上层海流对台风的反应

上层海流对台风的反应演示文稿目前一页\总数三十页\编于二十点Contents1.Introduction2.Reviewofobservations3.Amodeloftheupperoceanresponse4.SpecificationoftheEB-10/Eloisecase5.Overviewoftheresponse6.ComparisonofthemodelsolutionwiththeEB-10data7Numericalexperiments8.Conclusion目前二页\总数三十页\编于二十点1.IntroductionQuestionWhatisthereasonforSSTresponsetoahurricaneandrightwardbias?2.Howdoestheresponsedependuponsuchfactorsasthehurricanetranslationspeed,theoceaninitialcondition,etc.?3.Whatroledononlocaldynamicsplayintheupperoceanresponse4.Isthereevidencethatair-seatransfercoefficientsincreasesignificantlyunderhurricaneconditions?目前三页\总数三十页\编于二十点2.Reviewofobservationsa.HydrographicsurveysTable1HydrographicstudiesoftheseasurfacetemperatureresponsetohurricaneFig.1ResponseofSSTacrossthetrackofhurricaneElla&ResponseofsubsurfacetemperatureacrossthetrackofhurricaneElla目前四页\总数三十页\编于二十点Fig2SSTaroundthetrackofhurricaneTess&TemperaturesectionABmadeacrossthetrackofTessb.Buoy/hurricaneencountersa.HydrographicsurveysFig.3NationalHurricaneCenterstormtracksofhurricanesEloise(1975)andBelle(1976)目前五页\总数三十页\编于二十点1)EB-10/EloiseFig4MeteorologicalmeasurementsformEB-10duringthepassageofhurricaneEloise目前六页\总数三十页\编于二十点Fig5.OceantemperaturefromEB-10duringandafterthepassageofHurricaneEloise目前七页\总数三十页\编于二十点2)EB-04/EloiseFig6.Air-seameasurement(upper/lowerpanels)fromEB-04duringthepassageofEloise2)EB-15/EloiseFig7Air-seameasurement(upper/lowerpanels)fromEB-15duringthepassageofBelle目前八页\总数三十页\编于二十点3.Amodeloftheupperoceanresponsea.ScalesandphysicalapproximationsFig8.Schematicplanviewofthenumericalmodel目前九页\总数三十页\编于二十点Physicalapproximationsareasfollows:1)TheCoriolisparameterfisconstant,pressureishydrostatic,theBoussinespapproximationanddiffusiveprocessesareexcluded2)Density:Whereα=-3.3*10-4andβ=7.6*10-4aretheappropriatethermalandhalineexpansioncoefficientsandρ0=1.0235*103

kgm-3isthereferencedensity3)Theseasurfaceistreatedasarigidlid(excludesthebarotropicmode).4)Thesubthermoclineoceanistakenasinfinitydeepandunabletosustainapressuregradient。5）Thetemperatureandsalinityinlayer2areassumedtohavedepthdependence。Thevelocitywithinlayer2isassumedconstant.Theinitialthicknessoflayerischosensothatafterthehurricanepassage,h2≈h16)Verticaldensitygradientsinlayer2and3areheldconstantsincethestretchingissmall目前十页\总数三十页\编于二十点b.BudgetsLayerthickness:EntrainmentvelocityWe≥0

HeatandsaltbalanceintheML:TheheatfluxQ=Qs+QL+Risthesumofsensible,latentandradiativeHeatexchangeacrosstheseasurfaceFisthemassflux,equaltoevaporationminusprecipitationThetermδTWeiscalledtheentrainmentheatfluxandisthebulkRepresentationoftheturbulentheatflux

目前十一页\总数三十页\编于二十点HeatandsaltbalanceintheML:isunderstoodtobeverticalgradientofTwithinlayer2Momentumbalancesforthelayers:WherefistheCoriolisparametertimestheverticalunitvector,τiswindstress,Pisthehydrostaticpressureperturbation目前十二页\总数三十页\编于二十点Thepressuregradients:ThehorizontaldensitygradientintheML:Andinthelowerlayers

目前十三页\总数三十页\编于二十点C.Turbulent-fluxparameterizationsSensibleheatfluxLatentheatfluxDensityofairdividedbydensityofseawaterBulktransfercoefficient,=1.3*10-3Windspeedat10mheightBheatcapacityofairdividedbyheatcapacityofseaweaterq10,ssspecifichumidityat10mheight,andattheseasurfaceassumingsatuationattheseasurfacetemperatureKlatentheatofvaporationdividedbytheheatcapacityofseawaterC.Turbulent-fluxparameterizations目前十四页\总数三十页\编于二十点C.Turbulent-fluxparameterizationsWindstress:Wherethedragcoefficient0,ifRv>1,IfRv≤1isabulkRichardsonnumberParameterizeentrainment目前十五页\总数三十页\编于二十点Fig9Schematicplanviewofthenumericalmodeld.Implementation目前十六页\总数三十页\编于二十点Thetimestep△t=△x/mUH,WheremisthesmallestIntegerthatgives△t≤2*103sTheoceanismoveddownthegridonerowaftereverymstepsandthefirstrowofthegridpointsisupdatedwiththeoceaninitialcondition.Spacederivativeareestimatedwithasecond-ordercenteredForm,andtime-steppingiscarriedoutusingthethree-time-level,two-step,leapfrogtrapezoidalmethod.

目前十七页\总数三十页\编于二十点Fig10Upwellingcomputedbythenumericalmodel(leftside)andGeisler’sanalyticalsolution(rightside)AcheckoftheentrainmentcalculationsComparingwiththequasi-steadyentrainmentWheren=1/2foralinearlystraitifiedfluid,andn=1foratwo-layerstratifiedfluid,WhereRτ=(ghδρ)/(p0τ)istheexternalRichardsonNumber。目前十八页\总数三十页\编于二十点Table4EB-10/EloiseoceaninitialconditionSpecificationontheEB-10/Eloisecasea.Oceaninitialconditionb.ModelhurricaneFig12Radialandtangentialwind-speedradialprofilecomputedfromtheEB-10winddata(points),andthemodelofthehurricaneusedinthesimulationoftheEB-10/Eloise(Solidline)目前十九页\总数三十页\编于二十点Fig13.MLtransportV1h1computedfromthedirectlyobservedwindsofEloise(solidline)andfromthemodelhurricane(dashedline)theMLtransportscomputedfromalocalmomentumbalance:目前二十页\总数三十页\编于二十点Fig15Planviewofthemodel-predictedycomponentofMLvelocity&TheSSTresponseshownasthechangeinseasurfacetemperaturefromtheinitialconditionRightwardbiasFig16Aschematicthatshowstherotationofawind-stressvector&thecosineoftheanglebetweenthewindstressandtheMLvelocity(ameasureofhowefficientlythewindstressisworkingtoincreasetheMLkineticenergy)5.Overviewoftheresponse目前二十一页\总数三十页\编于二十点b.HorizontaladvectionofSSTFig15bTheSSTresponseshownasthechangeinseasurfacetemperatureFig23aObservedandpredictedseasurfacetemperaturefortheEB-10/EloiseReason:they-componentofvelocityintheMLcombinedwiththestrongy-gradientsin△C.Upwelling,pressuregradientsandvelocityresponseintheinteriorFig18bPumping&Fig19bUpwellingbelowthebaseoftheML目前二十二页\总数三十页\编于二十点Twodynamicalconsequencesoftheupwelling1)ThefirsthalfoftheupwellingcycleisupwardandthustendstocausetheMLthicknesstodecrease.2)Upwellingsetsupatime-dependentpressuregradientwhichcouplestheMLwiththeinteriorandcausestheMLvelocitytorotate~5%fasterthanthatinafreeinertialmotiond.ThesubsurfaceresponseoftemperatureFig21Predictedsubsurfacetemperatureresponseshownasacross-tracksectionfortheEB-10Eloisecase&Initial(solid)andfinal(dashed)temperatureprofilesaty=-100,0,+100km目前二十三页\总数三十页\编于二十点6.ComparisonofthemodelsolutionwiththeEB-10dataa.UpwellingFig22Observed(solid)andpredicted(dashed)upwellingbelowthebaseoftheMLduringtheEB-10/EloiseeventT(t)isthecorrectedtemperature,T0istheinitialtime-averagedtemperature,Islocaltemperaturegradient目前二十四页\总数三十页\编于二十点b.SeasurfacetemperatureFig23Observed(solid)andpredicted(dashed)seasurfacetemperaturefortheEB-10/Eloiseevent&TheMLheatbalanceforthesimulationoftheEB-10/Eloiseeventb.SeasurfacetemperatureAlongthetrack,thenetair-seaexchangeis0.2*102℃m(~2Kcalcm-2);thenetentrainmentheatfluxis1.3*102℃m(~13Kcalcm-2),or~85%ofthetotalirreversiblefluxintotheML.EntrainmentisimportantintheMLmomentumbalance.Becauselayer2isquiescentduringtheentrainmentprocess,entrainmentactstoincreasetheMLthicknessanddecreaseVl.TheincreaseinMLdepthbyentrainmentiscrucialindeterminingthemaximumMLvelocity.CQisdifficulttoinferfromsimulationsbecausetheair-seaexchangeissmall.AconstantdragcoefficientCD=1.5*10-3givesgreatlyreducedentrainmentandanSSTresponse~40%belowthatobserved.目前二十五页\总数三十页\编于二十点b.SeasurfacetemperatureAlongthetrack,thenetair-seaexchangeis0.2*102℃m(~2Kcalcm-2);thenetentrainmentheatfluxis1.3*102℃m(~13Kcalcm-2),or~85%ofthetotalirreversiblefluxintotheML.EntrainmentisimportantintheMLmomentumbalance.Becauselayer2isquiescentduringtheentrainmentprocess,entrainmentactstoincreasetheMLthicknessanddecreaseVl.TheincreaseinMLdepthbyentrainmentiscrucialindeterminingthemaximumMLvelocity.CQisdifficulttoinferfromsimulationsbecausetheair-seaexchangeissmall.AconstantdragcoefficientCD=1.5*10-3givesgreatlyreducedentrainmentandanSSTresponse~40%belowthatobserved.目前二十六页\总数三十页\编于二十点Numericalexperimentsa.ParametricdependenceHurricane:strengthU10max,translationspeedandsize(theradiusatwhichthewindspeedeaquals1/2U10max)Ocean:initialMLdepth,thetemper