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The2010PakistanFloodandtheRussiaHeatWave:1
TeleconnectionofExtremes2
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WilliamK.M.Lau1,andK.M.Kim24
1LaboratoryforAtmospheres,NASAGoddardSpaceFlightCenter,GreenbeltMD,207715
2GoddardEarthSciencesandTechnologyCenter,U.ofMarylandBaltimoreCounty,6
BaltimoreMaryland,212287
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SubmittedtoNatureGeoscience11
October201012
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Correspondingauthor:WilliamK.M.Lau,LaboratoryforAtmospheres,NASAGoddardSpace22FlightCenter,Greenbelt,MD20771.Email:[email protected]:301‐614‐633223
https://ntrs.nasa.gov/search.jsp?R=20110015271 2020-06-15T22:34:31+00:00Z
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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
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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
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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
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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
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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
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(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
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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
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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
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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
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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
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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
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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
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300
Acknowledgements301
ThisworkwassupportedbytheNASAInterdisciplinaryInvestigation,andtheTropicalRainfall302
MeasuringMission(TRMM).303
Authorcontributions304
W.K.M.L.ledthestudyandwrotethemanuscript.K.M.K.carriedoutthedataanalyses.Both305
authorscollaboratedinthediscussionoftheresultsandwriting.306
Additionalinformation307
Theauthorsdeclarenocompetingfinancialinterests.308
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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
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Rossbywavesignatureatthejetstreamlevel.Anomalieswerecomputedbasedonthe334
climatologyof1979‐2009.335
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Figure1338
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Figure2341
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Figure3345
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Figure4348
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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
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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
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