local and remote cloud radiative effect impacts onto the ... · 5-3_cfmip_2017_presentation1.pptx...

LocalandRemoteCloudRadiativeEffectImpactsontotheExtratropical AtmosphericCirculation

OliverWatt-MeyerDargan FriersonUniversityofWashington

CFMIP2017Tokyo,Japan

Responseof850hPazonal-meanzonalwindtoa+4Kseasurfacetemperatureanomaly

VoigtandShaw[2016]

Apoleward shiftinallmodels,butmagnitudevariesbyafactorof2

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Modelssuggestthathalformoreofthejetresponsetoglobalwarmingcomesfromchangesinclouds

Ceppi andHartmann[2016]

ResponsetoquadruplingCO2 withcloudslockedtocontrolclimate

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Latitude



ResponsetoquadruplingCO2 withcloudslockedtocontrolclimate

Responsetocloudsbeinglockedto4xCO2 simulationbutwithCO2itselfheldconstant

Latitude

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Latitude

Similarexperiment,butwithaspecified-SSTmodel,insteadofaslab-oceanmodel

VoigtandShaw[2015]2

However,theimpactsofcloudradiativeeffectsontothemidlatitudejetvarywidelyacrossmodels,evenforthepresent-dayclimate

Contours:time-meanzonalmeanzonalwindin“clouds-off”simulation

Shading:differencebetween“clouds-on”and“clouds-off”simulations

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Methods• UsetheCloudsOn-OffKlimate Intercomparison Experiment(COOKIE)

ensemble[Stevensetal.,2012]– Asetofspecified-SSTaquaplanet simulations,inwhichtheradiativetransfer

schemeismadetoignorethepresenceofclouds– Thesesimulationsarecomparedtocontrolsimulationsthatincludecloud

radiativeeffectsinordertoisolatetheimpactsofcloudsontothecirculationoftheatmosphere

• Inaddition,weperformexperimentswiththeGFDL-AM2.1andNCAR-CAM5.3modelsinwhichcloudradiativeeffectsareonlyimposedincertainregions– Tropics:equatorward of30°,extratropics:poleward of30°

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Responseofzonalmeanzonalwindtocloudradiativeeffectsintropicsvs.extratropics inGFDL-AM2.1andNCAR-CAM5.3models

Equatorward of30° Poleward of30°

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Equatorward of30° Poleward of30°

[kg/s]

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Responseofmassstreamfunction tocloudradiativeeffectsintropicsvs.extratropics inGFDL-AM2.1andNCAR-CESM1.2models

WhydotropicalcloudsdrivechangesinstrengthofHadleycell?

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Verticaldashedline:latitudeofeddy-drivenjetforclouds-offsimulation

ACRE:AtmosphericCloudRadiativeEffect

Interactionsbetweensubtropicalandmidlatitude jet• AstrengthenedHadleycell,andthusacceleratedsubtropicaljet,leadsto

anequatorward shiftededdy-drivenjet

• Twotheorieshavebeenproposed:– increasedbaroclinicity onthepoleward

flankofthesubtropicaljetwhenitisstrong[LeeandKim,2003]

– changesinmeridional eddypropagationwhenthesubtropicaljetstrengthens[Ceppi etal.,2013]

Ceppi etal.[2013]8

Whatabouttheextratropical clouds?

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• Locally,meridional gradientsinACREwillimpactthelatitudeofmaximumbaroclinicity oftheatmosphere

MeasuretheseeffectsacrossCOOKIEmodels• Eddydrivenjetposition:latitudeofmaximumzonalmeanzonalwindat

850hPa

• Hadleycellstrength:maximumofmassstreamfunction

• ACREgradient:,approximatemeasureofsecondderivativeofACREabout

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,andacrossCOOKIEmodels

Blue:equatorward shiftRed:poleward shift

Blacklinesshowleast-squaresbestfitto:

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Whatabouttheglobalwarmingresponseofthejet?

Responseof850hPazonalwindto+4KSSTperturbation

Cloudsoff Cloudson

Summary• Acrossmodels,theimpactofcloudradiativeeffectsontothepositionof

themidlatitude jetvarieswidelyinsignandmagnitude• Thisisprimarilycontrolledbyhowmuchcloudradiativeeffectsstrengthen

theHadleycell,andthusacceleratethesubtropicaljet• Animportantsecondarycontrolisthelocalimpactofcloudradiative

effectsontomeridional temperaturegradientsinthemidlatitudes• Worktobedone:

– Implicationsforglobalwarmingresponseofjets?– Whatwouldtheimpactofincludinganinteractiveoceanbe?(greaterroleforlowclouds)

• PaperoutinGRL:”LocalandRemoteImpactsofAtmosphericCloudRadiativeEffectsOntotheEddy-DrivenJet”

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ThisresearchwassupportedbytheNOAAClimateandGlobalChangePostdoctoralFellowshipProgram,administeredbyUCAR’sCooperative

ProgramsfortheAdvancementofEarthSystemScience.

Extraslides

Black:ACREinclouds-onsimulation.Red:ACREinclouds-offsimulation(whereavailable)

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