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1.
TOPEX/Poseidon satellite altimetry data from 1993 to 1999 were used to study mean annual variation of sea surface height anomaly
(SSHA) in the South China Sea (SCS) and to reproduce its climatological monthly surface dynamic topography in conjunction
with historical hydrographic data. The characters and rules of seasonal evolution of the SCS dynamic topography and its upper
circulation were then discussed. Analyses indicate that annual variation of the SCS large-scale circulation could be divided
into four major phases. In winter (from November to February), the SCS circulation is mainly controlled by double cyclonic
gyres with domination of the northern gyre. Other corresponding features include the Kuroshio intrusion from the Luzon Strait
and the northeastward off-shelf current in the area northwest off Kalimantan Island. The double gyre structure disassembled
in spring (from March to April) when the northern gyre remains cyclonic, the southern gyre becomes anticyclonic, and the general
circulation pattern shows a dipole. There is no obvious large-scale closed gyre inside the SCS basin in both summer (from
May to July) and autumn (from August to October) when the SCS Monsoon Jet dominates the circulation, which flows northeastward
across the SCS. Even so, circulation patterns of these two phases diverse significantly. From May to July, the SCS monsoon
jet flows northward near the Vietnam coast and bends eastward along the topography southeast off Hainan Island at about 18°N
forming an anticyclonic turn. It then turns northeastward after crossing the SCS. From August to October, however, the monsoon
Jet leaves the coast of Vietnam and enters interior of the basin at about 13°N, and the general circulation pattern becomes
cyclonic. The Kuroshio intrusion was not obvious in spring, summer and autumn. It is suggested from these observations that
dynamic adjustment of the SCS circulation starts right after the peak period of the prevailing monsoon. 相似文献
2.
Annual variation of sea surface height, dynamic topography and circulation in the South China Sea —— A TOPEX/Poseidon satellite altimetry study 总被引：1，自引：0，他引：1
The South China Sea (SCS) is a semi-enclosed deep basin with complex topography includ-ing broad continental shelves, steep slopes, and a large deep basin. It is dominated by prevailing southwest monsoon in summer and by much stronger northeast monsoon in… 相似文献
3.
We applied a three-dimensional general ocean and coastal circulation model to the Irish Sea in order to determine water renewal time scales in the region. The model was forced with meteorological data for 1995, a year with relatively warm summer and when extensive hydrographic surveys were conducted in the Irish Sea. We investigated intra-annual variability in the rates of net flow through the Irish Sea and carried out several flushing simulations based on conservative tracer transport. The results indicate that the net northward flow of 2.50 km3/d is seasonally highly variable and under certain conditions is reversed to southward. The variability in obtained residence times is high; baroclinic effects are significant. Obtained results point at the importance of spatial and temporal consideration for transport of pollutants in the shelf seas. Implications for management are numerous and involve activities such as transport, fishing, use of resources, nature conservation, monitoring, tourism and recreation. 相似文献
4.
利用1979—2013年NCEP/DOE再分析资料的大气多要素日平均资料、美国NOAA日平均向外长波辐射资料和ERSST月平均海温资料,分析赤道大气季节内振荡(简称MJO)活动对南海夏季风爆发的影响及其与热带海温信号等的协同作用.结果表明,赤道MJO活动与南海夏季风爆发密切联系,MJO的湿位相(即对流活跃位相)处于西太平洋位相时,有利于南海夏季风爆发,而MJO湿位相处于印度洋位相时,则不利于南海夏季风爆发.赤道MJO活动影响南海夏季风爆发的物理过程主要是大气对热源响应的结果,当MJO湿位相处于西太平洋位相时,一方面热带西太平洋对流加强使潜热释放增加,导致处于热源西北侧的南海—西北太平洋地区对流层低层由于Rossby响应产生气旋性环流异常,气旋性环流异常则有利于西太平洋副热带高压的东退,另一方面菲律宾附近热源促进对流层高层南亚高压在中南半岛和南海北部的建立,使南海地区高层为偏东风,从而有利于南海夏季风建立;当湿位相MJO处于印度洋位相时,热带西太平洋对流减弱转为大气冷源,情况基本相反,不利于南海夏季风建立.MJO活动、孟加拉湾气旋性环流与年际尺度海温变化协同作用,共同对南海夏季风爆发迟早产生影响,近35年南海夏季风爆发时间与海温信号不一致的年份,基本上是由于季节转换期间的MJO活动特征及孟加拉湾气旋性环流是否形成而造成,因此三者综合考虑对于提高季风爆发时间预测水平具有重要意义. 相似文献
5.
Seasonal variation of upper layer circulation in the northern part of the East/Japan Sea and its mechanism were investigated using empirical orthogonal function (EOF) analysis with satellite sea surface heights over the northern East/Japan Sea and a three-dimensional circulation model. The spatial structure and temporal variation of first EOF mode, which explains about 64% of the total variance, indicate that a large cyclonic circulation in the northern East/Japan Sea shows a semi-annual variation with maximum strength in summer and winter. According to numerical model result, the Liman Cold Current, accepted as a major current in the northern East/Japan Sea, is well mixed vertically by the winter monsoon and the current in the upper layer has a relatively deep structure, with a maximum westward speed of about 20 cm/s in winter. On the other hand, in summer the current has a stronger baroclinic structure of velocity than in winter. Numerical experiments showed that in summer the temporal variation of upper layer circulation is controlled by thermal forcing, such as sea surface heat flux and inflow of heat transport into the East/Japan Sea through the Korea/Tsushima Strait. Moreover, the cyclonic circulation in the upper layer of the northern East/Japan Sea is also generated and strengthened by the positive wind stress curl occupying most of the East/Japan Sea during the winter. The seasonal variation of each forcing that drives the circulation is responsible for the strength or weakness of the upper layer circulation in the northern East/Japan Sea. The contribution of each forcing to the seasonal variation of the upper layer circulation is examined through sensitivity experiments. According to these numerical experiments, the upper layer circulation in the northern East/Japan Sea is strengthened twice a year, in winter and summer, and this semi-annual variation is determined by a combination of wind (winter) and thermal (summer) forcing. 相似文献
6.
A chain of three nested models, based on the MARS 3D code, is used to simulate the North-western Mediterranean Sea circulation
with a finest grid of 1.2 km resolution and 30 vertical sigma levels. This modelling system allows to resolve the coastal
dynamics taking into account the influence of the general basin circulation. The aim of this study is to assess the ability
of the nested MARS-3D models to reproduce most of the circulation features observed in the North-western Mediterranean Basin
and in the Gulf of Lions. Comparisons of modelled sea surface temperature and salinity with MEDAR/MEDATLAS climatology and
NOAA/AVHRR satellite measurements show that the model accurately reproduces the large and coastal scale variability. Over
the Northern Basin, the seasonal changes of the cyclonic gyre extension are correctly simulated, even though in summer, the
modelled temperature of the surface layer remains in basin-average 1°C cooler than the satellite measured temperature. As
soon as the stratification erodes, modelled and observed temperatures become closer. Over the Gulf of Lions, realistic coastal
responses are obtained under different wind conditions. Upwellings are correctly located and their intensity and spatial extension
were here improved by the use of Aladin wind fields (10 km spatial resolution) and the introduction of a drag coefficient
fitted according to the stability of the planetary boundary layer. The dispersion of fresh Rhone water discharge and the mesoscale
circulation simulated by MARS-3D also agree with satellite measurements. 相似文献
7.
Time series of hydrographic sections in the northern North Atlantic from the period 1990 to 2004 are analyzed for changes
in the characteristics and distribution of water masses that are involved in the thermohaline circulation (THC). During the
1990s, the North Atlantic Oscillation (NAO) alternates from a positive phase (strong westerlies) to a negative phase (weak
westerlies). The reduced ocean heat loss confined the convection in the Labrador Sea to the upper 1,200 m, generating a new
salinity minimum layer characterizing the Upper Labrador Sea Water (ULSW), and led to a warming and salinization of the older
LSW below due to lateral mixing. The Lower LSW, formed in the first half of the 1990s, spread in the subpolar gyre and reached
the Newfoundland and Irminger basins after about 1 to 2 years, where the associated isopycnal doming contributed to eastward
frontal shifts in the upper layer. After 5 and 6 years, it arrived in the Iceland and West European basins, respectively.
The collapse of the isopycnal dome in the Labrador Sea, associated with the drainage of the Lower LSW, resulted in a slowing
of the cyclonic circulation of the subpolar gyre. This was accompanied in the upper layer by a westward shift of the southeastern
extension of the gyre and a northward advection of warm and saline subtropical water in its eastern part, which finally reached
the Labrador Sea after about 7 years. In the upper layer of the Labrador Sea, the advection of warm and saline water dominated
over the heat loss to the atmosphere and the freshwater gain from melting ice and precipitation in the NAO-low period, so
that no accumulation of freshwater but an increase of the heat and salt contents were observed, as in the whole eastern part
of the subpolar gyre. Within 1 to 2 years after the drop of the NAO in the winter of 1995/1996, the Subarctic (Subpolar) Front
shifted northward and westward north of about 50°N, favored by the retreat of the low-salinity tongue extending eastward from
the southern Labrador Sea, and it shifted southward and eastward in the Newfoundland Basin. Therefore, the enhanced northward
advection of subtropical waters in the northeastern North Atlantic is balanced by the enhanced southward advection of subarctic
waters, including Lower LSW in the Newfoundland Basin, indicating a strong response of the gyre component of the THC. 相似文献
8.
A three-dimensional prognostic hydrodynamic model in cross sectional form is used to examine the influence of bottom friction,
mixing and topography upon the spin-down and steady-state circulation in a cold water bottom-dome. Parameters characteristic
of the Irish Sea or Yellow Sea cold water domes are used. In all calculations, motion is induced by specifying an initial
temperature distribution characteristic of the dome, and an associated along frontal flow. The spin-down of the dome is found
to be influenced by the coefficient of bottom friction, with a typical time scale of order 10 days, and in general to be independent
of the chosen initial vertical profile of along frontal flow. However, in the case in which the along frontal flow is such
that the near bed velocity is zero, then bottom stress is also zero, and there is no appreciable spin-down. Calculations showed
that the formulation of viscosity and diffusivity had a greater effect upon the steady-state circulation than topography,
suggesting that background mixing of tidal origin is important. The lack of topographic influence was due mainly to the formulation
of the initial conditions which were taken to be independent of topography. The steady-state circulation was characterized
by a cyclonic flow in the surface region, with an anti-cyclonic current near the bed, where frictional effects produced a
bottom Ekman layer and an across frontal flow. This gave rise to vertical circulation cells in the frontal region of the dome
with prevailing downwelling motion inside the dome. A detailed analysis of the dynamic balance of the various terms in the
hydrodynamic equations yielded insight into the processes controlling the steady-state circulation in cold water domes.
Responsible Editor: Phil Dyke 相似文献
9.
A variable mesh finite element model of the Irish and Celtic Sea regions with/without the inclusion of the Mersey estuary is used to examine the influence of grid resolution and the Mersey upon the higher harmonics of the tide in the region. Comparisons are made with observations and published results from finite difference models of the area. Although including a high resolution representation of the Mersey had little effect upon computed tides in the western Irish Sea it had a significant effect upon tidal currents in the eastern Irish Sea. In addition the higher harmonics of the M2 tide in near-shore regions of the eastern Irish Sea particularly the Solway and Mersey estuary together with Morecambe Bay showed significant small scale variability. The Mersey was used to test the sensitivity to including estuaries because high resolution accurate topography was available. The results presented here suggest that comparable detailed topographic data sets are required in all estuaries and near-shore regions. In addition comparisons clearly show the need for an unstructured grid model of the region that can include all the estuaries. Such an unstructured grid solution was developed here within a finite element approach, although other methods in particular the finite volume, or coordinate transformations/curvilinear grids and nesting could be applied. 相似文献
10.
A coarse-grid (resolution of order 7 km) model of the west coast of Britain is used to examine the sensitivity of computed storm-surge elevations and currents to a range of open-boundary conditions. The storm-surge period 1 to 26 March 1994 is used for this comparison, as it is a time of significant wind activity. Also current measurements in the North Channel of the Irish Sea together with coastal elevation measurements are available for model validation. Elevations and currents previously computed with a coarse-grid shelf-wide model can also be incorporated into the open-boundary condition to examine the influence of far-field effects. Initial model calculations with no far-field input show the importance of including shelf-wide effects from either the external shelf model, or by using observations from coastal gauges interpolated along the open boundary of the west-coast model. Provided the west-coast models open boundary is taken sufficiently far away from the region of interest, in this case the Irish Sea, then either a radiation condition or an elevation-specified condition is appropriate provided far-field effects are taken into account. If these are not included, then neither boundary condition is successful. For the radiation condition it is necessary to include both elevations and currents from a far-field model in order to reproduce the surge. In the case of an elevation-specified boundary condition far-field effects can be incorporated in hindcast calculations by including observed sea-level changes. In a storm-surge prediction calculation the radiation condition with a far-field model is required. Calculations show that computed elevations are spatially more coherent than currents, with flows through the western Irish Sea showing the greatest sensitivity to open-boundary formulation during storm events.Responsible Editor: Phil Dyke 相似文献
11.
《中国科学:地球科学(英文版)》2015,(2)
Due to limited in situ data and diagnostic numerical models, the summer circulation structure and formation mechanism in the Beibu Gulf have always been in controversy in the past 50 years. Therefore, a new three-dimensional hindcast model was built within the northwestern South China Sea(SCS), forced with the daily averaged wind, heat flux, lateral flux, as well as tidal harmonic and eight major rivers discharges. And the east boundary was set up far away off the Qiongzhou Strait(QS). Lastly, the model results were consistent with not only the synchronous observation data from the project 908 but also the historical observed data. As a result, the summer circulation structure was revealed that the southern Gulf was occupied by an anticyclonic eddy whereas the northern Gulf was dominated by a cyclonic gyre. Although the circulation major structure was stable, its area and strength had yearly and monthly oscillation. The other three sensitive experiments indicated that the circulations in the southern and northern Gulf were driven by the SCS circulation and monsoon wind, respectively. After the theoretical analysis of the potential vorticity budget, it was further revealed the circulation in the northern Gulf was driven by the positive wind stress curl in summer. Besides, the river discharge was also significant as the vertical circulation had two layer structures outside the mouth of the Red River. Generally, this work calls for the further research on other subjects, such as ocean biogeochemical or marine fisheries. 相似文献
12.
Post-glacial sediment dynamics in the Irish Sea and sediment wave morphology: Data–model comparisons
Katrien J.J. Van Landeghem Katsuto Uehara Andrew J. Wheeler Neil C. Mitchell James D. Scourse 《Continental Shelf Research》2009,29(14):1723-1736
The irregular seafloor of the narrow Irish Sea on the NW European Shelf has been documented over several decades. From recently collected swath bathymetry data, very large trochoidal, nearly symmetrical sediment waves are observed in many parts of the Irish Sea and appear similar to those described from other continental shelf seas in North America that were covered by glacigenic sediments during the Last Glacial Maximum. Swath multibeam and single beam bathymetry data, backscatter intensity, shallow seismic imagery, video footage and sediment cores from the Irish Sea high sediment waves have been integrated to identify their genesis with reference to present and past hydrodynamic variability. From cross-sectional profiles over asymmetrical sediment waves in the Irish Sea the direction of asymmetry is used to map residual bed stress directions and associated bedload transport paths. Irish Sea peak bed stress vectors were generated using a two-dimensional palaeo-tidal model for the NW European shelf seas and compare well with the observations. Tidally induced bed stresses are modelled to have increased between 7–10 ka BP, to be nearly symmetrical in magnitude and to have reversed in dominant direction on a millennial scale. These environmental conditions during the post-glacial marine transgression are suggested here to help comprehend the construction of the very large sediment waves, with local variations due to differences in sediment grain size, sediment supply, water depth and intensified currents due to seafloor slopes. Model parameterisation using an open ocean boundary with time-dependent tidal changes and the implementation of high-resolution bathymetric information will improve future models of small-scale bed shear stress patterns and improve the predictive value of such modelling efforts. 相似文献
13.
Shigeru Aoki Yoshikazu Sasai Hideharu Sasaki Humio Mitsudera Guy D. Williams 《Ocean Dynamics》2010,60(3):743-757
Flow structure in the Australian–Antarctic basin is investigated using an eddy-resolving general ocean circulation model and validated with iceberg and middepth float trajectories. A cyclonic circulation system between the Antarctic Circumpolar Current and Antarctic Slope Current consists of a large-scale gyre in the west (80–110° E) and a series of eddies in the east (120–150° E). The western gyre has an annual mean westward transport of 22 Sv in the southern limb. Extending west through the Princess Elizabeth Trough, 5 Sv of the gyre recirculates off Prydz Bay and joins the western boundary current off the Kerguelen Plateau. Iceberg trajectories from QuickScat and ERS-1/2 support this recirculation and the overall structure of the Antarctic Slope Current against isobath in the model. Argo float trajectories also reveal a consistent structure of the deep westward slope current. This study indicates the presence of a large cyclonic circulation in this basin, which is comparable to the Weddell and Ross gyres. 相似文献
14.
A simple and efficient method to improve morphological predictions using depth-averaged tidal models is presented. The method includes the contribution of secondary flows in sediment transport using the computed flow field from a depth-averaged model. The method has been validated for a case study using the 3D POLCOMS model and ADCP data. The enhanced depth-averaged tidal model along with the SWAN wave model are applied to morphological prediction around the Lleyn Peninsula and Bardsey Island as a case study in the Irish Sea. Due to the presence of a headland in this area two asymmetrical tidal eddies are developed in which the cyclonic eddy is stronger as a result of Coriolis effects. The results show that the enhanced model can effectively predict formation of sand banks at the centre of cyclonic eddies, while the depth-averaged model, due to its inability to accommodate secondary flow, is inadequate in this respect. 相似文献
15.
Sea surface height and transport stream function of the South China Sea from a variable-grid global ocean circulation model 总被引：8，自引：0，他引：8
The study on the South China Sea (SCS) circulation has a history of more than 40 years. Nevertheless, the SCS circulation is not fully understood compared with the Bohai Sea, Yellow Sea and East China Sea (ECS). Many numerical studies on the SCS circulati… 相似文献
16.
In the western subarctic North Pacific, a wind-driven cyclonic circulation, called the western subarctic gyre (WSAG), exists. We examined year-to-year changes of the gyre and hydrographic structures, applying the altimetry-based gravest empirical mode (AGEM) method to hydrographic and altimetric sea surface height (SSH) data, and relation to the in situ variation of the temperature minimum layer, i.e., the dichothermal layer, depth at station K2 (47° N, 160° E). The AGEM-based geostrophic volume transport and the streamfunction of the WSAG in the top 1000-dbar layer show that the gyre changes substantially. From the late 1990s to the mid-2000s, the gyre shrunk northward. Due to the shrinkage, the halocline bottom, which is equivalent to the top of the main pycnocline, deepens at K2 outside the central part of the gyre. The downward displacement of the dichothermal layer at K2 was found to be significantly related to that of the underlying halocline due to the northward shrinkage of the WSAG. 相似文献
17.
The Yellow Sea is a semi-enclosed shallow sea with a deep trough of about 80 m. On the hy-drographic condition in the Yellow Sea, Lie[1] pointed out that it is strongly associated with winter cooling and summer heating, fresh input from rivers into the co… 相似文献
18.
Modeling the circulation in the Gulf of Tonkin, South China Sea 总被引：4，自引：0，他引：4
The circulation in the Gulf of Tonkin (Beibu Gulf) was studied using the Princeton Ocean Model, which was forced with the daily surface and lateral boundary fluxes for 2006 and 2007, as well as tidal harmonics and monthly climatological river discharges. In the southern Gulf, the vertically averaged circulation was anti-cyclonic in summer and changed to cyclonic in winter. Although it was highly correlated with the local wind, the southern gyre was driven primarily by the South China Sea (SCS) general circulation from the south. Flows in the Qiongzhou Strait that played a significant role in determining the circulation variability in the northeastern Gulf could be eastward or westward at any given day in summer or winter, but the seasonal mean current was eastward from late spring through summer and westward during the rest of the year, with an annual mean westward transport of ～0.1 Sv into the Gulf. Different water masses were distinguished at the surface with the warm and saline SCS water in the south, relatively fresh plume waters along the northern and western coasts of the Gulf, and the mixture of the two in between. At lower levels, two cold water masses were identified in the model, and each had T/S distributions qualitatively similar to the observations obtained in 2007. These two water masses were produced throughout the winter, sheltered from the surface warming by a thermocline as the season progressed, and eventually disappeared in late fall. 相似文献
19.
The western boundary current in the southern South China Sea (SCS) in summer does not always flow northward along the Indo-China Peninsula, it leaves the southeast coast of peninsula around 10–14°N, forming a strong eastward jet called “Vietnam Coastal Current” or “Southeast Vietnam Offshore Current” (SVOC). It is known that the wind stress curl is the major driving factor responsible for this current. In this paper, we carry on the study of the separation position, strength and forming time of this current. A connected single-layer/two-layer model is employed here to study these problems. According to the numerical experiments and analyses of the vorticity dynamics, it is found that, the local wind stress curl (including the northern cyclonic and the southern anticyclonic wind forcing curl), the nonlinear term, the topographic effect, the planetary vorticity advection and the water exchange between the SCS and Java Sea via the Sunda Shelf have an important effect on both the position where this current leaves the coast and its strength; when there is an inflow via the Sunda Shelf, the current is stronger and the separation position is more northward; whereas the water stratification, the coastline and the inflow of Kuroshio have little effect on its separation. In fact, two opposite flowing currents, the northward SVOC and the southward western branch of the cyclonic eddy to its north near the Indo-China Peninsula, collide with each other, and the strength of these two currents determine the separation position of the SVOC. Origin of the SVOC may be driven by the local negative wind stress curl in the middle SCS in mid-spring, this current flows along the coast of the Indo-China Peninsula and leaves the coast at high latitude, flowing northeastward; once the local positive wind stress curl near the northern Indo-China Peninsula or the negative one near the southern Indo-China Peninsula is large enough, this current will begin to leave the coast at low latitude. 相似文献
20.
Modelling travel and residence times in the eastern Irish Sea 总被引：2，自引：0，他引：2
The Irish Sea, which lies between 51 degrees N-56 degrees N and 2 degrees 50'W-7 degrees W, provides a sheltered environment to exploit valuable fisheries resource. Anthropogenic activity is a real threat to its water quality. The majority of freshwater input down rivers flows into the eastern Irish Sea. The structure of the water circulation was not well understood during the planning of Sellafield nuclear plant outfall site in the eastern Irish Sea. A three-dimensional primitive equation numerical model was applied to the Irish Sea to simulate both barotropic and baroclinic circulation within the region. High accuracy was achieved with regard to the prediction of both tidal circulation and surface and nearbed water temperatures across the region. The model properly represented the Western Irish Sea Gyre, induced by thermal stratification and not known during planning Sellafield. Passive tracer simulations based on the developed hydrodynamic model were used to deliver residence times of the eastern Irish Sea region for various times of the year as well as travel times from the Sellafield outfall site to various locations within the Irish Sea. The results indicate a strong seasonal variability of travel times from Sellafield to the examined locations. Travel time to the Clyde Sea is the shortest for the autumnal tracer release (90 days); it takes almost a year for the tracer to arrive at the same location if it is released in January. Travel times from Sellafield to Dublin Bay fall within the range of 180-360 days. The average residence time of the entire eastern Irish Sea is around 7 months. The areas surrounding the Isle of Man are initially flushed due to a predominant northward flow; a backwater is formed in Liverpool Bay. Thus, elevated tracer concentrations are predicted in Liverpool Bay in the case of accidental spills at the Sellafield outfall site. 相似文献