Study of seasonal transport variations in the ... - Wiley Online Library

JOURNAL

OF GEOPHYSICAL

RESEARCH,

VOL. 100, NO. C10, PAGES 20,517-20,541, OCTOBER

15, 1995

Study of seasonal transport variations in the Indonesian seas Toru Miyama, ToshiyukiAwaji, Kazunori Akitomo, and Norihisa Imasato Department of Geophysics,Faculty of Science,Kyoto University, Kyoto, Japan

Abstract. Seasonaltransportvariationsbetweenthe Pacificand Indian Oceansvia the Indonesianseaswere studiedby the Euler-Lagrangianmethod.The velocityfield was calculatedwith a fairly high resolutionrobustdiagnosticmodel. The model well reproducesthe featuresof seasonalvariationsin the Indonesianseas.The total volume

transport of theIndonesian throughflow is 20 _+3 Sv(1 Sv= 106m3 s-l), themaximum beingfrom boreal springto boreal summerand the minimum in boreal winter. The values are similar to thoseof previousgeneralcirculationmodelswith a wide Indonesianpassage despiteresolutionof the presenceof the many small islandsin the Indonesianseas. Although a large portion of the net transportis containedin the upper layer, deep transportbelow 1000-mdepth is about 5 Sv. This value correspondsto approximately25% of the total transport,which meansthat disregardof the deep transportleads to underestimationof the volume transportof the throughflow.Tracking of numerous labeledparticlesin the calculatedvelocityfield clarified the sourcesand pathwaysof the Indonesianthroughflow.The major route is a westernone throughboth the Makassarand Lombok Straits.Most of the North Pacificwater suppliedfrom the Mindanao Current passesalong this route, enteringthe Indian Ocean within severalmonthswith almostno lossof its properties(intenseverticalmixingaroundthe Lombok sill reportedby observations couldnot be reproducedin our model). In contrast,SouthPacificwater takes the easternroute into the easternIndonesianseasand subsequently mixeswith waters from the North Pacific and Indian Oceans in the Banda Sea, which means that it has a

long travel time (at least a few years).Water taking the easternroute therefore losesits originalpropertiesbefore arrivingin the Indian Ocean. The transportprocessesalso are significantlyaffectedby seasonalvariationsin equatorialcirculationin the westernPacific. In the surfacelayer, North Pacificwater is vigorouslysuppliedto the westernroute only from boreal springto summerin associationwith the linkage betweenthe current flowing through the MakassarStrait and the Mindanao Current. In other seasons,becausethe MindanaoCurrent is stronglylinkedwith the North EquatorialCountercurrentand the New Guinea CoastalCurrent primarily by northeasterlymonsoonalwinds,its upper water flowsback to the PacificOcean. In the subsurfacelayer, a pronouncedinflow of Mindanao Current water into the westernroute occursfrom boreal winter to spring,when the subsurfacelink betweenthat current and the Equatorial Undercurrent tendsto weaken. In the deep, the quasi-steady transportof Pacificwater into the Indian Ocean via the eastern route is fed by the westwarddeep current in the equatorialPacific. Despite their importance, the transport processesof the Indonesianthroughflowstill are not clear. In particular, the The Indonesianthroughflowis an important flow that links volume transporthasyet to be determinedbecauseof lack of the waters of the Pacific and Indian Oceans.The water prop- direct measurements.In fact, only one set of direct measureerties in these oceansare greatly influencedby this through- mentshas been made in the Lombok Strait [Murrayand Arief, flow [Piola and Gordon, 1984;Fine, 1985; Gordon, 1986]. For 1988].Table 1 showsthe volumetransportvaluesestimatedin example,the heat transportof the throughflowaffectsthe heat past studies.These values,determinedby a variety of indirect budgetin the warm region of the westernPacificcalled "warm methods, have a broad range. The box models [Piola and water pool" [Wyrtki, 1989]. Becausethe heat content of this Gordon, 1984;Fine, 1985; Fu, 1986; Toole et al., 1988] give a warm water pool is closelyrelatedto E1Nifio and the Southern variety of values that range from almost nothing to 14 Sv Oscillation(ENSO) [Wyrtki,1985], the throughflowcould af(1 Sv = 106m3 s-l), themeanvaluebeingabout7 Sv. fect ENSO phenomena.The dynamicsof the LeeuwinCurrent Another notable fact is that the general circulationmodels in the easternIndian Ocean is closelyconnectedto the thermal (GCMs) [Cox,1975;Takano,1975;Semtnerand Chervin,1988, forcing of the throughflow[Godfreyand Ridgway,1985; God1992;Fufio et al., 1992a]givevery similarvalues(about 20 Sv) frey and Weaver,1991]. Furthermore, the throughflowis an that are larger than those found with other methods. One important componentof the globaloceanthermohalinecircureason for this may be the poor horizontal resolution of the lation [Gordon,1986;Broecker,1991]. GCMs. In fact, the detailed geometry (e.g., the many small Copyright 1995 by the American GeophysicalUnion. islandsin the Indonesianseas)hasbeen insufficientlyresolved in previousGCMs (i.e., wider Indonesianpassage)although Paper number 95JC01667. 0148-0227/95/95 JC-01667505.00 the vertical resolutionis fairly high. In contrast,Kindle et al. 1.

Introduction

20,517

20,518

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IN INDONESIAN

SEAS

Table 1. Net Transport of IndonesianThroughflowEstimatedin PreviousStudies Investigators

Transport, Sv

Method Box Models

Piola and Gordon [1984] Fine [1985] Fu [1986] Tooleet al. [1988]

freshwater

14 5.1 6.6 0.7

freshwater Numerical

Cox [1975] Takano [1975] Semtnerand Chervin[1988] Semtnerand Chervin[1992]

box model of the Pacific and Indian

Oceans

(shallowerthan 27.6 c%) tritium box model (upper 300 m) inversemethod applied to the Indian Ocean

18 10-20 15-18 17

box model of the western

Pacific Ocean

Models

world GCM (2ø x 2ø) world GCM (4ø x 2.5ø) world GCM (0.5ø x 0.5ø;coarsegeometry) world

GCM

with seasonal variation

(0.5ø x 0.5ø;coarsegeometry) world GCM (2ø x 2ø;robustdiagnosticmodel) reduced-gravity model(0.5ø x 0.7ø)

Fujio et al. [1992a] Kindle et al. [1989]

21 7.5

Wyrtki [1961] Godfrey[1989]

1.7 16 +_4

Other Methods

dynamiccalculation Sverdrupmodel

Positivevaluesindicatesouthwardtransportfrom the Pacificto the Indian Ocean.

[1989]obtaineda net transportof 7.5 Svusinga fine-resolution reduced-gravitymodel that resolvedfairly detailed geometry. This value is similar to that of the mean transportfound with the box models.Except for the GCMs, the modelsusedto date focusmainlyon the upper transport,neglectingthe deeptransport. If we accept Godfrey's[1989] island rule based on the Sverdrup relation, deep transport provides another possible reason for the larger net transport obtained with the GCMs. To better understandthe volume transportof the throughflow and the detailed velocity structure, an investigationis needed that useshigh-resolutionGCM with fine geometryand bottom topography. In addition to the problem describedabove,it is very important to determine the origin and path of the throughflow. The heat and salt (freshwater) transportfrom the Pacific to Indian Oceans, which has a critical role in the heat and salt

(freshwater)balanceboth in the westernPacificandthe Indian Ocean [Gordon,1986; Wyrtki,1989], varieswith the temperature and salinityof the sourcewatersof the throughflow,even when the volume transports of the throughflow are equal. Accordingto recentstudies[e.g.,FfieM and Gordon,1992],the westernPacific'scentral and tropical waters,consideredto be possible sourcesof the throughflow, consist of North and South Pacific waters. The properties of these waters differ. Therefore knowledgeof the path taken by the North and South Pacific waters to the Indian essential

for

the

Ocean via the Indonesian

identification

and

characterization

seas is of the

throughflowwater. This in turn permits investigationof the physical mechanism of the transport processesbetween the Pacific

and Indian

Oceans

that

are associated

with

the

throughflowand contributesto our understandingof the water massbudgetand the heat and salt (freshwater)budgetsof the warm water pool and of the North Pacific and South Pacific Oceans[Wijffelset al., 1992]. Poor understandingof these pathwaysraises uncertainties about the specified temperature and salinity values of the throughflow, as the water property distributionsat the entranceof the throughflow(i.e., the westerntropicalPacific)are very complicatedbecauseof the vigorousand complexequatorial circulationsand the strongmassand heat exchanges with the atmosphere[e.g.,Reid, 1965;Tsuchiya,1968;Donguyet al.,

1982;Delcroixet al., 1987]. This leadsto misestimationof the heat and salt transportsfrom the Pacificto Indian Oceansvia the Indonesian seas. In the box models, because the volume

transportof the throughflowis estimatedfrom the property transport values, the resulting volume transport values are ambiguous.For instance,Tooleet al. [1988]obtaineda volume transportof 0.7 Sv using a box model. This value is smaller than the volume transport through the Lombok Strait alone reportedby Murray and Arief [1988]. This unacceptablevalue for the volume transport of the throughflowis thought to be due to the unreasonableassumptionthat the salinity of the throughflowis 33.5 psu,which is too low when comparedwith the observedvalue [Ffieldand Gordon,1992],exceptvery near the surface.The significantrange in the volume transportestimated with the box modelsmustbe due in part to uncertainties about the specifiedtemperatureand salinityvaluesof the throughflow. Any investigation of the sources and pathways of the throughflowencountersthe problem of marked variations in space and time in the currents in the Indonesian seas.The manyislandslocatedin the Indonesianseascreate a variety of possiblethroughflowroutes.The velocitystructurechangesin a multipletimescale[Serotrier and Chervin,1992].In particular, the Asian monsoonis responsiblefor strong seasonalvariations, in responseto which seasonalflow reversalstake place throughoutmost of the Indonesianseas [Wyrtki, 1961; Masumotoand Yamagata,1993].In sucha variablecurrentsystem, path lines (trajectoriesof fluid particles)are expectedto be largely differentfrom streamlines[Kundu, 1990]. Therefore it is desirableto investigatethe detailedsourcesand pathwaysof the Indonesianthroughflowfrom a Lagrangianrather than an Eulerian point of view [Flied, 1981; Shaw and Rossby,1984; Bowerand Rossby,1989;Awaji et al., 1991]. We first examined seasonalvariation in the velocity fields around the Indonesian seas,using a robust diagnosticmodel with fine horizontal and vertical resolution, to obtain velocities

faithful to the hydrographicdata. To get a better understanding of the origin and pathwaysof the Indonesianthroughflow, we then usedthe Euler-Lagrangianmethod to investigatethe Lagrangian movement of the water mass in the Indonesian seasand its seasonalbehavior by tracking numerouslabeled

MIYAMA

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40N-65S latitude, 10E~60W longitude Horizontally,112degree - 1/2degree Vertically, 19levels 10E

A

60W

No Inflow

ß

40N

ACC

130Sv outflow

inflow

B 2O

15

South China tO

Pacific Ocean

Sea

Celebes

Halmahera Sea

Java Sea Flores Sea t0

Lombok Strait

Indian Ocean

Sea

Banda Sea

xSea

avu Sea

t5

213

90

100

110

120

l•O

140

Figure 1. Configurationof the model basin used in the numerical experiment:(a) entire region and (b) magnifiedarea aroundthe lndonesianSeas(squarein Figure la) resolvedby the reportedmodel.The dashed line along the Lesser Sunda Islands correspondsto the section in which the volume transport of the Indonesianthroughflowwas evaluated.

particles(regardedaspassivetracers)in the calculatedvelocity tralasiais treated as an island,which permitsdirect evaluation field. both of the baroclinic and barotropic componentsof the In section2 the numericalmodel and the method of particle throughflow. We used"a robustdiagnosticmodel" that incorporatesthe trackingare described.The featuresof seasonalcycleof the velocityfield are givenin section3. The Lagrangianpathways 3'termsdescribedbelow to obtain a velocityfield faithful to the of the throughfloware explainedin section4, nnd the req,,ltq hvctraoranhic' clara [Sa,r,,mi•,nn an,4 Rr•,an I QR9I I Tnctprthp are discussed in section 5 and summarized in section 6. rigid-lid, the Boussinesq,and the hydrostaticapproximations, the governingequationsin sphericcoordinatesare 2.

Models

2.1.

Numerical

Ou

The model region in this studycoversthe Pacificand Indian Oceans between

40øN and 65øS latitude

u v tan 4>

Ot+Lu----fv= a

Model

and between

10øE and

60øWlongitude(Figure 1). Horizontally,the model domain is divided into 0.5ø x 0.5ø grids. Vertically, there are 19 levels expandingin thicknessfrom 20 m at the surfaceto 500 m at the bottom. With the DBDB5 topographicdata (National GeophysicalData Center, Boulder, Colorado), we resolved the geometryof the IndonesianSeasin greaterdetail (Figure lb) than was done in previousGCMs (Table 1). Note that Aus-

0v

-

u2 tan

at+ Lv- --

a

1

Op

poa cos 4>0h+F•'

+fu =

poa

+ F•,

(1) (2)

Op

0 = - c}•- Pg' L(I)

(3)

=0,

(4)

+ œ0= y(0*- 0) + ,r0,

(5)

00

20,520

MIYAMA ET AL.- SEASONALTRANSPORT VARIATIONS IN INDONESIAN SEAS

5 dyn/cm"2DAY= 50 A

> 2O

10

-10

-2O

90

100

110

120

150

140

longitude

D•Y=212

5 dyn/crm2

D

20 •//••••:••••:•.•::::•:•.•:•:•.•:•:•,•::.• ....................... •............ : •//• ...... :•:x::•, ............................... • •;; ;,,' ............................ :•

5 dyn/crm2DAY=504 2O

.....•.::•:.•.•::•:•:•:.•:•::•:•::•:•: ,,,, xx /,•:•:-:>,, ...... , •............ -

•• .:.::,..::'•::•::•f'•:::•:::•:::•::::•::•:•::::•::?• ••f•:*:-:• •}:.•, •//t•//••//•/•tzz tt/••;, •••........ •••.... _ •••:•::•:::•::•::•:::•:'•::::•:•::•f:•:•::•:'•:::•. •l••I///7I//'•:::• . :::::::::::::::::::::::::::::::::::::::::::::::::::::::::: • / '•--:.•::::•::• • - •,,,,,, .............

10

0 ......... , .:::::::::::::::::::::::::::::: •••(½"•½:::•?:•::•E:::•:::•F":; Y•::•:•:•"( (•((•(;•:•:fE•::: ;:•: ••:•:• 10

x••• ••••••

E'"•:"E"k • •:•.:•:•:.:•,:,• ......•;:•-:•,, ••..%:•..•................

90

100

110

:.t --.' ......

-10

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: -2O

120

150

140

90

longitude

100

110

120

150

140

longitude

Figure2. Climatological windstress vectors [afterHellerman andRosenstein, 198•]'(a) February, (b)May, (c) August,and(d) November. Reprintedbypermission of theAmericanMeteorological Society. OS •t

+ LS= 7(S* - S) + F s,

(6)

lateral viscosity anddiffusivity aretaken as3 x 10• m2s-• and 1 X 103 m2 s-•, respectively,. similarto thosein the previous

GCMs. Vertical mixing isbased ontheformtilas giv, enby

where u, v, and w are the eastward,northward, and upward Pacanowski andPhilander [19õ1]because theirmethod issuvelocitycomponents,respectively;0 is potentialtemperature; periorto the conventional technique thatusesconstant viscosity S is salinity;t is time;p is pressure;p is density;P0is reference anddiffusivity, especially whena strongverticalshearexistsasin

density;g is gravitationalacceleration;a is the radiusof the Earth; andf is the Coriolisparameter(= 212sin &). L is the advectionoperator definedas

L(p.)=a cos •(up.) +•-(vp. +•-z ' (7) 1&[a a cos&) ]OWl• The firsttermson the right-handsidesof (5) and (6) are the 7 termswhichrestorethe potentialtemperatureandsalinityto the observedvalues(0' andS* ). Accordingto FujioandImasato [1991] and Fujio et al. [1992a],who successfully made diagnosticcalculations for the Pacificand world oceancirculations, 7 is given as

y = yo [sin01.

(8)

a tropicalocean.The equationof statefor seawater isa nine-term

polynomial approximated totheInternational Equation ofState 80[UNESCO, 1978] according toBryan andCox[197•]. Boundaryconditionsare asfollows:The seasurfacefluxesof heat and salt are given by the Newtoniandampifigof the potentialtemperatureandsalinityin the top two levelsto the observedvaluesfor a timescaleof 30 days.Surfaceforcingby wind stressis imposedon the basisof the monthlymean cli-

matological datareported byHellerman andRosenst•in [1983] (Figure2). At the westernopenboundarythe AntarcticCircumpolarCurrent (ACC) flowsin and at the eastei'none it

flowsout,theinflowandoutflow across thebounda. riesbeing

fixedas130Sv[Whitworth etaJ.,1982]. At thenorthern open

boundarythe barotropiccomponentnormalto the boundaryis Here the coefficient 'Y0is takento be (1 year)-• (thiswill be forbidden,but the barocliniccomponentis possible.A no-slip Sincebottomstress discussed later). The observedpotentialtemperatures and sa- conditionis imposedat landboundaries. linities are given from Levitus' [1982] data. The terms in F mustplay an importantrole in the dynamicsof the shallow representthe effectsof turbulentviscosity anddiffusivity in the regionssuchas the JavaSea,its effectis addedin the bottom a dragcoeffici•ht Of5.0x ]0-4 harmonicform. Unlike prognosticmodels,the robustdiagnos- levelviaa lineardraglawusing models tic model is not stronglyinfluencedby the choice of eddy m s-•, whichis usuallymadein shallowembayment diffusivity [Sarmiento andBryan,1982].Hencethevalues of [Chapmanand Brink, 1987].

MIYAMA

ET AL.: SEASONAL

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IN INDONESIAN

SEAS

20,521

sensitiveto the choice of 3' in that range, becausethe density

Energy (cm/s)

VARIATIONS

field is almost fixed to the observed one. Hence on the basis of

2

theirstudies, we determined 3'to be (1 year)-1.Thisvalueis

-

5.40 -

5.20 --

4.80

-3

-2

-1

0 year

Figure 3. Kinetic energyper unit massduringthe last 3 years of integrationwith seasonalforcing.

basicallysimilar to their value but is chosento be somewhat smaller. The reason is as follows. The 3' term in the robust diagnostic model was introduced by Sarmiento and Bryan [1982] to alleviate an inconsistency between the observedand calculateddensityfields. Such an inconsistency leading to unrealistic flows arisesfrom the coarseresolution in spaceand time, with which the model can not fully resolvesmaller-scale features of the observeddensity field. Also, an inadequately large 3' has a tendencyto largely distort the heat and salt balancesbecauseof the artificialbuoyancysources.Thesefacts imply that in the present model, which can resolve seasonal variationsand relatively small-scalefluctuationsin the density field comparedwith their steadyrobustdiagnosticmodelswith coarse (2ø x 2ø) grids, a smaller value of 3' is desirablein diagnosingthe velocity field. A similar treatment has been made in the free-thermocline,high-resolutionrobust diagnostic model by Semtnerand Chervin[1992].Anyway,we have no generalcriterion of a suitablevalue of 3' for a variety of problems [Haineset al., 1993], so that the reliability of the diagnosedvelocity field shouldbe finally checkedby the observational results, which will be discussedin section 3. 2.2.

Method of Particle Tracking

Particle trackingby the Euler-Lagrangianmethod provides First,the modelis run for 4 yearsusingcoarse(2ø x 2ø)grids an excellent means for analyzing water mass movements andtheannualmean0', S*, andwind,afterwhicha 2-year [Lozierand Riser, 1990]. Studiesbasedon this techniquehave thewaterexchange processes in coastal embayments integrationwith fine (0.5ø x 0.5ø) grids is made. The high- explained resolutionmodel then is run usingthe seasonal0', S*, and [Awaji et al., 1980, 1991;Imasatoand Qiu, 1987] in the Pacific wind for 11 years, by which time the model almost has an Ocean [Fujio and Imasato, 1991],and in the world ocean[Fujio equilibrium seasonalcycle.The resultsto be shownhere are et al., 1992b]. The procedures are as follows. If the threedimensionalvelocity vector u is given, the time-varyingposifrom the last year of integration. Spin-upfor 11 yearswith the high-resolutionmodel using3'o tion X of a fluid parcel is obtainedby solvingthe initial value of (1 year)-• priorto analysis of seasonal transportvariation problem seemsto be on the low siderelativeto other robustdiagnostic dX/dt = ,, (9) simulationssuch,as thoseof Semtnerand Chervin[1992] and Fujio et al. [1992a, b]. Hence we simply describehere how x- x0 t= 0. (•0) sutBciently the presentdiagnostic calchlationis spunup. Figure 3 illustrates thetemporal change inthekinetic energy perunit The time integrationof (9) is donehere usingthe fourth-order massduring the last 3 years of integrationwith seasonalforc- Runge-Kutta schemewith a time increment of 1 hour. The ing, showingan almostcompleteseasonalcyclein the model. velocityfield at any time is obtainedby linear interpolationof Thusrobustdiagnosticcalculationshave an advantagethat the the velocitiesstoredeach day, and the velocityat any point is model reaches more rapidly an equilibrium state than the obtainedby linear interpolationof the calculatedvelocityfield. prognosticmodel, aswaspointedout by previousstudies[e.g., To prevent a particle from stickingto a boundary,particle velocitiesnormal to a boundaryare assumedto be zero when Fujio and Imasato, 1991]. It will alsobe necessaryto discussabout the determination a particleapproachesthat boundary(within one fourth of the of the parameter 3' in this model formulation, becauseresults horizontalgrid from the sidewallsor within one fourth of the of the robustdiagnostic modelvarywith the parametervalues. vertical level thicknessfrom the surfaceand bottom). Particle Performing several experimentswith different values of 3', movements around the Indonesian seas are calculated for 2 Fujio and Imasato [1991] and Fujio et al. [1992a] gave useful yearswith an annual cycleconditionfor the velocity field, in informationconcerningthis problem.Accordingto their re- order to better understand the role of seasonal variations in sults, the strong restoringto the observedtemperature and the velocityfield on the pathwaysof the throughflowand the salinity is requiredin orderto reasonably Obiainthevelocity resulting water exchange between the Pacific and Indian

field consistent with distributions of thesehydrographic data.

Oceans.

In particular,theyshowedthat aslongasa large 3'corresponding to a relaxationtimescaleof the order of 100 daygis used, 3. Seasonal Variations in the Eulerian the diagnosticmodelprovidessuccessful results(for example, Velocity Field diagnosedcirculationsare basicallyin good agreementwith observedones,with the temperaturedeviationfrom the ob- 3.1. Synoptic Features of the Large-Scale Velocity Field served data smaller than about 0.1øC and much smaller in the Before discussingthe detailed seasonaltransport processes deep). Moreover, they pointed out that the resultsare not so in the Indonesianseas,we brieflydescribethe synopticfeatures

MIYAMA ETAL.:SEASONAL TRANSPORT VARIATIONS ININDONESIAN SEAS

20,522

50

100

150

200

250

300

50

100

150

longitude

200

250

300

longitude

5Ocm/s DAY=120

50 cm/s DAY=504

--->40 •':"" '•-•..'• '•:'" •'"'"••••••••••••:• ••",• .............................................. •' ........................... '-";4' "'""'"'""""•"••"•'•••'-'• ..... •40 "'""'"'•"•'"-"'"'••'"•'""•'•" ;•••••••••i'•"""•i '•'••-"'• •"•'"-•":• :::'::::::: :::':::: :::z:-'"" •••• ............ ......... • ,•••••••••] ............................................. ••••••'"•*•4;•;'::: :::::::::::: ::•• :(..... '•'•"•'•'••••••l ......................... •:••"•••••*""½:= "½'½½•:• ':":':::::::::::: .......:'-•-"•'"•'"•••"• ........ •'•:½••-•••i• :::: •": •:½:•1•: :G:;;:::::::::::::::::;::::::::::: :•'""•'""•'•½••• ......... -•½•,,-:.•,:: ::•i::::-.-.,•,,•:============================== ....... N-•o-':-'•-.•••............ . ,•....,••••½• ...... ;•,•, ....•.,,,.............. ::::;:t::::::: .....

:: :: .... • -20•.•,•.•:4::?•:::::::::::::::{......_•t:::::::::::: ....::::::::::::::55•:,•1 • -20:::::::::::::::::::::::::::::::::::::::::::::::::: '"'"•:'•:•:i':::::::::::::::::::::: ::'•'•5• ................. :"::::::::::::::

'--

•

•*"•'"•5• 'g::::::::ttt:::::

-

:::::::::::::::::::::::

.........

........::.....:::::::::'..:.'.:.:.:-:.:.:.:-:.:.

-lO

-2o

90

100

90

100

110

120 longitude

150

110 120 150 longitude

140

140

90

100

110

120 longitude

150

140

90

100

110 120 150 longitude

140

Figure 14. Annual progression ofthesimulated velocity field atthedepth of300m:(a)February, (b)May, (c) August,and (d) November. the deeplayerof the SavuandTimor Seas,about25% of the the throughflow.We believethat this is one reasonfor the totaltransportof the throughflow, whereasthe volumetrans- discrepancies in thethroughflow transport valuesfoundwith

portabove 250m is9.52Sv,comparable to thenettransportGCMsandothermodels thattradeoffthedeepportionas reported byKindleet al. [1989],who,useda reduced-gravity described in section 1. Disregard of deeptransport therefore modelandthemeantransport of theboxmodels (Table1). mayleadto underestimation of thethroughflow transport. Thisfactstrongly suggests thatthetransport in thedeeppor- The simulated seasonal component of the throughflow t,ionisnotnegligible whenestimating thevolume transport of transportis about+3 Sv(Figure16).The season of the most ,

10 cm/s

month

DAY-2 ! 2

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M I

A M I

I

J I

J I

A I

$ I

O I

N I

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J

I , I

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