weatherforecastsand2thelowerstratosphericandtroposphericfeaturesinFig2persistfor3monthsAsisevidentinthefigurethe1090dayperiodfollowingweakeningsofthevortexisassociatedwithdailyvaluesofthetropos ID: 181789
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Stratosphere–TroposphereCouplingintheSouthernHemisphereW.J.TDepartmentofAtmosphericScience,ColoradoStateUniversity,FortCollins,ColoradoP.BNorthwestResearchAssociates,Bellevue,Washington weatherforecastsand2)thelower-stratosphericandtroposphericfeaturesinFig.2persistfor3months.Asisevidentinthefigure,the1090-dayperiodfol-lowingweakeningsofthevortexisassociatedwithdailyvaluesofthetroposphericSAMindexvaluesthatareonaverage0.7standarddeviationslowerthanthosefoundduringthe1090-dayperiodfollowingstrength-eningsofthevortex,adifferencethatexceedsthe95%confidencelevel.Thesignificanceofthisresultisnotsensitivetothespecifictimeintervalchosen.TheshiftsintheSAMevidentinFig.3areassociatedwithsubstantialanomaliesinthe500-hPageopotentialheightfield.Figure4(middle)showsthedifferenceinthe500-hPaheightfieldbetweenthe1090-dayperiodsfollowingweakandstrongeventsat10hPa,respec-tively(i.e.,thefigureisbasedonthesamesamplesusedinFig.3).Figure4(left)showsthestructureoftheSAMinthemonth-to-monthvariability,definedherebyregressingthe500-hPaheightfieldontomonthlymeanvaluesoftheSAMindexat500hPa.TheresultsinFig.4(left)areinverted,suchthatpositivevaluescorrespondtoconditionsassociatedwiththelowindexpolarityoftheSAM,andviceversa.AsisevidentinFig.4(middle),majorweakeningsintheSHstrato-sphericpolarvortexarefollowedbystatisticallysignifi-cantrisesintroposphericgeopotentialheightsthrough-outthepolarcapandfallsingeopotentialheightsatmidlatitudesthatbearastrongresemblancetothestructureoftheSAMinthemonth-to-monthvariabil-ity.ThespatialcorrelationbetweenthestructuresinFig.4(left)andFig.4(middle)isWhataretheclimateimpactsofthetroposphericanomaliesevidentinFigs.24?Attroposphericlevels,theSAMiscoupledwithvariationsinsurfacetempera-turethroughoutAntarctica(ThompsonandWallace2000;ThompsonandSolomon2002).Itshighindexpo- .3.(left)HistogramsoftheSAMindexat500-hPaduringthe1090-dayperiodfollow-ingtheonsetofweak(gray)andstrong(black)stratosphericevents.TheeventsarelistedinTable1.(right)Asintheleft,butforthe1090-dayperiodfollowingtheonsetofthe2002SHSSW(gray)andtheOctNovclimatology(black). .2.CompositedifferenceoftheSAMindexbetweentheweakandstrongstratosphericeventslistedinTable1.Day0correspondstotheonsetofthestratosphericeventat10hPa.Contourandshadingintervalisat0.5stddev.Shadingisdrawnforvaluesexceeding0.5stddev.RedshadingdenotespositivevaluesintheSAMindex(weaker-than-normalzonalflowalong602005THOMPSONETAL. Fig2live4/C arcticathatarebroadlyconsistentwiththosefoundinassociationwiththeSAM.OverAntarctica,thechangesinsurfacetemperaturearestatisticallysignifi-cantatonly4outof11individualstations(significanceisindicatedbythecircleswithblackoutlines).Never-theless,thetemperaturechangesareoftheexpectedsignat10outof11Antarcticstations,andtheareameanwarmingof0.75KovereasternAntarcticaandtheAntarcticPlateauisstatisticallysignificantatthe99%confidencelevel.4.TheSHSSWof2002Theresultsintheprevioussectiondemonstratethatlarge-amplitudeanomaliesintheSHstratosphericcir-culationaretypicallyfollowedbysimilarlysignedanomaliesintheSHtroposphericcirculationreminis-centoftheSAM.Inthissection,weexamineanalogousresultscomputedfortheSHsuddenstratosphericwarmingof2002.TheresultsintheprevioussectionmaybeviewedasprovidingabasisforanticipatingthestateoftheSHtroposphericcirculationduringthemonthperiodfollowingtheonsetofthisevent.Asnotedinpapersthroughoutthisissue,theSHSSWof2002wasunusualintworespects:1)thestrato-spherewasdisturbedbysubstantialwaveactivityear-lierintheyearthanistypicalinthehistoricalrecord(e.g.,NewmanandNash2005),and2)theamplitudeoftheeventisuniqueintheobservationalrecord.TheextraordinaryamplitudeoftheeventisevidencedinFig.6,whichshowsscatterplotsofthezonal-meanzonalflowat10hPaalong60Sandat50-hPatemperatureatthePolefor2002(blackline)superposedondatafortheyears19792001(graylines).Inboththezonal-meanzonalflowat10hPaalong60Sandat50-hPapolartemperatures,theeventapproached10stan-darddeviationsabouttheclimatologicalmeanforthemonthofSeptember.Figure7showsdailyvaluesoftheSAMindexatalllevelsfrom1June2002to31December2002.At10hPa,theSAMindexwasatleast1standarddeviationbelowitslong-termmeanthroughoutmostofJulyandbyAugust30,reachedsustainedvalueslessthanstandarddeviations.InlateSeptember,theSAMindexat10hPadroppedfrom2to9standarddeviationsinaperiodof7days,reachingapeakvalueofstandarddeviationsat10hPaon27September2002.Anomalieslowerthan2standarddeviationswereevi-dentinthestratosphereuntilDecember2002.TheverticalprofileoftheSSWof2002bearsconsid- .6.(top)Temperatureat50hPaattheSouthPoleshownasafunctionofcalendarday.Graylinesdenotedatafortheyears2001;theblacklinedenotesdatafortheyear2002.(bottom)Asintop,butforthezonal-meanzonalwind([])at10hPaat .7.ValuesoftheSAMindexduring2002.Contoursaredrawnat0.5stddev.Shadingisdrawnforvaluesexceeding0.5stddev.RedshadingdenotespositivevaluesintheSAMindex(weaker-than-normalzonalflowalong602005THOMPSONETAL. 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