简介：

简介：

简介：Adiscrepancyremainsinthefirsttwoleadingempiricalorthogonalfunction(EOF)modesofthetropicalPacificseasurfacetemperatureanomaly(SSTA)basedonobservationssincethe1980s.TheEOF1mode,representingtheElNino-SouthernOscillation(ENSO),isarobustresult.However,theEOF2featureseitherElNinoModoki(EM)orENSOevolutionduringdifferentperiods,whichisprobablyassociatedwiththeimpactsofglobalwarming.TheunderlyingquestioniswhattheEOF2modeofthetropicalPacificwouldbewithoutglobalwarming.UsingtheCMIP5preindustrialscenariotoexcludetheinfluenceofglobalwarming,wefindthattheEOF1modeofthetropicalPacificSSTArepresentsENSOandthattheEOF2modeisnotEM.Accordingtothelead–lagcorrelationbetweentheENSOandEOF2modes,thelinkagebetweenthesetwomodesisasfollows:…ElNino→EOF2→LaNina→–EOF2→ElNino….Byanalyzingtheevolutionofseasurfacetemperature,surfacewind,andsubsurfaceoceantemperatureanomalies,wefindthemechanismlinkingtheENSOandEOF2modesistheair–seainteractionassociatedwiththeENSOcycle.ThisresultsuggeststhattheEOF2moderepresentsanaspectofENSOevolutionunderpreindustrialconditions.Therefore,thisstudyfurtherindicatesthattheEMisprobablyduetotheinfluenceofglobalwarming.

简介：MeteoroidsenteringtheEarth'satmospherecancreatemeteortrailirregularityseriouslydisturbingthebackgroundionosphere.AlthoughnumerousobservationsofmeteortrailirregularitieswereperformedwithVHF/UHFcoherentscatterradarsinthepast,nosimultaneousradarandopticalinstrumentswereemployedtoinvestigatethecharacteristicsofmeteortrailirregularityanditscorrespondingmeteoroid.ByinstallingmultiplevideocamerasneartheSanyaVHFradarsite,anobservationalcampaignwasconductedduringtheperiodfromNovember2016toFebruary2017.Atotalof242opticalmeteorswithsimultaneousnon-specularechoesbackscatteredfromtheplasmairregularitiesgeneratedinthecorrespondingmeteortrailswereidentified.Agoodagreementbetweentheangularpositionsofnon-specularechoesderivedfromtheSanyaradarinterferometerandthoseofopticalmeteorswasfound,validatingthattheradarsystemphaseoffsetshavebeenproperlycalibrated.TheresultsalsoverifytheinterferometrycapabilityofSanyaradarformeteortrailirregularityobservation.Thenon-specularechoeswithsimultaneousopticalmeteorsweredetectedatmagneticaspectanglesgreaterthan~78°.Basedonthemeteorvisualmagnitudeestimatedfromtheopticaldata,itwasfoundthattheradarnonspecularechoescorrespondingtobrightermeteorssurvivedforlongerduration.Thiscouldprovideobservationalevidenceforthesignificanceofmeteoroidmassonthedurationofmeteortrailirregularity.Ontheotherhand,thesimultaneousradarandvideocommon-volumeobservationsshowedthatthereweresomecaseswithopticalmeteorsbutwithoutradarnon-specularechoes.Onepossibilitycouldbethatsomeoftheopticalmeteorsappearedatextremelylowaltitudeswheremeteortrailirregularitiesrarelyoccur.

简介：Irregularsurfaceflattening,whichisbasedonaboundaryconforminggridandthetransformationbetweencurvilinearandCartesiancoordinatesystems,isamathematicalmethodthatcanelegantlyhandleirregularsurfaces,buthasbeenlimitedtoobtainingfirstarrivalsonly.Bycombiningamultistageschemewiththefast-sweepingmethod(FSM,themethodtoobtainfirst-arrivaltraveltimeincurvilinearcoordinates),thereflectedwavesfromacrustalinterfacecanbetracedinatopographicmodel,inwhichthereflectedwavefrontisobtainedbyreinitializingtraveltimesintheinterfaceforupwindbranches.Alocaltriangulationisappliedtomakeaconnectionbetweenvelocityandinterfacenodes.Thenajointinversionoffirst-arrivalandreflectiontraveltimesforimagingseismicvelocitystructuresincomplexterrainsispresented.Numericalexamplesallperformwellwithdifferentseismicvelocitymodels.Theincreasingtopographiccomplexityandevenuseofahighcurvaturereflectorinthesemodelsdemonstratethereliability,accuracyandrobustnessofthenewworkingscheme;checkerboardtestingillustratesthemethod’shighresolution.Noisetolerancetestingindicatesthemethod’sabilitytoyieldpracticaltraveltimetomography.Furtherdevelopmentofthemultistageschemewillallowotherlaterarrivalstobetracedandusedinthetraveltimeinversion.