cam tutorial 2009 image: victoria, australia, feb 2009 · modal microphysics ... p. j. rasch and j....

CAMTutorial2009 Image:Victoria,Australia,Feb2009

Outline

• Whatis‘CloudMicrophysics’• DifferentApproaches• CAMimplementaFonofMicrophysics• AerosolModeling• OpFonsinCAM• InteracFons– Scavenging/DeposiFon– AerosolIndirectEffectsonClimate

CAMTutorial:Microphysics

Scope

• “CloudMicrophysics”referstothecondensedphasewaterprocessesintheatmosphere– MicrophysicalproperFesofcondensedspecies

• sizedistribuFons,shapes– DistribuFonofandtransformaFonofcondensedspecies

• precipitaFonandphaseconversion• InCAM:thisequatesto‘straFform’cloudmicrophysics– ConvecFvecloudshaveevenmoreheavilyparameterizedmicrophysics

• LargeScaleCondensaFonitselfisgenerallyhandledby“cloudmacrophysics”(cloudfracFon)


KeyoperaFonsonCondensedSpecies

• Condense/Sublimate• Sediment

• ConverttoprecipitaFon• DetermineproperFesforotherprocesses– Chemicalspecies(scavenging)– Physicalstate(size,number)forradiaFon


WhatdoesthismeanforSimulaFons?

• MicrophysicscontrolsdetailsofprecipitaFon– Rate,locaFon– OverallprecipitaFonlimitedbyenergybalanceconstraints(P‐E)

• CoupledwithCondensaFon(macrophysics)itdeterminescloudproperFes– InCAM:straFformcloudfracFonandproperFes– Also,usesconvecFvedetrainment


SampleImpact• ChangethevapordeposiFonprocessinthemicrophysicstobemoreefficient(removeH2O) LowerRHReducedCloudinessby20%(51‐41%) Globalchangeof2Wm‐2atTOA.

ΔRH ΔCldFrc


MoFvaFon

• Cloudsareaverysignificantuncertaintyinclimatemodels(IPCC,2007)

• Manywaystodefinemicrophysicalprocessesthatleadtopresentstate:thesemethodsmayresponddifferentlytoclimatechange

• CriFcaltoreduceuncertainFes.GoalhasbeentoincreasecomplexitysothatprocessmodelslookmorelikeobservaFons


DifferenttypesofMicrophysics

• BulkMicrophysics– Massbasedonly(2species:liquidandice)– BulktransformaFonsandprocesses– SpecifiedsizesorsizedistribuFons– EarlyschemeswerediagnosFc(e.g.:yesterday)

• BinMicrophysics– MulFplesizebins(manyconsFtuents)withamassineach.ExplicitrepresentaFonofsizedistribuFon

– TransformaFonsdependonmassandnumber


ModalMicrophysics

• UseananalyFcrepresentaFonofthesizedistribuFonandcarryaroundmomentsofthedistribuFon– Firstmoment=mass

– 2ndmoment=number– SizedistribuFonreconstructedfromanassumedshape.

– Advantage:representsizesconsistentlywithcomputaFonalefficiency


CAMMicrophysics

• CAM3.5:BulkMicrophysicswithprognosFccondensateP.J.RaschandJ.E.Kristjansson,1998

• CAM4.0:ModalMicrophysicsH.MorrisonandA.Gelelman,2008;Gelelmanetal2008

• StartwithRK98scheme,thenbriefdescripFonofMG08


CAMMicrophysics

• CAM3.5:BulkMicrophysicswithprognosFccondensate:P.J.RaschandJ.E.Kristjansson.AcomparisonofCCM3modelclimateusingdiagnosedandpredictedcondensateparameterizaFons.J.Clim.,11:1587‐1614,1998.

• CAM4.0:ModalMicrophysicsH.MorrisonandA.Gelelman,Anewtwo‐momentbulkstraFformcloudmicrophysicsschemeintheCommunityAtmosphericModel(CAM3),PartI:DescripFonandNumericalTestsJ.Climate,21:15,3642‐3659,2008


CAM3BulkMicrophysics

• CoupledtoSlingo(1987)RHbasedcloudfracFon– FracFonalcloudiness:A>0whenRH>0.88orso

• CondensaFonclosurefromZhangetal(2003)– AllowsparFalcloudiness

• Fixedice&liquidfracFonasafuncFonoftemperature– NotabadassumpFonbasedonobservaFons

• ForradiaFvetransfer&sedimentaFon,assumedFixedparFclesizesforliquidoverland/ocean(largeroverocean).

• IcecrystalsizeisafuncFonoftemperatureorpressure


CAM3BulkMicrophysics(2)

• PrognosFcvariablesforLiquid&Icemass• DetrainedliquidfromconvecFonputintostraFformmicrophysicsscheme


Macroscalecomponent

A=tendenciesduetootherprocessesQ=netcondensaFonEr=netevaporaFonRl=rain/snowformaFonrateMacrophysicsisconcernedwithdetermining“Q”

SubtleFes:arisedueto(1)in‐cloudv.outofcloudregions,(2)newlyformingcloud


VaporTendency

TemperatureTendency

CondensateTendency

MicroscaleComponent

• IceandliquidreparFFonedaccordingtoT– Typically‐40to‐10C(canbechanged)– HeatisassociatedwiththetransformaFon

• Detrainedcondensateadded• PrecipitaFonFluxesdetermined

• SedimentaFoniscalculated– IcevelocityisafuncFonofsize(effecFveradius,rei)– Liquidvelocityalso,butonly2values(land,ocean)


MicroscaleProcesses

ConversionTerms:• Liquid&iceconversiontorain(Auto‐conversion)• CollecFonofliquidandicebyprecipitaFon• CollecFonofLiquidbysnow(riming)

ConversiontermsareafuncFonofmodelstate,andgenerallyempiricalfitstofieldcampaigns(mostdatefrom1980’sorso): Tripoli&Colon1980,Kessler1969,Linetal1983,etc


ProcessRates

• Complexforms• Example,autoconversionofliquidwatertorain(PWAUT)

H=heavy‐side(binaryfuncFon0,1whenexpression>or<0)

N=assumednumberdensityCl,autisratebasedonsize

• Formfroma1Dmodelofstratocumulusclouds,modifiedfromearliercumulusexperiments.


RelaFveImportanceofProcesses

LiqRain

LiqCollecFon(rain)

IceSnow

IceCollecFon(snow)

LiqCollecFon(snow)


Notes

• ForopFcalcalculaFons,liquidparFclesassumedtobe8µmoverlandand14µmoverocean

• IcesizeisafuncFonoftemperature(alsoaffectsfallspeed)

Temperature

BulkIceEffecFveRadius


ModalMicrophysicsFeatures• Basedonaschemeformeso‐scalemodels• AddiFonofliquid&iceprognosFcnumber• MixedphasevapordeposiFon– notemperaturedependenceforliquidv.ice

• Icesuper‐saturaFon• Sub‐gridrepresentaFonoftotalwater• AcFvaFonofcloudliquidandicebyaerosols• Usesub‐gridverFcalvelocityfromTKE• DiagnosFcrepresentaFonofrainandsnowmass&number

• Processes(collecFon,auto‐conversion)similar.AddnucleaFonprocessesCAMTutorial:Microphysics


q,NCloudIce

(Prognos3c)

q,NSnow

(Diagnos3c)

q,NCloudDroplets(Prognos3c)

q,NRain

(Diagnos3c)

ConversionProcesses

Sedimenta3on Sedimenta3on

qWaterVapor(Prognos3c)

Evapora3on Sublima3on

Dep/SubEvap/Cond

q=mixingraFoN=numberconcentraFon

Aerosol(CCN

Number)

Aerosol(IN

Number)

q,NConvec3veDetrainment

Riming

IceFracFon(MixedPhase)


QuesFons?


AerosolsWhydowecareaboutaerosolsinaclimatemodel?


AerosolsAerosolsAffectRadiaFon


AerosolModeling

• Physicalprocessmodel(parameterizaFons)tosimulateasetofaerosolspecies

• BulkModel(CAM3)

• ModalTreatment(CAM4)

• Heritage(inorder):1.Simulatedirecteffectsofaerosolsforclimate2.ChemicaltransformaFonsofaerosolsandinteracFonsofmasswithclouds(scavenging&deposiFon)

3.Connectaerosolswithclouds


BulkAerosolModel• ComesfromMOZARTchemicaltransportmodel(nowCAM‐CHEM)

• Bulk(massbased)representaFonof:– Seasalt(2modes/bins)– Dust(4bins)– Sulfate:Natural(Volcanic)andAnthropogenic– BlackandOrganicCarbon(Hydrophilic&Hydrophobic):NaturalandAnthropogenic

• Externalmixturesonly:massesareindependent• Prescribedsizes:numberproporFonaltomass• WetDeposiFonandDryDeposiFon/Scavenging• CAM3includesAerosolShortwaveeffectsonly!CAMTutorial:Microphysics

DryDeposiFon

• ‘seriesresistance’methodusing‘aerodynamic’resistanceinlowestmodelleveltodeterminedeposiFonvelocity,Vd

• ThenFlux=Vdn1,n1=concentraFoninlowestlevel


WetDeposiFon/Scavenging

• Gasesscavengedonlybyliquid– BasedonHenry’slaw(solubility:f[pH,T])

• Aerosolsscavengedbyliquidandice– IncloudscavengingassumesafixedfracFonremainsincloudwaterandremovedalongwithfracFonofcloudwaterthatprecipitates

– BelowcloudscavengingassumedtobeafirstorderlossprocessL=CPqwhereC=collecFonefficiency,P=precipflux(mm/h)andq=speciesmixingraFo


ModalAerosolModel

• Versions:Benchmark7mode&Efficient3mode• Internalmixtures(coagulaFonwithin&betweenmodes)• Ultrafinesea‐salt• CondensaFonofTraceGases(H2SO4)onaerosols• AgingofcarbontoaccumulaFonmodebasedonsulfatecoaFng

• NewSecondaryOrganicAerosolTreatment• NewAerosolOpFcs:DirecteffectsinLWandSW• Emissionsavailable:– AEROCOM– NewIPCCAR5emissions


3‐ModeAerosolModel• Assumeprimarycarbonisinternallymixedwithsecondaryaerosol

• Sourcesofdustandseasaltaregeographicallyseparate

• Assumeammoniumneutralizessulfate

• 15totaladvectedspecies

AitkennumbersulfatesecondaryOMseasalt

AccumulaFonnumbersulfatesecondaryOMprimaryOMblackcarbonsoildustseasalt

coagulaFoncondensaFon

Coarsenumbersoildustseasaltsulfate


KeyInteracFons

• AerosolsandCloudMicrophysics– AerosolIndirectEffects

• CloudsandRadiaFon


Aerosol‐CloudInteracFons

Rosenfeldetal,Science2008CAMTutorial:Microphysics

AerosolCloudInteracFons

Aerosolsleadto:

• Brighterclouds• LongerLasFng,lessprecipitaFon(supressdrizzle)


AerosolsandMixed/IcePhase

• DrizzlesuppressionmightincreaseprecipitaFonintensityinmixed‐phaseclouds

• Iceindirecteffectsmaybedifferent:– Icenucleiarerare.SomemayinduceearliercloudformaFon(lowersuper‐saturaFon)

– ThisleadstofewerparFcles(oppositeeffect)– CirruscloudsalsohaveeffectsinLongwave


Aerosol‐CloudInteracFonsinCAM

• CAM3:DirecteffectsofAerosolsonly(SW)• CAM4/Modal:– DirectEffectsinLW&SW– IndirecteffectsforLiquidandIce

• CAM4:IndirectEffects– AerosolnumberaffectsacFvatednumberofclouddrops/crystals

– IcenucleaFon:dependsonsulfate&dustnumbers


CloudsandRadiaFon

• GoalhasbeenaconsistenttreatmentofcloudandradiaFonprocesses

• RadiaFoncodehasdetailedrepresentaFonofcloudverFcalstructure(overlap)

• Bulk(RK98)schemehasfixedcloudparFclesize• ModalMicrophysics(MG2008)prognosesnumber(&parFclesize):moreconsistentandflexibletreatment.

• Difficulty:wedonotknowwhattheparFclesizesreallyarefromobservaFons


LiquidWaterPath

• FundamentalobservaFonaluncertainty:– Howmuchcondensedwaterisintheatmosphere?

• WeknowbelertheradiaFvefluxes(RF,LW&SW)

• ButthenulFmatelyRF=f(LWP,re)

• MulFpleSoluFons:– DifferentmicrophysicsschemesproducesimilarcloudradiaFveforcingwithverydifferentsizesandLiquidWaterPaths

– SameradiaFoncode


OldandNewMicrophysics

CAMTutorial:Microphysics Gelelmanetal,2008

Summary• CloudmicrophysicsareacriFcalpartoftheclimatesystem

• BasicformulaFonisaseriesofprocessrates• BulkschemehasbeentradiFonalpath• New2‐modetreatmentavailable• ObservaFonalconstraintsoncloudsareprobablynotsufficienttoconstrainimportantglobaluncertainFes

• Goingfromsmallscaleglobalscaleisachallenge• Aerosolsalsoplayanimportantroleintheclimatesystemandinteractwithclouds

• Aerosol‐cloudinteracFonsareveryimportantinunderstandingclimatesensiFvity


Aerosols&ClimateChange


RadiaFveForcinginClimateModelsVarieswithAerosols!

GlobalConstraintsKiehl2007,GRL: λ=ΔQ2x/ΔT2xinequilibriumwhenH=0

ΔQ=λΔT+H20thCenturyΔT,H(Δoceanheatcontent)&ΔQ2xknown:.

Then, ΔQ=F(1/ΔT2x)VariaFonsinclimatesensiFvity(ΔT2x)correspondtodifferencesintotalforcing(ΔQ).ΔQchangesduetodirectand/orindirectAerosolforcing

Dashed:UncertaintyinOceanHeatcontent

References

Gelelman,A.,H.MorrisonandS.J.GhanAnewtwo‐momentbulkstraFformcloudmicrophysicsschemeintheCommunityAtmosphericModel(CAM3),PartII:Single‐columnandglobalresultsJ.Climate,21:15,3660‐36792008

H.MorrisonandA.Gelelman,Anewtwo‐momentbulkstraFformcloudmicrophysicsschemeintheCommunityAtmosphericModel(CAM3),PartI:DescripFonandNumericalTestsJ.Climate,21:15,3642‐3659,2008

P.J.RaschandJ.E.Kristjansson.AcomparisonofCCM3modelclimateusingdiagnosedandpredictedcondensateparameterizaFons.J.Clim.,11:1587‐1614,1998.

Slingo,J.M.1987:ThedevelopmentandverificaFonofacloudpredicFonschemefortheECMWFmodel.Quart.J.Roy.Meteor.Soc.,113,899–927.

M.Zhang,W.Lin,C.S.Bretherton,J.J.Hack,andP.J.Rasch.AmodifiedformulaFonoffracFonalstraFformcondensaFonrateinthencarcommunityatmosphericmodel(cam2).J.Geophys.Res.,108(D1),2003.


cam tutorial 2009 image: victoria, australia, feb 2009 · modal microphysics ... p. j. rasch and j....

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