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1.
Downstream transition of the Tsushima Current west of Kyushu in summer   总被引：1，自引：0，他引：1  
In order to clarify detailed current structures west of Kyushu, ADCP measurements were carried out in July and September 1990 by the quadrireciprocal method (Katoh, 1988) for removing diurnal and semidiurnal tidal flows from observed flows. On the basis of these results, together with data of routine oceanographic observations, we study the downstream transition of the Tsushima Current west of Kyushu in summer. In the southwest of the Goto Islands, a northward current identified as the Tsushima Current was clearly found. In the south of Cheju, a westward current bifurcated from the Tsushima Current. In the northwest of the Goto Islands, the Tsushima Current narrowed and its velocity became strengthened. Salinity of the Tsushima Current water was much diluted by a current from the Cheju Strait. Near the west coast of the Goto Islands, a countercurrent bifurcating from the Tsushima Current often occurred. The volume transport of the Tsushima Current was 2.3 Sv (1 Sv=106 m3s–1) on the northern side of latitude 31°N. The substantial bifurcation of the Tsushima Current toward the Eastern and Western Channels of the Tsushima Strait occurred in the vicinity of Tsushima. The volume transport through the Western Channel was two to three times larger than that through the Eastern Channel. The baroclinic component in volume transport of the Tsushima Current west of Kyushu was much smaller than that in the Japan Sea.  相似文献   

2.
I summarize the variations of the path of the Kuroshio and of the Tsushima Current mainly based on the results of my studies. The Tsushima Current forms three branches just after it enters the Japan Sea through the Tsushima Strait. The first and third branch currents flow along the Japanese and Korean coasts, respectively, and the second branch current flows from the western channel of the Tsushima Strait to the west of the Oki Islands only in summer from June to August. Properties of the topographic waves which are thought to work on the formation of the second branch are described mainly in terms of the dispersion relations. The Kuroshio has three typical paths,i.e., the nearshore and offshore non-large-meander paths and the typical large-meander path. The Kuroshio alternately takes the nearshore and offshore paths in the non-large-meander period, occasionally changes from the nearshore nonlarge-meander path to the large-meander path and, after having taken the large-meander path for several years, changes to the offshore non-large-meander path. Sea levels south of Japan are clearly different between the non-large-meander and large-meander periods, while they are not different between the periods of the nearshore and offshore non-large-meander paths. But, sea level and water properties in the coastal region show remarkable features during short periods of transitions between the typical non-large-meander paths. Future problems and subjects of studies on these currents are indicated. Especially, importance of velocity monitoring of the Kuroshio is emphasized, and a design of the observation across the Tokara Strait is proposed.  相似文献   

3.
Structure of the Tsushima Current in the southwestern Japan Sea   总被引：6，自引：0，他引：6  
We discuss the structure of the Tsushima Current in the southwestern Japan Sea using ADCP data, which are taken by the quadrireciprocal method (Katoh, 1988) for removing tidal currents, and previous temperature data. The first, second and third branches described in the triple-branch view are recognized in three observational periods: June and August 1988 and in June 1989. The first branch basically flows eastward along the 100 m isobath. Its velocity is mostly 0.5–1.0 kt (26–51 cm s–1) and 0.4–0.6 kt (21–31 cm s–1) in the Eastern Channel of the Tsushima Strait and off the San'in Coast, respectively. In waters north of Mishima, however, a part of the first branch happens to flow northeastward, without turning clockwise along the 100 m isobath. In waters northwest of Izumo, the remainder of the first branch tends to join the second one. The second branch, which has velocities of 0.5–0.8 kt (26–41 cm s–1) in general, flows eastward along a bunch of crowded isotherms at 100 m depth. The observational results clearly illustrate the changeability of the second branch. The maximum velocity of the third branch must be larger than those of the other two branches. The Tsushima Current after leaving the Western Channel is very changeable spatially and temporally, probably because the bifurcation occurs intermittently or transiently resulting from the fluctuation of inflow through the Western Channel and from that of spread of the cold water. The bifurcation into the second and third branches becomes often obscure north of Hamada owing to confluences, even though it is recognized near the Western Channel.  相似文献   

4.
By using Acoustic Doppler Current Profiler (ADCP) measurements with the four round-trips method to remove diurnal/semidiurnal tidal currents, the detailed current structure and volume transport of the Tsushima Warm Current (TWC) along the northwestern Japanese coast in the northeastern Japan Sea were examined in the period September–October 2000. The volume transport of the First Branch of the TWC (FBTWC) east of the Noto Peninsula was estimated as approximately 1.0 Sv (106 m3/s), and the FBTWC continued to flow along the Honshu Island to the south of the Oga Peninsula. To the north of the Oga Peninsula, the Second Branch of Tsushima Warm Current and the eastward current established by the subarctic front were recombined with the FBTWC and the total volume transport increased to 1.9 Sv. The water properties at each ADCP line strongly suggested that most of the upper portion of the TWC with high temperature and low salinity flowed out to the North Pacific as the Tsugaru Warm Current. In the north of the Tsugaru Strait, the volume transport of the northward current was observed to be as almost 1 Sv. However, the component of the TWC water was small (approximately 0.3 Sv).  相似文献   

5.
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   

6.
We discussed the detailed current structures in the Eastern Channel of the Tsushima Strait, using four sets of acoustic Doppler current profiler (ADCP) data, which were taken by the quadrireciprocal method (Katoh, 1988), for removing tidal currents, in summers of 1987–1989. In the Eastern Channel, diurnally averaged currents balanced almost geostrophically. In the upper layer of the deepest part of the Eastern Channel, there existed a current core which corresponded to one branch of the Tsushima Current. The current direction in this core was between NE and ENE in all observations but the magnitude of velocity in 1987 differed largely from that in 1988. Another current core with lower velocities was found near the north coast of Kyushu. Near the bottom at the deepest part of the Eastern Channel, the velocity was more or less 0.3 kt (15 cm s–1). Along the east coast of Tsushima and in waters northeast of it, countercurrents were observed. The continuity of these countercurrents was interpreted as follows: A part of the current flowing from the Western Channel of the Tsushima Strait into the Japan Sea turns clockwise in waters northeast of Tsushima, and flows southwestward along the east coast of Tsushima. The southwestward current along Tsushima was correlated with the northeastward current in the central part of the Eastern Channel. The transport through the Eastern Channel was between 0.59 and 1.30 Sv (1 Sv=106 m3s–1). The baroclinic component, which was defined as the transport based on calculations of geostrophic current with assuming zero velocity near the bottom, was very small.  相似文献   

7.
Review on current and seawater volume transport through the Taiwan Strait   总被引：12，自引：0，他引：12  
Patterns and features of currents and seawater volume transports in the Taiwan Strait have been reviewed by examining the results from more than 150 research papers in recent decades. It is noted that there are diverse or even conflicting viewpoints on these subjects. Here both common and different opinions are summarized. This review paper covers the studies involving in situ measurements and numerical modeling of current velocity, analyses of hydrographic data, and classification of water masses. Generally speaking, there are three currents in the Taiwan Strait: the China Coastal Current along the Fujian coast in the western Taiwan Strait, the extension of the South China Sea Warm Current in the western and central Taiwan Strait, and the Kuroshio’s branch or loop current intruding through the eastern Taiwan Strait. The current pattern in winter is quite different from that in summer, and the currents also exhibit differences between the upper and lower layers. The seawater volume transport through the Taiwan Strait is about 2.3 Sv northward in summer but about 0.8 Sv northward in winter. Both the current pattern and the seawater transport vary with local winds in the Taiwan Strait. This is particularly true in winter when the currents and the transport in the upper layer are significantly affected by strong northeasterly winds.  相似文献   

8.
We investigated the horizontal distribution of Nemopilema nomurai medusae using a midwater trawl in the southwestern Sea of Japan from September to October of each year from 2006 to 2012. Numerous medusae of this species found in 2006, 2007, and 2009 were mainly distributed far (>40 km) from the mainland of Japan in the western part of the survey area, but were distributed in the stations closest (<25 km) to the mainland in the eastern part, particularly in 2006 and 2009. These distribution patterns were associated with the path of the second branch of the Tsushima Warm Current (TWC) that flows offshore to the west of Oki Islands and usually approaches the mainland of Japan to the east of Oki Islands. Differences in jellyfish distribution across the survey periods were related to the distribution of the second branch being associated with types, position and intensity of eddies in the eastern part of the survey area. Hence, the formations of eddies and consequent variation in the path of the TWC would be responsible for transporting medusae from offshore to near the mainland to the east of Oki Islands. Individuals with large bells accumulated in the northwestern part of the survey area, where a cyclonic eddy was present downstream of the third branch of the TWC. This variation in bell size distribution may be ascribed to differences in the physical and/or biological factors among the three branches of the TWC.  相似文献   

9.
Northern and southern latitudinal transects were conducted west of Tsugaru Strait to estimate the volume transport in this area. It was found that the Tsushima Warm Current is the northward volume transport across the southern transect and the Northward Current is the northward volume transport across the northern transect. The current in Tsugaru Strait,viz. the Tsugaru Warm Current, is the flow remaining when the Northward Current is subtracted from the Tsushima Warm Current. Both CTD transects covered from near-shore to west of the subarctic front, and observed depths were from the surface to the bottom or to 1000-1500 m depth. Our estimations indicate that large interannual variations of volume transport occur, relative to the seasonal ones, with interannual variations sometimes exceeding seasonal variations in the Tsushima Warm Current and the Northward Current. The Tsugaru Warm Current has near-steady transport. Fluctuations in the Tsushima Warm Current are thus transmitted to the Northward Current. Further, our results revealed seasonal variations in the flow: the baloclinic structure became deeper in April and the current axis tended to shift in a near-shore direction in October. Therefore, previous studies, which had shallow reference levels and lacked nearshore stations, may have underestimated the transport and excessive seasonal variations.  相似文献   

10.
We discussed the short-term fluctuations of the Tsushima Current, using ADCP (acoustic Doppler current profiler) data taken by the quadrireciprocal method (Katoh, 1988) for removing tidal currents from observed currents. Transects were set in waters northwest of Yamaguchi Prefecture to capture the first and second branches of the Tsushima Current. Along the transects, ADCP and STD (salinitytemperature-depth recorder) measurements were repeated in May to July 1989. The velocity of the first branch fluctuated considerably in a short period, while the direction and position of its axis were steadly. The stability of its axis position probably results from the topographic effect. The baroclinic transport, which is based on calculations of geostrophic current with assuming zero velocity near the bottom, of the first branch was almost equal to the barotropic one. The range of fluctuation in the barotropic transport was much larger than that in the baroclinic transport. The barotropic fluctuation was correlated with the difference in atmospheric pressure between the east and west sides of the Tsushima Strait. As for the second branch, not only the velocity but also the position of its axis changed noticeably in a short period. There was such a case where the axis was hardly recognized. The changeability of the axis position for the second branch seems to result from that of the cold water front. The baroclinic transport of the second branch was much larger than the barotropic one, but the ranges of their fluctuations were very similar with each other.  相似文献   

11.
Although the Tsushima Current exhibits a complicated meander in the interior region of the Japan Sea, its path is more regular in the southwest region near the Tsushima Strait, and three branches have often been recognized there by many investigators. However, the detailed structures and temporal variabilities of these branches have not been clarified, and so they are studied here by analysing temperature, salinity and sea level data. It is shown that the existence of the first branch (the nearshore branch along the Japanese coast) can be detected from salinity distributions at least during the period from March to August. The third branch (the Eastern Korean Current) exists in all seasons. On the other hand, the second branch (the offshore branch) is seasonally variable and can be identified only in summer from June to August. Along the Japanese coast of southwest Japan Sea, the main pycnocline intersects the gentle slope on the shelf at a depth between 150 and 200 m. The first branch is found on the coastal side of the line where the main pycnocline intersects the bottom slope. On the other hand, the second branch is formed just on the seaward side of this line. Sea level differences in the Tsushima Strait, i.e., between Hakata and Izuhara and between Izuhara and Pusan, show that the seasonal variation of the surface velocity (or volume transport) is small in the eastern channel and large in the western channel. The period during which the surface velocity and volume transport in the western channel increase corresponds well to the period during which the second branch exists. These results suggest that the effects of bottom topography and oceanic stratification in the Japan Sea as well as the time variation of inflow through the western channel of the Tsushima Strait play important roles in the formation of the second branch.  相似文献   

12.
We examined the surface current structure in the Tsushima Warm Current (TWC) region of the Japan Sea based on a dataset from satellite-tracked surface drifters, including our new deployments during 2004–2008. The gridded mean current velocity and mean kinetic energy (KE) fields calculated from all available drifter data revealed the structure and seasonality of the three branches of the TWC. By comparing the eddy kinetic energy (EKE) field to the KE field, we found four regions where the ratio of EKE to KE was high. In particular, this ratio became extremely high east of the Oki Islands located between the first branch of the TWC (FBTWC) and the second branch of the TWC (SBTWC). Our analysis suggests that the generation of alternate warm and cold eddies east of the Oki Island induced this high ratio. The occurrence of a warm or cold eddy was related to the route—either nearshore or offshore—of the SBTWC. When the offshore route of the SBTWC became dominant, a warm eddy was frequently generated east of the Oki Islands. In contrast, when the nearshore route of the SBTWC became dominant, a cold eddy was more likely to be generated.  相似文献   

13.
Using hydrographic data and moored current meter records and the ADCP observed current data during May–June 1996, a modified inverse method is applied to calculate the Kuroshio east of Taiwan and in the East China Sea and the currents east of Ryukyu Islands. There are three branches of the Kuroshio east of Taiwan. The Kuroshio in the East China Sea comes from the main (first) and second branches of the Kuroshio east of Taiwan. The easternmost (third) branch of the Kuroshio flows northeastward to the region east of Ryukyu Islands. The net northward volume transports of the Kuroshio through Section K2 southeast of Taiwan and Section PN in the East China Sea are 44.4×106 and 27.2×106 m3s−1, respectively. The western boundary current east of Ryukyu Islands comes from the easternmost branch of the Kuroshio east of Taiwan and an anticyclonic recirculating gyre more east, making volume transports of 10 to 15×106 m3s−1. At about 21°N, 127°E southeast of Taiwan, there is a cold eddy which causes branching of the Kuroshio there.  相似文献   

14.
Variability of Sea Surface Circulation in the Japan Sea   总被引：3，自引：0，他引：3  
Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.  相似文献   

15.
A review is made of circulation and currents in the southwestern East/Japan Sea (the Ulleung Basin), and the Korea/Tsushima Strait which is a unique conduit for surface inflow into the Ulleung Basin. The review particularly concentrates on describing some preliminary results from recent extensive measurements made after 1996. Mean flow patterns are different in the upstream and downstream regions of the Korea/Tsushima Strait. A high velocity core occurs in the mid-section in the upstream region, and splits into two cores hugging the coasts of Korea and Japan, the downstream region, after passing around Tsushima Island located in the middle of the strait. Four-year mean transport into the East/Japan Sea through the Korea/Tsushima Strait based on submarine cable data calibrated by direct observations is 2.4 Sv (1 Sv = 106 m3 s−1). A wide range of variability occurs for the subtidal transport variation from subinertial (2–10 days) to interannual scales. While the subinertial variability is shown to arise from the atmospheric pressure disturbances, the longer period variation has been poorly understood.Mean upper circulation of the Ulleung Basin is characterized by the northward flowing East Korean Warm Current along the east coast of Korea and its meander eastward after the separation from the coast, the Offshore Branch along the coast of Japan, and the anticyclonic Ulleung Warm Eddy that forms from a meander of the East Korean Warm Current. Continuous acoustic travel-time measurements between June 1999 and June 2001 suggest five quasi-stable upper circulation patterns that persist for about 3–5 months with transitions between successive patterns occurring in a few months or days. Disappearance of the East Korean Warm Current is triggered by merging the Dok Cold Eddy, originating from the pinching-off of the meander trough, with the coastal cold water carried Southward by the North Korean Cold Current. The Ulleung Warm Eddy persisted for about 20 months in the middle of the Ulleung Basin with changes in its position and spatial scale associated with strengthening and weakening of the transport through the Korea/Tsushima Strait. The variability of upper circulation is partly related to the transport variation through the Korea/Tsushima Strait. Movements of the coastal cold water and the instability of the polar front also appear to be important factors affecting the variability.Deep circulation in the Ulleung Basin is primarily cyclonic and commonly consists of one or more cyclonic cells, and an anticyclonic cell centered near Ulleung Island. The cyclonic circulation is conjectured to be driven by a net inflow through the Ulleung Interplain Gap, which serves as a conduit for the exchange of deep waters between the Japan Basin in the northern East Sea and the Ulleung Basin. Deep currents are characterized by a short correlation scale and the predominance of mesoscale variability with periods of 20–40 days. Seasonality of deep currents is indistinct, and the coupling of upper and deep circulation has not been clarified yet.  相似文献   

16.
Satellite-derived sea surface temperatures illustrate the variability of the path of the Tsushima Current in the Sea of Japan. In the spring of 1981 the Tsushima Current did not split as it left the Korea Strait and flowed into the Sea of Japan, which is contrary to the historical concept of branching. Warm water remained along Honshu, the main island of Japan, making a strong front oriented in an east-west direction. Hydrographic data confirm that this spring condition lasted through to the fall of 1981. On the other hand, during the springs of 1982 and 1983 the branching is evident from satellite images: one branch flowed northward along the east coast of Korea, and the other flowed eastward along Honshu of Japan.  相似文献   

17.
田川  王树新  徐霄阳 《海洋科学》2015,39(1):110-115
利用在台湾海峡附近的下放式声学多普勒流速剖面仪(Lowered Acoustic Doppler Current Profiler,LADCP)观测资料和温盐观测资料,通过对连续站的两个季节观测进行正压和斜压潮流分析从而去除潮流得到准定常流,并在此基础上计算了南海和东海之间通过台湾海峡输运的水体及热盐通量。结果表明:台湾海峡大部分海域是半日潮海区(正规半日潮及不正规半日潮海区),半日潮主要分量为太阴半日分潮M2;台湾海峡的水体输运及热盐通量呈现明显的季节变化:夏季台湾海峡内表现为一支东北流向的海流,即台湾海峡暖流,存在3.3 Sv(1Sv=106 m3/s)的东北向水体输运,冬季东北季风较强,西南方向的海流加强,混合层可达到底部,存在1.8 Sv的东北向水体输运。与此对应的热盐通量分别为:夏季热通量为0.34×1015 W,盐通量为118.6×109 g/s;冬季热通量为0.14×1015 W,盐通量为72.9×109 g/s。该结果对台湾海峡通量的研究给出了一个直接观测的准确值,并为相关的数值研究提供了参考。  相似文献   

18.
The connectivity between the interannual salinity variations in the Tsushima and Cheju Straits has been investigated on the basis of historical hydrographic data. Salinity in the Cheju Strait correlates positively with that in the western channel of the Tsushima Strait, but does not show a significant correlation with that in the eastern channel. Empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses of temperature and salinity in the Cheju Strait revealed that salinity in the strait is associated with the cold bottom water in summer. Drastic freshening in the Cheju Strait occurs in a period when the Cheju Current intensifies. The results allow us to hypothesize that the mechanism of interannual salinity variations in the Cheju Strait and western channel of the Tsushima Strait is as follows. The intrusion of cold bottom water into the Cheju Strait in summer intensifies the Cheju Current by increasing the baroclinicity. Since colder bottom water develops a stronger eastward surface current, the larger volume of the Changjiang diluted water is drawn into the strait, which results in a lower salinity condition in the Cheju Strait. As the water in the Cheju Strait flows into the western channel of the Tsushima Strait, salinity in the western channel varies synchronously. This hypothesis is supported by SVD analysis of temperature in the Cheju Strait and salinity in the Tsushima Strait. The salinity condition in the East China Sea is suggested to be another important influence on salinity in the western channel of the Tsushima Strait.  相似文献   

19.
The Current System in the Yellow and East China Seas   总被引：18，自引：1，他引：18  
During the 1990s, our knowledge and understanding of the current system in the Yellow and East China Seas have grown significantly due primarily to new technologies for measuring surface currents and making high-resolution three-dimensional numerical model calculations. One of the most important new findings in this decade is direct evidence of the northward current west of Kyushu provided by satellite-tracked surface drifters. In the East China Sea shelf region, these recent studies indicate that in winter the Tsushima Warm Current has a single source, the Kuroshio Branch Current in the west of Kyushu, which transports a mixture of Kuroshio Water and Changjiang River Diluted Water northward. In summer the surface Tsushima Warm Current has multiple sources, i.e., the Taiwan Warm Current, the Kuroshio Branch Current to the north of Taiwan, and the Kuroshio Branch Current west of Kyushu. The summer surface circulation pattern in the East China Sea shelf region changes year-to-year corresponding to interannual variations in Changjiang River discharge. Questions concerning the Yellow Sea Warm Current, the Chinese Coastal Current in the Yellow Sea, the current field southwest of Kyushu, and the deep circulation in the Okinawa Trough remain to be addressed in the next decade. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

20.
The seasonal variation in the structure and volume transport of the Tsushima Warm Current through the Tsushima Straits is studied using the acoustic Doppler current profiler (ADCP) data obtained by the ferryboat Camellia between Hakata, Japan and Pusan, Korea from February 1997 to February 2007. A robust estimation method to eliminate the effects of aliasing and tidal signals more accurately leads to a significant increase in the volume transport in winter time compared to the previously reported one by Takikawa et al. (2005) who analyzed this ADCP dataset for the first 5.5 years. The 10 years average of volume transport through the Tsushima Straits is 2.65 Sv, and those through the channels east (CE) and west (CW) of the Tsushima Islands are 1.20 Sv and 1.45 Sv, respectively, which represent a 13% increase and an 8% decrease from those of Takikawa et al. (2005). The transport through the CE increases rapidly from winter to spring and then decreases gradually as winter approaches. On the other hand, the transport through the CW increases gradually from winter to autumn and then decreases rapidly as winter approaches. The transport through the CE is larger than that of through the CW from February to April. The contribution of the Ekman transport near the sea surface, which is not measured with the ADCP, to the seasonal volume transport variation across our ADCP section is not significant.  相似文献   

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