Several characteristics of water exchange in the Luzon Strait

Acta 0eceanologicaSinican 2004, Vol. 23, No.1, p.11~22htp://ww.oceapress.com.cnE-mail:hyxbe@263.netSeveral characteristics of water exchangein the Luzon StraitXU Jianping'2" , SH Maochong", ZHU Bokangl2, LIU Zenghong'21. Sccond Institutc ofOceanography, State Oceanic Administration, Hangzhou 310012, China2. Key Laboratory of Ocean Dynamic Processes and Satellite Oceanography of State Oceanic Administration,Hangzhou 310012,China3. China Ocean University, Qingdao 266003, ChinaReceived 22 September 2003; accepted 8 February 2004AbstractUsing the hydrographic data obtained from two sectional observations crossing the Luzon strait in the summer of 1994and in the winter of 1998, the volume transport through this strait is calculated. It is found that in winter the volumetransport(4.45x10* m2/s) is far larger than that in the summer (2.0 x100 m/s), respectively being about equal to 15.0%and 6.9% of the Kuroshio.And the paths of water in and out of the section of the strait vary dstictly with the season. Insummer, the water flows in and out of the South China Sea (SCS) three timnes ; that is, the inlet passages almost appearon the southem sides ofthe three deep troughs,the outlet passages are all located on the northern sides ofthe troughs,andthe in-out volume transports through the channel are not lower than 4.0x 100 m/s. The highest velocity (>80 cm/s) andthe largest entering water capacity (6.6x10* m/s) all occur in the BalintangChannel. Except for the north outlet passagein the section, all the higher velocities over 10 cm/s are mainly dstributed on the layer above 500 m. In winter,the waterflows in and out of the strait two times :the southem sides of the second and third deep troughs are the main passages ofthe Kuroshio water running into the SCS,while the whole section of the frst deep trough and the botom scction of thesecond deep trough are the outlet passages.The higher velocities over 10 cm/s are almost distributed on the layer above300 m. Numerical calculation shows that the northen side ofthe third troughmay be the ouletpassge.Key words: water exchange, Kuroshio, volum transport, Luzon Strait1 Introductioncalled the Bashi Channel. Its width is 386 kmand has a mean depth of1400 m.The Luzon Channel is situated on the west-To a great extent, the hydro-meteorologi-em side of the northem Pacific and betweencal conditions of the SCS，epecially in itsTaiwan and Luzon Islands. It is the main passagenortheast area, are influenced by the Kuroshioofthe Pacific water entering the SCS. There arewater intruding through the Luzon Strait.numerous different-sized islands forming manyEarly in 1961, based on the limited T/Snarrow water passages in this channel, so thedata at that time, Wyrtki calculated the northLuzon Channel is the general name of these pas-and south gravitational potential difference ofsages(including Babuyan, Balintang and Bashithe Luzon Strait, and then estimated the volumeChannels, etc,). Customarily,the Luzon Strait istransport through the strait: in winter, the* Crresponding butbor, E-mil: sioxu@zb.com.cn中国煤化工MYHCNMHG12XU Jianping ct al. AcaOeanologicnSinica 2004, Vol. 23, No. 1, p. 11~22.northerm Pacific upper water runs into the SCSthe local water and extends into the SCS, whileand in summer the SCS water flows into thethe other part of the water runs with the anticy-Pacific. Nitani (1970)， on the basis of ob-clone pattern to the north side of Luzon Strait,served data , also indicated the fact that theand from there, flows out of the SCS. The laterKuroshio water enters the SCS . Huang(1983,observed data and calculations have proven the1984), according to the data of cooperativeexistence of this loop(Su et al, 1990; Zhang etstudy of Kuroshio and adjacent regions (CSK)al, 1995; Xuet al, 1997).in the 1960s and some fragmentary data in theUsing the calculated geostrophic current1940s,analyzed the curent intensity throughvelocity(Xu et al, 2001)from the CTD data ofthe Luzon Strait.Using the observed data inthe two sectional observations crossing the Lu-September 1985, Guo and Fang( 1988 )estimat-zon Strait in August-September 1994 and ined the volume transport of Kuroshio near theNovember-December 1998 during the sCS en-Luzon Strait and described its westward flow-vironmental supplementary investigation,anding characteristics. Based on the observed datacombining with the underway ADCP data of theof the observation section PR2I made in WOCEsame time and some calculated results (Xue etProject, Liu et al.(2000)got the result that theal.,2001;Xue et al,2001),this paper discussesvolume transport through the Luzon Strait wasthe water excbange in the Luzon Strait , and8.0x 10* m/s in winter under the influencing oftries to find out the volume transports in sum-northeast wind, while in the other seasons themer and winter,and the water exchanging pas-capacity was only 3.0x 10% m/s.These previoussages in the strait.work is helpful for us to quantitatively analyzethe Kuroshio water into the SCS through the2 Topographic structure of the observation-Luzon Strait.al sectionSince the 1980s, there have appeared moreresearch work calculating the current in theThe bottomn configuration of Luzon StraitsCS with numerical modeling or describing theis rather complicated. Viewed from its depthwater exchange through the Luzon Strait .section, it is a deep trough. On the easterm sideBut there are few papers providing the quantita-of the trough,the Batan Islands and the Babuyantive volume transport through the Luzon StraitIslands are scattered like stars in the sky. On the(Liu et al,1992;Mao et al,1992;Li et al,westerm side, most of the water depths go be-1994; Cai and Su,1995; Shaw and Chao,1994;yond 1 000 m with exception of some shoals.Chao et al, 1995; Blumberg and Mellor,1987).According to the configuration and for discus-Only Metzger and Hurlburt(1996), who usedsion,we divide the Luzon Strait into three partsthe SCS,the Sulu Sea and the Pacific coupled(see Fig.l): (1) the first deep trough, with depthmodel, calculated and analyzed the volumereaching 3 000 m,is situated in the south of thetransport through the Luzon Strait and its sea-strait between Fuga Island and Calayan Islandsonal changes.(180 40'~19° 40"N); on the eastem side of theConcerning the moving pattem after thetrough there are numerous islands, such asKuroshio water into the SCS , Li et al.(1989)Calayan Island(199 20N) and Dalupri Islandsuggested a conception of the Kuroshio loop in(1 9°N), and the vast shallow water area(< 200m);the SCS.That is, when the Kuroshio water flowsconsequently, the complicated bottom config-along the south side of Luzon Strait into theuration has marked influence on the water ex-SCS, one part of the water body mingles withchange in this area;(2)the second deep trough is中国煤化工MYHCNMHGXU Jianping et al. ActaOreanologicaSinica 2004, Vol. 23, No. 1, p. 11~223ence on the strait and the northeast part ofsCS,0teven on the whole SCS. Certainly, the seasonalfirst dcp second dechange of the Kuroshio would result in the sea-Troughel 00*pwsonal difference of water exchange in the Lu-third deepzon Strait. Yet the understanding of this吕2 000troughchanging process is superficical due to lack ofwWobserved data at present.30003.1 Water exchange characteristics in summer19202:Wyrtki's (1961)calculation shows that:; .North ltitude H° )the surface SCS water driven by the summerFig.1. The water depth distribution crossing the Luzonsouthwest monsoon winds, runs through theStrait from Taiwan Oluanpi to Luzon Mailaila tip.Luzon Strait into the Pacific，wth outflowamountof 2.0~2.5x10* m*/s. But Liu et al.in the middle of the strait (19° 40' ~20° 50N)(2000),based on the investigation data of thewhere the Balintang Channel is located withCross- section PR2I in the Luzon Strait duringthe depth reaching 2000 m;(3) the third deepthe WOCE Project, got the calculating resulttrough is on the northern side of the straitthat in the summer the Kuroshio water flows in-(2120~21*45N), which is the shallowestto the SCS with a net water exchange amount oftrough in the Luzon Strait with the depth of3.0x10*m/s，which is just the opposite of600~1 000 m.what Wyrtki (1961 )did. Guan( 1990)analyzedthe data ofthe geostrophic current, temperature,3 Water exchange features and their sea-salinity and phosphate in 1971,and consideredsonal variationthat the Kuroshio water only appears in thestrait but not crosses the region of 120~121°E,Research results show that when the Norththat is,the Kuroshio water will not run into theEquatorial Pacific Current, flowing from east toSCS in summer.west, reaches Philippine Archipelago, it bifur-cates into two branches :one flows south called3.1.1 Analysis of the obseroational dynamic cal-culatingresultthe Mindanao Current,and the other flows northcalled the Kuroshio. The Kuroshio flows alongFrom late August to early September 1994,the narow belt between the west of 125° E tothe Second Instiute of Oceanography,SOAthe east coast of the Philippines.Using the ob-(State Oceanic Administration ), together withserved temperature and salinity data and by dy-other institutes,carried out a special investiga-namical calculating , Wyrtki(1961)and Nitanition in the Luzon Strait and its adjacent region(1970), respectively, got the Kuroshio capacity(Xu et al., 1997). There were two CTD and AD-of29.7x106 and 28.0x100 m2/s passing the zon-CP observation sections ( paralleling a longal section (18° 20' N)southeast of the Luzon120°00'and 120° 30'E)crossing the Luzon StraitStrait.Their calculated results were quitefrom north to south (see Fig.2).Using the CTDclose to each other. Such a huge current, sud-data and with the dynamic calculating method,denly having lost blocking frorm the Luzon coastwe obtained the flow velocity distribution atand then rushed into the Luzon Strait, un-the layer 0~1 000m in the observation sec -doubtedly would produce a signifcant influ-tion (see Fig.2b). It can be seen that the water中国煤化工MYHCNMHG14XU Jianping et al. Actu OceanologicaSinica 2004, Vol. 23, No.1, p.11~22113" 115" 117° 119° 121° 123° E:113”115° 117* 119° 121° 123* E199°L1717"LStation No.D49_ DAL D62 D75 D76 D77 D78 1D79 D80 S06X27 T60 T59 T58TS7 T56 TSS TS4 T53TS2DI20000W: 40000 t8 600600 I800I000|22 1021North latde!°")North ltitude(")Fig. 2. The velocity dstibution along the two longitudinal sctions in the Luzon Strait.a. 120°E section and b.121030'E section .exchange through the Luzon Strait presents avolume transport out of the SCS is about 4.30xcomplex situation,i.e, there exist peculiar phe-106 m/s.nomena of water body in and out of the SCSIt can be seen that the net volume transportthree times.via this trough is 0.7x10 m/s, that is, a small(1) Water into and out of the first deepamount of Kuroshio water enters the SCS.trough. The first deep trough inlet passage is at(2) Water into and out of the second deep18930'~1915N (according to the velocity ten-trough.The inlet passage in the second deepdency,expanding half a zonal distance of thetrough is at 19950'~20*20N, on the southermisogram line),which is exactly located on theside ofthe trough. The velocity over 10 cm/s ap-southern side of the trough.The velocity overpears in the surface and subsurface layers above10 cm/s appears in the surface/subsuface layers300 m. The maximum velocity is over 80 cm/s.less than 200 m. The maximum velocity is overThe inlet volume transport into the SCS is about40 cm/s here.The water inflow into the Scs is6.6X 10 m/s.about 5.0x 10 m2/s.The outlet passage in the second deepThe outlet passage of the first deep troughtrough is at 20920'~21°00N，on the northermis at 19°15'~19950N, on the northern side of theside oftrough. The velocity over 10 cm/s ap-trough. In the layer above 500 m(from suface topears in the mid-layer above 400 m. The max-intermediate layer), the velocity is over 10 cm/s.imum velocity is over 80 cm/s.Here the waterThe maximum velocity is over 40 cm/s. Theflows out of the sCS witb the volume transport中国煤化工MYHCNMHGXU Jianping et al, Acha OceanologicaSinica 2004, Vol. 23, No.1, p. 11~2215about 4.0x 10 m/s.SCS is about 5.8x 10* m2/s.Hence the net volume transport throughthe second deep trough is 2.6x 10° m/s, that is,the third deep trough is -1.30x 100 m/s, namely,the inlet water(into the SCS)dominates over thethe water flows out ofthe sCS.second deep trough. .Analyzing the whole observational sec-(3) Water into and out of the hird deeption, we find that there is a net volume transporttough. The inlet passage is at2100'~2!030N,of 2.0 x10* m/s passing through the Luzonon the southem side of the third deep trough.Strait, which flows into the SCS. Exactly, theThe velocity over 10 cm/s appears in the inter-water mainly flows through the second deepmediate layer above 400 m. The maximum ve-trough (the Balintang Channel)into the SCS,locity is over 50 cm/s. The water inflow into theand the third deep trough is the main passage ofSCS is about 4.5x106 m3/s.water running into the Pacific.The outlet passage is at 21°30~21*40N,3.1.2 Analysis of the numerical calculation re-on the northem side of the third deep trough.sultsThe maximum velocity does not appears in thesurface butin the deep layerbetween 600~800 m,Figure 3a is the distribution of salinity andalmost beneath the layer of the inlet passage.temperature and velocity along the whole Lu-Because there were no observed data in the areazon Strait section in August (Xue et al,2001).north of21°40N, we do not know the currentFigure 3b is the ditribution of salinity and tem-situation at that time. By analyzing data at pre-perature and velocity in the layer 0~400 m ofthesent,this is the area where the strongest outletsection (Xue et al.,2001). From Fig.3, we canflow appears. If we consider the out volumesee the characteristics of water exchange in thetransport in the northermost tip of 120°E sec-Luzon Strait as follows.tion as out volume transport in the northernmost(1) Water in and out in the south. Thetip of 121930'E section, the flow fux out of thesouth inlet passage is at 19*00'~19920N,in theE 800气1600200 -300 F2400 sli3200 salnty00 t。 salinit0n00出复160082400F00 F3 200temperature0oE rmpentre0100E 1600f200 t营2400300velocity00 CNorthDistance/mSouthFig 3. Distributions of salinity and temperaure and velocity across the Luzon Strait in August(according t0 the numerical calculating results). a. The wbole layer and b. the 0~400 m layer.Positive velocity forwater into the scs; negative velocity for water out the sCS.中国煤化工MYHCNMHG16XU Jjanping et al. ActuOcemnologicaSinicn 2004, Vol. 23, No.1, p. 11~22layer 50~200 m.The maximum velocity is over ed results are listed in Table 1. From Table 1, it10 cm/s. The outlet passageisat 1920~19950N,can be seen that the observed water inlet andTablc I. Comparison ofthe observed and calculated resultsWater pasagcsResultby deph/m .0- 5000--- 3000~ 600to forr(1997)north laitude( )18.5~ 193 19.3- 199 199~ 20.4 20.4~ 21.0 21.0~ 21.5 2.5~ 22.7current directionwestistResult bydepth/m0~ 700200- 400 0- 7000- 70(0--600.0to floorXie et aLsouth latitude/( )18.5~ 19.4194~ 19.719.7- 20.9209-- 21.121.1- 21.313~ 22.0(2001)current dretion westeastest时beneath the 800 m layer.outlet positions are consistent with the calculat-(2) Water in and out in the central part.ed ones.The water inlet passage is at 19950~20940N, inAccording to the calculations(Xue et al,the layer above 800m.The velocityover 15cm/s2001), in August the net volume transportappears in the layer between 100 and 400 m.through the Luzon Strait is 3.95 x l0* m/s,ie., .The outlet passage is at 2045'~21*05'N, locat-the Pacifc water still flls into the SCs, but theedon the northerm side of the second deepamount is two times the observed one. Whiletrough. The velocity over 5 cm/s appears in thein July, the calculated net volume transportlayer 150-400 m.through the Luzon Strait is 1.95X 10° m/s, equal(3) Water in and out in the north. The wa-to the observed result.ter inlet passage is at 21005'~21020N, i.e., at3.1.3 Analysis ofthe observedA DCPdatamiddle to south of the third deep trough. The ve-locity is not over 5 cm/s. The outlet passage is atFrom Fig.4, it can be seen that the observed21°20'~22*00'N, i.e., at the bottom layer tocurrent vector on the westemn side of the Luzonnorth ofthe third deep trough. The velocity overStrait has the distribution features as follows.15 cm/s appears beneath the layer 150 m.(1) In the area 21°00'~21-30N, the currentFor comparison,the observed and calculat-vector points to west and nothwest with the006108”10121416°18120N222*--20.8°18°t1 186↑6°4g 14呀12otr| 103”+|g°10 S10km/s0 50100cnv/sFig. 4. Observed ADCP results in June-July 1998. a.Layer 18~35 m, b. Layer 35~65 m andc. Layer 150-200m .中国煤化工MYHCNMHGXU Jianping ct al. ActaOceanologicaSinica 2004, Vol. 23, No. 1, p. 11~227maximum velocity over 100 cm/s , which ob-3.2.1 Analysis of the observed results of dynum-viously indicates this region is the water inletical calculationpassage. In 21030'~22930'N, the current vectorswifly turns to northeast with the maximum ve-During November 28 to December 28,locity reaching 80cm/s, which is clearly the1998, the Second Institute ofOceanographyplace where the outlet passage is located. Thevith other institutes made a special researchobserved inlet/outlet passages derived from thecruise in the SCS and designed a CTD observa-current vector by the ADCP observation coin-tional section crossing the Luzon Strait alongcide with the dynamic calculating results along19*30'E. Based on the CTD data and dynamicthe 120° E section, i.e, the inlet/outlet passagescalculations we obtained the flow velocity andin the third deep trough are completely consis-volume transport in this section (Fig.5), whichtent.indicated the water exchange in winter through(2) In the area 19050'~20° 20' N, the cur-the strait with the variations of two times in/outrent vector points to west with the maximum ve-ofthe SCS. From Fig.5 it can be seen:locity 40 cm/s, which is coincident with the po-Station No.sition of the inlet passage analyzed in the sec-8788899091929394ond deep trough. The outlet position(20° 20' ~100|21900'N)seems not to appear ( see Fig.4) in lay-200})ers 18~35 and 35~-65 m, but it can be seen clear-300/4001ly in Layer 150~200m.。 S00. 5001(3) In the area 1915'~19950' N, the cur-600{)rent vector points to northeast with the maxi-700)口mum velocity 50 cm/s , which is completely800-|90coincident with the outlet passage position in1 000the first deep trough analyzed above. In 18*30'~19°15'N，the curent vector in Layer 18~Fig. 5. Velocity dstribution along Sction 19930E.35 m tums to north, while in Layer 35~65 mStation 87 isal 18930N and Station 94 at2I°N.the vector turns to northwest with the velocity30 cm/s，which is obviously coincident with() In winter the inlet passage to the SCSthe inlet position analyzed in the first deepbecomes wider than that in summer, almosttrough,covering the range of the second and the thirddeep troughs (19930' ~21930'N)，above the3.2 The water exchange features in winter300 m layer. There are two main passages: oneWyrtki (1961) believed that the Kuroshiois located at 199 30' ~ 20° 15' N with the maxi-water, driven by the northeast monsoon wind inmum velocity over 20 cm/s; the other is atwinter, was transported into the SCS. Accord-20930'~22900'N, with the maximum velocitying to his calculated result, the net inlet volumeover 50 cm/s.transport was 2.5~3.0x 106 m/s. The calcula-(2) The outlet passage is located at the firsttion by Liu et al. (2000) was 8.0x 106 m/s fromdeep trough nearby 18*30'~19°30'N, with theOctober to February next year, far greater thanmaximum velocity less than 20 cm/s.the result by Wyrtki (1961). But both of them(3) Nearby 2030'N, between the above-did not provide the passage patterns ofwater ex-mentioned two high velocity passages, there ex-changing.ists a narrow outlet passage, but the outflow ve-中国煤化工MYHCNMHG18XU Jjanping et al. Acta OceanologicaSinica 2004, Vol. 23, No.1, p. 11~22locity is less than I0 cm/s.Kuroshio water,i.e.,in the layer 0~200 m theThe net volume transport of the Kuroshiowater has high salinity (34.20~34.80), and be-waterinto the ScS is 4.45x 106 m/s，fromlow the 50 m layer the temperature is higherwhich it can be seen that under the influence ofthan its surroundings,which is the typical char-the winter northeast monsoon the water amountacteristics of the surface and subsurfacc waterinto the SCS doubles that in summer.of Kuroshio; in Layer 400~600 m, the salinity3.2.2 Analysis of the temperature and salinity thepresents its minimum value(34.40), which is thetypical feature of the intermediate water ofobserved sectionKuroshio.Hence we can deduce that the regionTo further explain wintertime water ex-nearby 20°05' and 21900N is the main passagechange patterms in the Luzon Strait, we cite theof the Kuroshio entering the SCS.sectional distribution of temperature and salini-(2) In the first deep trough (19900'~tyby Shaw et al.(1994), which depicts the situa-19930'N), Layer 0~200 m has the tendency oftion during December16~30, 1990 (Fig.6). Itlow surface salinity(33.60~34.40), high sufaceshould be pointed out that the temperature andtemperature,and low subsurface temperature,salinity section west of19°N is perpendicular towhich shows the distinct types of the surfacethe Luzon Strait,， which could not demon-and subsurface water masses of the SCS.It is notstrate the water exchange through the strait,butdifficult to deduce that the first deep trough is .the fact that low temperature and low salinitythe main path of the SCS water flowing out.water appears in the southernmost tip shows the(3) Nearby 2030N , between the secondSCS water really exists in this area.Figure 6 alsoand third deep troughs, there exists a low salini-shows the distributing features of the SCS watertybelt in Layer 0~200 m, and in the intermnedi-2 times in/out via the channel.ate layer(350~900 m)the salinity appears a lttle(1) In the second and third deep troughshigh,which is also the feature of the SCS water.(1930'~20944N)，nearby 20*05' and 21*00'NThe fact indicates that the SCS water flows outrespectively, there are distinct characteristics ofbetween the second and third troughs.&第N 2G6嘴生 6-3%告&%N2826242219171412.10864128 262422 1917. 1412. 10 8. 6 4g 5(0P10015营150|2004200L图200)0F:00 F400600 t言6008001 000400 300 200 10000t00bDistance/mFig. 6. Sectional distributions oftemperature (a) and salinity(b) in the Luzon Stnait in winter .中国煤化工MYHCNMHGXU Jianping et al. Acta OceanolugicaSinica 2004, Vol. 23, No.1, p. 11-22193.2.3 Analysis of the results of numerical calcu-the area 19° 10'~20*15'N, while the locations of200 10'and 2100N are the strong current cen-lationters of the Kuroshio entering the SCS.Figure 7 gives the calculated results of the(5) The strong current appears in the lay-salinity, temperature and velocity distributionser; above 400 m.of the section across the Luzon Strait in JanuaryIt should be pointed out that the numerical(Xue et al, 2001). From it we can see the samemodeling results suggest there exists anotherfindings as those in Fig.6: .outlet path to the north of21920N, with velocity(1) In the region nearby 18930'~19900'N,over 20 cm/s. This outlet path does not appear inthe SCS water flows out in the layer 0~50 m,Fig.6, perhaps it is due to the limited length ofwith the velocity over 60 cm/s,which corre-the observation section line. In addition, the mu-sponds to the minimum salinity area (see Fig6)merical calculated net volume transport is alsoon Layer 0~50 m near 18955N.entering the SCs, but its amount(1.31x 10* m/s)1001600 E2002 2400t salinity300， salinity3 20040001600 t占2400temperatureemperature3000. 1600名2400 tvelocity400 tveloc生00 t3200NorthDistance/mSouthFig.7. TVS and velocity distibutions across the Luzon Cbannel in January (modeling result) a.The whole layer andb. 0-400m layer . Positive velocity refers to entering the SCS, and the negative refers to going outof the scs.(2) In the depth of 100 m, near 199 20N,is obviously smaller than the observed result,there is a strong current inlet region with maxi-which, perhaps, is related to the numerical mod-mum velocity over 30 cm/s. This corresponds toeling adopting the data of Levitus Even statis-the high salinity area (see Fig.6) approximatelyticclosed by the 34.6 isohaline in the layer 100 mnear 1920'N.4 Discussion and summary(3) In 20°30N, there is an outlet path withthe velocity varying among 0 ~10 cm/s, and the(1)The water exchange via the Luzonmaximum velocity about 20 cm/s appears at theStrait in the summer of 1994 did not have onlydepth of50 m.one patterm,but showed complex features of in-(4) The Kuroshio intnusion takes place interval distributions of flowing in and running中国煤化工MYHCNMHG20XU Jianping et al. Acla OceanologicaSinica 2004, Vol. 23, No.1, p. 11~22out .The capacities of water entering and flow-might be also the outlet path.ing out of the channel were over 4.0x10* m/s.(4) The results of numerical simulationThe maximum velocity(>80 cm/s) and the max-and the observed ADCP data indicate that inimum volume transport (6.6 x10° m3/s )allsummer and winter there truly exist several inletappeared in the Balintang Channel.Though thisand outlet paths in the channel. In summer therelocation is not the deepest place in the strait,presents the pattern with inlet and outlet threethere are few islands on the east and have lttletimes.The inlet paths almost appear on the southobstacle to the entering water. Hence, it seemssides of the three deep troughs,and the outletobviously simple to use the circulation pattempaths are located on the northem sides.In win-Table 2. Density(o )comparison between the Kuroshio water and the sCs waterDepth/mKurosbio water in the PhilippScs waterter in the Pippic Sca .SCS water24.75 ~ 25.750024.20-.25. 50.25.30 ~ 26.105024.50 ~ 25.8825.80 ~ 26.30to describe the path of the Kuroshio intrudingter, there is the pattern with inlet and outlet twothrough the Luzon Strait.times.The inlet paths appear on the southern(2) In summer, the more toward the northsides of the sccond and third deep troughs,whileof the strait, the more the curent outlet locationthe outlet paths occupy the whole bottoms of thetends to deepen.In the middle outlet path, thefirst and third deep troughs.depth is 100 m deeper than the inlet path. And at(5) In the summer of 1994 , the vol -the northermmost tip, the core ofthe outlet pathume transport through the Luzon Strait wasappears at the depth of600 m.2.00x 10* m/s, and in the winter of 1998, it wasThe reason why the outlet path deepens is4.45x10 m/s. Each accounted for 6.% andas follows:due to fact that the sea water has a15.0% of the total volume transport ofhigh temperature and salinity in the main cur-Kuroshio,respectively.rent region of Kuroshio,while the SCS waterhas a lower temperature and salinity,theAcknowledgmentsKuroshio water density is obviously lower thanthe SCS water in the same layer (Table 2).SoThe research is supported by the National Keywhen the Kuroshio water enters the strait andFoundation Program of China under contract No.mixes with the SCS water,the density of theG1999043805,the National Climbing Project "Southmixed water rises, and inevitably, when it runsChina Sea Monsoon Experiment' and the State OceanicAdminstration.out ofthe strait, the outlet layer deepens.(3) In the winter of 1998, the main currentReferencesinlet paths of the Kuroshio water into the SCSappeared on the southern sides of the secondBlumberg A F，Mellor G L.1987.A description ofand third deep troughs，while the main outletthree-dimensional coastal ocean circulation model.paths of the ScS water out were located at theIn: Heaps N S,ed. Three Dimensional Coastal Oceanbottom of the first and second deep troughs. TheModels. American Geophysical Union, 1~|6velocity over 10 cm/s was distributed in the lay-Cai Shuqun, Su Jilan,1995.A two-layer model oftbe cirer above 300 m.Numerical calculation indicat-culation in the SCS.Acta Oceanologica Sinica (inedthat the nortbern' side of the third troughchinese),17(2): 12~19中国煤化工MYHCNMHGXU Jianping et al. Acta OeeanologicaSinica 2004, Vol. 23, No.1, p. 11~2221Chao Shennyu, Shaw Pingtung, Wang Joe. 199S.WindNiani H.1970. Occanograpbic conditions in the Philip-relaxation as a possible cause of the sCS Warm Cur-pine Sea and Luzon Strait in summer of 1965 andrent, Joumal ofOccanography.5111~1321966. In: John C Mrred, The Kuroshio-A Sympo-Guan Bingxian. 1990.The distibution featurcs of thesium on the Japan Current. 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