1

The2010PakistanFloodandtheRussiaHeatWave:1

TeleconnectionofExtremes2

3

WilliamK.M.Lau1,andK.M.Kim24

1LaboratoryforAtmospheres,NASAGoddardSpaceFlightCenter,GreenbeltMD,207715

2GoddardEarthSciencesandTechnologyCenter,U.ofMarylandBaltimoreCounty,6

BaltimoreMaryland,212287

8

9

10

SubmittedtoNatureGeoscience11

October201012

13

14

15

16

17

18

19

20

21

Correspondingauthor:WilliamK.M.Lau,LaboratoryforAtmospheres,NASAGoddardSpace22FlightCenter,Greenbelt,MD20771.Email:William.K.Lau@nasa.gov.Tel:301‐614‐633223

https://ntrs.nasa.gov/search.jsp?R=20110015271 2020-06-15T22:34:31+00:00Z

2

2425ThePakistanfloodandtheRussiaheatwave/wildfiresofthesummerof2010weretwoof26

themostextremeeventsinthehistoriesofthetwocountriesoccurringataboutthesame27

time.Toacasualobserver,thetimingmayjustbearandomcoincidenceofnature,because28

thetwoeventswereseparatedbylongdistances,andrepresentedoppositeforcesofnature,29

i.e.,floodvs.drought,andwatervs.fire.Here,wepresentevidencesshowingthatthetwo30

eventswereindeedphysicallyconnected.Ourresultsshowthattherootcauseofthe201031

Russiaheatwave/wildfireswasanatmosphericblockingeventinhighlatitudeswhich,32

throughtheexcitationofalarge‐scaleatmosphericRossbywave,wasinstrumentalin33

affectingtherainfallevolutionoftheSouthAsiansummermonsoon,includingtriggeringthe34

developmentofamid‐troposphericcyclonethatwasresponsibleforthetorrentialrainover35

Pakistan.36

DuringJulyandAugust,2010Pakistansufferedtheworstfloodin100years.Over150037

peopleand1millionhomesperishedand20millionwererenderedhomeless,ordisplacedfrom38

theirhomesbythefloodwater.Thetotaleconomiclostfrompropertyandcropdamage,lossof39

businesseswasinthetensofbillions.Ataboutthesametime,Russiawasstrickenbyarecord40

heatwave,withtemperatureinMoscowrisingabove40oCforaprolongedperiodinJulyand41

August2010,andtheentirewesternRussiaregion(includingwesternSiberia)wassuffering42

fromaprolongeddrought.Intenseandextensivewildfiresragedovermorethan5000km2of43

forestedarea.TheRussiaheatwave,droughtandforestfiresmighthavetakenover5,000lives44

andcosttheeconomylossmorethan15billion.Byanymeasure,thePakistanfloodandthe45

Russianheatwave/wildfiresweresuperextremeevents,bothfromtheperspectivesof46

3

meteorologyandsocietyimpacts.Already,themedia,punditsandsomescientistswere47

wonderingaloudwhetherthePakistanfloodandRussiaheatwaveandmanyoftheextreme48

weathereventsexperiencedaroundtheworldin2010weretheresultsofglobalwarming.49

However,whilethe2010extremeeventswilllikelyaddtothestatisticsofextremeevents50

consistentwithprojectionsofglobalwarming,noattributioncanbemadebasedonasingle51

event.Frompastexperience,anextremeeventisseldomtheresultofasingularcause,but52

rathertheendproductofpositivefeedbackfromanalignmentofmultiplefactors,onboth53

largeandsmallscales.Inthisstudy,wefocusonsuchanalignmentoffactorsleadingtothe54

RussianheatwaveandthePakistanflood.Ourpaperdiffersfrompreviousstudiesofextremes55

inthatweidentifynotonlythecausesofeachevent,butalsothepossiblephysicalconnection56

betweenthem.MethodologyanddatausedforthisstudyaredescribedintheMethodSection57

attheendofthemanuscript.58

ThePakistanflood59

TuckedawayinthenorthwesterncorneroftheIndiansubcontinent,andboundedonthe60

northeastbythehighmountainsofKarakoram,onthewestbythearidregionsanddesertsof61

Afghanistan,SyriaandIran,andonthesouthbytheArabianSea,Pakistanisarelativedry62

regioncomparedtomonsoonIndia.Evenduringthepeakofthemonsoonseason,July‐August,63

theaveragetotalrainfalloverthewettestpartofthecountry(northernPakistan)isofthe64

orderof160‐180mm–ascantyamountcomparedtoraintotalof1600‐2000mmforthesame65

monthsoverthewettestmonsoonregionsofnortheasternIndiaandtheBayofBengal.Based66

ontheNOAAClimatePredictionCenterrainfallstationdata1,duringthe2weekperiod,July25‐67

August82010,torrentialrainofapproximately500mmfellinabout10daysinthenorthern68

4

PakistanSwatValley,exceedingmorethan70%ofthetotalannualmeanrainfalloverthesame69

region.AsshowninrainfallanomalyfieldinFig.1a,theheavyrainovernorthernPakistanwas70

notisolatedgeographically,butappearedtobeconnectedtoexcessivemonsoonrainfallover71

northernandnortheasternIndiaalongthefoothillsoftheHimalaya,andcentraland72

northeasternArabianSea.Reducedrainfallwasfoundovermostpartofcentralandsouthern73

India,andthesouthernBayofBengal,andalongthecoastofMyanmar.Thewidespread74

rainfallanomalysuggestedthatthePakistanheavyrainwasapartofamajorshiftintheentire75

monsoonrainfallpattern,whichnormallyhastheheaviestrainfalloverBangladeshandBayof76

BengalinAugust.77

TheRussianheatwave78

Russiaisavastcountry,coveringnortheasternEuropeandSiberia,stretchingfromthe79

ArcticCirclesouthwardtoUkraineandKazakhstan,southeastwardtoMongoliaand80

northeasternChina.Thedominantvegetationistundraintheextremenorthernregions81

aroundtheArcticCircle,tiaga(borealforest)innorthernandcentralSiberia,andtemperate82

forestandsteppegrasslandinthesouth.InwesternRussian,climatologicallyJuly‐Augustisthe83

rainyseason,withmeanmonthlyrainfallof75‐85mm.However,atmosphericblocking84

conditionwhichslowsorpreventsthepassageofrainstorms,maydevelopandlastforweeks,85

leadingtodryconditionsandwildforestfires2‐4.DuringJuly‐August2010,arecordheatwave86

anddroughtdevelopedandprevailedoverwesternRussia.TemperatureinMoscowinAugust87

soaredtoarecorddailyhighof40oC(about10degreeabovetheclimatologicalmean).Priorto88

2010,thehighesttemperaturerecordinMoscowwassetat36.8oCinAugust,1920.During89

thetwo‐weekperiodcoincidingwiththePakistanflood,theheatwaveexpandedtocover90

5

westernRussia,westernSiberia,andEasternEurope(Fig.1b).Theextremehotanddryweather91

spurredferociousforestfiresoverthevasttaigaregionsofwesternRussiaandSiberia,and92

Ukraine,asevidenceinthedensityofthesatellitefirecounts.Alsonoteworthyisthat93

temperaturecontrast,withmuchcoolertemperatureprevailedintheadjacentregionstothe94

heatwave,overcentralandeasternSiberia,andwesternEurope.95

Teleconnection96

Figure2showsthetimeseriesofrainfallfromTRMMovernorthernPakistan[32‐35N,70‐97

73E]andsurfacetemperaturefromAIRSandfirecountfromMODISoverwesternRussia[45‐98

65N,30‐60E].VeryheavyrainfellovernorthernPakistanintermittentlyinclustersof3‐4days99

duringthetwo‐weekperiodfromJuly25‐August10,followingaperiodofsteadilyincreasing100

rainfallbeginninginmid‐June.SurfacetemperatureoverwesternRussiaroserapidlyaround101

June20;remainedatahighlevelforthenext10daysorso,andsoaredfromaroundJuly18to102

reachaveryhigh‐level,withmaximumarea‐averagedtemperatureexceedingnearly9oCabove103

theseasonalmean,duringa2‐weekperiodcontemporaneouswiththeheavyrainover104

Pakistan.TheRussiaforestfireactivity,asevidentfromtheMODISfirecount,wasnear105

normalorslightlyelevatedaboutthesametimeastheheatwaveemerged,butdramatically106

intensifiedaroundJuly25andremainedataveryhighleveltillAugust10,anddroppedoff107

rapidly,asacoldfrontpassedthroughandbroughtraintothearea.Thecorrelationbetween108

surfacetemperatureandfirecountis0.70,andbetweenfirecount,surfacetemperatureand109

Pakistanrainfallis0.50and0.37,respectively.Allcorrelationsarestatisticallysignificantatthe110

95%level.Thehighcorrelationbetweenheatwaveandforestfireisexpected,becausethe111

abnormallyhotanddryairassociatedwiththeheatwaveisconducivetoforestfire.However,112

6

thesignificantcorrelationsofRussiansurfacetemperatureandforestfirecountwithPakistan113

rainfallhintatamoreprofoundteleconnectionbetweentheextratropicsandtropics.Inthe114

following,weexplorethephysicalbasisforsuchateleconnection.Tofacilitatethediscussion115

oftheevolutionoftheteleconnectionpattern,wecarryoutseparatebutidenticalanalysesfor116

the15‐dayperiod(PeriodII:July25‐August8)forthePakistanheavyrain,andforthe15‐day117

antecedentperiod(PeriodI:June10‐24).118

PeriodI:July10‐July24119

ThisperiodcharacterizedthedevelopmentoftheRussianheatwaveandlarge‐scale120

circulationandmoistureconditionsleadingto,butbeforethePakistanheavyrain.A121

pronouncedblockinghigh,with500hPageopotentialheightanomalyexceeding120‐140m122

wasfoundovernorthernEuropeandwesternRussia(Fig.3a).Theblockinghighwascoupledto123

adeeptroughtoitswest,andanotherhighpressurefeaturefurthereastoverwesternSiberia.124

Thetroughdisplayedapronouncedsouthwest‐to‐northeasttilt,penetratingintothesubtropics125

withacut‐offlowtothenorthofPakistan.ThispatternresembledthatofadispersiveRossby126

wave‐train6emanatingfromtheblockinghighoverwesternRussia,andpropagatingtowards127

theeastandsoutheastdirections.Aswillbeshownlater,thepenetratingtroughandcut‐off128

low(markedLinFig.3a)wereassociatedsubsequentlywiththeformationofamid‐129

tropopshericcyclone(MTC)whichwasresponsiblefortheheavyrainoverPakistan.AnMTCis130

ahybridmidlatitude‐tropical,rainbearingweathersystemcommonlyfoundintheSouthAsian131

monsoonregion7‐8.132

Coupledtothe500hPablockinghighwasalowertropospherelarge‐scaleanticyclone133

(Fig3b).Thesoutherlyflowonthewestsideoftheanticyclone,broughtwarmerandmoister134

7

(rising)airtocentralandnorthernEurope,whilethenortherlyflowontheeasternside135

broughtwidespreadcooler(sinking)anddrierairoverwesternSiberiatoregionsfurthersouth.136

[SeeFig.S1inSupplementaryMaterialforadescriptionofthe500hPaverticalmotionpattern].137

OverthemountainousregionofAfghanistanandPakistan,thelowlevelflowwasnotwell138

organized.However,overthelargerSouthAsianmonsoonregion,twodistinctbranchesof139

anomalouslow‐levelflowcouldbeidentified.Astronglow‐leveleasterlyflowfromtheBayof140

BengalwasfoundovernorthernIndia.Thisflowopposedtheclimatologicallowlevelwesterly141

monsoonflow,andimpliedananomaloustransportofmoisturefromtheBayofBengalto142

northwesternIndia/northernPakistanandthenorthernArabianSea.Additionally,an143

anomaloussoutherlylow‐levelflowwasfoundovernorthernArabianSea.Ouranalysis(figure144

omitted)showedthatthenorthernArabianSeawaswarmerthannormalatthistime.The145

warmerArabianSeacouldincreaseevaporation,allowingmoremoisturetransportbythe146

anomaloussoutherliesintotheGulfofOmanandsoutherncoastofPakistan(Fig.3b).147

PeriodII:July25–Aug7148

Duringthisperiod,theheatwavesoaredandtheRussianwildfiresgrewinareacoverage149

andintensity.At500hPa,theblockinghighshiftedabout20oeastwardinlongitude,andgrew150

toaveryimpressivesize,withanomalyatthecenterexceeding180m(Fig.3c).Examinationof151

thedailyvariabilityofthe500hPageopotentialheightrevealedthatduringthefirstweekof152

thisperiod,thesloweastwardmovementoftheblockinghighcoupledwiththerapidwestward153

retrogressionofthepenetratingtroughintheRossbywaveresultedinaseparationofthecut‐154

offlowfromthemaintrough.Anexplosivecyclogenesisofthelowintoafull‐blownMTCwest155

ofnorthernPakistan(markedC1inFig.3c)ensued.Thestrongmid‐troposphericascenteastof156

8

the500hPavortex‐anevidenceofthebaroclinicstructureoftheMTC,wasthereasonforthe157

heavyrainovernorthernPakistan[SeeFig.S1binSupplementaryMaterial].NoticethatC1was158

onlyapartofthelarge‐scaleanomalouscirculationpatternoftheentireSouthAsianmonsoon159

system,whichincludedthedevelopmentofasecondaryMTC(markedC2inFig.3c)over160

southernPakistanandnortheasternArabiaSea,andananomalousanticyclonicoverwestern161

China,northeastoftheTibetanPlateau.162

Inthelowertroposphere,contemporaneouswiththemid‐troposphericdevelopment,the163

lowlevelanticycloneovernorthernEuropeandRussiashiftedeastwardtowesternSiberia(Fig.164

3d).Strongsoutherlyflowonthewestoftheanticycloneadvectedmorewarmandmoistair165

tonorthernEuropeandtheArctic.Onthesoutheasternsideoftheanticyclone,thelowlevel166

northeasterly,andnortherlyflowbroughtatongueofdryandcold(sinking)airfromSiberiato167

Iran,andeasternPakistan,settingthestageforaconfrontationwiththewarm,moist(rising)168

airfromthenorthArabianSeatoPakistan,eventuallyleadingtotheMTCcyclogenesis.169

Computationsofthewinddivergence(figuresomitted)indicatedthattheMTCswere170

associatedwithstrongupperlevelwinddivergenceeastofthemid‐troposphericlowcenter.171

Thecombinationofstrongmid‐troposphereascentandupperleveldivergenceassociatedwith172

theMTCswouldactlikeapumpdrawingthelowlevelsoutheasterlyflowovernorthernIndia,173

alongtheIndian/NepalHimalayas,andtransportingadditionalmoisturefromtheBayofBengal174

toPakistan(Fig.3d).ThemoistsoutheasterlyflowalongtheHimalayasfoothillscouldleadto175

orographicallyforcedheavyrainalongthefoothillsregion.Thenorthandnorthwesterlyflow176

fromananomalousanticycloneoverthesoutherntipoftheIndiasubcontinentcouldalsohave177

contributedadditionallow‐levelmoisturefromtheArabianSea,fuelingthedevelopmentofthe178

9

secondaryMTC(C2inFig.3c).Overall,thelarge‐scalecirculation,theMTCs,andassociated179

large‐scaleverticalmotionandupperwinddivergencearedynamicallyconsistentwiththe180

rainfallanomalyoverPakistan,theIndian/NepalHimalayafoothills,andthenortheastern181

ArabianSeaasshowninFig.1a.182

Jetstreammodulation183

DuringPeriod‐Iand–II,thestrengthofatmosphereblockingandtheaccompanying184

Rossbywaveweresuchthattheydistortedtheflowofthepowerfuljetstreamintheupper185

troposphere,whichinturnalteredthesteeringofstormtracks.Climatologically,theboreal186

subtropicaljetstreamcomprisesofabeltoffastmovingwesterlyintheuppertroposphere187

aroundtheglobal,centeredaround35‐40oN,withcompensatingeasterliesoverthetropics.188

Stormswithmid‐latitudeoriginsaregenerallyconfinedtothevicinityjustsouthofthe189

jetstreammaximum,andnorthofthezero‐wind(zonal)line.DuringPeriod‐I(figureomitted),190

associatedwiththeblockingdevelopment,therewasastrengtheningoftheclimatological191

subtropicaljetstream,andanew,weakerpolarjetstreamemergedoverScandinavia.During192

Period‐II,theRossbywaveinfluenceonthejetstreamwasverypronounced.Here,thesplit193

polarjetstreamwasdisplacedeastwardfromPeriod‐IandfoundovernorthwesternSiberiaand194

theArcticregionofEurasia(Fig.4a).Thesubtropicalbranch,wheretheclimatologicalwesterly195

beltwasnormallylocated(linecontoursinFig.4a),showedahighlywavypatternspanning196

southernEurope,theMediterranean/NorthAfrica,theCaspianSea,Syria,northwesternChina197

andMongolia,withthesouthernmostextentofthemainjetstreamhangingnorthwestof198

Pakistan(Fig.4a).ThesignatureoftheRossbywavetrainwasevenmorepronouncedinthe200199

hPameridionalwindcomponent(Fig.4b),showinganortherncomponentaroundtheArctic200

10

circleofEurasiaandasubtropicalcomponentfromtheMediterraneantothewesternPacific.201

Themagnitudeofthesubtropicalbranchwasmuchstrongerthanclimatology(linecontoursin202

Fig.4b),andthephaseoftheRossbywavewasalmostinquadrature,withawestwardphase203

shiftrelativetothatfromclimatology.Theanomaloussoutherliesandthenortherliesat35‐40o204

NwestofPakistan,indicatedcycloniccirculation,consistentwiththeMTCformedoverthe205

region.Giventheplanetaryscaleofthejetstreamanomalies,itisconceivablethatthese206

anomaliesareconnectedtoothermajorextremeweathereventsfromEuropetoAsia,inboth207

thetropicsandextratropicsduringthesummerof2010.208

Conclusionanddiscussion209

Wehavepresentedpreliminaryevidencessuggestingthatthetworecordsettingextreme210

eventsinthesummerof2010,i.e.,theRussiaheatwave/wildfiresandthePakistanfloodare211

meteorologicallyconnected.Theprolongedatmosphericblockingsituationassociatedwiththe212

extremeheatwave/droughtandwildfiresoverwesternRussiaisinstrumentalinforcinga213

large‐scaleatmosphericRossbywavetrainconnectingwesternRussiatotheSouthAsian214

monsoonregion.AdeeptroughintheRossbywavepenetratingfromthemid‐latitudestothe215

tropicsmayhavetriggeredtheexplosivecyclogenesisofasubtropicalMTC,spawningthe216

extremerainfalleventsoverPakistan,theIndian/NepalHimalayas,andnortheasternArabian217

Sea.TheMTCsareknownrainactivatorsintheSouthAsianmonsoonregion,withboth218

midlatitude(baroclinic)andmonsoonal(condensationalheating)characteristics,including219

warmcorestructureabove600hPa,pronouncedcyclonicstructureinmid‐troposphere,and220

strongupperleveldivergence7,9‐10.FurtherstudiesofthecausesofthePakistanfloodshould221

revivetheattentiontotheMTCasanimportantheavyrain‐bearingmonsoonweathersystem.222

wlau � 10/6/10 9:37 PMDeleted: found

11

Thepresentresultsraiseimportantunansweredquestions.FortheSouthAsian223

monsoonregion,rainfallisgenerallyenhancedbyLaNina,i.e.,belownormalseasurface224

temperature(SST)intheeasterntropicalPacific,andabovenormalSSTinthewesternPacific225

andIndianOcean.Duringthesummerof2010,aweakLaNinaconditionwasbrewingoverthe226

centraleasternPacific.DidtheLaNinaconditionin2010,includingthewarmerArabianSea,227

furtheraddtothealignmentoffactors,favoringmorerainfalloverPakistan?Couldthe228

Pakistanfloodhaveoccurred,iftherewerenoRossbywaveforcing?OrwithRossbywave229

forcingbutnopre‐conditioningofthetropics,suchasLaNinaandwarmerArabianSea?For230

theRussiaheatwaveandwildfires,thekeyquestionis:whatcausedtheprolongedblocking231

situationthatledtotheunprecedentedseverityofthedroughtandwestRussianforestfires?232

Previousstudiesshowedthatsoilmoistureandlandsurfaceprocessesplayedavitalroleinthe233

blockingeventassociatedwithseveresummerheatwaves,suchasthatoccurredoverEurope234

in200311.Arethe2010and2003heatwavessimilarordifferentintermsofforcingand235

responses?Theexceptionallargeamountofaerosolsemittedfromthe2010Russiawildfires236

duringPeriod‐II(seeSupplementaryMaterialFig.S2)wouldcertainlyhaveaffectedthesurface237

andatmosphericenergybudgetoverthewestRussiaandadjacentregions.Didaerosolsfrom238

theforestfiresplayarole,viaradiativeheatingandfeedbackprocessesintheatmosphereand239

atthesurface,inamplifyingand/orsustainingtheatmosphericblocking?Ifso,thisraisesthe240

intriguingpossibilitythattheRussiawildfiresmayhavecontributedtothePakistanflood!241

Finally,isthisextraordinaryteleconnectionofextremesasignofachangingatmospheric242

generalcirculationassociatedwithglobalwarming,favoringmoreextratropical‐tropical243

12

interaction?Theseareimportantandurgentquestionsthatthescientificcommunitieshaveto244

provideanswers,thesoonerthebetter.245

Methods246

Forthisinvestigation,weusedacombinationofin‐situ,satelliteandreanalysisdatato247

carryoutcorrelativeanddiagnosticanalyses.Anomaliesweredefinedasthedeviationsfrom248

theclimatologyofeachdataset.Weusedthesatelliterainfall,firecount,andsurface249

temperaturetoexaminethespatialpatternsofthePakistanheavyrain,andtheRussianheat250

waveandwildfires,andestablishthetemporalcorrelationsamongthesevariables.Wethen251

definedtwo15‐dayperiodstoidentifythequasi‐stationaryfeaturesinthegeopotential,wind252

andmoistureteleconnectionpatterns,priorto,andduringtheRussianheatwaveandthe253

Pakistanflood.Weseekphysicalanddynamicalconsistencyamongtheseindependentdata254

withrespecttoevolvingcoherentspatialpatternsduringthetwoperiods.Forrainfall,weused255

dailygriddedraingaugedatafromNOAAClimatePredictionCenter(CPC)1,aswellasdaily256

rainfallproduct(3B42)on0.25x0.25degreelatitude‐longitudegridfromtheTropicalRainfall257

MeasuringMission(TRMM)5.SurfacetemperaturewasestimatedfromtheAdvancedInfra258

RedSounder(AIRS),firecountsandaerosolopticalthicknessfromtheModerateResolution259

ImagingSpectro‐radiometer(MODIS)onboardtheNASAAquaandTerrasatellites.AIRSisa260

highspectralresolutionspectrometeronboardAquasatellitewith2378bandsinthethermal261

infrared(3.7‐15.4μm)and4bandsinthevisible(0.4‐1.0μm).TheMODISFirePixelCount262

hasaspatialresolutionof1kmx1kmandisdeterminedbyasignificantincreaseinradianceat263

4umcomparedto11umradiance.ItisavailablefromtheTerraandAquasatellitestwicedaily,264

nightandday.LocationsoffirepixelfromallfourdailymeasurementsareusedinFig.1and265

13

Fig.2.Dataandmeta‐dataforAIRSandMODISfirecountwereobtainedfromattheGoddard266

EarthSciencesDataandInformationServiceCenter(http://disc.sci.gsfc.nasa.gov/AIRS)and267

MODISHotspots/ActiveFiresTextfileFTPsite(ftp://mapsftp.geog.umd.edu),respectively.For268

geopotentialheight,wind,andmoisture,weusedtheNationalCenterforEnvironmental269

Prediction(NCEP)reanalysisdataavailablefrom(http://ftp.cdc.noaa.gov).270

271

14

271

References272

1. Xie,Petal.,Agauge‐basedanalysisofdailyprecipitationoverEastAsia,J.273

Hydrometeorol.8607‐626(2007)274

2. Ogi,M.,Yamazaki,K.andTachibana,Y.Thesummernorthernannualmodeand275

abnormalsummerweatherin2003.Geophys.Res.Lett. 32,L04706,276

doi:10.1029/2004GL021528(2005)277

3. Groisman,P.Y.,Sherstyukov,B.G.,Razuvaev,V.N.etal.,Potentialforestfiredangerover278

NorthernEurasia:changesduringthe20thcentury.GlobalandPlanetaryChange56,371–279

386(2007)280

4. Girardin,M.P.etal.,Heterogeneous response of circumboreal wildfire risk to climate 281

change since the early 1900s. Global Change Biology 15, 2751–2769, doi: 10.1111/j.1365-282

2486.2009.01869.x (2009) 283

5. Huffman,G.J.etal.,TheTRMMMultisatellitePrecipitationAnalysis(TMPA):Quasi‐284

Global,Multiyear,Combined‐SensorPrecipitationEstimatesatFineScales.J.Hydrometeor.285

8,38–55(2007)286

6. Hoskins,B.J.andAmbrizzi,T.RossbyWavePropagationonaRealisticLongitudinally287

VaryingFlow.J.Atmos.Sci.50,1661‐1671(1993)288

7. Krishnamurti,T.N.andHwakins,R.S.Mid‐TroposphericCyclonesoftheSouthwest289

Monsoon.J.Appl.Meteor.9,442‐458(1970)290

8. Carr,F.H.Mid‐troposphericcyclonesofthesummermonsoon.PureAppl.Geophys.115,291

1383‐1412(1977)292

15

9. Mak,M.K.TheMonsoonalMid‐TroposphericCyclogenesis.J.Atmos.Sci.32,2246‐2253293

(1975)294

10. Goswami,B.N.,Keshavamurty,R.N.andSatyanV.Roleofbarotropic,baroclinicand295

combinedbarotropic‐baroclinicinstabilityforthegrowthofmonsoondepressionsandmid‐296

troposphericcyclones.J.EarthSys.Sci.89,79‐97(1980)297

11. Ferranti,L.andViterbo,P.TheEuropeanSummerof2003:SensitivitytoSoilWaterInitial298

Conditions.J.Climate19,3659–3680(2006).299

300

Acknowledgements301

ThisworkwassupportedbytheNASAInterdisciplinaryInvestigation,andtheTropicalRainfall302

MeasuringMission(TRMM).303

Authorcontributions304

W.K.M.L.ledthestudyandwrotethemanuscript.K.M.K.carriedoutthedataanalyses.Both305

authorscollaboratedinthediscussionoftheresultsandwriting.306

Additionalinformation307

Theauthorsdeclarenocompetingfinancialinterests.308

309

310

311

312

16

312

FigureCaptions313

Figure1Spatialdistributionofa)TRMMrainfallanomalyoverPakistanandtheSouthAsian314

monsoonregionforperiodJuly25–Aug8,2010,b)AIRSsurfacetemperature315

anomaly,andMODISdailyfirecount(greendots)forthesameperiod.Therainfall316

anomaly(mmday‐1)wasderivedfromthebaseperiodof1988‐2009,andthesurface317

temperatureanomaly(oC)fromthebaseperiodof2003‐2009.318

Figure2TimeseriesofAIRSdailysurfacetemperature(oC)averagedwesternRussia[45‐65oN,319

30‐60oE],withpositive(negative)deviationsfromclimatologyshadedred(blue),320

MODISfirecountperday(rightordinate)overthesamedomain,andTRMMdaily321

rainfall(mmday‐1,leftordinate)overnorthernPakistan[32‐35oN,70‐73oE],forthe322

June1‐August27,2010.323

Figure3Spatialpatternsofa)500hPageopotentialheightandwindanomaliesduring324

Period‐I,b)850hPawindandmoistureanomaliesduringPeriod‐I,c)500hPa325

geopotentialheightandwindanomaliesduringPeriod‐II,andd)850hPawindand326

moistureanomaliesduringPeriod‐II.Thegeopotentialheight(m)andwind(ms‐1)data327

werefromtheNOAANationalCenterforEnvironmentalPredication(NCEP).Centersof328

theblockinghigh(H),andlow(L)andthemid‐troposphericcyclones(C1andC2)are329

marked.Anomalieswerecomputedbasedontheclimatologyof1979–2009.330

Figure4Spatialpatternofa)200hPazonalwindanomalyandclimatology(showningreen331

linecontours)showingtheinfluenceofRossbywavesonthejetstreamflow,b)200hPa332

meridionalwindanomalyandclimatology(showningreenlinecontours),showingthe333

17

Rossbywavesignatureatthejetstreamlevel.Anomalieswerecomputedbasedonthe334

climatologyof1979‐2009.335

18

336

337

Figure1338

339

19

339

340

Figure2341

342

20

342

343

344

Figure3345

346

21

346

347

Figure4348

22

SupplementaryMaterial349

Mid‐troposphericverticalmotion350

DuringPeriod‐I,wide‐spreadlarge‐scalesinkingmotion(negativeanomaly)wasfound351

eastof,andrisingmotion(positiveanomaly)westandsouthwestoftheblockinghigh(H)(Fig.352

S1a).Theverticalmotionpatternwasconsistentwiththeanticyclonicflowassociatedwiththe353

blocking,havingsubsidingcolderairmovingtowardthesubtropicsandpolewardmoving354

warmerairtowardswesternEurope.Strongsinkingmotionwasalsonotedoverwestern355

AfghanistanandIran,probablyassociatedwithalarge‐scaleanomalousanticyclonefoundover356

SaudiArabiaandIran(seeFig.3a).Withrespecttothemid‐troposphericlow(L),risingmotion357

wasfoundtoitssoutheast,andsinkingmotiontoitsnorthwest,typicalofthebaroclinic358

structureofadevelopinglowinmid‐latitudes.Inthetropics,risingmotionwasfoundover359

northernPakistan,northernIndia,andthenorthernArabianSea,coupledtosinkingmotion360

overtheBayofBengal,andIndo‐China.Therisingmotion,thoughstillmoderateinmagnitude361

providedverticaltransportofmoisturetothelowerandmiddletroposphere,readytobe362

tappedforMTCdevelopment.DuringPeriod‐II(Fig.S1b),thesubsiding(colder)airover363

westernSiberiaeastoftheblockinghigh(H)becamemoreexpansiveandamplified,withthe364

southerntipofthesinkingairreachingbelow30NoverIran.Atthesametime,easternand365

northernEuropeexperiencedgenerallyrisingmotionastheblockshiftedeastward.Inthe366

subtropicsandtropics,theMTCs(C1andC2)werefullydevelopedoverIran/Afghanistan,and367

thenorthernArabiaSea.Clearlyfromtheverticalmotionfield,strongupwardmotion368

coincidingwiththePakistanfloodwasfoundtotheeast,andsinkingmotiontothewestofthe369

primaryMTC(C1),whichwastheprimaryweathersystemthatcausedtheheavyrainover370

23

northernPakistan.ForC2,therisingmotionwasmorecoincidentwiththevortexcenter,more371

representativeofamonsoonweathersystem.Itshouldbepointedoutthatthevertical372

motionfieldswerederivedfromrathercoarseresolution(2.5ox2.5olatitude‐longitude)wind373

analyses,andthereforereflectedonlythelarge‐scaleverticalmotionpertainingtothesynoptic374

scaleforcingassociatedwiththeblockinginhighlatitudesandtherainfallinthemonsoon375

region.Theconvectivescaleverticalmotionsdirectlyassociatedwithupdraftsintheheavyrain376

werenotresolvedintheanalysis.377

378

Aerosoldistribution379

The2010Russiawildfiresemittedabundantsmoke,noxiousgases(CO2,CO,CH4,NOx,380

andothers)andaerosols(blackcarbonandorganiccarbon)harmfultohumanhealth,and381

possiblyalterthelandsurfaceandatmosphericheatbalance,dependingontheradiative382

propertiesofthegasesandaerosols.Thesegasesandaerosolsweretransportedbythe383

atmosphericcirculationtohighelevationsandregionsfarfromtheforestfire.DuringPeriod‐I384

(July10‐24),atmosphericloadingofaerosolsoverRussiaandSiberiawasactuallyslightlybelow385

normalovervastregionsofEurasiaandtheAsianmonsoonregion(Fig.S2a).DuringPeriod‐II386

(July25‐August8),astheheatwavesoaredandtheforestfireraged,theaerosolloadinginthe387

atmosphereincreaseddramatically(Fig.S2b).Maximumhighlevelofaerosolconcentration388

(AOD>1)wasfoundoveralargeregion,nearbutslightlyoffsettothewestofthecenterof389

surfaceanticyclone,anddownwindoftheregionofmaximumfirecount(SeeFig.1binmain390

text).High‐to‐moderateaerosolconcentrations(AOD>0.5)werefoundovernorthwestern391

Europe,theArcticcircle,regionsnorthoftheCaspianSea,westernRussiainconjunctionof392

24

thesloweastwardmigration,andgrowthinsizeandmagnitudeoftheblockingevent.Large393

negativeAOD(<0.6‐0.8)anomalywasfoundoverPakistan,northwestIndiaandtheIndo‐394

GangeticPlain.Thiswasassociatedwiththewash‐out,bytheexcessiverain,ofthedense395

aerosol(mostlydustandblackcarbon)whichaccumulateintheregionduringtheearly396

monsoonseason1,2.Thestrongcontrastbetweenthelargeareasofhighaerosolloadingover397

westernRussia,andtheoverallreducedaerosolloadingoverthepan‐continentalregionsof398

Eurasian,Mediterranean,AfricaandmonsoonAsiawouldmostlikelyhaveaffectedthe399

energybalancethroughthedirectandsemi‐directeffects3,andthuscouldplayarolein400

sustainingand/oramplifyingtheRussianheatwave,theblockinghighandindirectlythe401

Pakistanflood,throughtheRossbywaveteleconnection.402

403

25

403

404

ReferencesforSupplementaryMaterial405

1. Lau,K.M.,Kim,M.K.,andKim,K.M.,AerosolinducedanomaliesintheAsiansummer406

monsoon:TheroleoftheTibetanPlateau.ClimateDynamics26(7‐8),855‐864,407

doi:10.1007/s00382‐006‐0114‐z(2006).408

2. Gautam,R.,Hsu,C.,andLau,K.M.,Pre‐monsooncharacterizationandradiativeeffects409

overtheIndo‐GangeticPlain:Implicationsforregionalclimatewarming.J.Geophys.Res.410

115,D17208,doi:10.1029/2010JD0(2010).411

3. Hansen,J.,Sato,M.andRuedy,R.Radiativeforcingandclimateresponse.J.Geophys.412

Res.102,6831‐6864(1997)413

wlau � 10/6/10 9:40 PMFormatted: List Paragraph, Indent: Left: 0", Hanging: 0.31", Line spacing: double,Numbered + Level: 1 + Numbering Style:1, 2, 3, ... + Start at: 1 + Alignment: Left +Aligned at: 0.44" + Indent at: 0.69", Tabs:wlau � 10/6/10 9:40 PM

wlau � 10/6/10 9:40 PMFormatted: Font:12 pt

Deleted: <#>

26

3. 414

FigureCaptionforSupplementaryMaterial415

FigureS1.Spatialpatternofverticalmotionat500hPafora)Period‐Iandb)Period‐II.416

Ascending(descending)motionisshadedred(blue).Labelsdenotepositionoflow417

centersat500hPa.Signoftheverticalmotionisreversed,andtheunitisPas‐1418

Thecentersofthe500hPAblockinghigh(H)andlow(L),andtheMTC’s(C1andC2)are419

markedtoshowtheirrelativepositionswithrespecttotheverticalmotionfield.420

FigureS2Spatialpatternsofa)MODISAerosolOpticalDepth(AOD)and850hPawind421

anomalies(ms‐1)duringPeriod‐I,andb)Sameasina),butforPeriod‐II.422

423

27

423

FigureS1424

425

426

wlau � 10/6/10 9:40 PMDeleted: Page Break

28

427

428

FigureS2429

430