简介:WesternChinaexperiencedanextremehotsummerin2015,breakinganumberoftemperaturerecords.Thesummermeansurfaceairtemperature(SAT)anomalywastwicetheinterannualvariability.Thehottestdaytimetemperature(TXx)andwarmestnight-timetemperature(TNx)werethehighestinChinasince1964.Thisextremehotsummeroccurredinthecontextofsteadilyincreasingtemperaturesinrecentdecades.Wecarriedoutasetofexperimentstoevaluatetheextenttowhichthechangesinseasurfacetemperature(SST)/seaiceextent(SIE)andanthropogenicforcingdrovetheseverityoftheextremesummerof2015inwesternChina.Ourresultsindicatethatabout65%-72%oftheobservedchangesintheseasonalmeanSATandthedailymaximum(Tmax)anddailyminimum(Tmin)temperaturesoverwesternChinaresultedfromchangesinboundaryforcings,includingtheSST/SIEandanthropogenicforcing.Fortherelativeroleofindividualforcing,thedirectimpactofchangesinanthropogenicforcingexplainabout42%oftheSATwarmingand60%(40%)oftheincreaseinTNxandTmin(TXxandTmax)inthemodelresponse.ThechangesinSST/SIEcontributedtotheremainingsurfacewarmingandtheincreaseinhotextremes,whicharemainlytheresultofchangesintheSSToverthePacificOcean,whereasuperElNi?oeventoccurred.OurstudyindicatesaprominentroleforthedirectimpactofanthropogenicforcingintheseverityoftheextremehotsummerinwesternChinain2015,althoughthechangesinSST/SIE,aswellastheinternalvariabilityoftheatmosphere,alsomadeacontribution.
简介:TheArcticsea-iceextenthasshownadecliningtrendoverthepast30years.Icecoveragereachedhistoricminimain2007andagainin2012.Thistrendhasrecentlybeenassessedtobeuniqueoveratleastthelast1450years.Inthesummerof2010,averylowsea-iceconcentration(SIC)appearedathighArcticlatitudes--evenlowerthanthatofsurroundingpackiceatlowerlatitudes.Thisstrikinglowiceconcentration--referredtohereasarecordlowiceconcentrationinthecentralArctic(CARLIC)--isuniqueinouranalysisperiodof2003-15,andhasnotbeenpreviouslyreportedintheliterature.TheCARLICwasnottheresultoficemelt,becauseseaicewasstillquitethickbasedonin-situicethicknessmeasurements.Instead,divergenticedriftappearstohavebeenresponsiblefortheCARLIC.AhighcorrelationbetweenSICandwindstresscurlsuggeststhattheseaicedriftduringthesummerof2010respondedstronglytotheregionalwindforcing.ThedrifttrajectoriesoficebuoysexhibitedatranspolardriftintheAtlanticsectorandaneastwarddriftinthePacificsector,whichappearedtobenefittheCARLICin2010.Undertheseconditions,moresolarenergycanpenetrateintotheopenwater,increasingmeltthroughincreasedheatfluxtotheocean.Wespeculatethatthisdivergenceofseaicecouldoccurmoreofteninthecomingdecades,andimpactonhemisphericSICandfeedbacktotheclimate.
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