MJOinidealizedandcomprehensivemodels(andobserva6ons)

AdamSobelColumbiaUniversity

(ThanksDaehyunKim,EricMaloney,ShuguangWang,andothersascited)

PhototakenfromAdduAtollduringDYNAMO,November2011

Mo6va6on

•  WeseektounderstandthebasicphysicsoftheMJO.•  Understandingshouldul6matelybecapturedinanidealizedmodel.•  ThehistoryofaOemptstodothisisoneoffailureovermanydecades–

manyidealizedmodels,nocommunityagreement.•  Whathaschangednowisthatwehavethecapabilitytosimulate(and

predict!)theMJOincomprehensivemodels.Weshouldusethis.

EvensomeCMIP-classmodelsarenottoobad!

Klingamanetal.2015

Moisture-convection feedback is critical to the MJO. The convection has to be sufficiently sensitive to moisture.

D.Kimetal.2012(andWangandSchlesinger1999;MaloneyandHartmann2001;Leeetal.2003;Linetal.2008;Benedictetal.2013)

Moisture-convection feedback is critical to the MJO. The convection has to be sufficiently sensitive to moisture.

D.Kimetal.2012(andWangandSchlesinger1999;MaloneyandHartmann2001;Leeetal.2003;Linetal.2008;Benedictetal.2013)

ThissuggeststhatthemoisturefieldcarriesthesignaloftheMJO.

Radia6ve-convec6vefeedbackmaintainstheMJO(andtosomeextentsurfacefluxesdotoo)

•  MJOweakensoverland(Sobeletal.2008,2010);modeldiagnos6cs(AndersenandKuang2011,Chikira2014)

•  mechanismdenial(LanduandMaloney2011,Kimetal.2011,ArnoldandRandall2015,Wangetal.2013,2016,MaandKuang2016)

•  budgetstudies(InoueandBack2014;Sobeletal.2014,Woldingetal.2015)

MJOasself-aggrega6onontheEquatorialbetaplaneorsphere(ArnoldandRandall2015)Radia6oniscri6cal.

Nonrota6ng,uniformSST

Rota6ng,uniformSST

Advec6vedrying

Advec6vemoistening

“Moisture mode”: the MJO is essentially a huge blob of moisture that maintains itself by longwave radiative feedback (and maybe surface fluxes) and moves by horizontal moisture advection

LW flux from atmosphere

MaxcolumnMSE&PW

Radia6vewarming

Flow=forcedKelvin/Rossbyresponsetoquasi-steadyhea6ng

W’ is perturbation column moist static energy; U is constant background wind; P’ = P’(W’) – if linear P=W’/¿c; (moisture-convection feedback) E’ = cu‘; zonal wind anomaly is computed diagnostically from P’ using projection (Green’s) function R’ = rP’; Normalized gross moist stability is constant, <1.

A linear moisture mode model (Sobel and Maloney 2012, 2013, JAS)

Green’sfunc6onforwindderivedfromGill(1980)

Extended by Adames and D. Kim (2015) to include meridional moisture advection and horizontal wavenumber-dependent radiation

ObservedsymmetricOLRspectum&theore6caldispersioncurves–westwardgroupvelocityfork>1

Moistureanomaly(contour)Low-levelflow(arrows)MoisturetendencyduetoKelvin(top)

&Rossby(boOom)components

Avarietyofthingscanhappenonaqua-planets.Ifthey’rezonallysymmetric,anMJOokendoesn’tappear.

BrethertonandKhairoutdinov2015

PritchardandYang(2016)–MJO(orsomething)surviveseveninverycoldclimates.S6lllivesbyradia6vefeedback!Doesn’tnecessarilyprefereastwardpropaga6on.

PritchardandYang(2016)–MJO(orsomething)surviveseveninverycoldclimates.S6lllivesbyradia6vefeedback!Thesemeanclimatesareverydifferent–fromeachother,andfromEarth’s.

YetevensmallchangesinbasicstatecanhavealargeimpactonMJOdynamics(MaandKuang2016)

Mul6scalemodels

•  “Skeleton”–MajdaandStechmann(2009)andmanysubsequentpapers•  High-frequencygravitywavecoupling(YangandIngersoll)•  Theseneglectradia6on&surfacefluxesapriori•  Thekeymechanisms(notjustthedispersionrela6onorotherpredicted

MJOfeatures)oftheseidealizedmodelsshouldbediagnosableincomprehensivemodels(andobserva6ons)

Finalthoughts•  Amodeinwhichmoisture+convec6onanomalieslivealong6me,

maintainedbymoisture-convec6onfeedbackandlongwaveradia6vefeedback,seemsquitegenericinmodelswithenoughmoisturesensi6vity.

•  Whenitisneartheequator,largeinhorizontalscale,andgoesslowlyeastward,asittendstodoinourpresentclimate,wecallittheMJO.

•  Eastwardpropaga6on(andotherMJOspecifics)appeardependentonthemeanclimate.

•  Simplemodelscandomanythingsformanyreasons.Wenowhavethecapabilitytousecomprehensivemodelstotestmechanisms.

Roundy(2012)showsthattheMJO-Kelvinsepara6oninspectraldiagramsresultsfrommixingofeventswithdifferentproper6esineasterly&westerlybasestates.Nosepara6oninmeanwesterlies.Con6nuousMJO-Kelvintransi6on(2012b)?

Infactwecanseethetransi6oninpressure-windrela6oninmanyindividualeventsastheymoveeastfromIndiantoPacificOcean(Sobel&Kim2012).

Surfacepressure(contours)Zonalwindat850hPa(arrows)OLR(colors)

In other models, radiative feedbacks are important while surface turbulent flux feedbacks are not – but both are moist static energy sources

radiative contribution to maintenance of MSE anomaly

Andersen and Kuang 2011