简介:Theanalysisof43yearsofNCEP-NCARreanalysisdataandstationobservationsrevealstheconnectionsbetweentropospherictemperaturevariationsandtheweakeningoftheIndiansummermonsooncirculation.TheIndiansummermonsoonvariationisstronglylinkedtotropospherictemperatureoverEastAsia,showingsignificantpositivecorrelationsofmeantropospherictemperaturewithall-Indiansummerrainfallandthemonsooncirculationintensity.TheresultshowsthatIndiansummermonsooncirculationunderwenttwoweakeningprocessesinrecentdecades.Thefirstoccurredincircathemid-1960s,andtheotheroccurredincircathelate1970s.ThefindingindicatesthatthemeantropospherictemperaturemayplayacrucialroleintheweakeningoftheIndiansummermonsoonintensityviachangingland-seathermalcontrast.TheroleofthetropospherictemperaturecontrastbetweenEastAsiaandthetropicalareafromtheeasternIndianOceantothetropicalwesternPacificistoweakentheIndiansummermonsooncirculation.
简介:Basedondynamicrupturesimulationsonaplanarfaultinahomogeneoushalf-space,weinvestigatedthenucleationprocessesusingthetime-weakeningfrictionlaw.Boththecharacteristictimeandtherupturespeedinthenucleationasperityplayanimportantroleindeterminingrupturebehaviorsonafaultplanefollowingthetime-weakeningfrictionlaw,withwhichrupturestartsfromasinglepointinthenucleationasperityandpropagatesatagivenspeedtowardtheboundaryofthenucleationarea.Rupturewithasmallcharacteristictimeoralargerupturespeedinthenucleationasperitypropagatesearlierfromthehypocenter.Rupturefollowingtheslipweakeningfrictionlawrequiresasmallerradiusofnucleationpatchtohavesimilarrupturefrontcontoursofthetime-weakeningfrictionlaw.Eveniftherupturevelocityinthenucleationpatchofthetime-weakeningfrictionlawincreasestoinfinity,thepeaksliprateinthenucleationasperityissmallerthanthatoftheslip-weakeninglaw.Thepeakgroundvelocitydistributionsofrupturesfollowingthetwofrictionlawsarealsocompared.
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:塑造耳朵的热前面(ESTF),由黄海温暖的水流(YSWC)和山东沿海的水流(SCC)的集中形成了,在冬季是在黄海(YS)的很重要的海洋的现象。在所有表明的situ大小和分析数据集,ESTF在1950s-1990s,和一个类似的变弱趋势期间一直在变弱,这是也在YS上在冬季季风发现。数字实验证明变弱冬季季风能沿着瓷器海岸和向南方的异常水流与向北方异常的水流在多十的timescale上在YS导致异常发行量在里面中央对季节的吝啬的循环YSgenerally相反。异常发行量引起YSWC和SCC的减速,并且因此削弱ESTF。因为ESTF在地区性的海洋动力学和由空至海的相互作用起重要作用,它变弱在冬季在YS为地区性的气候有重要含意。
简介:Rockexperimentresultsindicatethattheload/unloadresponseratio(LURR)ofrocksexpressedviastrainenergymayhavesingularornegativevalueafterthestressintherockreachesitsmaximumbeforerockfailureorwhentherockgoesintothestrain-weakeningphase.Theuniversalityofthisphenomenonisdiscussed.ExpressedviastrainorstrainenergyandthetraveltimeofPwave,thevariationformofthereciprocalofLURRduringtheprocessofrockfailurepreparationisderived.TheresultsshowthatafterasharpdecreasethereciprocalofLURRreachesitsminimumwhenthemainfractureoftherockisabouttoappear.Thisfeaturecanbetakenasanindicationthattherockmainfractureisimpending.
简介:TheonsetofSouthChinaSeasummermonsoonin1998occurredonMay21st.UsingtheU.S.NationalCentersforEnvironmentalPredictionreanalysisdata,thispaperexaminesthephysicalprocessoftheweakeningofasubtropicalanticycloneinWestPacificduringtheonsetperiodusingtheZwack-Okossivorticityequation.Resultsshowthatduringthepre-onsetperiod,thepositivevorticityadvectioninfrontofanuppertropospherictroughwasthemostdominantphysicalmechanismfortheincreaseofthecyclonicvorticityonthe850-hPalayerovertheSouthChinaSeaanditsnearbyregion.Thesecondarycontributiontotheincreaseofthecyclonicvorticitywasthewarm-airadvection.Aftertheonset,themagnitudeofthelatent-heatwarmingtermrapidlyincreasedanditseffectontheincreaseofthecyclonicvorticitywasaboutthesameasthepositive-vorticityadvection.Theadiabatictermanddivergencetermcontributednegativelytotheincreaseofthecyclonicvorticitymostofthetime.Thus,thepositivevorticityadvectionisthemostimportantphysicalmechanismfortheweakeningoftheWestPacificsubtropicalanticycloneovertheSouthChinaSeaduringtheonsetperiod.
简介:High-velocityfrictionexperimentswereconductedonclayeyfaultgougecollectedfromHongkououtcropofBeichuanfault,locatedatthesouthwesternpartofLongmenshanfaultsystemthatcausedthedisastrous2008Wenchuanearthquake.Theultimatepurposeofthisstudyistoreproducethisearthquakebymodelingbasedonmeasuredfrictionalproperties.Drygougeofabout1mminthicknesswasdeformeddryatslipratesof0.01to1.3m/sandatnormalstressesof0.61to3.04MPa,usingarotary-shearhigh-velocityfrictionaltestingmachine.Thegougedisplaysslipweakeningbehaviorasinitialpeakfrictiondecaystowardssteady-statevaluesafteragivendisplacement.Bothpeakfrictionandsteady-statefrictionremainhighatslowslipratesareexaminedandgougeonlyexhibitsdramaticweakeningathighsliprates,withsteady-statefrictioncoefficientvaluesofabout0.1to0.2.Specificfractureenergyrangesfrom1to4MN/minourresultsandthisisofthesameorderasseismicallydeterminedvalues.LowfrictioncoefficientsmeasuredonexperimentalfaultsareinbroadagreementwithlackofthermalanomalyobservedfromtemperaturemeasurementsinWFSD-1drillhole(WenchuanEarthquakeFaultScientificDrillingProject),whichcanbeexplainedbyevensmallerfrictioncoefficientfortheWenchuanearthquakefault.High-velocityfrictionexperimentswithporewaterneedstobedonetoseeifevensmallerfrictionisattainedornot.Shinyslickensidesurfacesformathighsliprates,butnotatslowsliprates.Slipzonewithslickensidesurfacechangesitscolortodarkbrownandformsduplex-likemicrostructures,whicharesimilartothosemicrostructuresfoundinthefaultgougesfromtheHongkououtcrop.DetailedcomparisonsbetweenexperimentallydeformedgougesamplesandWFSDdrillcoresinthefuturewillrevealhowmuchwecouldreproducethedynamicweakeningprocessesinoperationinfaultzonesduringWenchuanearthquakeatpresent.