Three types of monsoons?

Threetypesofmonsoons?

• Whatisamonsoon?

• Threetypesofmonsoons

• Examplesofmonsoontypes

• AcloserlookattheIndianMonsson

• Summary

DavidSBattisti

UniversityofWashington


• Whatisamonsoon?

– Seasonalchangeinwinds

– Seasonalchangeinprecipitation

DavidSBattisti

UniversityofWashington

Seasonalchangesinwind

Majorcomponentofwindmustreverse;annualave windspeedmustaverage>4m/s

Austral-Asian-EAfrica

N-SAfrica

Seasonalchangesinprecipitation

Austral-Asian

SouthAmerica

N-SAfrica

SEUS&E.Africacouldbeincluded(wind),ascouldSWUS

Seasonalchangesinprecipitation

Austral-Asian

N- SAfrica

AtlanticITCZs

WesternC.America

Placeswhere2/3ofannualprecipitationisaccumulatedin≤4months


• Whatisamonsoon?




– Classicmonsoon:land-oceaninteraction

– MarineMonsoon:atmosphere-oceaninteraction

– ITCZs

Classic monsoon: land-ocean interaction

Ruddiman 2007

SummerMonsoon• Landheatsfasterthan

ocean

• Drawsairwithmoisture

fromoceantoland

• Condensationalheating

drivescirculation(positive

feedback)

WinterMonsoon• Oppositehappens

Monsoonsasatmosphere-oceaninteraction

• Aquaplanet:atmospherecoupledtomotionlessoceanw/no

land

Precipitation

Observed

(IndianSector)

1mocean

100mocean

Zonalwindat15N

DayofYear

Observed;100m and1m ocean

West’ly

East’ly

Bordoni andSchneider2008

• Dynamics~followPrivé &

Plumb2005a,b,Bordoni and

Schneider2008

• Abrupttransitions

ITCZs

• 2Dview:symmetricinstabilitydueto

hemispherically asymmetricPBL

pressuregradients

(Stevens1983,Emanuel1995)

• 3Dview:precipitationmainlyatime

averageofwestwardpropagating

easterlywaves(ATL)andmixedRossby-

gravitywaves(PAC)

(Privé andPlumb2007;Holtonetal1971;Wallace

andHobbs1977;Liebmann andHendon1990)

GlobalIRMovie

~- 7m/s

Monsoonvs.MarineITCZ

Monsoon Marine ITCZWhere found Off-equatorial(>15º lat) Within~15º ofequator

Positionsetby Location ofmaxPBLMSE

2D:Symmetricinstability

(�2

θe)

3D: synopticwaves

Precip intensityprimarily

setby

maxPBLMSE max PBLMSE&eddy

momentumtransports(aloft)

StrengthofHadley

circulationcontrolledby

diabatic heating(condensation;

radiativecoolingequatorwardof

precip maximum)&byeddy

momentumtransports(aloft)

eddymomentumtransports

(aloft)

Central&Eastern

PacificandAtlantic

Examples:Indiansummermonsoon

Anexplanationforabruptmonsoononsets?

Ittakesalargeoff-equatorialheatingtoconvertanITCZtoamonsoon(ie,toovercomethestabilizationofthe(symmetric)meanstatebysynopticeddies)


• Whatisamonsoon?





– MarineMonsoon:atmosphere-oceaninteraction

– ITCZs


– Classicland-ocean:S.Africanmonsoon,S.AmericanMonsoon,

EasternNorthAmericanmonsoon

– Marinemonsoon(withsomelandassist):Australian,Indian

– ITCZ:Pacific,Atlantic,IndianOceaninNHWinter(?)

NearsurfaceθeandPrecipitationmaximum

Jan

July

MaxPrecip

Nearsurfaceθe

*MSEandΘearefunctionallyequivalent

?

?

Jan

July

Landmonsoon MarinemonsoonITCZOther

NearsurfaceθeandPrecipitationmaximum

AB

Meiyu:orographic&diabatic (Chiangetal,inrev) SEUS:Africa&orographic


• Whatisamonsoon?





– Atmosphere-oceaninteraction

– ITCZs


– Classicland-ocean:S.Africanmonsoon,S.American

Monsoon,EasternNorthAmericanmonsoon


• AcloserlookattheIndianMonsoon

NearsurfaceMoistStateEnergy

May June

JulyAug

I.Fung,pers.Comm.Data:MERRA

Precessional Forcing

207kyr(Low)

218kyr(High)

• ExperimentswithECHAM4.6AGCM

– T42horizontalresolution(2.8°), coupledtoaslaboceanwithSST

adjustedto~moderndayvalueswhenforcedbymodernday

insolation,greenhousegasesandboundaryconditions

– Isotopemoduleincluded

• TwocoreExperiments

– 218Kinsolation(High)

– 207Kinsolation(Low)

– Moderndaygeometry,orography&greenhousegasconcentration

HighminusLowNHsummerinsolation

Thechangeinforcing

W/m

2

Notsurprisingly,thesimulatedNH

climateinthe“LowForcing”at207kyr

BPissimilartothemodernclimate

For“high”summerinsolation• HeavyrainfallfromtheSaheltoArabiatoNorthernIndia

• 50%lessoverSEAsia

• MoreoverChina(~40%)

• GreenSahara?

• CollapseofAtlanticITCZ/Trades

Simulatedchangesinδ18Oofprecipitationshowaremarkableagreewithspeleothemrecordsthroughouttheglobaltropics

ChangeinPrecipitationand850hPa Winds

JJA(218minus207kyr)

mm/day

Battisti etal2014

TopoftheAtmosphereNetRadiation

207kyr218kyr

Observed2001-2012

• Withsufficientlyhighsummer

insolation,thereisa

fundamentaltransitionto

entirelydifferentclimate

state.

Battisti etal2014

• Not duetosinkingbranchoftheHadleyCell(maxinDJF)

• Today– inlowphaseofprecessionalcycle – monsoonprecipitationis

maximuminthenorthernBayofBengal(notoverland)

• CondensationalheatingintheBayofBengalforcesawestwardRossby

waveandcoldairadvectionovertheeasternMedandCentralAsia thatis

balancedbysubsidence

WhyistheEasternMediterraneanadeserttoday?

Rodwell andHoskins1996

JJAObservedOmega(477hPA)

(1983-1988)

PEModelOmegaResponsetoHeating

H

(c.i. 0.014Pa/s)

RegionalHeatingduringHighPrecession

• Howdoyoubreakthedesertificationmechanism?

– Hypothesis:Moreintensesummerinsolationheatsland

(fast)enoughtocreateasufficientlylargeland-ocean

temperaturecontrasttoshiftthemaximuminMSE– and

henceconvection– tobeoverland.Aclassicmonsoon.

Battisti etal2014

207kbp

218kbp

218minus207kbp

Convectioniscentered

overmaximumΘeà over

oceansinlowNHsummer

insolation(e.g.,today)

Equivalentpotentialtemperature,Θe

*

Convectioniscentered

overlandinhigh

insolation(atextbook

monsoon)

*MSEandΘearefunctionallyequivalentBattisti etal2014

Mid-Holocene(PMIP3)minustoday

Zonalmeanorzonallyasymmetric?

Total

[Δpcent

] =+0.3º

Zonally

Asymmetric

Atwoodetalinprep


• Whatisamonsoon?





– Atmosphere-oceaninteraction

– ITCZs


– Classicland-ocean:S.Africanmonsoon,S.American

Monsoon,EasternNorthAmericanmonsoon


• AcloserlookattheIndianMonsoon

• TheeastAsian(Meiyu):afauxmonsoon

– SeeMolnaretal2009;Chiangetal(inreview)


• Withstrongenoughasymmetrichemisphericheating,a

monsoon….

– Duemainlytoocean-atmosphere(e.g.,Indianmonsoontoday)

orclassicland-atmosphere(e.g.,S.Africa,S.America)interaction

– Thermodynamics(maxMSE)important

• Withmodestasymmetrichemisphericheating,anITCZ

– Duetoflowinstabilitythatshedsequatorialwaves(e.g.,easterly

wavesinAtlanticandfareasternPacific)

– DuetoconvectionorganizedbymixedRossby gravitywaves(e.g.,

centralPacific);IndianOceaninDJF(?)

– Thermodynamics(maxMSE)anddynamics(symmetricinstability,

PBLpressuregradients,eddymomentumfluxesaloft)important

Three types of monsoons?

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