cam tutorial 2009 image: victoria, australia, feb 2009 · modal microphysics ... p. j. rasch and j....
TRANSCRIPT
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)
CAMTutorial:Microphysics
KeyoperaFonsonCondensedSpecies
• Condense/Sublimate• Sediment
• ConverttoprecipitaFon• DetermineproperFesforotherprocesses– Chemicalspecies(scavenging)– Physicalstate(size,number)forradiaFon
CAMTutorial:Microphysics
WhatdoesthismeanforSimulaFons?
• MicrophysicscontrolsdetailsofprecipitaFon– Rate,locaFon– OverallprecipitaFonlimitedbyenergybalanceconstraints(P‐E)
• CoupledwithCondensaFon(macrophysics)itdeterminescloudproperFes– InCAM:straFformcloudfracFonandproperFes– Also,usesconvecFvedetrainment
CAMTutorial:Microphysics
SampleImpact• ChangethevapordeposiFonprocessinthemicrophysicstobemoreefficient(removeH2O) LowerRHReducedCloudinessby20%(51‐41%) Globalchangeof2Wm‐2atTOA.
ΔRH ΔCldFrc
CAMTutorial:Microphysics
MoFvaFon
• Cloudsareaverysignificantuncertaintyinclimatemodels(IPCC,2007)
• Manywaystodefinemicrophysicalprocessesthatleadtopresentstate:thesemethodsmayresponddifferentlytoclimatechange
• CriFcaltoreduceuncertainFes.GoalhasbeentoincreasecomplexitysothatprocessmodelslookmorelikeobservaFons
CAMTutorial:Microphysics
DifferenttypesofMicrophysics
• BulkMicrophysics– Massbasedonly(2species:liquidandice)– BulktransformaFonsandprocesses– SpecifiedsizesorsizedistribuFons– EarlyschemeswerediagnosFc(e.g.:yesterday)
• BinMicrophysics– MulFplesizebins(manyconsFtuents)withamassineach.ExplicitrepresentaFonofsizedistribuFon
– TransformaFonsdependonmassandnumber
CAMTutorial:Microphysics
ModalMicrophysics
• UseananalyFcrepresentaFonofthesizedistribuFonandcarryaroundmomentsofthedistribuFon– Firstmoment=mass
– 2ndmoment=number– SizedistribuFonreconstructedfromanassumedshape.
– Advantage:representsizesconsistentlywithcomputaFonalefficiency
CAMTutorial:Microphysics
CAMMicrophysics
• CAM3.5:BulkMicrophysicswithprognosFccondensateP.J.RaschandJ.E.Kristjansson,1998
• CAM4.0:ModalMicrophysicsH.MorrisonandA.Gelelman,2008;Gelelmanetal2008
• StartwithRK98scheme,thenbriefdescripFonofMG08
CAMTutorial:Microphysics
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
CAMTutorial:Microphysics
CAM3BulkMicrophysics
• CoupledtoSlingo(1987)RHbasedcloudfracFon– FracFonalcloudiness:A>0whenRH>0.88orso
• CondensaFonclosurefromZhangetal(2003)– AllowsparFalcloudiness
• Fixedice&liquidfracFonasafuncFonoftemperature– NotabadassumpFonbasedonobservaFons
• ForradiaFvetransfer&sedimentaFon,assumedFixedparFclesizesforliquidoverland/ocean(largeroverocean).
• IcecrystalsizeisafuncFonoftemperatureorpressure
CAMTutorial:Microphysics
CAM3BulkMicrophysics(2)
• PrognosFcvariablesforLiquid&Icemass• DetrainedliquidfromconvecFonputintostraFformmicrophysicsscheme
CAMTutorial:Microphysics
Macroscalecomponent
A=tendenciesduetootherprocessesQ=netcondensaFonEr=netevaporaFonRl=rain/snowformaFonrateMacrophysicsisconcernedwithdetermining“Q”
SubtleFes:arisedueto(1)in‐cloudv.outofcloudregions,(2)newlyformingcloud
CAMTutorial:Microphysics
VaporTendency
TemperatureTendency
CondensateTendency
MicroscaleComponent
• IceandliquidreparFFonedaccordingtoT– Typically‐40to‐10C(canbechanged)– HeatisassociatedwiththetransformaFon
• Detrainedcondensateadded• PrecipitaFonFluxesdetermined
• SedimentaFoniscalculated– IcevelocityisafuncFonofsize(effecFveradius,rei)– Liquidvelocityalso,butonly2values(land,ocean)
CAMTutorial:Microphysics
MicroscaleProcesses
ConversionTerms:• Liquid&iceconversiontorain(Auto‐conversion)• CollecFonofliquidandicebyprecipitaFon• CollecFonofLiquidbysnow(riming)
ConversiontermsareafuncFonofmodelstate,andgenerallyempiricalfitstofieldcampaigns(mostdatefrom1980’sorso): Tripoli&Colon1980,Kessler1969,Linetal1983,etc
CAMTutorial:Microphysics
ProcessRates
• Complexforms• Example,autoconversionofliquidwatertorain(PWAUT)
H=heavy‐side(binaryfuncFon0,1whenexpression>or<0)
N=assumednumberdensityCl,autisratebasedonsize
• Formfroma1Dmodelofstratocumulusclouds,modifiedfromearliercumulusexperiments.
CAMTutorial:Microphysics
RelaFveImportanceofProcesses
LiqRain
LiqCollecFon(rain)
IceSnow
IceCollecFon(snow)
LiqCollecFon(snow)
CAMTutorial:Microphysics
Notes
• ForopFcalcalculaFons,liquidparFclesassumedtobe8µmoverlandand14µmoverocean
• IcesizeisafuncFonoftemperature(alsoaffectsfallspeed)
Temperature
BulkIceEffecFveRadius
CAMTutorial:Microphysics
ModalMicrophysicsFeatures• Basedonaschemeformeso‐scalemodels• AddiFonofliquid&iceprognosFcnumber• MixedphasevapordeposiFon– notemperaturedependenceforliquidv.ice
• Icesuper‐saturaFon• Sub‐gridrepresentaFonoftotalwater• AcFvaFonofcloudliquidandicebyaerosols• Usesub‐gridverFcalvelocityfromTKE• DiagnosFcrepresentaFonofrainandsnowmass&number
• Processes(collecFon,auto‐conversion)similar.AddnucleaFonprocessesCAMTutorial:Microphysics
CAMTutorial: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)
CAMTutorial:Microphysics
QuesFons?
CAMTutorial:Microphysics
AerosolsWhydowecareaboutaerosolsinaclimatemodel?
CAMTutorial:Microphysics
AerosolsAerosolsAffectRadiaFon
CAMTutorial:Microphysics
AerosolModeling
• Physicalprocessmodel(parameterizaFons)tosimulateasetofaerosolspecies
• BulkModel(CAM3)
• ModalTreatment(CAM4)
• Heritage(inorder):1.Simulatedirecteffectsofaerosolsforclimate2.ChemicaltransformaFonsofaerosolsandinteracFonsofmasswithclouds(scavenging&deposiFon)
3.Connectaerosolswithclouds
CAMTutorial:Microphysics
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
CAMTutorial:Microphysics
WetDeposiFon/Scavenging
• Gasesscavengedonlybyliquid– BasedonHenry’slaw(solubility:f[pH,T])
• Aerosolsscavengedbyliquidandice– IncloudscavengingassumesafixedfracFonremainsincloudwaterandremovedalongwithfracFonofcloudwaterthatprecipitates
– BelowcloudscavengingassumedtobeafirstorderlossprocessL=CPqwhereC=collecFonefficiency,P=precipflux(mm/h)andq=speciesmixingraFo
CAMTutorial:Microphysics
ModalAerosolModel
• Versions:Benchmark7mode&Efficient3mode• Internalmixtures(coagulaFonwithin&betweenmodes)• Ultrafinesea‐salt• CondensaFonofTraceGases(H2SO4)onaerosols• AgingofcarbontoaccumulaFonmodebasedonsulfatecoaFng
• NewSecondaryOrganicAerosolTreatment• NewAerosolOpFcs:DirecteffectsinLWandSW• Emissionsavailable:– AEROCOM– NewIPCCAR5emissions
CAMTutorial:Microphysics
3‐ModeAerosolModel• Assumeprimarycarbonisinternallymixedwithsecondaryaerosol
• Sourcesofdustandseasaltaregeographicallyseparate
• Assumeammoniumneutralizessulfate
• 15totaladvectedspecies
AitkennumbersulfatesecondaryOMseasalt
AccumulaFonnumbersulfatesecondaryOMprimaryOMblackcarbonsoildustseasalt
coagulaFoncondensaFon
Coarsenumbersoildustseasaltsulfate
CAMTutorial:Microphysics
KeyInteracFons
• AerosolsandCloudMicrophysics– AerosolIndirectEffects
• CloudsandRadiaFon
CAMTutorial:Microphysics
Aerosol‐CloudInteracFons
Rosenfeldetal,Science2008CAMTutorial:Microphysics
AerosolCloudInteracFons
Aerosolsleadto:
• Brighterclouds• LongerLasFng,lessprecipitaFon(supressdrizzle)
CAMTutorial:Microphysics
AerosolsandMixed/IcePhase
• DrizzlesuppressionmightincreaseprecipitaFonintensityinmixed‐phaseclouds
• Iceindirecteffectsmaybedifferent:– Icenucleiarerare.SomemayinduceearliercloudformaFon(lowersuper‐saturaFon)
– ThisleadstofewerparFcles(oppositeeffect)– CirruscloudsalsohaveeffectsinLongwave
CAMTutorial:Microphysics
Aerosol‐CloudInteracFonsinCAM
• CAM3:DirecteffectsofAerosolsonly(SW)• CAM4/Modal:– DirectEffectsinLW&SW– IndirecteffectsforLiquidandIce
• CAM4:IndirectEffects– AerosolnumberaffectsacFvatednumberofclouddrops/crystals
– IcenucleaFon:dependsonsulfate&dustnumbers
CAMTutorial:Microphysics
CloudsandRadiaFon
• GoalhasbeenaconsistenttreatmentofcloudandradiaFonprocesses
• RadiaFoncodehasdetailedrepresentaFonofcloudverFcalstructure(overlap)
• Bulk(RK98)schemehasfixedcloudparFclesize• ModalMicrophysics(MG2008)prognosesnumber(&parFclesize):moreconsistentandflexibletreatment.
• Difficulty:wedonotknowwhattheparFclesizesreallyarefromobservaFons
CAMTutorial:Microphysics
LiquidWaterPath
• FundamentalobservaFonaluncertainty:– Howmuchcondensedwaterisintheatmosphere?
• WeknowbelertheradiaFvefluxes(RF,LW&SW)
• ButthenulFmatelyRF=f(LWP,re)
• MulFpleSoluFons:– DifferentmicrophysicsschemesproducesimilarcloudradiaFveforcingwithverydifferentsizesandLiquidWaterPaths
– SameradiaFoncode
CAMTutorial:Microphysics
OldandNewMicrophysics
CAMTutorial:Microphysics Gelelmanetal,2008
Summary• CloudmicrophysicsareacriFcalpartoftheclimatesystem
• BasicformulaFonisaseriesofprocessrates• BulkschemehasbeentradiFonalpath• New2‐modetreatmentavailable• ObservaFonalconstraintsoncloudsareprobablynotsufficienttoconstrainimportantglobaluncertainFes
• Goingfromsmallscaleglobalscaleisachallenge• Aerosolsalsoplayanimportantroleintheclimatesystemandinteractwithclouds
• Aerosol‐cloudinteracFonsareveryimportantinunderstandingclimatesensiFvity
CAMTutorial:Microphysics
Aerosols&ClimateChange
CAMTutorial:Microphysics
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.
CAMTutorial:Microphysics