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1.
Behavior of warm water flowing into a model ocean with flat bottom filled with cold water is investigated numerically with a three-dimensional level model in a rotating system.The warm water which flows through the southern opening into the ocean is found to progress in two directions. The east front of the warm water progresses along the east coast and reaches the northern opening. And an eastern boundary current associated with this density structure is formed. The west front progresses along the west coast with the speed much less than that of the eastside front. However, the progression of the west front slows down remarkably half way between the southern and northern boundaries due to-effect, and a baroclinic western boundary current system is formed. Unstable waves whose scales are 200–400 km are found in the region of the eastern boundary current and propagate toward the west. These waves seem to be caused by the baroclinic instability.The boundary currents obtained in the present model are considered to represent some characteristics of the Tsushima Current system in the Japan Sea.  相似文献   

2.
Branching of the Tsushima Current in the Japan Sea   总被引：4，自引：0，他引：4  
Three branches of the Tsushima Current are reproduced in a numerical model, and their formation mechanisms are studied. Two types of a two-layer, inflow-outflow model with a bottom slope along the Japanese coast are used. One has a bottom slope only in the lower layer (Model A), and the other has bottom slopes in both layers (Model B). Model B represents the typical situation in the Japan Sea, i.e., the main pycnocline intersects the bottom slope. The onshore side of the line where the pycnocline intersects the bottom slope has only one layer in Model B. Seasonal variation of inflow in the upper layer of the western half in the entrance section (the Tsushima Strait) is incorporated into the model.Three branches are formed in Model B and not in Model A. The first branch is the bottom-controlled steady current due to the topographic-effect on the upper-layer slope which exists in the one-layer region along the Japanese coast. The second branch is a temporal current which is formed along the offshore edge of the coastal one-layer region in association with the variation of inflow. The third branch is the steady western boundary current due to the planetary-effect. These results compare favorably with observations in Part I of this study.The mechanism of formation of the second branch is examined in detail. This branch is caused by the propagation of the lowest two modes of the upper shelf wave caused by the topographic-effect on the upper-layer slope which are generated by the significant increase in inflow from June to August.  相似文献   

3.
The generation of small meanders of the Kuroshio off southern Kyûshû is investigated. Basing on the fact that the small meanders tend to follow an increase in velocity of the Kuroshio in the Satsunan region (Sekine andToba, 1981), the influence of this velocity increase on the quasi-stationary path of the Kuroshio is studied numerically. Simplified bottom and coastal topographies are employed in a two layer model ocean. A quasi-stationary numerical solution with a constant inflow is used for the initial condition, and a temporal increase in the inflow with corresponding leakage is employed as the boundary condition to investigate nonlinear effects due to the increase in current velocity. Experiments for four different physical models are carried out to determine the specific roles of the continental slope, the planetary-effect, and density stratification. Temporal increase in the inflow tends to cause offshore shift of the current path. But the topographic effect of the continental slope is strong enough that no significant shift of the current path occurs in the case of the barotropic ocean. However, in the case of a baroclinic ocean, temporal increase in the inflow does cause generation of small meanders, because density stratification diminishes the topographic effect. A larger density stratification provides more favorable condition for the appearance of the small meander, and a cyclonic eddy is formed on the continental side of the small meander path.  相似文献   

4.
Recent advances in ocean-circulation research on the Yellow Sea and East China Sea shelves are summarized. Observations using acoustic Doppler current profilers (ADCPs) suggest that the connectivity of mean-volume-transports is incomplete between the Tsushima (2.6 Sverdrups; 1 Sv = 106 m3/s) and Taiwan Straits (1.2 Sv). The remaining 1.4-Sv transport must be supplied by onshore Kuroshio intrusion across the East China Sea shelf break. The Yellow Sea Warm Current is not a persistent ocean current, but an episodic event forced by northerly winter monsoon winds. Nevertheless, the Cheju Warm Current is detected clearly regardless of season. In addition, the throughflow in the Taiwan Strait may be episodic in winter when northeasterly winds prevail. The throughflow strengthens (vanishes) under moderate (severe) northeasterly wind conditions. Using all published ADCP-derived estimates, the throughflow transport (V) in the Taiwan Strait is approximated as
where V 0, V 1, K are 1.2 Sv, 1.3 Sv, and 157 days, respectively, t is yearday, and T is 365.2422 days (i.e., 1 year). The difference between the throughflow transports in the Tsushima and Taiwan Straits suggests that the onshore Kuroshio intrusion across the shelf break increases from autumn to winter. The China Coastal Current has been observed in winter, but shelf currents are obscure in summer.  相似文献   

5.
The amount of penetration of a western boundary current into a marginal sea which is connected to an open ocean by two narrow straits is estimated from a linear, steady and barotropic theoretical model. In this model the western boundary current in the open ocean is driven by a wind stress imposed at the sea surface. The inflow of the water of the open ocean into the marginal sea is caused by the pressure difference between two straits produced by the wind-driven circulation in the open ocean.Main external parameters are combined into two non-dimensional parameters; and (the ratio of the depth of the marginal sea to that of the open ocean), whereb is the distance between north and south boundaries of the ocean,D 0 is the depth of the open ocean, is the latitudinal variation of the Coriolis parameter andR is the coefficient of friction. The friction is assumed to be proportional to the flow velocity.In the limit of infinite the volume transport into the marginal sea is not affected by the width of two straits and . It is mainly controlled by the wind stress and the positions of two straits. For finite values of , however, the volume transport depends considerably on and the width of the straits.Guided by both this model and physical considerations, we obtained a relation between the volume transport into the marginal sea and the external parameters. This relation predicts that about 2 % of the volume transport of the Kuroshio penetrates into the Japan Sea.  相似文献   

6.
The most plausible scenarios for seasonal to interannual variabilities and their possible causes are investigated for the Tsushima Current system passing through the Japan Sea. The study is based on the north and south two-box model across the polar front in an idealized upper ocean of the Japan Sea. The boxes are connected by lateral diffusive heat transport and cooled by atmospheric forcing at the annual mean state. The south box, i.e. the Tsushima Current region, only interacts with the outside warmer box in the East China Sea and has an eastward thermal-driven current originating in the outside box. The magnitude of this current depends on the strength of the thermal gradient between the north and south boxes; the inflow of warm waters can therefore be maintained by net heat loss through the sea-surface. I call such a thermal-driven inflow process a "Cooling-Induced Current" system in the present study. Under periodical heat forcing, the perturbation response of the model to water temperature fields and inflow transport were examined. It is shown that the lateral diffusion time across the polar front (over a period of 10 years) is crucial to the interannual modeled response. An analysis of the seasonal heat budget suggests that the heat transported into the Japan Sea from the East China Sea in summer is stored mainly within the Tsushima Current region and contributes to heat loss by the sea-surface cooling in winter.  相似文献   

7.
Seasonal Variation of the Cheju Warm Current in the Northern East China Sea   总被引：1，自引：1，他引：1  
The Cheju Warm Current has been defined as a mean current that rounds Cheju-do clockwise, transporting warm and saline water to the western coastal area of Cheju-do and into the Cheju Strait in the northern East China Sea (Lie et al., 1998). Seasonal variation of the Cheju Warm Current and its relevant hydrographic structures were examined by analyzing CTD data and trajectories of satellite-tracked drifters. Analysis of a combined data set of CTD and drifters confirms the year-round existence of the Cheju Warm Current west of Cheju-do and in the Cheju Strait, with current speeds of 5 to 40 cm/s. Saline waters transported by the Cheju Warm Current are classified Cheju Warm Current water for water of salinity greater than 34.0 psu and modified Cheju Warm Current for water having salinity of 33.5–34.0 psu. In winter, Cheju Warm Current water appears in a relatively large area west of Cheju-do, bounded by a strong thermohaline front formed in a "" shape. In summer and autumn, the Cheju Warm Current water appears only in the lower layer, retreating to the western coastal area of Cheju-do in summer and to the eastern coastal area sometimes in autumn. The Cheju Warm Current is found to flow in the western channel of the Korea/Tsushima Strait after passing through the Cheju Strait, contributing significantly to the Tsushima Warm Current.  相似文献   

8.
A wind-driven, general circulation for a two-layer ocean with continental shelf-slope along the western boundary is studied numerically. Special attention is focused on the formation process of the western boundary current in the subtropical gyre. The western boundary current develops in the upper layer along the western boundary on the shelf-slope with a bottom trapped poleward flow in the lower layer. The poleward undercurrent is concentrated approximately along the contour lines of the potential vorticity,f/D, wheref is the Coriolis parameter andD the depth of the ocean. The separation of upper- and lower-layer flows on the shelf-slope represents a typical transient response. As the response approaches a steady state, the poleward undercurrent decreases in amplitude, and the motion tends to be confined to the upper layer. The flow pattern becomes similar to that found in a flat bottom ocean. A steady-state response is expected to be isostatic (no motion in the lower layer), even on the shelf-slope, as conservation of potential vorticity would suggest.The remarkable increase in transport of the western boundary current produced by the formation of an anticyclonic vortex on the shelf-slope extending throughout the hemisphere (Holland, 1973) does not occur in the wind-driven general circulation.  相似文献   

9.
An internal wavetrain, generated by a tidal current in superposition with the Tsushima Warm Current, has been observed by use of an acoustic echo-sounder upstream of the Shichiri-Ga-Sone Seamounts in the East Tsushima Strait of the Japan Sea. The sea surface above the internal wavetrain was simultaneously observed and was found to be undulated at the wavelength of the internal wave.  相似文献   

10.
Seasonal variation in the wind-driven circulation in the Japan Sea is studied with reference to the branching of the Tsushima Current using a two-layer model with simplified bottom and coastal topography. The system is driven by wind stress, an inflow corresponding to the Tsushima Current and by the two outflows corresponding to the Tsugaru and Soya Currents.In the first phase, an annual mean wind stress is imposed and a quasi-stationary state is obtained. In the next phase, a seasonally varying wind stress is imposed. Seasonal variation in the wind stress plays an important role in the branching system of the Tsushima Current. In winter, an intensified western boundary current with a prominent inner circulation is formed as a result of a strong wind stress of winter monsoon with negative wind stress curl. In spring to summer, the western boundary current is weak, but the topographic branch along the Japanese coast is intensified. The weak western boundary current is caused by weak wind stress with positive wind stress curl, which induces cyclonic Sverdrup flow in the Japan Sea and causes its western boundary current to flow in the opposite direction to the prescribed northward boundary inflow current. The topographic branch is strongest in late spring and moves offshore in summer, in agreement with the central branch denoted by Kawabe (1982b). Some of the observational features of the Tsushima Current are successfully simulated.  相似文献   

11.
Steady response of a linear, two-layer baroclinic ocean to a steady thermal forcing was investigated on a mid-latitude -plane. Surface heat flux and its relaxation processes were parametrized as a form of heating function and Newtonian cooling term of cross interfacial velocityw in the continuity equation. Ageostrophic linear drag terms were employed to represent the western boundary layer for accomplishment of the steady circulation in the closed domain. In the interior, the dynamics belongs to thef-plane regime. The flow in the upper layer is zonal and eastward, which is the same as that expected in the channel without meridional boundary. The eastern boundary region is the so called Sverdrup region, in which the vortex stretching balances the term, thoughw contains a damping term. It directs the zonal flow southward (northward) in the south (north) followed by upwelling (downwelling) and forms the two gyres. Western boundary region is of the Stommel type except the upwelling (downwelling) in the south (north). The meridional circulation is similar to the Hadley Cell except southern and northern boundary layers. However, its strength is much greater than the latters.  相似文献   

12.
Current measurements were made at five moored stations over the continental shelf off the San'in coast of the Japan Sea for a month in the summer of 1980 to study the vertical structure of the nearshore branch of the Tsushima Current. The time-mean current for the observational period is 20 to 25 cm sec–1 eastward near the surface and about 10 cm sec–1 westward near the sea bottom except at the shallowest station. The time-mean current,i.e. the nearshore branch of the Tsushima Current is mainly due to the baroclinic modes. The currents are less variable in the first half of the observational period, but fluctuate with a several-day period in the latter half. The obtained current data were decomposed into barotropic and baroclinic modes to investigate the detailed characteristics of the fluctuations. In the latter half, the current fluctuations of the two modes with about a 5-day period are well correlated with each other, as the baroclinic mode lagging behind the barotropic mode by 12 hr. The barotropic current fluctuation is correlated to the sea level, with the former leading the latter by about 12 hr. The baroclinic current is correlated to the temperature at the subsurface layer with a shorter time lag.  相似文献   

13.
The theoretical problem of formation of boundary currents in an idealized basin subject to seasonally varying buoyancy forcing is considered in an attempt to apply it to the seasonally varying Tsushima Current. Until now, all the theories intended to explain the branching of the Tsushima Current have been for the annual mean Tsushima Current—the seasonally varying Tsushima Current has never been properly explained. A simple numerical experiment shows that eastern and western boundary currents change in time, concurrently, when local buoyancy forcing is sufficient, as it is in the Tsushima Current. However, this is not true for ineffective local buoyancy forcing. The importance of the role played by local buoyancy forcing is further supported by simple theoretical considerations. Overall, this study suggests that effective local buoyancy forcing is probably essential to the formation of seasonally varying eastern and western boundary currents of the Tsushima Current.  相似文献   

14.
The diets of breeding seabirds can be a good monitor of marine environmental changes. From 1984 to 2001 we monitored the diets of black-tailed gulls (Larus crassirostris) (“surface foragers”), rhinoceros auklets (Cerorhinca monocerata) (“epipelagic divers”), and Japanese cormorants (Phalacrocorax filamentotus) (“bottom divers”) that breed on Teuri Island at the northern boundary of the Tsushima Warm current in the Sea of Japan/East Sea. Between 1984 and 1987, both the gulls and the auklets foraged on the sardine (Sardinops melanostictus), but after 1992, they switched to the anchovy (Engraulis japonica). This change might reflect the collapse of the sardine stock in the late 1980s. In the 1990s, the year-to-year variations of the percentage of anchovy in the diets of the three seabird species showed similar trends: High in 1994 and 1998–2001; and low in 1992–1993 and 1995–1997. The estimated stock size of the anchovy population in the Tsushima Current area was positively correlated with the percentage of mass of anchovy in the seabirds’ diets. Thus, the short-term annual changes of the total anchovy availability, which might reflect SST or the volume transport of Tsushima Current, possibly affected the seabirds diets on this island.  相似文献   

15.
The Current Structure of the Tsushima Warm Current along the Japanese Coast   总被引：4，自引：0，他引：4  
The branching of the Tsushima Warm Current (TWC) along the Japanese coast is studied based upon intensive ADCP and CTD measurements conducted off the Wakasa Bay in every early summer of 1995–1998, the analysis of the temperature distribution at 100 m depth and the tracks of the surface drifters (Ishii and Michida, 1996; Lee et al., 1997). The first branch of TWC (FBTWC) exists throughout the year. It starts from the eastern channel of the Tsushima Straits, flows along the isobath shallower than 200 m along the Japanese coast and flows out through the Tsugaru Strait. The current flowing through the western channel of the Tsushima Straits feeds the second branch of TWC (SBTWC) which develops from spring to fall. The development of SBTWC propagates from the Tsushima Straits to Noto Peninsula at a speed of about 7 cm sec−1 following the continental shelf break with a strong baroclinicity. However, SBTWC cannot be always found around the shelf break because its path is influenced by the development of eddies. It is concluded that SBTWC is a topographically steered current; a current steered by the continental shelf break. Salient features at intermediate depth are the southwestward subsurface counter current (SWSCC) between 150 m and 300 m depths over the shelf region in 1995–1998 with the velocity exceeding about 5 cm sec−1, although discrepancies of the velocity and its location are observed between the ADCP data and the geostrophic currents. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

16.
The general statement of a non-linear problem in modelling a barotropic tide for the limited part of a real shelf and the problems related to artificial division of the computation area in the ocean by a liquid boundary are considered. Linear combinations of various types of boundary conditions and analytical expressions are used to describe the tidal wave structure at the liquid boundaries. The results of test computations for basins with the simplest outlines are given. The model is used to reconstruct the spatial distribution of characteristics of theM 2 tide on the shelf of Guinea. The methods of computation and specification of unambiguously determined model parameters are described. Joint analysis of the modelling results and the field data has been carried out. The tidal map of theM 2 wave is plotted for the area under investigation.Translated by Mikhail M. Trufanov.  相似文献   

17.
闾国年 《海洋科学》1989,13(3):13-20
本文探讨了西北太平洋流系统变化的研究方法,并利用这些方法恢复了距今三万年以来这一地区洋流系統变化的过程。  相似文献   

18.
In order to clarify detailed current structures over the continental shelf margin in the East China Sea, ADCP measurements were carried out in summers in 1991 and 1994 by the quadrireciprocal method (Katoh, 1988) for removing diurnal and semidiurnal tidal flows from observed flows, together with CTD measurements. We discussed the process of the Tsushima Current formation in the East China Sea. The Tsushima Current with a volume transport of 2 Sv (1 Sv=106 m3s–1) was found north of 31°N. A current with a volume transport of 0.4 Sv was clearly found along the 100 m isobath. Between the Kuroshio and the current along the 100 m isobath, southeastward component of velocity was dominant compared to northwestward one. Four eastward to southeastward currents were found over the sea bed shallower than 90 m depth. Total volume transport of these four currents was 1 Sv, and they seemed to be originated from the Taiwan Strait. Intrusion of offshore water into the inner shelf northwest of Amami Oshima was estimated to have a volume transport of 0.6 Sv. It is concluded that the Tsushima Current is the confluence of these currents over the continental shelf margin with the offshore water intruding northwest of Amami Oshima.  相似文献   

19.
The surface circulation in the Japan Sea is investigated using a 1.5 layer reduced gravity model. Historical observations suggest strongly that an anti-clockwise circulation is dominant in the subpolar region north of the Polar Front as a general feature. This anti-clockwise circulation as well as the branching of the Tsushima Warm Current was simulated well by incorporating the Naet al. (1992)'s wind stress. The positive curl of the wind stress in the northern and the northwestern Japan Sea was found to play an important role in the formation of the subpolar gyre and the separation of the western boundary current (the East Korean Warm Current) in the Japan Sea.  相似文献   

20.
A Box Model of Glacial-Interglacial Variability in the Japan Sea   总被引：2，自引：0，他引：2  
The Japan Sea has experienced drastic changes in the last 60 ka: the surface water was colder than the present value by five degrees and extremely freshened (24 ppt) in the last glacial maximum (15 ka), and then it contained Oyashio water for a few thousand years. It is an open question whether the inflow-outflow pattern was entirely reversed, opposite to the present exchange with an inflow through Tsushima Strait and an outflow through Tsugaru Strait. A box model is employed with two boxes representing the northern and the southern half domains in the upper (300-m-thick) layer. The model is driven by atmospheric forcing and inflow through Tsushima Strait and/or Tsugaru Strait. Here, the net transport through Tsushima to Tsugaru is given in the model. A baroclinic component is added to the net transport through each strait. It is the baroclinic components that allow the upper and the lower portions to flow to the opposite directions in the straits, and hence a reversal flow becomes possible against the net transport, under the condition of an extremely freshened Japan Sea. The fresh surface layer in 1814 ka is attributable to a near-shutoff of the inflow due to the low sea level. Shortly after the near-shutoff, the baroclinic transport through Tsugaru Strait yields intrusion of the Oyashio water into the Japan Sea. Thus, it is implied that Oyashio water existed in the Japan Sea a few thousand years after the reopening of Tsugaru Strait, even though the net transport was one-way, similar to the present state.  相似文献   

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