简介：Theanalysisof43yearsofNCEP-NCARreanalysisdataandstationobservationsrevealstheconnectionsbetweentropospherictemperaturevariationsandtheweakeningoftheIndiansummermonsooncirculation.TheIndiansummermonsoonvariationisstronglylinkedtotropospherictemperatureoverEastAsia,showingsignificantpositivecorrelationsofmeantropospherictemperaturewithall-Indiansummerrainfallandthemonsooncirculationintensity.TheresultshowsthatIndiansummermonsooncirculationunderwenttwoweakeningprocessesinrecentdecades.Thefirstoccurredincircathemid-1960s,andtheotheroccurredincircathelate1970s.ThefindingindicatesthatthemeantropospherictemperaturemayplayacrucialroleintheweakeningoftheIndiansummermonsoonintensityviachangingland-seathermalcontrast.TheroleofthetropospherictemperaturecontrastbetweenEastAsiaandthetropicalareafromtheeasternIndianOceantothetropicalwesternPacificistoweakentheIndiansummermonsooncirculation.

简介：UsingtheNationalCenterforEnvironmentalPredictionreanalysisdataon1.0°×1.0°gridsanddatafromtheTropicalCycloneyearbook(2000),adiagnosticanalysisandnumericalsimulationwereperformedtoinvestigatethecharacteristicsandmechanismunderlyingtherapidweakeningoftyphoonXangsane.TheresultsshowthatasharpdeclineintheintensityoftyphoonXangsaneresultedfromitsmovementintothecoolseasurfacetemperatureareaintheEastChinaSea,theintrusionofcoldairfromthemainlandintothetyphoon,andarapidincreaseoftheverticalwindshearinthesurroundingenvironment.Animportantfactorthatledtothedemiseofthetyphoonwasasignificantdecreaseinthemoisturetransportintothetyphoon.Furthermore,theresultsofthenumericalsimulationandsensitivityexperimentsindicatethatseasurfacetemperaturelargelymodulatedtherapidweakeningoftyphoonXangsane.

简介：BasedontheTropicalCyclone(TC)YearbooksdataandJRA-25reanalysisdatafromtheJapanMeteorologicalAgency(JMA)during1979-2008,dynamiccompositeanalysisandcomputationofkineticenergybudgetareusedtostudytheintensifyingandweakeningTCsduringExtratropicalTransitionoverChina.TheTCIshowsstrongupper-leveldivergence,strengthenedlow-levelconvergenceandsignificantlyenhancedupwardmotionundertheinfluenceofstrongupper-leveltroughsandhigh-leveljets.TheTCIiscorrespondinglyintensifiedafterExtratropicalTransition(ET);TCWexhibitsstrongupper-leveldivergence,subduedlow-levelconvergenceandslightlyenhancedupwardmotionundertheinfluenceofweakupper-leveltroughsandhigh-leveljets.ItthenweakensafterET.Theincrease(decrease)ofthegenerationofkineticenergybydivergencewindinTCI(TCW)atlowlevelisoneofthemajorreasonsforTCI’sintensification(TCW’sweakening)aftertransformation.Thegenerationofkineticenergybydivergencewindiscloselyrelatedtothedevelopmentofalow-levelbaroclinicfrontalzone.ThegrowthofthegenerationofkineticenergybyrotationalwindinTCIatupperlevelisfavorableforTCI’smaintenance,whichisaffectedbystrongupper-leveltroughs.ThedissipationofthegenerationofkineticenergybyrotationalwindinTCWatupperlevelisunfavorableforTCW’smaintenance,whichisaffectedbyweakupper-leveltroughs.

简介：TheonsetofSouthChinaSeasummermonsoonin1998occurredonMay21st.UsingtheU.S.NationalCentersforEnvironmentalPredictionreanalysisdata,thispaperexaminesthephysicalprocessoftheweakeningofasubtropicalanticycloneinWestPacificduringtheonsetperiodusingtheZwack-Okossivorticityequation.Resultsshowthatduringthepre-onsetperiod,thepositivevorticityadvectioninfrontofanuppertropospherictroughwasthemostdominantphysicalmechanismfortheincreaseofthecyclonicvorticityonthe850-hPalayerovertheSouthChinaSeaanditsnearbyregion.Thesecondarycontributiontotheincreaseofthecyclonicvorticitywasthewarm-airadvection.Aftertheonset,themagnitudeofthelatent-heatwarmingtermrapidlyincreasedanditseffectontheincreaseofthecyclonicvorticitywasaboutthesameasthepositive-vorticityadvection.Theadiabatictermanddivergencetermcontributednegativelytotheincreaseofthecyclonicvorticitymostofthetime.Thus,thepositivevorticityadvectionisthemostimportantphysicalmechanismfortheweakeningoftheWestPacificsubtropicalanticycloneovertheSouthChinaSeaduringtheonsetperiod.