simulation of convectively coupled kelvin waves using the ... · aqua-planet 3d cam fixed sst slab...
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SimulationofconvectivelycoupledKelvinwavesusingtheSingleColumnAtmosphereModel(SCAM)coupledtotheDampedGravityWave
(DGW)method
I-Kuan Hu,BrianMapes,RichNeale,andAndrewGettelman
Specialthanksto:KevinReed,BrianMedeirosandJohnTruesdale
• Scientificgoal:Understandingtheinteractionsamongsubgrid physicalparameterizations,andbetweenthemandresolveddynamics,byutilizingclimatemodelhierarchies(Held,2005).
Introduction
• Scientificgoal:Understandingtheinteractionsamongsubgrid physicalparameterizations,andbetweenthemandresolveddynamics,byutilizingclimatemodelhierarchies(Held,2005).
• ClimatemodelhierarchiesofCommunityAtmosphereModel(CAM)- Fromthelower-lefttoright:thehierarchyofconfigurationsforevaluatingdynamicalcores(Fig.1ofReed&Jablonowski,2012)
- Fromtheupper-lefttoright:thehierarchyofconfigurationsforevaluatingsubgrid physicalparameterizations
+modelphysics
AMIP
+surfaceexchange+topography
3DCAM
IncreasingComplexityà
SimplifiedForcing
3DCESM
FullComplexity
FixedSST SlabOcn
CMIP
+non-uniform SSTs+rotation
Localcolumn
DryHeld-Suarez
1DSCAM
3DCAM
MoistHeld-Suarez
3DCAM
+simplemoistphysics
SimplifiedDynamics&Forcing
SimplifiedPhysics&Forcing
+dynamicalcore- “localized”forcing
Aqua-planet
3DCAM
FixedSST SlabOcn
+couplingwithland/ocean/ice/humans
Shallowwater
2DCAM
+verticaldimension
RCE
3DCAM
Introduction
• Scientificgoal:Understandingtheinteractionsamongsubgrid physicalparameterizations,andbetweenthemandresolveddynamics,byutilizingclimatemodelhierarchies(Held,2005).
• ClimatemodelhierarchiesofCommunityAtmosphereModel(CAM)- Fromthelower-lefttoright:thehierarchyofconfigurationsforevaluatingdynamicalcores(Fig.1ofReed&Jablonowski,2012)
- Fromtheupper-lefttoright:thehierarchyofconfigurationsforevaluatingsubgrid physicalparameterizations
+modelphysics
AMIP
+surfaceexchange+topography
3DCAM
IncreasingComplexityà
SimplifiedForcing
3DCESM
FullComplexity
FixedSST SlabOcn
CMIP
+non-uniform SSTs+rotation
Localcolumn
DryHeld-Suarez
1DSCAM
3DCAM
MoistHeld-Suarez
3DCAM
+simplemoistphysics
SimplifiedDynamics&Forcing
SimplifiedPhysics&Forcing
+dynamicalcore- “localized”forcing
Aqua-planet
3DCAM
FixedSST SlabOcn
+couplingwithland/ocean/ice/humans
Shallowwater
2DCAM
+verticaldimension
RCE
3DCAM
Introduction
• Scientificgoal:Understandingtheinteractionsamongsubgrid physicalparameterizations,andbetweenthemandresolveddynamics,byutilizingclimatemodelhierarchies(Held,2005).
• ClimatemodelhierarchiesofCommunityAtmosphereModel(CAM)- Fromthelower-lefttoright:thehierarchyofconfigurationsforevaluatingdynamicalcores(Fig.1ofReed&Jablonowski,2012)
- Fromtheupper-lefttoright:thehierarchyofconfigurationsforevaluatingsubgrid physicalparameterizations
+modelphysics
AMIP
+surfaceexchange+topography
3DCAM
IncreasingComplexityà
SimplifiedForcing
3DCESM
FullComplexity
FixedSST SlabOcn
CMIP
+non-uniform SSTs+rotation
Localcolumn
DryHeld-Suarez
1DSCAM
3DCAM
MoistHeld-Suarez
3DCAM
+simplemoistphysics
SimplifiedDynamics&Forcing
SimplifiedPhysics&Forcing
+dynamicalcore- “localized”forcing
Aqua-planet
3DCAM
FixedSST SlabOcn
+couplingwithland/ocean/ice/humans
Shallowwater
2DCAM
+verticaldimension
RCE
3DCAM
Introduction
• SCAM-PLSD(ParameterizedLarge-ScaleDynamics)- Thistalk:couplingSCAMtotheDGWmethodforsimulatingconvectivelycoupledKelvinwaves(CCKWs).
- Alternative:theweaktemperaturegradientmethod
• SCAM-RCE(Radiative-ConvectiveEquilibrium)- Setadvectiontermstozero; representsanaverageoverthebroadtropics,oramediancolumntherein.
- UsingtheRCEMIPprotocols(Wingetal.,2018)withsomemodifications
RCE
+dynamicalcore
Aqua-planet AMIP
+surfaceexchange+topography
1DCAM
3DCAM 3DCAM
RCE+PLSD
IncreasingComplexityà
+parameterizeddynamics
SimplifiedDynamics&Forcing SimplifiedForcing
1DSCAM 3DCESM
FullComplexity
+couplingwith land/ocean/ice/humans
Localcolumn
1DSCAM
FixedSST SlabOcn FixedSST SlabOcn
CMIPRCE
3DCAM
+non-uniformSSTs+rotation
Introduction
Considerthe3D,non-rotational,linearizedperturbationequationsofmomentum,continuity,andhydrostaticbalanceinpressurecoordinate:
𝛼:themechanicaldampingcoefficient.
SCAM-DGWCoupling
Theaboveequationscanbecombinedintoasingleequationrelating𝑇#$ and𝜔$:
Nowweassumethe2D(i.e.thex-pspace),monochromatic(i.e.asinglewavenumberk)wave-formsolutionsforalltheprimevariables.
Foragiven𝑥 = 𝑥(,forwhichwemultiplytheaboveequationbyexp(−𝑖𝑘𝑥() andtaketherealcomponent,wehave
Thesingleequationrelating𝑇#$ and𝜔$ thenbecomes
SCAM-DGWCoupling
Conceptually,inthiscouplingsystem,anatmosphericcolumn”behavesasifitwereimmersedinabathofweaklydampedplanewaves”(Edman andRomps,2014)
Thecomputed𝜔$ isusedintheverticaladvectionofTandqvtoupdatethethermodynamicstateofanatmosphericcolumn.Thisnewthermodynamicstate(i.e.new𝑇#$)isthenusedintheaboveequationagaintoupdate𝜔$ forthenexttimestep,completingtheinteractionbetweentheatmosphericcolumnandtheDGW.
𝑥(
SCAM-DGWCoupling
Kuang (2008):“Becausethesignofthewavenumberdoesnotenterinthecalculation,theresultscanbeviewedasrepresentingaverticallineineithereastward- orwestward-propagatingwaves.”
ExperimentalDesign
• SCAMinCESM2.1.0• RCEMIPprotocols(Wingetal.,2018):water-coveredsurface,norotation,noaerosol
effects,fixedinsolation&surfacealbedo,prescribedozone&tracergases• Boundaryforcing:SST=302.5K,verticallyuniformU=5m/s• Modelphysics:[CAM5,CAM6]- CAM6usestheCLUBBscheme,andtheupdatedmicrophysicsanddeepconvectionschemes
• Modelverticalresolution:[L30orL32,L60]• Modeltimestep:600s• Prescribinganidealizedradiativecoolingprofile
• Parameterizationoflarge-scalehorizontaladvectionofmoisture:the“lateralentrainment”approach(RaymondandZeng,2004)- DrawingtheRCEreferenceairintothecolumnbythelocaldivergentwind,whichisdiagnosed from
theDGW-inducedverticalmassflux
• VerticaladvectionofTandqv:theEULbuilt-incenterdifferencescheme- Bydefault,verticaladvectionofqviscomputedusing theSemi-Lagragian Transportscheme
• Upperboundarycondition:rigidlid@175hPa• Couplingtimestep:600s(sameasmodeltimestep)• Wavelength(2𝜋/𝑘):5000,7500,10000km• Dampingstrength(𝛼56):2,4,6,8days
(Sessions etal.,2015)
ExperimentalDesign
Results
Procedureof running anewSCAM-DGWsimulation:1. Running anewSCAM-DGWsimulationwithoutDGW
coupling (reproducing RCE)for200days.
Results
Procedureof running anewSCAM-DGWsimulation:1. Running anewSCAM-DGWsimulationwithoutDGW
coupling (reproducing RCE)for200days.2. ActivatingtheDGWcouplingafterday200,forwhich
themeanprofilesofTandqvoverdays100-200aretakenasthereferencestate,andrunning theSCAM-DGWcoupledsystemforanother200days.
• Wavegraduallygrowswithindays200-260• Abiascomponent (ofascent)+wavedisturbances• Phasespeed∼ 14.5m/s(2.5cycleswithindays280-300)• Thetiltedverticalstructuresofverticalmotion and
thermodynamics resemblethatof“westward-propagating”CCKWs
Results:SCAM5-DGW
(Kiladis etal.,2009)
Results:SCAM5-DGW• Coupledsystemswithlonger
wavelengthcharacterizelongerperiodsofoscillations(“nondispersiveness”).
• Waveinstabilitygenerallyenhancesasthestrengthofdampingdecreases
• Abiascomponentofascentexistsinalmostalltheruns.
Results:SCAM6-DGW• FeaturesgenerallyresembletheSCAM5-DGWcase• Astrongerbiasofascent• Fasterphasespeed,∼ 17.4m/s(3cycleswithindays
280-300)
Largerscalingmagnitudes thanthatoftheSCAM5_L30-DGWcase!
Results:SCAM6-DGW• Theoverallwaveinstabilityismuch
strongerthantheSCAM5-DGWsets;probablyduetothealready-strongintrinsicvariabilityofSCAM6-RCE
• Coupledsystemswithshorterwavelengthcharacterizestrongerwaveinstability
Largerscalingmagnitudes thanthatoftheSCAM5_L30-DGWcase!
• ZMnumcin, thenumberofnegativebuoyancyregionsthatareallowedfordeterminingtheconvectiontopandCAPEintheZMscheme,issetto5 inSCAM5and1 inSCAM6.
RCEinSCAM5vs.SCAM6
SCAM5,ZMnumcin =5(default)
SCAM6,ZMnumcin =1(default)
SCAM6,ZMnumcin =5
Results:SCAM6ZMnumcin5-DGW• Waveperturbations oscillatearound theRCEstate
almostlinearly• Slowphasespeed,∼ 11.6m/s(2cycleswithindays262-
282)• Thereferencestateisveryhomogeneous
Smallestscalingmagnitudesamongthethreetestedsets
Results:SCAM6ZMnumcin5-DGW• Lower-frequencywaves(vs.other
sets)whenlongerwavelengthsandweakerdamping isused.
CAM5 CAM6 CAM6ZMnumcin5
PRECT,30N-30S,nDaySkip =30EUL,128x256,dt =600s
Results:Aquaplanet CAM
PRECT,30N-30S,nDaySkip =30EUL,128x256,dt =600s
Results:Aquaplanet CAMRelativelystrong(w.r.t. theother twosets)signalsatshorterwavelengths
CAM5 CAM6 CAM6ZMnumcin5
PRECT,30N-30S,nDaySkip =30EUL,128x256,dt =600s
Results:Aquaplanet CAMRelativelystrong(w.r.t. theother twosets)signalsatshorterwavelengths
Preferenceof low-frequencywaves?
CAM5 CAM6 CAM6ZMnumcin5
Conclusions
• TheSCAM-DGWconfigurationisbuiltforcomplementingtheevaluationhierarchyofphysicalparameterizationsuitesinCAM.
• Somecasesproducethedesiredresult,withthecoupledwavesoscillatingcenteredontheRCEclimatereferencestate,whilemostothercasesfeatureabiascomponent.
• Thesimulatedphasespeed(11-17m/s)andtheverticalstructuresoftheDGW-associatedverticalvelocityandthermodynamicsresemblethoseoftheCCKWsfromobservations.
• TheSCAM6_L32-DGWsetshowsstrongercoupledinstabilityatshorterwavelengths;theSCAM6ZMnumcin5_L32-DGWsettendtoproducelower-frequencywaves.Bothfeaturesseemtobecapturedintheaquaplanet simulationstosomedegrees.
SCAM5_L60-DGW• Nondispersiveness of thephase
speedandthedependenceofwaveinstabilityondampingstrengtharesimilartotheSCAM5_L30-DGWset
• TheoverallwaveinstabilityismuchweakerthantheSCAM5_L30-DGWset;someexhibitslinearity,especiallywhenstrongerdamping isused.
• Lower-frequencywaves(vs.SCAM5_L30-DGW)whenlongerwavelengthsandweakerdamping isused.
SCAM6_L60-DGW• GenerallysimilartotheSCAM6_L32-
DGWset,exceptforirregularoscillationsinsomecases.
Note:largerscalingmagnitudes!
SCAM6ZMnumcin5_L60-DGW• Theoverallwaveinstabilityis
strongerthantheSCAM6ZMnumcin5_L32-DGWset,butweakerthantheSCAM5_L30-DGWandSCAM6-DGWsets.
• Higher-frequency wavesvs.SCAM6ZMnumcin5_L32-DGWset.
ComparedtotheSCAM5_L30-DGWcase,• Growthofwavesappearsandstopsmorequickly,with
themagnitudeofinstabilitybeingapproximatelytwicesmaller
• MorelinearanomaliesagainsttheRCE• Slowerphasespeed,∼ 11.6m/s(2cycleswithindays
260-280)• TheintrinsicSCAM5_L60-RCEoscillationsretain,
particularlyintheupper troposphere (destructiveinterference?)
OnethirdofthescalingmagnitudesusedintheSCAM5_L30-DGWcase!
SCAM5_L60-DGW,10000-kmwavelength,𝛼56 =6days
SCAM6_L60-DGW,10000-kmwavelength,𝛼56 =6days• Coupledwavesfeaturetwodistinctfrequencies:onehas
aperiodof∼ 7days(16.5-m/sphasespeed), theother∼5days(23-m/sphasespeed); theyappearbyturns(irregularly) totheendofsimulation
• The7-daywavesgenerallyresemblethecoupledwavesoftheSCAM6_L32-DGWcase
• Astrongbiasofascent,similartotheSCAM6_L32-DGWcase
SamescalingmagnitudesoftheSCAM6_L32-DGWcase
SCAM6ZMnumcin5_L60-DGW,10000-kmwavelength,𝛼56 =6days• GenerallysimilartotheSCAM5_L60-DGWcase,butwith
strongerwaveinstability(aweakascentbias)andfasterphasespeed(∼ 14.5m/s,2.5cycleswithindays280-300)
• ThereferencestateisverysimilartothatoftheSCAM5_L60-DGWcase
SamescalingmagnitudesoftheSCAM5_L60-DGWandSCAM6ZMnumcin5_L32-DGWcases
DGWfreeparameters,withKuang (2008)asareference:1. Dampingtimescale(𝛼56):2,4,6,8days.
Linetal.(2008)suggeststhatamechanicaldampingwithtimescaleofafewdaysispossibleinthetropics;possiblesourceareconvectivemomentumtransportorhorizontaladvection.
2. Wavelength(= 2𝜋 𝑘⁄ ):5000,7500,10000km.CCKWswiththesewavelengthsareobserved.
Note inKuang (2008):“Becausethesignofthewavenumberdoesnotenterinthecalculation,theresultscanbeviewedasrepresentingaverticallineineithereastward- orwestward-propagatingwaves.”
SCAM-DGWCoupling
Thetime-derivativetermcanbeneglectedifthesimulatedcolumnvariesontimescalesmuchlongerthan𝛼56 (usuallyontheorderofafewdays).Mostpreviousstudiesneglectthisterm,e.g.,Daleu etal.(2015),Kuang (2011,2012),Wangetal.(2016)
ButinsimulatingCCKWs,weshouldkeep thisterm,asthecolumnanomalieschangeonasimilartimescaleof𝛼56 .
DGWfreeparameters,withKuang (2008)asareference:1. Dampingtimescale(𝛼56):2,4,6,8days.
Linetal.(2008)suggeststhatamechanicaldampingwithtimescaleofafewdaysispossibleinthetropics;possiblesourceareconvectivemomentumtransportorhorizontaladvection.
2. Wavelength(= 2𝜋 𝑘⁄ ):5000,7500,10000km.CCKWswiththesewavelengthsareobserved.
Note inKuang (2008):“Becausethesignofthewavenumberdoesnotenterinthecalculation,theresultscanbeviewedasrepresentingaverticallineineithereastward- orwestward-propagatingwaves.”
SCAM-DGWCoupling
• ZMnumcin, thenumberofnegativebuoyancyregionsthatareallowedfordeterminingtheconvectiontopandCAPEintheZMscheme,issetto5 inSCAM5and1 inSCAM6.
RCEinSCAM5vs.SCAM6SCAM
5_L30
SCAM
6_L32
SCAM-RCE,interactiveradiation(RRTMG)
ZMnumcin =5(default)
ZMnumcin =1(default)
ZMnumcin =1
ZMnumcin =5
SCAM5_L30,ZMnumcin =5(default)
SCAM6_L32,ZMnumcin =1(default)
SCAM6_L32,ZMnumcin =5
SCAM-RCE,prescribedradiation
• ZMnumcin, thenumberofnegativebuoyancyregionsthatareallowedfordeterminingtheconvectiontopandCAPEintheZMscheme,issetto5 inSCAM5and1 inSCAM6.
RCEinSCAM5vs.SCAM6
S1-1hr S1
DefaultSCAM5_L60,instant DefaultSCAM6_L60,instant
S1-1hr S1
SCAM5:ThedeepconvectivetopisthelevelthatgivesthemaximumCAPE
SCAM6:SometimestheCAPEassociatedwiththeselecteddeepconvectivetopislowerthanagiventhreshold➔ theZMschemeisnotactivated
Remarksforthe10000-kmcoupledwaves:• Wavesgrowgradually,withdisturbancescentered
around theRCEstate(linearity)• Period∼ 10days,phasespeed∼ 11m/s• Opposite(westward-propagating) tiltedvertical
structuresofCCKWs• Top-heavyprofilesofconvectiveheating, convective
drying, andverticalmotion
Whatweexpecttosee,basedonKuang (2008)
(Kiladis etal.,2009)
T
qv
1. CRM:SystemforAtmosphericModeling (SAM)2. 192x192gridpoints (2-kmres.),64verticallevels,15-s
timestep,29.5°C(302.65K)SST3. Prescribeabackgroundascent(inboth theRCEand
DGWruns)
4. PrescribethemeanradiativecoolingprofileofthepreviousRCErun,whichusesCCM3’sradiationscheme
5. RadiationUBC(buttheresultsaresimilarwhenusingarigid-lidUBC)
6. Periodiclateralboundary condition7. NoHADVqv8. Usethe1st-orderupwindschemeforZADVT andZADVqv9. Use𝛼56 = 10days10. UpdateDGWcoupling ateverytimestep
DifferencesinNumericalSetupbetweenKuang (2008)vsSCAM-DGW
1. SCM:SCAM,withCAM5orCAM6physics2. 30(SCAM5), 32(SCAM6), and60verticallevels,600-s
timestep,302.5KSST3. Nobackground ascent4. Prescribeanidealizedradiativecoolingprofile5. Rigid-lidUBC(rigid lid@175hPa)6. Nolateralboundary condition7. HADVqv: thelateralentrainmentmethod8. Usetheaveragedcentered-differencingschemefor
ZADVT andZADVqv9. Preferable𝛼56 ≥ 6days10. UpdateDGWcoupling ateverytimestep
SCAM-RCE:meanstate(SST=302.5K)
• TheTandqvprofiles resembletheobservations
• 𝑄: = −𝑄6; ,𝑄<; = 0 (RCEvalidated!)
• SCAM6generatesacoolertroposphere thanSCAM5
• TheRHprofilesfeature- ~ 100%intheupper
troposphere- thezigzag-shapedstructures
inthemiddle troposphere