ExtratropicalStratosphereTroposphereDynamicalCoupling温带平流层对流层的动力耦合课件

OutlineReviewUsingasimpledryAGCMtostudyThetroposphericgeneralcirculation.Thedistributionofrelativehumidityinthetroposphere.Theconnectionsbetweenthestratosphereandthetroposphere.StrengthsandweaknessesofsimplemodelsOutlineReview1TermsandConceptsQuasigeostrophicScaling:Potentialvorticitydefinition:TermsandConceptsQuasigeostro2AnAdjustmentProblem:Homework!(Sortof)airwaterThisexampleillustratestheimpactofrotation(andsomesubtleties).Thediagrambelowrepresentsthecrosssectionofachannelgoingintothescreen.Initially,thefluidissloped(gently)andisatrest.(Imagineholdingitinplacewithasheetofplexiglass.)1.Non-rotatingcase(f=0):estimatethecrosschanneltransportofmassandcross-channelspeedyouwouldobtainafterwards,intermsoftheslope,ofg,andofthemeanlayerdepth.AnAdjustmentProblem:Homewor3AnAdjustmentProblem:Homework!(Sortof)airwater2.Rotatingcase(f>0).Onthefplane,youcouldimagineremovingtheplexiglassandsettingupageostrophicallybalancedflowintothescreenwiththisoriginalslope.Inthiscase,therewouldbenocross-channelmassflux.Thiscan’thappen:why?(Thereareacoupleofreasons.)3.Fortheambitious:solvefortheequilibriumheightandestimatethecross-channelmassflux.Makeasmanysimplifyingassumptionsasnecessary.AnAdjustmentProblem:Homewor4Review-1 Top-of-AtmosphereRadiationHartmann1994TransportisneededtoexplaintheobserveddistributionofTOAradiationandthetemperaturedistributionoftheatmosphere.Rotationsupresseszonallysymmetriccirculations,so……Baroclinicwaves(transientandstationary)mustdothetransport.Review-1 Top-of-AtmosphereR5Review–2MeridionalVelocityCorrelationsChangandYu1999,Chang1993Transientbaroclinicwavestransportmuchoftheenergyintheextratropics.Theytravelinpacketsandhavecharacteristicphasetiltsthatcorrespondtosystematiceffectsonthemeanflow.Asetofmodelsofincreasingcomplexityaccountsforthesestructures.Review–2MeridionalVelocity6Review–3Phillips(Holton)Wedescribedasequenceoflinearmodelsofbaroclinicwaves.Eady(Gill)Charney(Gill)SimmonsandHoskinsReview–3Phillips(Holton)We7Review–4NonlinearBaroclinicLifecyclesNonlinearprimitiveequationsmodelsshowedhowbarocliniceddiescanbesetup,grow,andsaturate.Butthereneedstobeawayofrestoringthebaroclinicityforthemtobesustained.Review–4NonlinearBaroclinic8TransientEddiesinClimateModelsWehaveseenthatweneed(atleast)athree-dimensionalprimitiveequationsmodeltoproperlycapturebarocliniceddystructure.Webegantalkingaboutadrynonlinearprimitiveequationsmodelwiththefollowingforcinganddissipation:TransientEddiesinClimateMo9BaroclinicTurbulenceModels:T.Schneider

Schneider2004Let’sfirstlookatadryGCMdevelopedbyTapioSchneider.Inhismodel,thetroposphericequilibriumtemperatureprofileisconvectivelyunstable.Thedeeptropicsareconstrainedtobeclosetoan“effective”moistadiabatwithstrongthermaldamping.Inmidlatitudes,thedampingisweaker.Noticethattheendclimateisstablystratified.Thedarklineintheupperthirdofthefigureisthetropopause(definedinaspecialway).EquilibriumPotentialTemperature(input)TimeMeanPotentialTemperature(output)BaroclinicTurbulenceModels:10BaroclinicTurbulenceModels:T.Schneider

Schneider2004What’sinterestinghereisthatthereisnodryconvectiveadjustmentinthemodel:thebarocliniceddiessetthestratificationoftheextratropics.Inthesamepaper,Schneiderarguesthatthesamedynamicsestablishesthegrossfeaturesofthetropopause.EquilibriumPotentialTemperatureTimeMeanPotentialTemperatureBaroclinicTurbulenceModels:11BaroclinicTurbulenceModels:T.Schneider

Schneider2004Hisdefinitionofthetropopauseisbasedonthefluxofmassbetweenisentropicsurfaces,representedatrightinapotential-temperature/latitudeplotofmassstreamfunction(bottom).ThisistheBrewer-Dobsoncirculationofthetroposphere,withastrongmidlatitudeeddydrivencomponent.Thedottedlinesmarktypicalsurfacepotentialtemperaturevalues.Mostofthereturnflowoccursattemperaturesbelowtheaveragesurfacetemperature,in“coldairoutbreaks.“TimeMeanPotentialTemperatureMassStreamfunctionBaroclinicTurbulenceModels:12BaroclinicTurbulenceModels:T.Schneider

Schneider2004BasedontheideathatbarocliniceddiesdiffusePVintheinteriorandpotentialtemperatureatthesurface,Schneiderderivesthefollowingscalingrelationship:Thisimpliesthatthelowermostisentropethatreachesthetropopauseshouldoriginateinthetropics.TheplotatleftrepresentstheLHSandRHSofthisestimateforaverywiderangeofsimulations.Theestimateisveryrobust.BaroclinicTurbulenceModels:13EddyDiffusivityHereissomeobservationalsupportfortheideathatbarocliniceddiesarediffusiveinsomeway.Thecontoursintheplotrepresent850mbDJFtemperatures.Theredvectorsrepresent(thedivergentpartof)theheatfluxfromtheNCEPReanalysis.Thebluevectorsrepresent(thedivergentpartof)thedowngradientfluxusingtheformulaatright.KushnerandHeld1998EddyDiffusivityHereissomeo14ASimpleModelofTroposphericHumdityIthasrecentlybeenrealizedthatthehumiditydistributioncanbereconstructedbyadvectingawater-liketracerbythelargescaleflow.Thisfigureshowshowthe“Held-Suarez”dryAGCMrepresentsthis.LikeSchneider’smodel,onlybarocliniceddiesareactiveinmidlatitudes.Anon-interactivewatertracerfluxissetatthesurface.Thetracerisadvecteduntilsaturationisreached,atwhichpointitisremoved.Noticethedrysubtropics.SubtropicaldrynessisoftenascribedtothedescendingbranchoftheHadleyCell(heredrivenbythemodel’sdiabaticcooling).RHinHeld-SuarezDryGCM.Galewskyetal.2005.ASimpleModelofTropospheric15ASimpleModelofTroposphericHumdityThedarkestredcolorsindicatethepointoforiginofsaturatedparcels.Lightershadingindicatestheprobabilitythattheairataparticularlatitudeandheightwaslastsaturatedatthepointoforigin.Thisplotsuggeststhatthelower-troposphericsubtropicsaredrybecausebarocliniceddiestransportairfromthesubtropics,alongisentropes,tothecoldextratropicaluppertroposphere,andbackagain.Thelower-troposphericRHminimumthushasrelativelylittletodowiththeHadleyCell.Asimilaranalysisworksfortheobservations(NCEPReanalysis+MATCH).TracersofLastSaturation.(Galewskyetal.2005)ASimpleModelofTropospheric16SimpleModelsofStratosphere-TroposphereCouplingScinoccaandHaynes1998ScinoccaandHaynesshowedthataddingastratospherelayertothistypeofGCMresultedinaninterestingcouplingbetweenstratosphereandtroposphere.Theirmodelhasnostationarywaves.Instead,synoptic-scalewavepacketsgeneratelow-wavenumberwavesthatpropagateintothestratosphere…animations.LorenzoPolvaniandIusedthiskindofmodeltostudytheproblemofthecouplingbetweenthestratosphereandtroposphere.Wefocusedontheimportanceofthesetransienteddies.EquilibriumwindsandtemperaturesTimeEvolutionofSpatialSpectrumSimpleModelsofStratosphere-17Teq(g=3)PolvaniandKushner2002Troposphere:baroclinicallyunstableprofile.Flatlowerboundary,sonostationarywaves(SouthernHemisphereconditions)…animations.Stratosphere:blendpolarnightandsummerprofiles.Strengthofpolarvortextunedbyg.Teq(g=3)PolvaniandKushne18ASpontaneousSuddenWarmingThetopplotshowsatimeseriesofpolar-capaveragetemperatureat50hPafromasimulationwithtime-independentforcing.AtDay7121,thereisasevenstandarddeviationpeakintemperature.Thiscorrespondstoasplit-vortexmajorwarmingeventinthemodel(bottomleft,in750KPV).Forcomparison,asimilarplotisshownfromthe2002Southern-HemispheremajorWarming(Baldwinetal.).ThetransienteddyactivityfromthetroposphereisthereforeabletogenerateaKushnerandPolvani2005KushnerandPolvani2005;Baldwinetal.2003ASpontaneousSuddenWarmingTh19Stratosphere-TroposphereCoupling SpringtimeozonelossintheSouthernHemisphere...TrendinAntarcticOzoneTrendinAntarcticPolar-CapAverageGeopotentialHeightGillettandThompson2004ThompsonandSolomon2002 ...hascooledthelowerstratosphere.

Butnoticethelike-signedtrendinthetroposphere.Theproblemweareinterestedin:influenceofspringtimeozonelossonthetroposphericcirculation.Stratosphere-TroposphereCoupl20g=2g=3g=4CoolingthePolarStratosphereWhathappensinoursimplemodelaswecoolthepolarstratosphere?g=2g=3g=4CoolingthePol21ResponsetoStratosphericCoolingAsPolarStratosphereCools,JetStreamShiftsPolewardResponsetoStratosphericCool22TheResponseis“Modal”Inthetroposphere,theresponsematchesthemodel’s“annularmode.”Theresidualisconcentratedinthestratosphere.Intheresponse,thebarocliniceddyactivityshiftspoleward.Thecouplingbetweenthetroposphereandthestratosphereisverytight.AnnularModeResponseResidualTheResponseis“Modal”Inthe23ResponseofUpwellingWave-ActivityFluxg=2g=4Biggestreductionatsynopticscales:synopticeddyEPfluxintothelowerstratospheredecreases.100mbVerticalEPFluxResponseofUpwellingWave-Act24TheResponseisRobustLatitudeofSurfaceWindMaxvsgcolderstrat®

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20levels40levels80levelsTheResponseisRobustLatitude25TheWorldofGeneralCirculationModels ThetroposphericresponseaccountsfortheobservedDJFtrends. Althoughoursimplemodelshowedthisgeneralbehaviour,GillettandThompsondemonstratedquantitativeagreementwiththeobs.InacomprehensiveGCM,weseethesametroposphericresponsetoozonedepletion(GillettandThompson2004):Simulatedresponsetoozonedepletion(UKMOmodel)TrendinAntarcticPolar-CapAverageGeopotentialHeight

TheWorldofGeneralCirculati26StrengthsoftheseSimpleModelsWehaveseenseveralexamplesofhowbarocliniceddiesandtheirassociatedcirculationsinfluencetheclimatesystem.Theresidualcirculationseemstosetoratleastinfluencetropopausestructure.Theeddiesseemtodryouttheextratropicaltroposphere.Theeddiesdriveplanetarywavesandareimplicatedstrat-tropcoupling.Weusethemodeltogetahandleonthemechanisms.Butwemustbearinmindtheirlimitations.StrengthsoftheseSimpleMode27WeaknessesoftheseSimpleModelsThesemodelsarehighlytunableandsocanbe“forced”toagreewithobservations.Theyarethusdifficulttocomparedirectlywithobservations,whichisthemainthemeofthisworkshop.Eventhoughtheyaresimple,theyarenotsimpletounderstand.WewillhavetomoveintotheworldofGCMs–thiswillbetomorrow’sstory.WeaknessesoftheseSimpleMod28OutlineReviewUsingasimpledryAGCMtostudyThetroposphericgeneralcirculation.Thedistributionofrelativehumidityinthetroposphere.Theconnectionsbetweenthestratosphereandthetroposphere.StrengthsandweaknessesofsimplemodelsOutlineReview29TermsandConceptsQuasigeostrophicScaling:Potentialvorticitydefinition:TermsandConceptsQuasigeostro30AnAdjustmentProblem:Homework!(Sortof)airwaterThisexampleillustratestheimpactofrotation(andsomesubtleties).Thediagrambelowrepresentsthecrosssectionofachannelgoingintothescreen.Initially,thefluidissloped(gently)andisatrest.(Imagineholdingitinplacewithasheetofplexiglass.)1.Non-rotatingcase(f=0):estimatethecrosschanneltransportofmassandcross-channelspeedyouwouldobtainafterwards,intermsoftheslope,ofg,andofthemeanlayerdepth.AnAdjustmentProblem:Homewor31AnAdjustmentProblem:Homework!(Sortof)airwater2.Rotatingcase(f>0).Onthefplane,youcouldimagineremovingtheplexiglassandsettingupageostrophicallybalancedflowintothescreenwiththisoriginalslope.Inthiscase,therewouldbenocross-channelmassflux.Thiscan’thappen:why?(Thereareacoupleofreasons.)3.Fortheambitious:solvefortheequilibriumheightandestimatethecross-channelmassflux.Makeasmanysimplifyingassumptionsasnecessary.AnAdjustmentProblem:Homewor32Review-1 Top-of-AtmosphereRadiationHartmann1994TransportisneededtoexplaintheobserveddistributionofTOAradiationandthetemperaturedistributionoftheatmosphere.Rotationsupresseszonallysymmetriccirculations,so……Baroclinicwaves(transientandstationary)mustdothetransport.Review-1 Top-of-AtmosphereR33Review–2MeridionalVelocityCorrelationsChangandYu1999,Chang1993Transientbaroclinicwavestransportmuchoftheenergyintheextratropics.Theytravelinpacketsandhavecharacteristicphasetiltsthatcorrespondtosystematiceffectsonthemeanflow.Asetofmodelsofincreasingcomplexityaccountsforthesestructures.Review–2MeridionalVelocity34Review–3Phillips(Holton)Wedescribedasequenceoflinearmodelsofbaroclinicwaves.Eady(Gill)Charney(Gill)SimmonsandHoskinsReview–3Phillips(Holton)We35Review–4NonlinearBaroclinicLifecyclesNonlinearprimitiveequationsmodelsshowedhowbarocliniceddiescanbesetup,grow,andsaturate.Butthereneedstobeawayofrestoringthebaroclinicityforthemtobesustained.Review–4NonlinearBaroclinic36TransientEddiesinClimateModelsWehaveseenthatweneed(atleast)athree-dimensionalprimitiveequationsmodeltoproperlycapturebarocliniceddystructure.Webegantalkingaboutadrynonlinearprimitiveequationsmodelwiththefollowingforcinganddissipation:TransientEddiesinClimateMo37BaroclinicTurbulenceModels:T.Schneider

Schneider2004Let’sfirstlookatadryGCMdevelopedbyTapioSchneider.Inhismodel,thetroposphericequilibriumtemperatureprofileisconvectivelyunstable.Thedeeptropicsareconstrainedtobeclosetoan“effective”moistadiabatwithstrongthermaldamping.Inmidlatitudes,thedampingisweaker.Noticethattheendclimateisstablystratified.Thedarklineintheupperthirdofthefigureisthetropopause(definedinaspecialway).EquilibriumPotentialTemperature(input)TimeMeanPotentialTemperature(output)BaroclinicTurbulenceModels:38BaroclinicTurbulenceModels:T.Schneider

Schneider2004What’sinterestinghereisthatthereisnodryconvectiveadjustmentinthemodel:thebarocliniceddiessetthestratificationoftheextratropics.Inthesamepaper,Schneiderarguesthatthesamedynamicsestablishesthegrossfeaturesofthetropopause.EquilibriumPotentialTemperatureTimeMeanPotentialTemperatureBaroclinicTurbulenceModels:39BaroclinicTurbulenceModels:T.Schneider

Schneider2004Hisdefinitionofthetropopauseisbasedonthefluxofmassbetweenisentropicsurfaces,representedatrightinapotential-temperature/latitudeplotofmassstreamfunction(bottom).ThisistheBrewer-Dobsoncirculationofthetroposphere,withastrongmidlatitudeeddydrivencomponent.Thedottedlinesmarktypicalsurfacepotentialtemperaturevalues.Mostofthereturnflowoccursattemperaturesbelowtheaveragesurfacetemperature,in“coldairoutbreaks.“TimeMeanPotentialTemperatureMassStreamfunctionBaroclinicTurbulenceModels:40BaroclinicTurbulenceModels:T.Schneider

Schneider2004BasedontheideathatbarocliniceddiesdiffusePVintheinteriorandpotentialtemperatureatthesurface,Schneiderderivesthefollowingscalingrelationship:Thisimpliesthatthelowermostisentropethatreachesthetropopauseshouldoriginateinthetropics.TheplotatleftrepresentstheLHSandRHSofthisestimateforaverywiderangeofsimulations.Theestimateisveryrobust.BaroclinicTurbulenceModels:41EddyDiffusivityHereissomeobservationalsupportfortheideathatbarocliniceddiesarediffusiveinsomeway.Thecontoursintheplotrepresent850mbDJFtemperatures.Theredvectorsrepresent(thedivergentpartof)theheatfluxfromtheNCEPReanalysis.Thebluevectorsrepresent(thedivergentpartof)thedowngradientfluxusingtheformulaatright.KushnerandHeld1998EddyDiffusivityHereissomeo42ASimpleModelofTroposphericHumdityIthasrecentlybeenrealizedthatthehumiditydistributioncanbereconstructedbyadvectingawater-liketracerbythelargescaleflow.Thisfigureshowshowthe“Held-Suarez”dryAGCMrepresentsthis.LikeSchneider’smodel,onlybarocliniceddiesareactiveinmidlatitudes.Anon-interactivewatertracerfluxissetatthesurface.Thetracerisadvecteduntilsaturationisreached,atwhichpointitisremoved.Noticethedrysubtropics.SubtropicaldrynessisoftenascribedtothedescendingbranchoftheHadleyCell(heredrivenbythemodel’sdiabaticcooling).RHinHeld-SuarezDryGCM.Galewskyetal.2005.ASimpleModelofTropospheric43ASimpleModelofTroposphericHumdityThedarkestredcolorsindicatethepointoforiginofsaturatedparcels.Lightershadingindicatestheprobabilitythattheairataparticularlatitudeandheightwaslastsaturatedatthepointoforigin.Thisplotsuggeststhatthelower-troposphericsubtropicsaredrybecausebarocliniceddiestransportairfromthesubtropics,alongisentropes,tothecoldextratropicaluppertroposphere,andbackagain.Thelower-troposphericRHminimumthushasrelativelylittletodowiththeHadleyCell.Asimilaranalysisworksfortheobservations(NCEPReanalysis+MATCH).TracersofLastSaturation.(Galewskyetal.2005)ASimpleModelofTropospheric44SimpleModelsofStratosphere-TroposphereCouplingScinoccaandHaynes1998ScinoccaandHaynesshowedthataddingastratospherelayertothistypeofGCMresultedinaninterestingcouplingbetweenstratosphereandtroposphere.Theirmodelhasnostationarywaves.Instead,synoptic-scalewavepacketsgeneratelow-wavenumberwavesthatpropagateintothestratosphere…animations.LorenzoPolvaniandIusedthiskindofmodeltostudytheproblemofthecouplingbetweenthestratosphereandtroposphere.Wefocusedontheimportanceofthesetransienteddies.EquilibriumwindsandtemperaturesTimeEvolutionofSpatialSpectrumSimpleModelsofStratosphere-45Teq(g=3)PolvaniandKushner2002Troposphere:baroclinicallyunstableprofile.Flatlowerboundary,sonostationarywaves(SouthernHemisphereconditions)…animations.Stratosphere:blendpolarnightandsummerprofiles.Strengthofpolarvortextunedbyg.Teq(g=3)PolvaniandKushne46ASpontaneousSuddenWarmingThetopplotshowsatimeseriesofpolar-capaveragetemperatureat50hPafromasimulationwithtime-independentforcing.AtDay7121,thereisasevenstandarddeviationpeakintemperature.Thiscorrespondstoasplit-vortexmajorwarmingeventinthemodel(bottomleft,in750KPV).Forcomparison,asimilarplotisshownfromthe2002Southern-HemispheremajorWarming(Baldwinetal.).ThetransienteddyactivityfromthetroposphereisthereforeabletogenerateaKushnerandPolvani2005KushnerandPolvani2005;Baldwinetal.2003ASpontaneousSuddenWarmingTh47Stratosphere-TroposphereCoupling SpringtimeozonelossintheSouthernHemisphere...TrendinAntarcticOzoneTrendinAntarcticPolar-CapAverageGeopotentialHeightGillettandThompson2004ThompsonandSolomon2002 ...hascooledthelowerstratosphere.

Butnoticethelike-signedtrendinthetroposphere.Theproblemweareinterestedin:influenceofspringtimeozonelossonthetroposphericcirculation.Stratosphere-TroposphereCoupl48g=2g=3g=4CoolingthePolarStratosphereWhathappensinoursimplemodelaswecoolthepolarstratosphere