄海后有沿黄海深槽西侧传播的倾向, 波动幅度在传播过程中逐渐减小。 相似文献
9.
Effect of River Discharge on Bay of Bengal Circulation 总被引：2，自引：1，他引：1
The seasonal circulation and mixed layer depths in Bay of Bengal is modeled using the three-dimensional Princeton Ocean Model (POM). Along the coastal boundaries a higher resolution is accomplished using the curvilinear orthogonal grid. Model uses a free-surface and terrain following sigma coordinates. The initial climatological salinity and temperature fields for the model are derived from the World Ocean Atlas-2001(WOA01). The Model is forced with wind stress derived from COADS wind climatology. Bilinear interpolation is used to obtain the initial fields and wind stress to the required model specification. Using the seasonal fields and wind stress the model is integrated for simulating Bay of Bengal circulation. The numerical simulations on climatological scale for monsoon months were conducted to study the evolution of dynamics. The simulations bring out not only the typical characteristic features of fresh water plume along the coast but also intensification of the flow over the monsoon period. The increase in the fresh water flow found to affect only the western parts of the BoB. The opposing currents due to monsoon winds and southward flowing fresh water discharge (FWD) were also delineated. The model results show that the wind stress induced turbulence process is subdued in the presence of strong vertical salinity stratification due to the influence of FWD. The simulated mixed layer depths are in agreement with the reported analytical energy required for mixing values. 相似文献
10.
We establish a mathematically consistent theory of the pseudo-sound pressure fluctuation in the deep ocean induced by nonlinearly interacting random plane waves on the surface. In the process, a new set of the second-order perturbation equations is derived and power-correlation coefficients between random plane waves are introduced. A phenomenological model is adopted for wind pressure which excites the surface waves consisting of wind-driven sea and swell. By solving the first-order- and the second-order-perturbation equations with this wind pressure as the excitation, we obtain an expression for the pressure fluctuation and its power spectral density in the gravity-wave regime. It is concluded that only the swell part of the surface waves generates the pressure fluctuation and the spectral density is modified by the power correlation coefficient. 相似文献
11.
由于分辨率不足等原因，当前大部分全球耦合气候模式对南海等海洋区域的模拟能力仍然较低。本文基于超高分辨率（Ultra high-resolution） CESM-UHR耦合模式（大气和海洋水平分辨率分别达到约25 km和约10 km）研究了南海动力海平面对全球变暖的响应。研究发现：（1） CESM-UHR能够较好地模拟出南海冬、夏季节性动力海面高度和表层环流变化；（2）在四倍二氧化碳试验下，冬季南海动力海平面变化呈现出中部低、近岸高的分布特征；夏季则呈现出西北部低、东南部高的分布特征，分别对应冬、夏表层地转流增强趋势；（3）冬、夏动力海平面变化特征与风应力旋度变化具有很好的对应关系；（4）全球变暖下南海海平面变化存在季节循环放大效应，这将增大南海极端水位灾害风险。 相似文献
12.
A regional ocean model with a horizontal resolution of 1/6° encompassing the New Zealand Exclusive Economic Zone is described. The regional model successfully downscaled solutions from a high resolution, global, coupled model HadCEM. Transport estimates from the global and regional models were compared with observations, and both models supported largely consistent, climatological mean solutions. The regional model used monthly mean forcing at the surface. Nevertheless, the regional model eddy kinetic energy (EKE) spatial patterns compared favourably with long‐term mean satellite altimetric estimates, although the modelled background EKE amplitudes were much lower than observed. A series of permanent eddies associated with the western boundary current system around the top of the North Island of New Zealand were reproduced, and an eddy adjacent to Norfolk Ridge was identified in both the global and regional models. The western boundary current system around the North Island of New Zealand and the associated eddies were the most sensitive components of the model solutions, being influenced by initial conditions, wind forcing, and the model domain size. 相似文献
13.
W.R. Geyer 《Estuarine, Coastal and Shelf Science》1997,44(6):713-722
Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events. 相似文献
14.
Intercomparison of three South China Sea circulation models 总被引：1，自引：1，他引：1
1IntroductionTheSouthChinaSeaisthelargesttropicalmarginaldeepsealocatingbetweenthewesternPacificOceanandtheeasternIndianOcean.AsapartofAsia-Australiamaritimecontinent,monsoonisaprimaryfactorforcingtheSouthChinaSeaCurrent(SCSC)variation.Drivenbynortheasterlymonsooninwinterandsouth-westerlymonsooninsummer,respectively,theSCSCbehavesacyclonicgyreandananticy-clonicgyre,correspondingly(Wyrtki,1961;Xuetal.,1982).Owingtotheshortageandexpen-sivenessofdirectobservationsintheSCS,fur-therunder… 相似文献
15.
The physical mechanism by which seasonally varying atmospheric wind stress exerted on the sea surface is communicated to the solid earth as oceanic pressure torque (continental torque) and bottom frictional torque is investigated with a linear shallow‐water numerical model of barotropic oceans. The model has a realistic land–ocean distribution and is driven by a seasonally varying climatic wind stress. A novel way to decompose the wind stress into rotational and non‐rotational components is devised. The rotational component drives ocean circulations as classical theories of wind‐driven circulations demonstrate. The non‐rotational component does not produce ocean circulations within the framework of a barotropic shallow‐water model, but balances with the pressure gradient force due to surface displacement in the steady state. Based on this decomposition, it is shown that most of the continental torque which plays a major role in producing the seasonal variation of length of day (LOD) is caused by the non‐rotational component of the wind stress. Both continental torque due to the wind‐driven circulation produced by the rotational component of the wind stress and the bottom frictional torque are of minor importance. 相似文献
16.
17.
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
18.
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
19.
东海海平面变化的综合分析 总被引：3，自引：2，他引：1
利用1993年1月至2011年12月的卫星高度计数据,研究了东海海平面变化的季节信号、线性趋势和低频信号,并结合风应力资料、Ishii温盐数据和海表面温度数据分析了季节信号和低频信号的驱动机制。东海季节性海平面变化主要由年信号组成,其占海平面变化的大部分;年信号振幅和相位的分布具有明显的区域差异;东海季节性海平面变化主要受海面风和海水热膨胀驱动,而且在不同季节、不同区域,两种驱动机制的作用存在明显差异,主导地位也不断变化;季节信号还受到黑潮的一定影响。1993-2011年间东海海平面线性上升速率为3.28mm/a,各海域海平面上升速率不同。东海海平面变化低频信号与比容海平面变化低频信号具有显著相关性,最大相关系数为0.55;东海比容海平面变化低频信号与SOI低频信号同样具有一定的相关性,最大相关系数为0.3。ENSO通过大气环流和黑潮洋流等对东海海域的比容海平面变化产生影响,比容海平面变化进而对东海年际间海平面变化产生调制作用,因此ENSO可以通过东海年际间比容海平面变化对东海年际间海平面变化产生影响。 相似文献