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Sea surface temperature distribution and its variability across the Tsushima Strait

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Abstract

The sea surface temperature distribution across the Tsushima Strait was monitored over a one-year period on board the ferry Kampu which runs between Shimonoseki, Japan and Pusan, Korea. A cold water region is always observed just near the Korean Coast, and a sharp temperature front is always present in the western channel. A temperature maximum or a warm core is usually found just on the southeast side of the front. The position of the warm core exhibits large short period fluctuations, but no significant seasonal variation is found. Sudden temperature increases followed by sudden temperature decreases are frequently observed in the temporal variation curves at fixed positions during the warming season from April to August. Such events are related to temperature maxima found sporadically in the temperature distribution in the eastern channel during this season, and seem to be caused by warm water intrusion into the Tsushima Strait from the East China Sea.

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... In general, the currents in the strait topography and flows through the eastern channel are thought to exhibit considerable variation in along the Japanese coast as the Nearshore Branch current velocity (Egawa et al., 1993). (Yoon, 1982b). The second and third branches Transports variations across the east and west originate in the western channel and bifurcate into channels of the Korea/Tsushima Strait are not well two branches downstream (Katoh, 1994). ...
... In particular, such a problem intense along the north line from September to area is located near the western end of the north November at N1 and N2. A counter flow is section, where intense coastal currents are surobserved from May to December at N3 and from mized to occur just off Korea (Miita and Ogawa, August to November at N4. Velocities are 1984;Tawara and Fujiwara, 1985;Egawa et al., generally lower at N5 and N6 than at NI and 1993). Narrow currents can also be realized N2. ...
Article
Transport variations are calculated across the Korea/Tsushima Strait using continuous current measurements made between May 1999 and March 2000. Twelve bottom-mounted acoustic Doppler current profilers provide velocity profiles along two sections: one section (south line) at the strait entrance southwest (upstream) of Tsushima Island and the other section (north line) at the strait exit northeast (downstream) of Tsushima Island. Transport variations across the strait are large, particularly in the lee of Tsushima Island where a countercurrent commonly exists. The Tsushima Current transport, averaging 2.65 Sverdrups (Sv) (1 Sv =106 m3 s-1), is split into two cores by Tsushima Island, which divides the strait into eastern and western channels. Transport in the western channel is 23% higher than in the eastern channel over the measurement period. Some seasonality in transport variability is observed for both the western and eastern channels. Transports are largest in fall and smallest during winter. The single-velocity core, observed upstream of Tsushima Island, is estimated to split directly behind Tsushima Island over an aperture of about 31 km along the south line. A wake zone that averages 40 km in width is observed downstream of Tsushima Island and appears to follow island-wake-zone dynamics. Reynolds numbers can range from 22 to 90 in the wake zone, and eddy shedding can occur throughout the year.
... 1996). A large anticyclonic warm eddy detached from the Kuroshio meander has been often observed at the head of the trough west of Kyushu (Huh, 1982 ;Tawara and Fujiwara, 1985;Muneyama et aI., 1984;Qiu et aI., 1990). An anticyclonic sense of circulation in the trough is also verified by the climatological mean surface currents derived from geoelectrokinetograph (GEK) data (Hsueh et aI., 1996). ...
... Many previous studies reported that an anticyclonic warm eddy exists at the head of the trough west of Kyushu (Huh, 1982;Tawara and Fujiwara, 1985 ;Muneyama et a!., 1984;Qiu et a!., 1990;Hsueh et a!., 1996). Yamagata and Kamachi (1989) proposed that the anticyclonic warm eddy in the trough is formed through the evolution of the cyclonic eddy initially induced by the Kuroshio instability. ...
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A perturbation scheme called Poincare method is applied to the differential equation expressing a volcanic model given by Ida. We constructed a solution up to the 8-th order approximation analytically. Because of a special form of the equation, half of the integration constants are undermined but some of the constants can be prefixed. There seems optimal values for these constants, but we failed to find an algorithm for that. the approximate solution works well in the neighborhood of the fixed point.
... It is reported that several spikes (abrupt rise and consecutive fall) of SST with periods of several days are found in the Tsushima Straits from April to August (Tawara and Fujiwara, 1985). They conclude that this fluctuation is due to the intrusion of the Kuroshio water. ...
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Sea surface temperature (SST) and sea surface salinity variations at Fukue Island (located southwest of the Tsushima Straits) were investigated. In spring, low-frequency SST fluctuations with periods of 10-20 days predominate. Synthetic analysis of in situ observation and satellite infrared image reveals that these SST fluctuations are caused by movement of mixed warm water masses which have a temperature inter- mediate between those of the Kuroshio and the East China Sea (ECS) shelf waters. Since these fluctuations do not correspond with those in the Tsushima Straits, it is indicated that these water masses can hardly pass the Tsushima Straits while retain- ing their original water properties. In July, SST fluctuations with a period of several days are also found at Fukue Island. Since these SST fluctuations show an opposite correspondence with its salinity fluctuations and a good correspondence with the SST fluctuations at Okinoshima in the Tsushima Straits, it is inferred that warm and low- salinity water originated from the ECS shelf water causes these fluctuations and in- trudes into the Tsushima Straits.
... Various studies have investigated the volume transport through the Tsushima Strait (e.g., Egawa et al., 1993;Isobe et al., 1994;Teague et al., 2002;Takikawa et al., 2005), and hence our understanding of it has improved considerably. Besides the volume transport, Tawara and Fujiwara (1985) investigated the temporal variation of the sea-surface temperature (SST) in the Tsushima Strait using data obtained by a ferryboat plying between Shimonoseki and Busan three times a week, and suggested that SST increases with periods of several days in the warming season (April to August) were due to the intrusion of the Kuroshio water. Manda et al. (2000), however, found that such SST increases were accompanied by a decrease in sea-surface salinity (SSS), and concluded that SST and SSS variations with a period of several days are not due to the passage of the Kuroshio water. ...
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Temporal variations in temperature and salinity observed in 2004 were investigated on a short time scale in the Tsushima Strait. The data were obtained by long-term in situ measurements at Mitsushima and Futaoi Island using an instrument equipped with a piston-type wiper to avoid biofouling. In addition, the temperature and salinity values of the surface layer obtained by a commercial ferryboat between Hakata and Busan were used to investigate their spatiotemporal variations. Temperature and salinity variations with a time scale of several days had a negative correlation in the summer. This evidence suggests that a warm and less saline water mass, which is considered to be mainly the Changjiang Diluted Water (CDW), flowed intermittently through the Tsushima Strait in summer. In late July 2004, a large low-salinity water mass was detected in the Tsushima Strait. At that time, the freshwater transport through the Tsushima Strait transiently reached about 12 × 104 m3s−1, which is estimated from observed acoustic Doppler current profiler (ADCP) data along a ferryboat line and inferred salinity profiles. This estimated value is more than double the maximum of the climatological monthly mean of the Changjiang discharge. Furthermore, salinity and surface current data obtained by high frequency ocean radar (HF radar) indicate that water properties at Mitsushima may occasionally represent part of the water flowing through the western channel via a countercurrent, although Mitsushima is geographically located in the eastern channel.
... This suggests that the interaction between the Kuroshio current and detached cyclonic eddy causes the Kuroshio meander with a large meridional amplitude. Many previous studies reported that an anticyclonic warm eddy exists at the head of the trough west of Kyushu (Huh, 1982; Tawara and Fujiwara, 1985 ; Muneyama et a!., 1984; Qiu et a!., 1990; Hsueh et a!., 1996). Yamagata and Kamachi (1989) proposed that the anticyclonic warm eddy in the trough is formed through the evolution of the cyclonic eddy initially induced by the Kuroshio instability. ...
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... This suggests that the interaction between the Kuroshio current and detached cyclonic eddy causes the Kuroshio meander with a large meridional amplitude. Many previous studies reported that an anticyclonic warm eddy exists at the head of the trough west of Kyushu (Huh, 1982; Tawara and Fujiwara, 1985 ; Muneyama et a!., 1984; Qiu et a!., 1990; Hsueh et a!., 1996). Yamagata and Kamachi (1989) proposed that the anticyclonic warm eddy in the trough is formed through the evolution of the cyclonic eddy initially induced by the Kuroshio instability. ...
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A bottom trapped cyclonic eddy was detected over the trough southwest of Kyushu in the hydrographic and current observations during June 6-18, 1997. Successive satellite images of sea surface temperature between May 20 and June 17 indicate its formation process as follows. A cyclonic circulation is intially induced at the continental shelf break region by the Kuoshio instability. It propagates northeastward along the Kuroshio, and then it is trapped at the mount of the trough southwest of Kyushu. After its detachment from the Kuroshio, a cyclonic eddy moves northward along the trough while the Kurosshio moves southward significantly. The hydrographic observation indicates that the cyclonic eddy reaches the depth deep enough to be affected by side walls of the trough. These observational results suggest that: 1) the blocking effect of the bottom topography southwest of Kyushu plays an important role in the detachment of the cyclonic eddy initially induced by the Kuroshio instability, and 2) the interaction between the detached eddy and the Kuroshio causes the Kuroshjio meander with a large meridional amplitude.
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ii Table of Contents Foreword...............................................................................................v Introduction............................................................................................1 References.............................................................................................9 Author list............................................................................................ 75
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The aim of this study is to elucidate the seasonal variation in the volume transport through the Tsushima-Korea Strait using the sea level difference across the Strait. The sea level difference associated with the baroclinic motion is estimated from the geostrophic current profile, which is calculated as its vertical integrated transport is zero, using the CTD data from 1988 to 1990. The sea level difference associated with the barotropic motion is estimated by subtracting the sea level difference associated with the baroclinic motion from the observed one. The range (maximum-minimum) of the seasonal variation in the volume transport is evaluated about 0.7 Sv on the average, using the sea level difference associated with the barotropic motion. It is one third of the seasonal variation in the volume transport which is estimated from observed sea level difference on the assumption that no baroclinic component exists. Such analyses also indicate that the volume transport was at a maximum in early winter and at a minimum in early spring from 1988 to 1990. The negative correlation is also found between the volume transport through the eastern channel and that through the western channel. Moreover, it is noticed that the seasonal variation in the surface current velocity in the Strait largely contains baroclinic motions which are locally caused in the Tsushima-Korea Strait.
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The ADCP data obtained in the Tsushima Strait in the period from February 1987 to November 1990 on board twelve patrol vessels and one research vessel belonging to Maritime Safety Agency was analyzed. Total amount of the data is 200,053, but after quality check, we used 158,401 data for the analysis of the current field and its variability in the strait. The seasonal variation of the currents had been believed to be large. However, no direct current observation throughout the season had been made, and the knowledge on the seasonal variation was derived indirectly from the data of the sea level difference across the strait and of the density field given by hydrographic observations. ADCP data indicates that the seasonal variation of the current field is considerably small in all sub-regions. In the relatively strong current region to the west of the Tsushima Island, the northeast current component has maximum value in the early winter season.
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By using a rectangular basin of uniform depth with inflow and outflow openings, the circulation in the Japan Sea is investigated numerically. Heat flux through the sea surface is determined from the annual mean atmospheric conditions for the Japan Sea, but no wind stress is considered. In the transient state, the warm water supplied through an inflow opening travels cyclonically along the coast as a density-driven boundary current in a rotating system. In the quasi-steady state, the warm water flows northward as a western boundary current which corresponds to the East Korean Warm Current and gradually separates from the coast as it flows northward. No strong boundary current corresponding to the nearshore branch of the Tsushima Current exists. Under annual mean atmospheric conditions, formation of the deep water characteristic of the Japan Sea and of the thermal front corresponding to the Polar Front do not take place.
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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 β-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 β-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 β-effect on the upper-layer slope which are generated by the significant increase in inflow from June to August.
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By using a two-dimensional barotropic model on a β-plane, the effect of the bottom topography on the path of the Tsushima Current is investigated. The rectangular model ocean with continental slopes has two openings: one is located at the southern boundary and the other at the eastern boundary. In a steady state, most of the water supplied into the model ocean through the inflow opening, flows along the continental slope with the coast to the right. Continental shelf waves play an important role in the process of adjustment to a steady state. It is suggested that the nearshore branch of the Tsushima Current might be largely topographically controlled.
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Attempts to determine where and how separation between the Kuroshio and Tsushima Current occurs have been inconclusive. Spring season satellite data acquired over a number of years reveals two conditions important to this question: (1) an areally extensive zone of mixing between the Kuroshio and shelf waters occurring along the edge of the East China Sea shelf, and (2) plumes of warm water from the Kuroshio extending into the mixed water west of Kyushu. This mixed water is observed to form the Tsushima Current in the outer shelf of the northern East China Sea and Korea Strait. Warm plumes branching from the north wall of the Kuroshio are seen with particular clarity in imagery of April 23, 1981, and February 21, 1982. Details of the split suggest that branching was a transient event.
Article
Seasonal variations in the circulation in the Japan Sea are investigated numerically by using a model basin of uniform depth with three openings, one inflow opening corresponding to the Tsushima Straits and two outflow openings corresponding to the Tsugaru- and Sôya Straits. From winter to spring, warm water supplied through the inflow opening flows northward along the Korean coast as a western boundary current corresponding to the East Korean Warm Current. From summer to autumn, the warm water splits into two branches; one flows northward along the Korean coast as from winter to spring and the other flows along the Japanese coast as a density-driven boundary current due to the large density difference between the inflowing warm and low salinity water and the interior water which was cooled during winter. The lack of a boundary current along the Japanese coast from winter to spring results in a large discrepancy between calculated and observed salinity field distributions. Therefore, the nearshore branch of the Tsushima Current can not be explained only as a density-driven boundary current. The seasonal variation of atmospheric conditions plays an important role in the formation of the Proper Water and the Polar Front in the Japan Sea.
Article
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.
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In winter a remarkable coastal front is formed off the southeastern coast of the Kunisaki Peninsula in the Sea of Iyo in the western part of the Seto Inland Sea. This coastal front is generated in late November when the density difference between onshore colder water and offshore warmer water vanishes due to the cooling effect of the cold atmosphere. It barely changes its horizontal position and its sharpness increases until late January. The sea surface begins to be warmed in late February and the coastal front does not exist in mid-March.
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On the observed oceanographic structure and the development of stratified water current in the Straits of Tsushima and the Sea of Goto-Amakusa in the Western Japan
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On the oceanic front Kii Channel developed in winter (1) Umi to Sora
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Coastal water temperature observation monthly report
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The formation of fishing ground in relation to temporal variation of the Kuroshio
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Numerical experiment on the circulation in the Japan Sea Part-II. Influence of seasonal variation in atmospheric condition on the Tsushima Current
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The variation of oceanic front in Kii Channel-Observation of surface water temperature by the use of ferry boat-. Ann. Disas
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On the oceanic front Kii Channel developed in winter (1)
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