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Monsoonsh,ps://vimeo.com/106827999

MonsoonsAffectmorethan3billionpeopleCri>calforagriculturalplanning,floodanddroughtmi>ga>on

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Monsoons•  Mechanisms•  Howaremonsoonsdefined?•  Regionalmonsoondynamics:

1.  SouthAsian/Indian2.  EastAsian3.  WesternNorthPacific4.  Asian-Australian5.  American6.  WestAfrican7.  GLOBALmonsoons?

•  ENSO–Monsoon•  Climatemodeling/future

monsoon?

“Monsoons”•  derivedfromtheArabicwordforseason•  seasonalreversalinthedirec>onofthewind•  monsoonalregionsdefinedbyasignificantchangeinthewinddirec>onbetweenwinter

andsummer•  extendsoveralargepartofthetropics

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Land heats and cools rapidly Water heats and cools slowly

HeatCapacity=thenumberofjoulesofenergyrequiredtoheatonegramofasubstancebyonedegreeKelvin

(orthecapacityofamaterialtostoreheat)

Lowheatcapacity(Granite=0.79J/g)

Highheatcapacity(H20=4.184J/g)

This is why the ocean says warm into fall even though the weather is getting cool

Local/regional geographic scale:

sea breezes mountain-valley winds

AND MONSOONS!

Warm air rises

Onshore wind

DAY

Sea Breezes

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Sea Breezes

Warm air rises

Onshore wind

DAY

Offshore wind

NIGHT

Con>nentalityTheinfluenceoflandmassanddistancefromtheoceanresultsinthediurnal(fromnighttoday)rangeoftemperatures,aswellasthedifferenceintemperaturebetweensummerandwinter.

SeasonalTemperatureRANGEgreatestonland,(eventhoughmostoftheHEATisintheoceans)

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Monsoon circulation

Warm air rises

Onshore wind

Warm/wet (monsoon) season

Offshore wind

Cool season

DAY

NIGHT

Role of topography?

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Role of topography? NCEP(yearly-climatology) Topography/bathymetry

Role of topography? Topography/bathymetryNCEP(JJA-DJFavgtemp)

1.875°x1.875°

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Role of topography? Topography/bathymetryNCEP(JJA-DJFavgtemp)

0.5°x0.5°

Monsoon circulation

Thermal/SLPgradient +Coriolisdeflec<on

Non-rota>ngearth: Rota>ngearth:

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Role of topography? Topography/bathymetryNCEP(JJavgprecipita>on)

0.5°x0.5°

Monsoon circulation

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Monsoons•  Mechanisms•  Howaremonsoonsdefined?•  Regionalmonsoondynamics:

1.  SouthAsian/Indian2.  EastAsian3.  WesternNorthPacific4.  Asian-Australian5.  American6.  WestAfrican7.  GLOBALmonsoons?

•  ENSO–Monsoon•  Climatemodeling/future

monsoon?

Monsoon“regions”?

•  Onmostbasiclevel:monsoonalregionsdefinedbyasignificantchangeinthewinddirec<onbetweenwinterandsummer

•  Morecomplexspa>alpa,erns/dynamics

àDividedintomonsoonsub-regionsbysource,<mingandloca<onofprecipita>on

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Wangetal.2003

1.  IndianSummerMonsoon/

SouthAsianmonsoon2.  EastAsianmonsoon

a.  EastAsianb.  WesternNorth

Pacificmonsoon

Note:pentad1(January1-5)topentad73(December27-31).

EASM

WNPMISM

E.g.,Asianmonsoon“system”

AsianMonsoonSystem

•  earliestonset:southernBayofBengalinlateApril

•  overtheIndo-ChinesepeninsulaandsouthIndiainearlyMay

•  progressesnorthandnorthwestwardintothecon>nentreachingJapanbylateJunetoJuly

•  BytheendofthepeakseasonoverJapan,themonsoonisalreadyretrea>ngoverIndia

WangandLinHo2002

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Wangetal.2003

•  Strongestandbestknownoftheregionalmonsoons•  CarriesmoistairfromtheIndianOceantoSouthAsia•  Accountsforapproximately80%oftherainfallinIndia•  Drivenbystronghea>ngovertheTibetanPlateau,whichreversesthe

low-levelpressuregradient

IndianSummer/SouthAsian

Wangetal.2003

1.  CarriesmoistairfromSouthAsiatoEastAsia2.  Affectsapproximatelyone-thirdofglobalpopula>on(China,Korea,Japan)3.  Drivenbytemperaturedifferencesbetween(warm)Asiaandthe(cool)Pacific

Ocean&N-Sgradientsbetween(cool)Australiaand(warm)westernNorthPacific

EastAsianMonsoon

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Wangetal.2003

1.  AnoceaniccomponentoftheAsianmonsoonsystem2.  ImportantfortropicalcyclonetracksinthePacific(tracks

determinedbyloca>onofmonsoontrough–convergenceoflow-levelwesterlyandeasterlytradewindswinds)

WesternNorthPacific

Regionaliza>on

ConroyandOverpeck2011

•  empiricalorthogonalfunc>on(EOF)-basedregionaliza>onofgriddedprecipita>onvalue

•  Arobustwayofdividingalargeareaintocoherentsub-regionswithsimilarvariability

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ConroyandOverpeck2011

Asia-AustralianMonsoonAssociatedwiththeseasonalmigra>onofhea>ngbetweenthenorthernandsouthernhemispheres

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Borealwintervssummermonsoons

Fig.3.43.DifferencesofTRMMPRrainfallandQuikSCATwindsbetweenborealwinterandborealsummer(DJFminusJJA).Warmcolorsaretheborealsummermonsoonregimeandcoolcolorsaretheborealwintermonsoonregime.(Changetal.2005)

Ocean-atmospherefeedbacks•  theoceanmovesenergyfromsummerhemispheretowinterhemisphere,whilethe

atmospheremovesenergyfromwinterhemispheretosummerhemisphere•  monsoonseasonalcyclemodulatedbynega<veatmosphere–oceanfeedback

associatedwithEkmantransport

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WestAfricanMonsoon

IntertropicalFront(ITF)orIntertropicaldiscon>nuity(ITD):boundarybetweenthemoistsouthwesterlymonsoonflowandthehot,drynortheasterlywindfromtheSahara.

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WestAfricanMonsoon

AEJ:AfricanEasterlyJetSAL:SaharaAirLayer

SeasonalityofWestAfricanMonsoon

1.  BeginsalongtheGuineacoastinearlyMay

2.  lateJuneintoearlyJuly–themaximuminrainfallshimstotheSahel

3.  BeginsitssouthernretreatinlateAugustandthecoastalrainyseasonendsinearlyNovember

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AmericanMonsoons

**donotmeettheclassicalcriteriaformonsoonasthereisnoopposi>onalwindshimduringthewinter(butthereAREwindanomaliesrela>vetoannualmean)

Monsoons•  Mechanisms•  Howaremonsoonsdefined?•  Regionalmonsoondynamics:

1.  SouthAsian/Indian2.  EastAsian3.  WesternNorthPacific4.  Asian-Australian5.  American6.  WestAfrican7.   GLOBALmonsoons?

•  ENSO–Monsoon•  Climatemodeling/future

monsoon?

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TheGlobalMonsoon1.Monsoonclimatescharacterizedbyseasonalreversalofwinds.Thisreversalis

global,notjustregional2.Regionalmonsoonsarecoordinatedprimarilybytheannualcycleofsolarhea>ng

“Sols>ceMode”

“EquinoxMode”

WangandDing(2008)

Explain84%ofprecipita<onvariance!!

Globalmonsoonregions

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Monsoons•  Mechanisms•  Howaremonsoonsdefined?•  Regionalmonsoondynamics:

1.  SouthAsian/Indian2.  EastAsian3.  WesternNorthPacific4.  Asian-Australian5.  American6.  WestAfrican7.  GLOBALmonsoons?

•  ENSO–Monsoon•  Climatemodeling/future

monsoon?

Temporalvariability

biweekly,intraseasonal(30-60days),interannual(e.g.,ENSO),interdecadal(andlonger!)

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Monsoons•  Mechanisms•  Howaremonsoonsdefined?•  Regionalmonsoondynamics:

1.  SouthAsian/Indian2.  EastAsian3.  WesternNorthPacific4.  Asian-Australian5.  American6.  WestAfrican7.  GLOBALmonsoons?

•  ENSO–Monsoon•  Climatemodeling/future

monsoon?

Simula>ngtheAsianMonsoon

Sperberetal.2013

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Sperberetal.2013

Simula>ngtheAsianMonsoon

Whatarewelookingat?

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Simula>ngtheAsianMonsoon

Sperberetal.2013

Simula>ngtheAsianMonsoon

Sperberetal.2013

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Simula>ngtheglobalmonsoons

LeeandWang2014

Problemareas:•  EasternIndianOcean•  BayofBengal•  equatorialwesternPacific•  tropicalBrazil•  Mari>meCon>nent•  Philippines•  high-eleva>onareaslikethe

AndesandtheTibetanPlateau

Simula>ngtheglobalmonsoons

Hsuetal.2013

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Summary

•  Seasonalvaria>onsinwindsandprecipita>onduetoseasonalvaria>onsinhea>ngandT,pgradients

•  Canbedefinedeitherregionallyorglobally•  Monsoonsarisefromcoupledinterac>onsbetweentheatmosphereandocean

•  Coupledmodelsareomenabletocapturethebasicsofmonsoondynamics,butthemul>-modelensemblemeangenerallyperforms‘be,er’thananyindividualmodels

•  Modelrepresenta>onsofthemonsoonhaveimprovedoverthepastdecade