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DOMINANT

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DOMINANT

    DOMINANT

    Vb1.15No.2JoURNAL0FTR0PICALMETE0RoLoGYDecember2009

    ArticleID:10068775(2009)01014808

    DoMlNANTPHYSICALPRoCESSESASSoCIATEDWITHPHASE

    DIFFERENCESBETWEENSURFACERAINFALLANDCoNVECTIVE

    AVAILABLEPoTENTIALENERGY

    XiaofanLI(李小凡)

    (NOAA/NESDIS/CenterforSatelliteApplicationsandResearchCampSprings,Maryland,USA)

    Abstract:Alagcorrelationanalysisisconductedwitha21dayT0GAC0AREcloud

    resolvingmodel

    simulationdatatoidentifythephaserelationbetweensurfacerainfallandconvectiveavailablepotential

    energyfCAPE1andassociatedphysicalprocesses.Theanalysisshowsthatthemaximumnegativelag

    correlationsbetweenthemode1domainmeanCAPEandrainfalJoccursaroundlaghour6.Theminimum

    meanCAPElagsmeanandconvectiverainfal1throughthevaporcondensationanddepositions.water

    vaporconvergence.andheatdivergencewhereasitlagsstratiformrainfallviathetransportofhydrometeor

    concentrationfromconvectiveregionstorainingstratiformregions,vaporcondensationanddepositions,

    watervaporstorage,andheatdivergenceoverrainingstratiformregions. Keywords:phaserelation;convectiveavailablepotentialenergy;surfacerainfall;cloud

    resolvingmodel

    simulation

    CLCnumber:P426.61Documentcode:Adoi:10.3969/j.issn.10068775.2009.02.003 1INTRoDUCTloN

    Surfacerainfallisa

    energyduringconvective

    resultofreleaseofunstable

    development.Thebuildupof

    unstableenergyusuallyoccursinfavorable environmentalthermodynamicconditionswhenthe rainfallisabsent.Thereleaseofunstableenergy triggeredbylargescalecirculation,topography,and interactionswithotherweathersystemsleadstothe growthofcloudsystems,withtheaidofwatervapor transport,andthusthetorrentialrainfa11.Thetorrential rainfaIlisusuallyassociatedwithstrongweather systemssuchastropicalcyclones(tropicalstormsand typhoonsintropicalwesternPacific).Thebuildupof unstableenergyandrainfa11cannotOCCur simultaneously.Thephaserelationbetweenthe unstableenergyandsurfacerainfallisanimportant issuendevelopingcumuluspa

    

    rameterization

    schemesl_j_.XuandRandallanalyzed

    twodimensionalr2D1cloudresolvingmodel

    simulations,demonstratedthattheminimumconvective availablepotentialenergy(CAPE)lagstherainfall peakbyafewhours,andarguedthatthephaselagis theadjustmenttimescalefromdisequilibriumto equilibriumstatesinthepresenceof

temporallyvaryinglargescaleforcing.Lieta1._)J

    examinedbudgetsofmeanmoistavailablepotential energyandperturbationkineticenergythatrepresent CAPEandsurfacerainfa11.respectively.andconducted processstudyassociatedwiththephaselagbetween meanmoistavailablepotentialenergyandperturbation kineticenergy.一一

    r,1

    Recently.Gaoeta1.LoJandGaoandLiL/Jderiveda setofsurfacerainfallequationsbycombiningwater vaDorandheatbudgetswithcloudbudget.Thedirect linkageofwatervapor,heat,andcloudprocessesto surfacerainfa11allowsustodirectlyrevisitthephase differencebetweenCAPEandsurfacerainfa11.without theaidofenergyanalysis.Inthisstudy,alag correlationanalysisbetweenCApEandsurfacerainfa11 isconductedusinga2Dcloudresolvingmodel

    experimentthatisforcedbythelargescaleforcing

    derivedfromTropicalOceanGlobalAtmosphere CoupledOceanAtmosphereResponseExperiment

    (TOGACOARE).Inthenextsection,thecloudmodel, forcing.andexperimentaredescribed.111eresultsare presentedinsection3.Thesummaryisgiveninsection 4.

    2MoDELANDEXPERIMENT

    Receiveddate:20090328;reviseddate:20090901

    Biography:XiaofanLI,PhD,undertakingtheresearchoncloudresolvingmodeling,oceanm

    odeling,

    geophysicalfluiddynamics.

    Emailforcorrespondenceauthor:xiaofan.1i@noaa.gov No-2XiaofanLI(李小凡)149

    Thedataanalyzedinthisstudyisfromthe2D cloudresolvingmodelsimulationconductedbyLiet a1.Themodelisforcedbyzonally-uniformvertical velocity,zonalwind,andthermalandmoisture advectionbasedon6hourlyTOGACOARE

    observationswithintheIntensiveFluxArray(IFA) regionandhourlyseasurfacetemperature(SST)atthe ImprovedMeteorologica1(IMET)stirfacemooring buoy(1.75.S,156.E)(Fig.1).Themodelis

    integratedfrom0400LSTl8Decemberl992to1000 LST9Januaryl993rAtotalof486hours).Themode1 simulationdatahavebeenusedtostudysurfacerainfal1 processes[,,]

    ,

    precipitationefficiency[,13,

    ,

    convective,moistanddynamicvorticityvector eff-ectsoficecloudsonrainfallL"J.rainfa11responsesto large.scaleforcing[,

    cloudclustersandmerging[

    ,

    diurnalvariationsoftropicaloceanicrainfa11,and convectiveandstratiformrainfallandpartitioning f22241

    E

    

    n)

    E

    Z

    吣?旺C?叩旺JA

    Fig.1Timeheightcrosssectionsoffa)vertica1 velocity(cms-I1,fb1zonalwind(ms),and timeseriesof(c)seasurfacetemperature f.C,observedandderivedfromTOGA

    COAREforthe21dayperiod.Upward

    motionsinfa1andwesterlywindsin(b)are shaded.

    Thecloudresolvingmodelusedinthepaperhas prognosticequationsofpotentialtemperature,specific humidity,mixingratiosofcloudwater,raindrop,cloud ice,snow,andgraupel,andperturbationmomentum. Themodelalsoincludesthecloudmicrophysical parameterizationschemes,andinteractivesolarand ————————,,

    \

    .......

    

    

    .

    .

    ,,:_,

    ==

    9876543210123456789

    Time(Hour)

    Fig.2LagcorrelationbetweenmodeldomainmeanCAPE andmeansurfacerainrate(solid),meanCAPEand stratiformrainrate(dash),andmeanCAPEandconvective

rainrate(dotdash).

    thermalinfraredradiationparameterizationschemes. Themodelusescycliclateralboundaries,anda horizontaldomainof968km,ahorizontalgrid resolutionof1.5km,33verticallevels,andatimestep of12s.Thedetaileddescriptionsofthemode1canbe foundinGaoandLi.Thevalidatedmodelsimulation datahavebeenanalyzedforprocessstudiessuchas effectsofverticalwindshearLandcloudradiative processesLonrainfallofTropicalStormBilis(2006). sensitivitiesofcloudandrainfallsimulationsto uncertaintiesofinitialconditions.j.tropicalclimate

    equilibriumstates..

    anddiurnalvariationsof

    tropicalconvectiveandstratiformrainfallDo,. 3RESULTS

    Thephasedifferencebetweensurfacerainfall(Ps) andconvectiveavailablepotentialener'gY(CAPE)is examinedbycalculatinglagcorrelationcoefficients betweenPandCAPE.PositivelaghourdenoteCAPE lagsPsandnegativecorrelationmeanscorrelationof minimumCAPEwithmaximumPs.Figure2shows

    thatminimummodeldomainmeanCAPElags

    maximumPsbyabout6hours.Thisindicatesthatthe maximumreleaseofCAPEisresponsibleforthe rainfallpeak.TneCAPEiscalculatedunderreversible moistadiabaticprocess.Thelagcorrectionis0.33.

    AStudent'st-testonthesignificanceofthelag correlationcoefficientsisfurtherconductedusing474

degreesoffreedomandacriticalcorrelationcoecient

    atthel%significantlevelis0.13.11}1us,thelag correlationofmaximummeansurfacerainfallby minimummeanCAPEisstatisticallysignificant. Themeansurfacerainfallconsistsofstratiform 0000

    oH0u

    150JournalofTropicalMeteorologyVO1.15 andconvectiverainfa11.Theconvectivestratiform

    rainfallpartitioningschemeusedinthisstudyjs developedbyTaoeta1.[38]andmodifiedbySuieta1. 39]39

    .

    Thisschemeseparateseachverticalcolumncontaining cloudsina2D.zframeworkintoconvectiveor stratiformbasedonthefollowingcriterion.Modelgrid pointisidentifiedasconvectiveifithasarainrate twiceaslargeastheaveragetakenoverthe

    surroundingfourgridpoints,theonegridpointon eithersideofthisgridpoint,andanygridpointwitha rainrateof20millhormore.A11nonconvective

    cloudypointsareconsideredasstratiform.Inaddition, gridpointsinthestratiformregionarefurtherchecked andidentifiedasconvectivewhenthefollowing conditionsaremet.Intherainingstratiformregion, cloudwaterbelowthemeltinglevelisgreaterthan0.5 gkgorthemaximumupdraftabove600hPaexceeds 5ms.orinthenon.rainingstratiformregion.cloud waterof0.025kg-ormoreexistsorthemaximum

updraftexceeds5msbelowthemeltingleve1.The

    minimummeanCAPElagsmaximumstratiform rainfaIlby7hourswiththemaximumnegative correlationof_0.28.whereasitlagsmaximum convectiverainfallby6hourswiththemaximum negativecorrelationof-0.32.Bothareabovethe1% significantleve1.

    Toexaminedominantrainfa11processesthatare responsibleforthephasedifferencesbetweenCAPE andsurfacerainfa11,surfacerainfa11budgetsare analyzed.Thesurfacerainfallequationcanbewritten incloudbudget.whichisexpressedby

    =++M,(1)

    where

    :一一[[w],(1a)

    OtOz

    :

    [+[]+[fD+[],(1b)

    Qw=[][][].(1c)

    Here,issurfacerainrate;andwarezonal

    andverticalwindcomponents,respectively; qtq+qr+qi-t-q+qg,q,q,,qi,q,qgare

    themixingratiosofcloudwater,raindrops,cloudice, snow,andgraupel,respectively;

    andZb

    model

    [0]=triO&,

    6

    aretheheightsofthetopandbottom

    atmosphererespectively;the

ofthe

    cloud

    microphysicalprocessesinEqs.(1b)and(1c)canbe foundinTable1.Incloudbudget,surfacerainfallis determinedbyvaporcondensationanddeposition (),evaporationofprecipitationhydrometeor (),andhydrometeorstorageminusconvergence ().Thesurfacerainfallequationcanbederived bycombiningwatervaporbudgetwithcloudbudgetas proposedbyGaoeta1.oJ,whichiswrittenas

    =

    Q+Q+Q+Q,(2)

    where

    =

    a[g]

    Q:_[.墨卜[.[]ox0zox

    

    [.卜【.]'[w',

    oxdzOZ

    QE:Es

    (2a)

    (2b)

    (2c)

    Here,qvisspecifichumidity;Esissurfaceevaporation; theoverbardenotesamodeldomainmean;theprimeis aperturbationfrommodeldomainmean;andthe superscript"."isanimposedCOARE-observedvalue. Thesurfacerainfallisdeterminedbywatervapor storage(e),watervaporconvergence(Q),

    surfaceevaporation(),andhydrometeorstorage minusconvergence()inthesurfacerainfall

    equationderivedfromcloudandwatervaporbudgets.

    Thesurfacerainfallequationcanbederivedby

    combiningheatbudgetwithcloudbudgetasproposed

    byGaoandLi7]

    ,

    whichiswrittenas

    P=SHT+SHF+SHS+SLHLF+SAD+QCM, where

    cp0IT]

    ,

    =

    Cp0(.++.

    +.

    (+')+'_O0,ozdz

    (3a)

    (3b)

    SHs--H,(3c)

    f

    :舭F一?<8>,(3d)

    1

    ,j

    ?<>,(3e)

    =+‰十一一

    +c(<to)+(<)+c(<ro) +(<)+(<ro)+(<ro) +G(<)P~cs(T>ro)(>)

    NO.2XiaofanLI(李小凡)l51

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