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Modeling_0Modeli

    Modeling

ChineseJournalofPolarScience,Vo1.19,No.2,193211,December2008

    ;ModelingtheoceancirculationintheBeringSea

    ;HuHaoguoandWangJia

    ;JCooperativeInstituteforLimnologyandEcosystemsResearch(CILER),SchoolofNaturalResourcesandEnvi

    ;ronment(SNe~),UniversityofMichigan.,4840SStateRoad,AnnArbor,Michigan48108,USA

    ;2NOAAGreatLakesEnvironmentalResearchLaboratory(GLERL),4840SStateRoad,AnnArbor,Michigan

    ;48108,USA

    ;1Introduction

    ;ReceivedSeptember20,2008

    ;AbstractWithparameterizedwavemixing.thecirculationandthetidalcuITentin ;theBeringSeaweresimulatedsimultaneouslyusingthethree.dimensionalPrinceton ;OceanMode1.Thesimulatedcirculationpatterninthedeepbasinisrelativelvstable. ;cyclonic,andhaslittleseasonalchange.TheBeringSlopeCurrentbetween200.1000 ;misobathswasestimatedtobe5Svinvolumetransport.TheKamchatkaCurrentwas ;estimatedtobe2OSvofftheKamchatkaPeninsula.TheBeringshelfcirculationsvary ;withseason,drivenmainlybywind.Thesefeaturesareconsistentwithhistoricalesti. ;mates.Acountercurrentwascapturedflowingsoutheastwardapproximatelyalongthe ;200misobathoftheBeringSlope,oppositetothenorthwestwardBeringSlopeCur

    ;rent,whichneedstobevalidatedbyobservations.Anupwellingcurrentislocatedin ;theshelfbreak(1201000m)area,whichmayimplytheverticaladveetionofnutri

    ;entsforsupportingtheBeringSeaGreenBeltseasonalplanktonbloomsinthebreak

    ;slopearea.TheBeringSlopeCurrentislocatedinadownwellingarea. ;KeywordsArcticOcean,theBeringSea,

    ;OCeancirculation.

    ;TheBeringSeaisasemienclosedsubpolarsea.

    ;whichisconnectedtotheArcticO.

    ;eeanonthenorth,andboundedonthewestbyRussia,ontheeastbyAlaska,andonthe ;southbytheAleutianIslands(FigureI,modeIdomain).BowersRidge(withaminimum ;depthof184m)andShirshovRidge(withminimumdepthof500m)dividetheBeringSea ;Intothreebasins--theBowersBasin,theKamchatkaBasin,andtheAleutianBasin.The ;BeringSeaisdividedalmostequallybetweendeepbasinsandthecontinentalshelvesf< ;200m).Thebroadshelfintheeastcontrastswiththenarr0wshelfinthewest.ThesteeD ;bathymetricfeaturesincludethedeepAleutianTrench(>5500m)andtheBeringBasin ;(>35O0m)andtherelativelyshallowAleutian(<100m)Islandsehain.whichchallen. ;gesallthe3Dphysicaloceanmodelswithsigmacoordinates[11.

    ;Observationsshowthecirculationpattern(Figure2,afterStabenoeta1..1999[2])in

    ;thedeepBeringSeabasinisoftendescribedasacyclonicgyre[2]:theAleutianNoahSlope ;Current(ANSC)flowseastwardalongtheAleutianIslands:theBeringSeaSlopeCurrent ;194HuFlaoguoandWangJia

    ;fl0wsnorthwestwardly,andthesouthwardfowingKamchatkaCurrentormsthewestern ;boundarycurrent.Observations[]showthecurrentsontheBeringSeashelfarebasically ;northwardornorthwestward.However,measurementsarenotsufficienttodeterminethe ;seasona1circulationvariation,anditalSOcannotrepresentthewholedomainwithsuffieient

    ;spatialcoverage.Modelswithrealisticsettingscanhelptoderivemoredetailedintbrmation ;aboutthegeneralcirculationintheBeringSea.Overlandeta1.(1994)L4jusedathree

    ;laverhydrodynamicmodeltosimulatethecirculationoftheBeringSeaBasin,whiletheBe

    ;ringSeashelfandsloperegionsshallowerthan500m,hencethecrossshelfflux,wereex

    

    ;cludedf.0mthem0de1.SeveralothermodelswereappliedtopartsoftheBeringSea’’..

    ;Thus.thegeneralcirculationpatterniSstillnotwellunderstood.

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    ;Fig.1Mode1domainandbathymetryoftheBeringSea(inmeters).ThedepthsalongAleutianIslandsand

    ;DassesweremodifiedaccordingtoNOAAoceancharts.Redlineindicatesthetransectinthetext?

    ;Observati0nsshowthatthecoldwater(<1.oC)nearthebottominthemiddleshelf ;Dersiststhroughoutthesummer[7..

;Itwasspeculatedthatthiscoldwaterisformedfocally

    ;inwinterandinsulatedbystrongstratificationinsummer.Themechanismofthermocline ;f0rmali0nseemswellunderstood,i.e.,bytidalstirringandsurfacewindwavemlxmg; ;whereas.itisstilldiffieuIttoreproducecirculation,themocline,andfrontsusinga3-Dba’

    dimensionalmodelt;r0clinicDhysica10ccanmode1.Overlandeta1.(1999)lJusedaone

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    ;hindcastthe1980spring.summerthermaltransitionoftheBeringSeashelfasafunctionof ;waterdepth,butwithouthorizontalprocesses.

    ;ModelingtheoceancirculationintheBeringSeal95

    ;Fig.2SchematicdiagramforsurfacecirculationpatternintheBeringSeabasedonhistoricalobservations(re

    ;producedfromStabenoeta1.1999).

    ;Thus,asystematicmodelingapproachinabasinscalethatcoversboththedeepbasins ;andshelvesappearstobeessentialtosimulatethecirculationandtidalcurrentsimuhane

    ;ously.Sincefewbasinwide3-Doceanmodelsexistformodelingoceancirculationandtidal

    ;current,weattempttodevelopsuchamodelwithparameterizationsofwind?wavemixingfor

    ;thestudyof1)thecirculationandtransportsofmajorcurrentsystemsand2)dynamiclea

    ;turesintheshelf-sloperegionsuchastheBeringSlopeCurrent.Thispaperisorganizedas ;follows:Section2describesthemodelconfiguration:Section3discussessimulatedresults ;incomparisonwithavailableobservations,followedbyconclusionsanddiscussioninSec. ;ton4

    ;2Themodeldescription

    ;ThemodelusedhereiSthePrincetonOceanModelfPOM)describedindetailby ;BlumbergandMellor(1987)L9JandMellor(2004)lllJj.Itisathreedimensiona1.primi.

    ;tiveequation.vertical叮一

    coordinatemodelandhorizontalgridusingcurvilinearorthogonal

    ;andanArakawaC.grid.HorizontaltimedifferencingiSexplicit.whereastheverticaldiffer

    ;encingiSimplicit:thelattereliminatestimeconstraintsfortheverticalcoordinateandper

    ;mitstheuseoffineverticalresolutioninthesurfaceandbottomboundarylayers.Complete ;thermodynamicsiSimplemented.POMhasafreesurfacewithasecondorderturbulence

    ;closureschemel?jtocalculatevertica1mixingcoefficients.Horizontalmixingcoefficients ;employtheSmagorinskyparameterization.

    ;2.Wavemixingparameterization

    ;Themodeledsurfaceboundarylayerisoftentooshallowintemperatureandsalnitydur

    ;HuHaoguoandWangJia

    ;ingthespringsummertimewarmingl12jandfresheningevenusingthe2.5closureturbu

    ;lencemode1.Onemajorreasonisthatthemechanicwindwavemixingprocessesarenoti

    n

    ;cluded.CraigandBanner(1994)13jusedwavebreakingasasurfacediffusionboundary

    ;condition,whichisproportionaltou;,whereMfisthesurfacefrictionvelocity.Mellorand

    ;Blumberg(2004)[.]foundthattheCraigandBanner(1994)[13]modeldoesdeepenthe ;mixedlayerina1-Dcalculation,andhasapositive,butrelativelysmallinfluenceonthe3

    ;Dcalculation.EzerandMellor(1997)[14]provedthattheabsorptionofshortwaveradia. ;tionbelowthesurface,duetothelossofsurfaceheat,causestheupperlayertobelesssta- ;ble,increasesmixing,andthusdeepensthesummertimethermoeline.Inthispaper,sur? ;facewavemixingisparameterizedintothemodelasinHueta1.(2004)lDJ: ;=

    ;z~-

    ;.

    ;6/3U3e

    ;g

    ;K?isthewavemixingcoefficient,Bisthewaveage,6isthewavestemed,where ;PisanempiricalconstantdependingontheRichardsonnumber.FollowingthePOMl16], ;weset

    ;Kh=

    ;LM

    ;where

    ;K=qlSM,Kh=qlSn

    ;S[1(3A2B2+18AlA2)GH]=A2(16A1/B1)

    ;S(19A1A2GH)S[(18A}+9AlA2)GH]=A1(13cl6l/B1)

    ;(Al,Bl,A2,B2,C1)=(0.92,16.6,0.74,10.1,0.08)

    ;G:(塞一言20z)

    ;whereKmistheverticalturbulencemomentumviscositycoefficient,Khistheverticalturbu-

    ;lenceheatdiffusioncoefficient,qistheturbulencevelocity,Zistheturbulencemixing ;lengthscale,csisthesoundvelocity,Pisthewaterdensity,P0isthemostimportantandperiodicdrivingforceintheBeringSea.The

    ;tidesandtidalcurrentsontheBeringSeashelfplayanimportantroleinsuchoceanographic ;processesasthemaintenanceofthedensitystructure,sedimentresuspenslonandnutrients ;transport.Circulationcanbesimulatedwithouttideanditisacceptablewhenthetidalcur

    ;rentisweakinthedeepocean/sea.However,sincethetidalcurrentisverystronginthe ;ModelingtheoceancirculationintheBeringSea197

    ;BeringSeashelfcomparedtothecirculation,thetidalenergyaccountsfor90%ofthetotal ;energy[

    ;,

    ;dominatingtidalstirringshouldnotbeignored.Thus,thetidalcurrentisinthis ;study.

    ;TheopenboundaryconditionsofvelocitiesweregiVenby

    ;+?()cos(o)it+)=

    ;1

    ;whereVaistidalamplitude,0istidalphase,60isthetidalfrequency,andnisthenumber ;oftidalconstituents.

    ;2.3Modelconfiguration

    ;ThehorizontaIgridshaveasphericalcoord]inatesystemwitharesolutionof1/12.lon-

    ;gitude(about9.3km)and1/6.latitude(from10kmneartheAleutianIslandsto7.4km ;intheBeringStrait.)Thereare24orlayersinthevertical,or=(77)/(+’7),where

    ;r/(,Y)and(,y)arethesurfaceelevationandwaterdepth,respectively.Thevertical ;resolutionishighernearthesurfaceandthebottomforabetterrepresentationofthesurface

    evelsweredefinedator=0,0.008,0.016, ;andbottomboundarylayers.Vertical

    ;0.031.0.063.0.125.0.188,0.250,0.3l3,0.375,0.438,

    ;

    ;0.500,0.563,0.625,0.688,0.750,0.813,0.875,0.938,

    ;

    ;0.969,0.984,0.992,0.996.1.Themodellhassplitmodes.The2Dexter-

    ;nalmodeusesatimestepof20seconds.andthe3DinternaJmodeusestimestepof600

    ;seconds.

    ;Bathymetryisobtainedhom5minuteresolutionETOPO05data:howeverthedepthsof

    ;theAleutianIslandsandpassesweremodifiedaccordingtoNOAAoceancharts(NOAA ;Chart).Smoothingoftopographywasconductedforthesteepdopes.Subtractingthearea. ;averagedclimatologicaldensityfieldbeforecalculatingpressuregradienttermswasapplied

    ;tosubstantiallyreduceerrorstobelessthan10%ofthemeanflowandothernumericale

    ;rors

    ;[t6]l141.

    ;Theaboveprocedureiswidelyusedinpreviousapplicationsoforcoordinate ;modelsThemaximumbottomslopeallowedbetweentwoadjaeentgadpoints1sH/H<0. ;1.Maximumandminimumdepthsweresetto3000mand10m.respectively.Upwindad- ;vectionboundaryconditionsallowtheadvectionofthemonthlymeantemperatureandsalini

    ;tyintothemodeldomainunderinflowconditions.Attheopenboundaries.verticallyaver.

    

    ;agedinflow/outflowwasprescribedonthebasisofobservations(describedlater).Forthe ;baroelinievelocities.SommerfeMtyperadiationconditionswereused~.Observations

    ;sincethe1940sshowthattheannualmeannetnorthwardtransportisabout0.8Svjnthe ;Be1ringStnlit[18-223.

    ;andseasonalvariationsexistwithalargertransportinsummerthanin ;winter.Therefore,theoutflowtransportwasspecifiedaccordingtothemonthlydata. ;VolumetransportoftheAlaskanStreamhasbeendescribedbydirectandjindirect ;measurementdata.Cokeleteta1.(1996)l23Jusedvesse1.mountedAcousticDopplerCur--

    ;rentProfiler(ADCP)measurementstoobtainanAlaskanStreamtransportof24Svbased ;onanabsoluterefere]nceforgeostrophiecurrents(0/1500db).OnishiandOhtanj ;(1999)l241.usingcurrentmetermooringdata,showthattheAlaskanStreamvolume

    ;transportfrefe:rredto3000m)is27.5?6.5Sv.ReedandStabeno(1999b)l?Jused

    ;CTD(Conductivity/Temperature/Depth)casteddatatoobtainavolumetransportof25Sv ;l98HuHaoguoandWangJia

    ;freferredtothebottom).ThewestwardflowingAlaskanStreamwasspecifiedatthewest

    ;ella_openboundarywithaconstantthroughputof25Sv.TheeasternboundaryinflowiS29

;Svp]usatransportthatequalsthenorthwardoutflowattheBeringStrait.

    ;Themodelwasinitializedwiththeannualclimatologicaltemperatureandsalinitydata

    ;fromthePolarsciencecenterHydrographicClimatology(PHC3.0,Steeleeta1.

    ;2001l26J,.TheseaicemodelintheBeringSeawasnotincludedinthisstudy.Monthly

    ;seasurfacetemperature(SST)andsalinity( ;conditions.BecauseourinthisstudyfocusiS ;inthisstudy,monthlymeanwindstressdata ;mosphereDataSet(COADS).Themonthly

    ;timestep.

    ;SSS)datawereusedasthesurfaceboundary ;onlyonseasonalvariationofoceancirculation ;wasusedfromtheComprehensiveOcean-At--

    ;meandatawereinterpolatedlinearlytoeach ;Then,were.ranthemodelforanotherfouryearsusingtheprevioussixthyearoutput ;astherestartorinitialconditions.Duringthefouryearrun,allthemonthlyatmospheric ;foreingsremainedthesame.Then,thelastyearvariableswereusedforexaminingthesea

    ;sonalcycleinthisstudy.

    ;3Simulationresults

    ;3.Thevalidationoftidesandtidalresidualcurrent ;TwoharmonicanalyzedCOamplitude(solidlines)andCO-phase(dashedlines)maps

    ;oftheprincipalsemidiurnallunarconstituentM2anddiurnallunarconstituentK1areshow

    n

    ;inFig3

    ;1nCreaSe

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    ;ModelingtheOCeancirculationintheBeringSea ;66.N

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    ;2meters.Thereare

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    ;southofSt.LawrenceIs.,andat(167.W,54.N).Theseresultsaresimilartotheprevi

    ;ousstudies[271.

    ;DifferingfromtheM2distribution,theKamplitudeincreasesfromtheopenocean,

    ;deepbasintotheBeringSlopeandthendecreasesintheoutermiddleshelf,butagain

    ;quicklvincreasesneartheAlaskancoast.AnotablefeatureisthattheK1amplitudere

    ;ducessharplyacrosstheBeringSlope,whichwasalsoobservedbyKowalik(1999)L27J ;suchthatatidalwavespropagatingintothecontinentalslopeandshelfareaslocallyinduce ;topographicwaveswherethelocalperiodofrotational-gravitationalmodeisequaltothetid

    ;alperiod.Tidally-generatedtopographicwavesoccuronlyintheregionspolewardfromthe ;criticallatitude:thelatitudeis30NforK1tideand74.5NforM2.Thus,onlydiurnaltopo- ;graphicwavescanbegenerated.

    ;Theenergyofthebasictidalconstituentsistransferredtowardlongerperiodsandthe ;tidalcurrentsaveragedovertidalperiodgenerateresidualcurrent.Thetidalstirringsignifi

    ;cantlyaffectslocalvertiealmixingandacceleratestheresuspensionofsedimentsandthere

    ;leaseofnutrients.Theresidualtidalcurrentcontributestolongtermtransportofnutrients

    ;andparticlematerials.Measurementofresidualtidalcurrentsisalmostimpossiblebecause ;itisdifficultt0separatethetidalresidualcurrentsfromwindgeneratedcurrent(alsoresid

    

    ;ua1).Inthisstudy.atideonlymodelwasimplementedtoexaminethetidalresidualcur

    ;rent.

    ;Thetidalresidualcurrent(alsocalledLagrangianresidualcurrent)wascalculatedby ;1r1r寺上udtJ)u,7

    ;whereTisthetidalperiod,uisthetidalvelocity,Disthewaterdepth,andisthesea

    ;surfaceelevation.ThefirsttermontherightsideiscalledtheEulerianresidualcurrentand ;thesecondt.eHniscalledtheStocks’residualcurrent.TheresultisshowninFigure3c,

    ;plottingevery4

    gridsinbothlongitudeandlatitude.Thetidalresidualcurrentsinthemid

    ;dleshelfandoutershelfflowconsistentlynorthwestwardornorthwardwithamagnitudeofa

    ;bout0.5cm/s.andpartoftheresidualcurrentsflowsintoBeringStrait.Thismayindicate ;thelong-tetintransportofmaterialandneutrienttransportfromthesouthernBeringShelfto ;thenorthernBeringShelf.andtotheArcticOceanviaBeringStrait.

    ;3.2GeneralCirculationandTransport

    ;Thesimulatedsummercirculations(Figure4a)showthattheAlaskanStreamflows ;westwardalongtheAleutianIslandsandenterstheBeringSeaviatheAleutianPassesmain

    ;lvfromtheKamchatkasait,theNearstrait,theAmchitkaPass,theAmuktaPass,and ;theUnimakPass.WaterenterstheBeringSeafromtheeasternsideoftheKamchatkaStrait ;andtheNearStraitandflowseastwardalongthenorthsideoftheCommanderIslandsto

    ;wardstheBowersRidge.Thiscurrentisnotwelldocumentedexceptforaschematicdia

    ;gramoftheBeringSeacirculationpattern(Figure2).Thiscurrentflowsclockwisealong ;theisobathsoftheBowersRidge:partoftheflowturnseastwardat178.E,56.N

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