the tsushima warm current through tsushima straits

The Tsushima Warm Current through Tsushima Straits Estimated from FerryboatADCP Data

TETSUTARO TAKIKAWA*

Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Science, Kyushu University,Kasuga, Fukuoka, Japan

JONG-HWAN YOON

Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka, Japan

KYU-DAE CHO

Department of Oceanography, Pukyong National University, Nagu, Pusan, Korea

(Manuscript received 20 October 2003, in final form 19 November 2004)

ABSTRACT

Current structures across the Tsushima Straits are studied using results from long-term acoustic Dopplercurrent profiler (ADCP) observations by a ferryboat between Hakata and Pusan conducted since February1997. Two maxima of the northeastward current are observed in the central parts of the eastern and westernchannels, and the maximum velocity in the western channel is stronger than that of the eastern channel.Downstream of the Tsushima Islands, a southwestward countercurrent is observed associated with a pair ofcyclonic and anticyclonic eddies. In the western channel, the deep countercurrent is observed pronouncedlyon the bottom slope of the Korean side from summer to winter. The volume transport of the TsushimaWarm Current through the straits has strong seasonal variation with a minimum in January and two maximafrom spring to autumn (double peaks). The spring peak of the volume transport through the eastern channelis more pronounced than the autumn peak, and the autumn peak of the western channel is more pro-nounced than the spring peak. The inflow volume transport into the Japan Sea through the western channelsignificantly increases in autumn because of an incrementation of the freshwater transport. The total volumetransport averaged over the observation period (5.5 yr) is 2.64 Sv (Sv � 106 m3 s�1). The average volumetransports through the eastern and western channels are 1.10 and 1.54 Sv, respectively.

1. Introduction

The Tsushima Warm Current flows into the JapanSea from the East China Sea through the TsushimaStraits with width, length, and mean water depth ofabout 180 km, 330 km, and 100 m, respectively. Thestraits are divided by Tsushima Island into the easternand western channels with widths of about 140 and 40km, respectively. Most of the water flows out to thePacific Ocean and the Sea of Okhotsk through theTsugaru and Soya Straits.

The Tsushima Warm Current is divided by the

Tsushima Islands. According to Hase et al. (1999), thecurrent through the eastern channel of Tsushima Straitsfeeds the first branch of the Tsushima Warm Currentroughly following the 200-m isobath of the continentalshelf along the Japanese coast. The current through thewestern channel of Tsushima Straits feeds the secondbranch, which flows along the continental shelf breakand slope along the Japanese coast. Another branchalong the Korean coast, which is called the East KoreanWarm Current, flows as a western boundary current(Kawabe 1982; Yoon 1982a,b) and separates from theKorean coast at about 37°–39°N with synoptic mean-ders accompanied by warm and cold mesoscale eddies(Beardsley et al. 1992; Isoda and Saitoh 1993; Jacobset al. 1999). A part of the East Korean Warm Currentflows southward as a countercurrent and the rest ofit flows northeastward toward Tsugaru Strait, formingthe polar front at about 40°N with the northern coldwater (Kim and Yoon 1996). Furthermore, a watermass with a vertical salinity minimum called the Japan

* Current affiliation: Department of Fishery Science and Tech-nology, National Fisheries University, Shimonoseki, Japan.

Corresponding author address: Tetsutaro Takikawa, Depart-ment of Fishery Science and Technology, National Fisheries Uni-versity, 2-7-1 Nagata-Honmachi, Shimonoseki 759-6595, Japan.E-mail: [email protected]

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FIG. 1. (a) The track (thick solid line) of the ferry Camellia along which current measure-ments by ADCP were carried out. The eastern and western channels are defined as the black(south of 34.75°N) and gray (north of 34.75°N) lines, respectively. Stations A and B are thedeepest points on the observation line in the eastern and western channels, respectively. CTDobservations were carried out at stations 1–5. Contour lines show the water depth in meters.(b) Cross-section view along the ferry track. Solid line indicates the water depth (m). Outflowvolume transports associated with countercurrent downstream of the Tsushima Islands anddeep countercurrent in the western channel flow through black and gray regions, respectively.

JUNE 2005 N O T E S A N D C O R R E S P O N D E N C E 1155


FIG. 2. Monthly averaged current vectors at 18-m depth on the Camellia line from Feb 1997 to Aug 2002(1 kt � 51.4 cm s�1).



Sea Intermediate Water is found below the TsushimaWarm Current (Senjyu 1999; Yoon and Kawamura 2002).

So far, many studies have been made to estimate thevolume transport of the Tsushima Warm Current. How-ever, long-term current measurements in TsushimaStraits are difficult because of heavy fishing and trawl-ing activities (Kawatate et al. 1988). Hence, most of theestimates were given by geostrophic calculations(Miyazaki 1952; Yi 1966; Isoda and Yamaoka 1991) or

short-term direct measurements using current meters(Miita 1976). Miyazaki (1952) concluded that the vol-ume transport of the Tsushima Warm Current had alarge seasonal variation with maximum of 2.5 Sv (Sv �106 m3 s�1) in summer and minimum of 0.2 Sv in winter,and Yi (1966) obtained almost the same result. Isodaand Yamaoka (1991) estimated the volume transport insummer to be about 3 Sv, where the ratio of the trans-port through the eastern channel to that of the westernchannel was about 1 to 3. Miita (1976) also showed thatthe volume transport attained a maximum in summer(3.3–3.7 Sv).

Over the past decade, there have been many directcurrent observations using a ship-mounted or towedacoustic Doppler current profiler (ADCP) to elucidatethe volume transport and spatial current structure ofthe Tsushima Warm Current in Tsushima Straits(Kaneko et al. 1991; Kawano 1993; Egawa et al. 1993;Katoh 1993; Isobe et al. 1994). These results were av-eraged by Isobe (1994), who obtained an annually av-eraged volume transport of 2.2 and 0.7 Sv throughTsushima Straits and the eastern channel, respectively.

Teague et al. (2002) carried out current measure-ments at 12 stations along two lines (northeast andsouthwest of Tsushima Islands) across Tsushima Straitsfor about 11 months using ADCPs housed in trawl-resistant bottom mounts (TRBM). Annually averagedvolume transports of the Tsushima Warm Current wereestimated to be 2.3 Sv at the northeastern sectionand 2.7 Sv at the southwestern section. The disagree-ment of the two transports between the northeasternand southwestern sections is considered to be due tothe large interpolation errors of the ADCP data nearthe surface layer, especially near the Korean coast,where strong northeastward currents are observed (Ja-cobs et al. 2001).

The Research Institute for Applied Mechanics(RIAM) of Kyushu University has been conductinglong-term ADCP observations since 21 February 1997

FIG. 3. Current vectors (kt) at 26-m depth from 16 to 18 Jun2000, using Camellia ADCP observations (west) and ADCP ob-servations from the T/V Kakuyo-Maru of Nagasaki University(east).

FIG. 4. Numerical simulation of the Tsushima Straits velocities (cm s�1) using the 1.5-layerreduced-gravity model of Maruyama et al. (2003). The horizontal grid space is 2 km.



6 times per week using the ferryboat Camellia betweenHakata and Pusan (Fig. 1). We use these data to esti-mate the averaged volume transport and seasonalvariations through Tsushima Straits. The characteristicsof the Tsushima Warm Current structure are discussedfirst, and the volume transport is discussed second.

2. Data and methodThe data used in this study were obtained for 5.5 yr

from 21 February 1997 to 25 August 2002 from the

multilevel ADCP (VMBBADCP, 300 kHz, RD Instru-ments) mounted on the ferryboat Camellia. The Camel-lia makes round trips between Hakata and Pusan 3times per week at a cruising speed of about 17 kt. Thedata sampling intervals are about 24 s and 8 m in depthfrom 18 to 258 m. However, the data within 15% of thetotal depth from the bottom are not reliable (missingdata). Surface and bottom velocities are obtained byextrapolating the values at 18-m depth and at the deep-est depth of reliable ADCP measurements to calculate

FIG. 5. Monthly averaged velocities (cm s�1) on the vertical section along the ferry track from Feb 1997 to Aug2002. The velocities are normal to the section, and positive velocities are toward the Japan Sea.


Fig 5 live 4/C


the volume transport through the section. Since themaximum water depth is about 240 m along the ferrytrack, the ship velocity relative to the bottom can bemeasured everywhere through the bottom tracking bythe ADCP, implying that the current velocity can bemeasured relative to the bottom.

Since tidal currents are very strong and comparableto the mean current due to the shallow depth and nar-row width of the straits, tides must be removed from theADCP data in order to study processes with time scaleslonger than a few days. Since the data interval between

current sections is roughly one day, the current datamay contain significant aliasing errors associated withsome of the tidal constituents. However, the samplingintervals (the time between two successive cruises) arenot constant and vary from point to point along theferry track. The duration of the data is long enough todecompose each tidal constituent. Ten tidal constitu-ents (Q1, O1, P1, K1, N2, M2, S2, K2, MSf, and Mf) wereremoved by harmonic analysis from the ADCP datafollowing the method by Takikawa et al. (2003), and themean currents were accurately obtained without tidal

FIG. 6. Standard deviations (cm s�1) of the velocities in Fig. 5.


Fig 6 live 4/C


aliasing errors. In this paper, currents after removal ofthe 10 tidal current constituents are shown.

3. Results

a. Structure of the Tsushima Warm Current

Monthly averaged current vectors at 18-m depth onthe Camellia line from February 1997 to August 2002are shown in Fig. 2. The current maxima are located atall times in the central parts of the eastern and westernchannels, flowing northeastward into the Japan Sea.The maximum velocity of the eastern channel currentranges from 15 cm s�1 in January to 35 cm s�1 in Au-gust with an average of 26 cm s�1. The maximum in thewestern channel ranges from 37 cm s�1 in January to 57cm s�1 in November with an average of 49 cm s�1. Thecurrent maxima tend to be weaker from winter tospring and stronger from summer to autumn, especiallynear the Korean coast.

Downstream of the Tsushima Islands, a southwest-ward countercurrent is almost always present. Thecountercurrent is relatively weak, but becomes strongerfrom summer to autumn. East of the observation line,concurrent ADCP measurements were made during16–18 June 2000 by the T/V Kakuyo-Maru of NagasakiUniversity. Figure 3 shows the current vectors at 26-mdepth using both datasets, suggesting a pair of cyclonicand anticyclonic eddies east of the Tsushima Islandswith the southwestward countercurrent between thetwo eddies downstream of the islands. Takikawa et al.(2003) calculated contributions of tidal currents to thetotal kinetic energy and the eddy kinetic energy on thesection, suggesting that eddy activities are comparableto the tidal currents and much stronger than the meancurrent downstream of the Tsushima Islands. Numeri-cal simulation of flow through Tsushima Straits using a1.5-layer reduced-gravity model (Maruyama et al. 2003)also showed a pair of eddies (Fig. 4) in the region.Strong eddy activities with a few days time scale, which

FIG. 7. The time change of vertical profile of monthly mean velocity for 5.5 yr at stations (a)A and (b) B (see Fig. 1a). Contours indicate the isopleths of velocities normal to the section,and the positive velocities are toward the Japan Sea. The contour interval is 10 cm s�1. Grayshading indicates negative values, associated with the countercurrent from the Japan Sea.Length and direction of vectors indicate current velocity and direction.



are much longer than tidal motions, were also observedby HF radar observation (Yamamoto et al. 2002). Sincethe countercurrent was also found in the result byTeague et al. (2002) at the observation line locatedabout 50 km east of the Tsushima Islands, it is sug-gested that the horizontal scale of the countercurrent isalmost 50 km. Such countercurrents were also foundresults of observations by Miita and Ogawa (1984),Egawa et al. (1993), Katoh (1993), and Isobe et al.(1994).

Downstream of Iki Island, the current is also rela-tively weak and a southwestward countercurrent isobserved from August to February (Fig. 2). Near theKyushu coast, the northeastward current is weakerfrom autumn to winter and stronger from spring tosummer.

The distributions of the monthly averaged currentvelocities and standard deviations of these currents onthe vertical section along the ferry track from February1997 to August 2002 are shown in Figs. 5 and 6, respec-tively. The velocity variability for all seasons in thewestern channel is larger than that in the eastern chan-nel (Fig. 6). The standard deviation near the northerntip of the Tsushima Islands (about 34.8°N) is large fromlate spring to autumn, corresponding to the strongcountercurrent downstream of the Tsushima Islands.According to Maruyama et al. (2003), because of baro-clinicity of current structure, although the countercur-rent is formed by the numerical simulation of the 1.5-layer reduced-gravity model (Fig. 4), it is not formed by

barotropic model, suggesting generation of baroclinicinstability near the northern tip of the Tsushima Islandsin summer season.

In the eastern channel, the velocity variations fromthe surface to the bottom in winter are very small (Fig.5); that is, the current structure is barotropic. Fromspring to early autumn, velocities increase near the sur-face, and the current structure becomes baroclinic.From late autumn to winter, velocities decrease and thecurrent structure becomes more barotropic. The largeand small standard deviations (Fig. 6) correspond to thebaroclinic and barotropic current structures, respec-tively.

Figure 7 shows the time change of the vertical profileof monthly mean velocity for the five and a half years atstations A and B at the deepest parts of the two chan-nels (Fig. 1a). The seasonal variation of the verticalcurrent structure at the eastern channel mentionedabove is clearly visible (Fig. 7b).

In the western channel, the current structure in win-ter becomes barotropic from the surface down to about100 m, and the surface velocities gradually increasefrom spring (Fig. 5). From summer to autumn, the cur-rents become strongest with strong baroclinicity. Thevelocity increases are found not only at the core of thenortheastward current but also near the Korean coastaccompanied by the large standard deviation (Fig. 6).In autumn, the current maximum shifts from the sur-face to the subsurface (about 40-m depth).

The southwestward countercurrent is observed be-

FIG. 8. Monthly averaged volume transport in Sverdrups (open circle) of the TsushimaWarm Current into the Japan Sea through the Camellia line from Feb 1997 to Aug 2002, andtransports of the eastern (open triangle) and western (open square) channels (see Fig. 1a).Straight lines indicate the mean value of the each volume transport. Error bar indicatesstandard error in each month.



low about 130 m in the western channel from summerto winter but is absent in spring (Figs. 5 and 7b). Sincethis countercurrent is on the slope of the Korean side(Fig. 5), it might be associated with the topographic �effect. According to Fig. 7b, the seasonal variation of

the deep countercurrent is clearly visible. This counter-current exists from April to January with two maximain September (16 cm s�1) and December (12 cm s�1) atstation B.

According to Lim and Chang (1969), the deep coun-

FIG. 9. The inflow volume transport (Sv; open circle) into the Japan Sea through the westernchannel (see Fig. 1a), the salinity (psu; open diamond) averaged vertically and horizontally atstations 1–5 in Fig. 1a, and the outflow volume transport (open triangle) from the Japan Seain deep layer in the western channel (see Fig. 1b). The salinity data were provided by theKorea Oceanographic Data Center.

FIG. 10. The inflow volume transport (Sv; open circle) into the Japan Sea through theeastern channel (see Fig. 1a) and the outflow volume transport (open triangle) from the JapanSea downstream of the Tsushima Islands (see Fig. 1b). The open diamonds are as in Fig. 9.



tercurrent is an intrusion of cold water into TsushimaStraits from the Japan Sea. According to Cho and Kim(1998), the bottom cold-water advection has a seasonalcycle with maximum in summer and minimum in winterassociated with variation of the salinity minimum layerin the Japan Sea. On the other hand, Johnson andTeague (2002) did not find an annual cycle in the bot-tom cold water using temperature records betweenMay 1999 and March 2000 (Teague et al. 2002). Theyhypothesized that the bottom cold-water intrusions arethe product of relatively weak advection augmented byhorizontal diffusion. However, the deep countercurrentwas weaker during their observation period than usual(transport associated with the deep countercurrent isgiven by open triangles in Fig. 9, described below). Al-though the maximum of the deep countercurrent insummer (Fig. 7b) supports the result of Cho and Kim(1998), that of winter suggests that the bottom coldwater intrudes by horizontal diffusion when transportto the Japan Sea is reduced (Johnson and Teague2002).

b. Volume transport of the Tsushima WarmCurrent through Tsushima Straits

Monthly averaged volume transports of the Tsushi-ma Warm Current into the Japan Sea across the Ca-mellia line from February 1997 to August 2002 areshown in Fig. 8. The total volume transport has a sea-sonal variation with a minimum in January and twomaxima in spring and autumn. The seasonal variationwith double peaks is found to be more pronounced in1997 (July and October), 1998 (May and November),and 2001 (March and October) than in 1999 (July andOctober) and 2000 (May and September). Over theobservation period, the amplitude of seasonal variationof volume transport is relatively stable except in 1999when the total volume transports exceeds 3.5 Sv in Oc-tober and November. The total volume transportthrough the observation line averaged for five and ahalf years is 2.64 Sv. The average volume transportsthrough the eastern (south of 34.75°N) and western(north of 34.75°N) channels are 1.10 and 1.54 Sv, re-spectively.

Isobe (1994) showed that the average volume trans-port through Tsushima Straits from 1987 to 1991 is 2.2Sv, without any pronounced double peaks of volumetransport. The differences of volume transport betweenthis study and Isobe (1994) might originate from thedifference of observation period. According to Taki-kawa and Yoon (2005), who estimated the volumetransport using sea level data from 1965 to 2001, thetransport over the same period of Isobe (1994) is 2.4 Sv.Time series of the volume transport from May 1999 toMarch 2000 are shown by Teague et al. (2002), showinggood agreement between that of the southern sectiondescribed by Teague et al. (2002) and this study in thetime variations and the time-averaged mean (2.7 Sv).

Although the seasonal variation of volume transportthrough the western channel has double peaks, thespring peak is relatively smaller than that of autumn(Fig. 8). The inflow transport in the western channel(Fig. 9) varies seasonally with a single peak (minimumin winter and maximum in autumn), except in 2001.Salinity data in the western channel were provided bythe Korea Oceanographic Data Center (KODC). Thesalinity is inversely correlated with the inflow volumetransport, except in spring of 2001 (Fig. 9). The lowsalinity from August to October in the western channelis likely caused by the seasonal freshwater dischargefrom the Changjiang River into the East China Sea,with a maximum in July and minimum in January(Chen et al. 1994; Yanagi 1994; Zhu et al. 2001). Thefreshwater transport through Tsushima Straits in-creases pronouncedly in summer and autumn with twoor three months delay to the river discharge (Isobe etal. 2002). Although the variation of the outflow volume

FIG. 11. (a) The inflow volume transports (Sv) into the JapanSea through the eastern (open triangle) and western (opensquare) channels averaged monthly for 5.5 yr, and (b) the outflowvolume transports of the countercurrent east of the TsushimaIslands (open triangle) and the deep countercurrent in the west-ern channel (open square) averaged monthly for the observationperiod.



transport from the Japan Sea in deep layers below 100m (north of 34.85°N) is small (Fig. 9), the outflow trans-port associated with the intrusion of the cold water(Lim and Chang 1969) in Figs. 5 and 7b from summer towinter increases with the increase of the inflow trans-port, except in 1999. The cold water is not observedwest of the Tsushima Islands (Johnson and Teague2002), suggesting that the outflow water is recirculatedback into the Japan Sea.

In autumn 1999, a large volume transport, exceeding4 Sv, is observed (Fig. 8). Since the salinity decreasesabruptly in the western channel (Fig. 9) in the sameperiod, it is suggested that a large amount of freshwateris transported from the rivers around the Yellow Seaand the East China Sea. In fact, according to the AsianDisaster Reduction Center (ADRC), the precipitationover East Asia increased and river floods occurred fre-quently in July during that year.

Double peaks in the seasonal variation of the volumetransport through the eastern channel (Figs. 8 and 10)are more pronounced than that in the western channel(Fig. 8). The countercurrent downstream of theTsushima Islands is associated with a dipole of eddies(Fig. 3), suggesting that the outflow water returns to theJapan Sea by eddy recirculation. The countercurrenttransport (Fig. 10) shows relatively clear seasonal varia-tion with a maximum in summer and a minimum inwinter. The outflow transport peaks when the inflowtransport is a minimum in summer. The autumn peak ofthe inflow volume transport is weakly correlated withlow salinity (Fig. 10).

The inflow volume transport averaged monthly for5.5 yr through the eastern channel (Fig. 11a) has a mini-mum in January (0.90 Sv) and two maxima in March(1.38 Sv) and October (1.45 Sv). Although the variationof the inflow transport is very small from spring to au-tumn, its transport has a minimum in July (1.23 Sv)between two maxima. The average inflow transportthrough the eastern channel is 1.28 Sv. Double peaksare not found in the inflow volume transport throughthe western channel with a minimum (1.16 Sv) in Janu-ary, a maximum (2.12 Sv) in October, and an average of1.67 Sv.

The monthly averaged transport downstream of theTsushima Islands (Fig. 11b) has a minimum (0.10 Sv) inFebruary and a maximum (0.26 Sv) in September withan average of 0.17 Sv. The monthly averaged transportin deep layer through the western channel has twominima in February (0.04 Sv) and November (0.08 Sv)and two maxima in January (0.26 Sv) and August (0.17Sv) with an average of 0.10 Sv.

Total volume transport and the eastern and westernchannel transports are averaged monthly (Fig. 12).Each of the three is fit by functions with annual andsemiannual cycles,

FIG. 12. The total volume transport (Sv; open circle) of the Tsushima Warm Currentthrough Tsushima Straits averaged monthly for 5.5 yr, and those of the eastern (open triangle)and western (open square) channels. Each solid line is fitted by functions with annual andsemiannual cycles.

TABLE 1. Coefficients of the volume transport, Eq. (1).

T0 a1 a2 b1 b2

Eastern channel 1.098 �0.107 0.014 �0.081 �0.123Western channel 1.536 �0.077 �0.287 �0.055 �0.159Total 2.635 �0.184 �0.273 �0.136 �0.282



TABLE 2. The monthly mean volume transport through the Tsushima Straits and its standard variation for the years from (a) 1997through (f) 2002.

Total (Sv) Eastern (Sv) Western (Sv)

No. of observations Transport Std dev Transport Std dev Transport Std dev

(a) for 1997

Feb 7 2.33 1.61 1.04 0.86 1.29 0.77Mar 21 2.41 0.91 1.07 0.51 1.34 0.44Apr 26 2.40 0.84 1.08 0.45 1.32 0.44May 22 2.47 0.65 0.99 0.43 1.48 0.28Jun 26 2.70 0.55 1.12 0.33 1.58 0.31Jul 29 2.73 0.56 1.00 0.47 1.73 0.27Aug 25 2.54 0.86 0.82 0.56 1.72 0.43Sep 24 2.62 0.95 0.84 0.70 1.78 0.34Oct 22 3.02 1.23 1.02 0.70 1.99 0.76Nov 20 2.34 1.00 0.75 0.66 1.59 0.41Dec 26 2.28 0.73 0.81 0.48 1.46 0.33

(b) for 1998

Jan 27 1.67 0.67 0.68 0.35 0.99 0.43Feb 23 2.13 0.83 1.00 0.44 1.12 0.47Mar 14 2.15 0.53 1.08 0.38 1.07 0.25Apr 27 2.70 0.47 1.21 0.33 1.50 0.27May 26 2.99 0.70 1.32 0.45 1.67 0.29Jun 28 2.99 0.59 1.41 0.33 1.58 0.34Jul 27 2.82 0.67 1.17 0.44 1.65 0.33Aug 26 2.42 0.49 0.96 0.42 1.46 0.35Sep 23 2.33 1.23 0.77 0.87 1.56 0.50Oct 27 2.97 0.88 1.21 0.45 1.77 0.65Nov 26 3.00 1.00 1.17 0.53 1.82 0.51Dec 22 2.22 0.60 0.91 0.41 1.32 0.27

(c) for 1999


(d) for 2000




T�t� � T0 � a1 cos�

6t � b1 sin

�

6t � a2 cos

�

3t

� b2 sin�

3t, �1�

where the unit of time t is month and coefficients (a1, a2,b1, and b2) are listed in Table 1. According to Fig. 12,the eastern and western channel transports each haverelatively weak double peaks. However, they reinforceeach other, yielding more pronounced double peaks inthe total volume transport. The annual ranges of vol-ume transport through the eastern and western chan-nels are estimated at 0.5 and 0.8 Sv, respectively, andthe total range is 1.2 Sv.

4. Summary and conclusions

Characteristics of the Tsushima Warm Current havebeen described analyzing the ADCP data obtained bythe ferry Camellia for 5.5 years. The maximum north-eastward currents are observed in the central parts ofthe eastern and western channels, and the western coreis stronger than the eastern core. The current structurechanges seasonally from a barotropic structure in win-ter and spring to a baroclinic structure in summer andautumn. Downstream of the Tsushima Islands, south-westward countercurrents are observed, correspondingto a pair of the cyclonic and anticyclonic eddies. In thewestern channel, a deep countercurrent is observed on

the Korean slope from summer to winter, with the av-erage transport of 0.10 Sv.

The total volume transport of the Tsushima WarmCurrent through Tsushima Straits varies seasonallywith a minimum in January and two maxima fromspring to autumn (double peaks). Although the easternand western channel transports each have relativelyweak double peaks, they reinforce each other, yieldingmore pronounced double peaks in the total volumetransport. The monthly and yearly mean volume trans-ports over the observation period are listed in Tables2a–f and 3. The average volume transport through theobservation line is 2.64 Sv. The average volume trans-ports through the eastern and western channels are 1.10and 1.54 Sv, respectively.

The inflow volume transport into the Japan Seathrough the western channel varies seasonally (mini-mum in winter and maximum in autumn), and is in-versely correlated with the salinity. The low salinityfrom August to October in the western channel is likelycaused by the freshwater discharge from the riversaround the Yellow Sea and the East China Sea.

Although the correlation between the transportthrough the Tsushima Straits and the freshwater dis-charge is mentioned in this paper, the detail of what isdriving the Tsushima Warm Current will be addressedas future issues and problems from the standpoint ofcomparing with the variability of transport through theTaiwan Strait or the Kuroshio variability in the EastChina Sea. According to You (2005), most of the vol-ume transport estimated using a general circulation

TABLE 2. (Continued)


No. of observations Transport Std dev Transport Std dev Transport Std dev

(e) for 2001


(f) for 2002

Jan 18 1.60 1.09 0.85 0.70 0.75 0.57Feb 8 2.28 0.63 1.13 0.32 1.15 0.39Mar 26 2.77 0.76 1.29 0.43 1.48 0.45Apr 26 2.70 0.67 1.25 0.43 1.45 0.37May 17 2.99 0.58 1.43 0.34 1.56 0.32Jun 25 2.72 0.76 1.10 0.43 1.62 0.39Jul 28 2.80 0.65 1.00 0.46 1.80 0.32Aug 23 2.65 0.62 0.90 0.42 1.75 0.39



model comes from Taiwan Strait from June to Augustand it comes from the Kuroshio region from October toJanuary, suggesting that the double peaks of the trans-port through Tsushima Straits in spring (early summer)and autumn are associated with the Taiwan–TsushimaWarm Current System (Frang et al. 1991) and Kuroshiovariabilities, respectively. The results consist the cross-isobath transport from the Kuroshio region in autumndue to the joint effect of baroclinicity and relief (Isobe1999).

Although transport variations with a few weeks ordays time scale is not discussed in this study, surfacewind stress and air pressure forcing with short periodsare highly responsible to cause the significant sea levelrise and fall in small straits. The high-frequency vari-ability of pressure- and wind-driven current will be dis-cussed in Hirose et al. (2004, manuscript submitted toCont. Shelf Res.).

Acknowledgments. The authors express their sincerethanks to the captain and crew of the ferryboat Camel-lia and the staff of the Camellia Line, Ltd. Specialthanks are extended to Dr. Hideaki Hase of JAMSTECfor his kind help in the ADCP data analyses. The au-thors are very grateful to the captain and crew of theT/V Kakuyo-Maru of Nagasaki University for theirhelpful assistance. This work was supported partiallyfrom Korea Research Foundation (KRF). Doctors Wil-liam J. Teague and Lynne D. Talley and an anonymousreviewer provided comments that helped to improvethe presentation.

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TABLE 3. The yearly mean volume transport through the Tsushima Straits and its standard variation.


Year No. of observations Transport Std dev Transport Std dev Transport Std dev

1997 248 2.55 0.89 0.96 0.56 1.59 0.471998 296 2.56 0.87 1.08 0.51 1.48 0.491999 273 2.94 1.02 1.29 0.57 1.65 0.592000 283 2.54 0.77 1.09 0.44 1.45 0.482001 305 2.66 0.85 1.09 0.51 1.57 0.482002 171 2.62 0.82 1.12 0.49 1.50 0.50



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