学科分类
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81 个结果
  • 简介:Thisstudycomparestheclimatologyandlong-termtrendofnorthernwinterstratosphericresidualmeanmeridionalcirculation(RMMC),aswellasitsresponsestoElNi?o-SouthernOscillation(ENSO),stratosphericQuasiBiennialOscillation(QBO),andsolarcycleintenreanalysesandastratosphere-resolvingmodel,CESM1-WACCM.TheRMMCisalarge-scalemeridionalcirculationcellinthestratosphere,usuallyreferredtoastheestimateoftheBrewerDobsoncirculation(BDC).ThedistributionoftheBDCisgenerallyconsistentamongmultiplereanalysesexceptthattheNOAAtwentiethcenturyreanalysis(20RC)largelyunderestimatesit.Mostreanalyses(exceptERA40andERA-Interim)showastrengtheningtrendfortheBDCduring1979–2010.AllreanalysesandCESM1-WACCMconsistentlyrevealthatthedeepbranchoftheBDCissignificantlyenhancedinElNi?owintersasmorewavesfromthetropospheredissipateinthestratosphericpolarvortexregion.AsecondarycirculationcelliscoupledtothetemperatureanomaliesbelowtheQBOeasterlycenterat50hPawithtropicalupwelling/coolingandmidlatitudedownwelling/warming,andsimilarsecondarycirculationcellsalsoappearbetween50–10hPaandabove10hPatobalancethetemperatureanomalies.ThedirectBDCresponsetoQBOintheupperstratospherecreatesabarriernear30°Ntopreventwavesfrompropagatingtomidlatitudes,contributingtotheweakeningofthepolarvortex.TheshallowbranchoftheBDCinthelowerstratosphereisintensifiedduringsolarminima,andthedownwellingwarmstheArcticlowerstratosphere.ThestratosphericresponsestoQBOandsolarcycleinmostreanalysesaregenerallyconsistentexceptinthetwo20CRs.

  • 标签: residual mean MERIDIONAL stream function(RMMSF) Brewer-Dobson
  • 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.

  • 标签: El Nino-Southern Oscillation(ENSO) ENSO evolution global
  • 简介:PrecipitationobservationscollectedatweatherstationsineasternChina,theNCEP/NCARreanalysisdata,thetropicalcyclone(TC)BestTrackDataset,andasensitivitynumericalexperimentwereusedinthepresentstudytoinvestigatetheroleintheEastAsiansummermonsoon(EASM)systemplayedbyfrequentTCactivitiesoverthewesternNorthPacific(WNP).Resultsindicatedthat,inactiveTCyears,theEASMisstrongerandthesoutherlywindsinthelowertroposphereadvancefarthernorthandreachhigherlatitudes.Meanwhile,themonsoonrainbeltremainsinthelowerandmiddlereachesoftheYangtzeRivervalleyforarelativelyshortperiod,leadingtolessprecipitationthere.BoththewesternPacificsubtropicalhighandtheSouthAsianhighweakenwiththenorthwardshiftoftheridgelinesforbothhigh-pressuresystemsaswellastheEastAsiansubtropicalupper-leveljet.Therefore,theimpactsoffrequentTCactivitiesovertheWNPoneachindividualcomponentoftheEASMareinphasewiththoseofthestrongerEASMitself,amplifyingfeaturesofthealreadystrengthenedEASM.

  • 标签: East Asian summer MONSOON TROPICAL CYCLONE
  • 简介:Observationsofaquasi-90-dayoscillationinthemesosphereandlowerthermosphere(MLT)regionfromApril2011toDecember2014arepresentedinthisstudy.Thereisclearevidenceofaquasi-90-dayoscillationintemperaturesobtainedfromtheKunmingmeteorradar(25.6°N,103.8°E)andSoundingoftheAtmosphereusingBroadbandEmissionRadiometry(SABER),aswellasinwindobservedbytheKunmingmeteorradar.Thequasi-90-dayoscillationappearstobeaprominentfeatureinthetemperaturesandmeridionalwindtidesandpresentsquiteregularcyclesthatoccurapproximatelytwiceperyear.Theamplitudesandphasesofthequasi-90-dayoscillationintheSABERtemperatureshowafeaturesimilartothatofupward-propagateddiurnaltides,whichhaveaverticalwavelengthof~20kmabove70km.Intheloweratmosphere,asimilar90-dayvariabilityispresentedinthesurfacelatentheatfluxandcorrelateswiththetemperatureintheMLTregion.Similartothequasi-90-dayoscillationintemperature,a90-dayvariabilityofozone(O3)isalsopresentintheMLTregionandisconsideredtobedrivenbyasimilarvariabilityintheupwardly-propagateddiurnaltidesgeneratedintheloweratmosphere.Moreover,the90-dayvariabilityintheabsorptionofultraviolet(UV)radiationbydaytimeO3intheMLTregionisaninsitusourceofthequasi-90-dayoscillationintheMLTtemperature.

  • 标签: quasi-90-day OSCILLATION METEOR radar TEMPERATURES SABER
  • 简介:Theradiancesscatteredoremittedbycloudsdemonstratediversefeaturesatdifferentwavelengthsduetodifferentcloudphysicalstructures.Thispaperpresentsamethod(thesmallest-radiance-distancemethod,SRaDM)ofrevealingthephysicalstructuresofclouds.Themethodisbasedonmulti-spectralradiancesmeasuredbytheModerateResolutionImagingSpectroradiometer(MODIS)onboardAqua.TheprincipleandmethodologyofSRaDMisdeducedandprovidedinthispaper.CorrelationanalysisbasedondatafromMODISandCloudProfilingRadar(onboardCloudSat),collectedfromJanuary2007toDecember2010overanoceanarea(15°N–45°N,145°E–165°E),ledtoselectionofradiancesat13wavebandsofMODISthatdemonstratedhighsensitivitytocloudphysicalstructures;radiancesattheselectedwavebandsweresubjectedtoSRaDM.TheStandardizedEuclideandistanceisintroducedtoquantifythedegreeofchangesinmulti-spectralradiances(termedDrd)andinphysicalstructures(termedDst)betweencloudprofiles.StatisticsbasedonnumerouscloudprofilesshowthatDrddecreasesmonotonicallywithadecreaseinDst,whichimpliesthatsmallDrdalwaysaccompaniessmallDst.AccordingtothelawofDrdandDst,thenewmethod,SRaDM,forrevealingphysicalstructuresofcloudsfromthecollocationofcloudprofilesofsimilarmulti-spectralradiances,ispresented.Then,twosuccessfulexperimentsarepresentedinwhichcloudphysicalstructuresarecapturedusingmulti-spectralradiances.SRaDMprovidesawaytoobtainknowledgeofthephysicalstructuresofcloudsoverrelativelylargerareas,andisanewapproachtoobtaining3Dcloudfields.

  • 标签: CLOUD physical structure RADIANCE RADAR
  • 简介:Thetriangulationofredspriteswasobtained,basedonconcurrentobservationsoveramesoscaleconvectivesystem(MCS)inNorthChinafromtwostationsseparatedbyabout450km.Inaddition,broadbandsfericsfromthesprite-producinglightningweremeasuredatfivegroundstations,makingitpossibletolocateandidentifytheindividualcausativelightningdischargesfordifferentelementsinthisdancingspriteevent.TheresultsofouranalysesindicatethatthespriteswereproducedabovethetrailingstratiformregionoftheMCS,andtheirparentstrokeswerelocatedmainlyintheperipheralareaofthestratiform.Thelateraloffsetbetweenspritesandcausativestrokesrangesfromafewkmtomorethan50km.Inaparticularlybrightsprite,withadistincthalofeatureandstreamersdescendingdowntoanaltitudeofapproximately48km,thespritecurrentsignalidentifiedintheelectricsferic,measuredatarangeofabout1,110km,peakedatapproximately1msafterthereturnstroke.

  • 标签: SPRITE TRIANGULATION PEAK current hybrid location
  • 简介:Leaderpropagationisafundamentalissueinlightningphysics.Thepropagationcharacteristicsofpositiveleadersandnegativeleadersaresummarizedandcomparedbasedondatafromhigh-speedcameraandelectromagneticfieldinrocket-triggeredlightningandtower-initiatedlightningdischarges;availablechannelbasecurrentdatarecordedinrocket-triggeredlightningarealsoused.Thenegativeleaderspropagateinasteppedfashionaccompaniedbymanybranches.Thestemsaheadofthenegativeleadertipdeterminethemanneranddirectionoftheleaderpropagation,andeventhebranchingandwindingofthelightningchannel.Theimpulsivecurrent,electromagneticfield,andrelatedopticalimagessuggestthatthepositiveleadermaydevelopinastep-likefashionatitsinitialstageoftriggeredlightning.However,thesteppingprocessesofthepositiveleaderareobviouslydifferentfromthoseofthenegativeleader.Tower-initiatedlightningrevealedthatthemostconspicuouscharacteristicsofthestepwisepositiveleaderinvolvetheintermittentbrush-likecoronazoneinfrontoftheleadertipandtheluminosityenhancementofthechannelbehindthetip.Inrockettriggeredlightningflashes,thechargetransferredduringanindividualstepforthenegativeleaderwasnearlyanordergreaterthanforthepositivecounterpart.Thesuccessivestreamersaheadoftheleadertipareessentialforbothnegativeandpositiveleaderpropagation,andthestemscouldbeformedfromoneormorestreamersinthepreviousnegativestreamerzonewiththemainleaderchanneldim.High-resolutionobservationoftowerlightningalsorevealedanewtypeofbidirectionalrecoilleader,withpolaritycontrarytothetraditionalone,traversinginnegativechannelsassociatedwithtower-initiatedandrocket-triggeredlightning.

  • 标签: LIGHTNING PROPAGATION NEGATIVE LEADER POSITIVE LEADER
  • 简介:Usingfoursatellitedatasets(TOMS/SBUV,OMI,MLS,andHALOE),weanalyzetheseasonalvariationsofthetotalcolumnozone(TCO)anditszonaldeviation(TCO*),andrevealtheverticalstructureoftheOzoneLow(OV)overtheAsiancontinent.Ourprincipalfindingsare:(1)TheTCOovertheAsiancontinentreachesitsmaximuminthespringanditsminimumintheautumn.TheOzoneLowexistsfromMaytoSeptember.(2)TheOzoneLowhastwonegativecores,locatedinthelowerandtheupperstratosphere.Thelowercoreisnear30hPainthewinterand70hPaintheotherseasons.Theuppercorevariesfrom10hPato1hPaamongthefourseasons.(3)ThepositionoftheOzoneLowinthelowerandtheupperstratosphereovertheAsiancontinentshowsseasonalvariability.

  • 标签: OZONE LOW DOUBLE core ASIAN CONTINENT
  • 简介:TheuniquegeographicallocationandhighaltitudeoftheTibetanPlateaucangreatlyinfluenceregionalweatherandclimate.Inparticular,theAsiansummermonsoon(ASM)anticyclonecirculationsystemovertheTibetanPlateauisrecognizedtobeasignificanttransportpathwayforwatervaporandpollutantstoenterthestratosphere.Toimproveunderstandingofthesephysicalprocesses,amulti-locationjointatmosphericexperimentwasperformedovertheTibetanPlateaufromlateJulytoAugustin2018,fundedbythefiveyear(2018–2022)STEAM(stratosphereandtroposphereexchangeexperimentduringASM)project,duringwhichmultipleplatforms/instruments—includinglong-durationstratosphericballoons,dropsondes,unmannedaerialvehicles,specialsoundingsystems,andground-basedandsatellite-borneinstruments—willbedeployed.Thesecomplementarymethodsofdataacquisitionareexpectedtoprovidecomprehensiveatmosphericparameters(aerosol,ozone,watervapor,CO2,CH4,CO,temperature,pressure,turbulence,radiation,lightningandwind);therichnessofthisapproachisexpectedtoadvanceourcomprehensionofkeymechanismsassociatedwiththermal,dynamical,radiative,andchemicaltransportsovertheTibetanPlateauduringASMactivity.

  • 标签: TIBETAN PLATEAU Asian summer MONSOON STRATOSPHERE
  • 简介:AsalientfeatureoftheEastAsianorographyisthehugeTibetanPlateauinthewestandthebroadPacificintheeast.ReversalsinthetemperaturegradientbetweentheEurasiancontinentandtheadjacentPacificOceanassociatedwiththeprogressionoftheseasonshaveproducedtheprominentEastAsianmonsoonsystem.Thesummermonsooncontributesabout49%oftheannualprecipitationoverEastAsia.Anomalousmonsoonactivitieshaveandwillcontinuetoaffectmorethanonebillionpeoplelivinginthisarea(ZhouTJetal.,2009,2011).

  • 标签: ATMOSPHERE STRATOSPHERE and troposphere exchange LIGHTNING
  • 简介:IntheSoutheastMarginoftheTibetanPlateau,low-velocitysedimentarylayersthatwouldsignificantlyaffecttheaccuracyoftheH-κstackingofreceiverfunctionsarewidelydistributed.Inthisstudy,weuseteleseismicwaveformdataof475eventsfrom97temporarybroadbandseismometersdeployedbyChinArrayPhaseItoobtaincrustalthicknessesandPoisson’sratioswithintheChuxiong-SimaoBasinandadjacentarea,employinganimprovedmethodinwhichthereceiverfunctionsareprocessedthrougharesonance-removalfilter,andtheH-κstackingistime-corrected.Resultsshowthatthecrustalthicknessrangesfrom30to55kminthestudyarea,reachingitsthickestvalueinthenorthwestandthinningtowardsouthwest,southeastandnortheast.TheapparentvariationofcrustalthicknessaroundtheRedRiverFaultsupportstheviewofsoutheasternescapeoftheTibetanPlateau.RelativelythincrustalthicknessinthezonebetweenChuxiongCityandtheRedRiverFaultindicatespossibleupliftofmantleinthisarea.ThepositivecorrelationbetweencrustalthicknessandPoisson’sratioislikelytoberelatedtolowercrustthickening.Comparisonofresultsobtainedfromdifferentmethodsshowsthattheimprovedmethodusedinourstudycaneffectivelyremovethereverberationeffectofsedimentarylayers.

  • 标签: receiver functions sedimentary layer SOUTHEAST MARGIN
  • 简介:TheTibetanPlateau,knownas“theroofoftheworld”and“thethirdpoleoftheearth”,isaproductofthecollisionbetweenIndiaandAsiaduringthelast~50Ma.Theregionaltectonics–inparticular,growthandexpansionoftheplateau–hasbeenattributedprimarilytodeformationwithinthelithosphere.Theroleandpatternoftheunderlyingasthenosphericflow,however,remainmostlyunaddressed.Inlightofrecentseismictomographicimagesandpublishedseismicanisotropicdescriptionsoftheuppermantle,hereweproposethatanentrainedmantleflowislikelytoexistunderTibet,inducedbythenorthwardadvancingIndianplate.ThedirectionofmantleflowischaracterizedbyagradualrotationfromnorthwardinthesouthtoeastwardinthenorthasaresultofdeflectionbythedeeprootoftheTarimblock.Thepresenceofanunderlyingmantleflowisnotonlyabletoaccountforthewest-eastorientedfast-axisofseismicanisotropyinnorthernTibet,butcanalsoadequatelyexplainthesporadicnullsplittinginsouthernTibet.Specifically,thenullsplittingresults,atleastinpart,fromupwellingsofasthenosphericflowthroughtearsoftheunderthrustingIndianplatethathavebeenrevealedbyvariousseismicobservations.ThemantleflowmayinturnpromotetheblockextrusionunderTibetthathasbeenobservedinGPSmeasurements;hotasthenosphericupwellingsmayalsoleadtowidespreadpost-collisionalmagmatisminsouthernTibet.

  • 标签: TIBET seismic anisotropy MANTLE flow NULL
  • 简介:Weanalyzed360permanentandcampaignGPSdatafrom1999to2017inthesouthernSichuan-Yunanblock,andobtainedcrustalhorizontaldeformationinthisregion.Then,wederivedthestrainrateusingamulti-scalesphericalwaveletmethod.ResultsrevealacomplexpatternoftectonicmovementinthesouthernSichuan-Yunnanblock.ComparedtothestableEurasianplate,themaximumrateofthehorizontaldeformationinthesouthernSichuan-Yunnanblockisapproximately22mm/a.TheXiaojiangfaultshowsasignificantlylowerdeformation—aleft-lateralstrike-slipmovementof9.5mm/a.TheHonghefaultclearlyshowsacomplexsegmentaldeformationfromthenorthtosouth.ThenorthernHonghefaultshows4.3mm/arightstrike-slipwith6.7mm/aextension;thesouthernHonghefaultshows1.9mm/arightstrike-slipwith1.9mm/aextension;thejunctionzoneintheHongheandLijiang–Xiaojinhefaultsshowsanobviousclockwise-rotationdeformation.Thestraincalculationresultsrevealthatthemaximumshear-strainrateinthisregionreaches70nstrain/a,concentratedaroundtheXiaojiangfaultandatthejunctionoftheHongheandLijiang–Xiaojinhefaults.Wenotethatmostoftheearthquakeswithmagnitudesof4andabovethatoccurredinthisregionwerewithinthehighshearstrain-ratezonesandthestrainrategradientboundaryzone,whichindicatesthatthemagnitudeofstrainaccumulationiscloselyrelatedtotheseismicactivities.Comparisonofthefastshear-wavepolarizationdirectionoftheupper-crustwiththeupper-mantleanisotropyandthedirectionofthesurfaceprincipalcompressivestrainrateobtainedfromtheinversionoftheGPSdatarevealsthatthedirectionofthesurfaceprincipalcompressivestrainisbasicallyconsistentwiththefastshear-wavepolarizationdirectionoftheuppercrustanisotropy,butdifferentfromthepolarizationdirectionoftheuppermantle.OurresultssupportthehypothesisthattheprincipalelementsofthedeformationmechanisminthesouthernSichuan-Yunnanblockaredeco

  • 标签: GPS DATA CRUSTAL horizontal deformation extension
  • 简介:ThelinkbetweenthecrustaldeformationandmantlekinematicsintheTibetanPlateauhasbeenwellknownthankstodenseGPSmeasurementsandtherelativelydetailedanisotropystructureofthelithosphericmantle.However,whetherthecrustdeformscoherentlywiththeuppermantleintheShan-Thaiterrane(alsoknownastheShan-Thaiblock)remainsunclear.Inthisstudy,weinvestigatethedeformationpatternsthroughstrainratetensorsinthesoutheasternTibetanPlateauderivedfromthelatestGPSmeasurementsandfindthatintheShan-Thaiterranetheuppercrustmaybecoupledwiththelowercrustandtheuppermantle.TheGPS-derivedstrainratetensorsareinagreementwiththeslippingpatternsandratesofmajorstrike-slipfaultsintheregion.Themostprominentshearzone,whoseshearstrainratesarelargerthan100×10^–9a^–1,isabout1000-km-longinthewest,trendingnorthwardalongSagaingfaulttotheEasternHimalayanSyntaxisinthenorth,withmaximumrateofcompressivestrainupto–240×10^–9a^–1.AsecondaryshearzonealongtheAnninghe-XiaojiangFaultintheeastshowssegmentedshearzonesnearseveralconjunctions.WhilethestrainratealongRRFisrelativelylowduetothelowsliprateandlowseismicitythere,inLijiangandTengchongseverallocalshearzonesarepresentunderanextensionaldominatedstressregimethatisrelatedtonormalfaultingearthquakesandvolcanism,respectively.Furthermore,bycomparingGPS-derivedstrainratetensorswithearthquakefocalmechanisms,wefindthat75.8%(100outof132)oftheearthquakeT-axesareconsistentwiththeGPS-derivedstrainrates.Moreover,wefindthattheFastVelocityDirection(FVDs)atthreedepthsbeneaththeShan-Thaiterraneareconsistentwithextensionalstrainratewithgraduallyincreasingangulardifferences,whicharelikelyresultingfromthebasalshearforcesinducedbyasthenosphericflowassociatedwiththeobliquesubductionoftheIndiaplatebeneaththeShan-Thaiterrane.Therefore,inthisregiontheuppercrustd

  • 标签: strain rate TENSOR GPS measurement LITHOSPHERIC
  • 简介:TheGarouaZoneinNorthCameroon,thesubjectofthisstudy,isknowntohaveundergonetectonicmovementsduringtheCretaceous,butthezone’sstructuraldataremainpoorlyknown.ThisstudyexploitstheBougueranomalytoimproveknowledgeofGarouatectonicsstructures.Inordertocharacterizethesestructures,twomethodsareused:Euler’sdeconvolutionmethodandthemethodofthehorizontalgradientoftheverticalderivative.SuperpositionoftheEuler’ssolutionsmapforindexN=1withthemapfromthehorizontalgradientoftheverticalderivativemethodallowsdeterminationofgravimetriclineaments,interpretedasfaultsoraslinearcontacts,fromwhichwededuceastructuralmapofthestudyarea.Basedonthismap,weidentifysixteenlineaments,ofwhichwecounteightaslinearcontactsandeightasfaults.Amongthefaults,wedenoteoneofdepthbetween4and8km,fivefaultsofdepthrangingbetween8and13km,andtwofaultsofdepthsbetween13and36km.Analysisofthesefaultsshowsthatthesevendeepestfaultsmightpresentanaturalriskinourstudyarea.Forpurposesofcivilprotection,suchdeepfaultsshouldbemonitoredandtakenintoconsiderationintheimplementationoflargepublicworks.Thestructuralmap,establishedhereinfromdataonthein-depthextensionofeachfault,thusincreasesscientificknowledgeintheareathatcanbeusedtositepublicworksinwaysthatreducerisk.

  • 标签: Bouguer ANOMALY horizontal DERIVATIVE vertical DERIVATIVE
  • 简介:Thequantitativeinterpretationofgravityanomaliesduetoshallowstructuresneedsseparationbetweenlongwavelengthanomalies(regionalanomalies)andshortwavelengthanomalies(residualanomalies).Theregional-residualfieldseparationcanbecarriedoutusingthepolynomialmethod.Inthiscase,theso-calledregionalfieldofordernistreatedasapolynomialofdegreen.Thepresentstudyshowsthatthedegreenmustvarybetweenasmallestvaluenminandamaximumvaluenmax.Thisarticlepresentsamethodtoprocessgravitydatathatallowsdeterminationofnminandnmaxforagivenstudyarea.WeapplythemethodtogravitydataoftheSouth-WestCameroonzone.Inthischosenstudyarea,wefindthatregionalanomalymapsofordersrangingfrom1to9andresidualanomalymapsofordersrangingfrom1to8canbeusedforsuitableinterpretation.Theanalysesshowthatonemayneedresidualanomalymapsofseveralorderstoperformsatisfactoryquantitativeinterpretationofthedifferentintrusivebodiesfoundinagivenarea.

  • 标签: gravity REGIONAL ANOMALY RESIDUAL ANOMALY upward
  • 简介:AnewcombinedFermi,betatron,andturbulentelectronaccelerationmechanismisproposedininteractionofmagneticislandsduringturbulentmagneticreconnectionevolutioninexplosiveastrophysicalphenomenaatlargetemporal-spatialscale(LTSTMR),theratioofobservedcurrentsheetsthicknesstoelectroncharacteristiclength,electronLarmorradiusforlow-βandelectroninertiallengthforhigh-β,isontheorderof10^10–10^11;theratioofobservedevolutiontimetoelectrongyroperiodisontheorderof10^7–10^9).Theoriginalcombinedaccelerationmodelisknowntobeoneofgreatestimportanceintheinteractionofmagneticislands;itassumesthatthecontinuouskinetic-dynamictemporal-spatialscaleevolutionoccursastwoseparateindependentprocesses.Inthispaper,wereconsiderthecombinedaccelerationmechanismbyintroducingakinetic-dynamic-hydrofull-coupledmodelinsteadoftheoriginalmicro-kineticormacro-dynamicmodel.Weinvestigatedifferentaccelerationmechanismsinthevicinityofneutralpointsinmagneticislandsevolution,fromthestageofshrinkandbreakupintosmallerislands(kineticscale),tothestageofcoalescenceandgrowthintolargerislands(dynamicscale),tothestagesofconstantandquasi-constant(contracting-expanding)islands(hydroscale).Asaresult,wegiveforthefirsttimetheaccelerationefficienciesofdifferenttypesofaccelerationmechanismsinmagneticislands’interactionsinsolaratmosphereLTSTMRactivities(pico-,10^–2–10^5m;nano-,10^5–10^6m;micro-,10^6–10^7m;macro-,10^7–10^8m;large-,10^8–10^9m).

  • 标签: hybrid PARTICLE ACCELERATION mechanism LARGE temporal-spatial
  • 简介:Inthispaper,theSpaceWeatherModelingFramework(SWMF)isusedtosimulatethereal-timeresponseofthemagnetospheretoasolarwindeventonJune5,1998,inwhichtheinterplanetarymagneticfieldshifteditsdirectionfromnorthtosouth.Sincemostcurrentmodelsdonottakeintoaccountconvectiveeffectsoftheinnermagnetosphere,wefirststudytheimportanceofRiceConvectionModel(RCM)intheglobalmodel.Wethenfocusonthefollowingfouraspectsofthemagnetosphere’sresponse:themagnetosphere’sdensitydistribution,thestructureofitsmagneticfieldlines,theareaofthepolarcapboundary,andthecorrespondingionosphericcurrentchange.Wefindthat(1)whentheIMFchangesfromnorthtosouthinthisevent,highmagnetosheathdensityisobservedtoflowdownstreamalongthemagnetopausewiththesolarwind;low-latitudereconnectionatdaysideoccursunderthesouthwardIMF,whilethemagneticfieldlinesinthetaillobecaudal,causedbythenightsidehighlatitudereconnection,extendintotheinterplanetaryspace.Openmagneticfieldlinesexistsimultaneouslyatbothhighandlowlatitudesatthemagnetopause;(2)theareaofthepolarcapisobviouslyincreasediftheIMFturnsfromthenorthtothesouth;thisobservationishighlyconsistentwithempiricalobservations;(3)theionosphericfieldaligncurrentinthenorthernhemisphereisstrongerthaninthesouthernhemisphereandalsoincreasesastheIMFchangesfromnorthtosouth.SWMFwiththeRiceConvectioneffectprovidesreliablemodelingofthemagnetosphericandionosphericresponsetothissolarwindvariation.

  • 标签: MAGNETOSPHERE global MHD simulation POLAR cap
  • 简介:Low-frequencychorusemissionshaverecentlyattractedmuchattentionduetothesuggestionthattheymayplayimportantrolesinthedynamicsoftheVanAllenBelts.However,themechanism(s)generatingtheselow-frequencychorusemissionshavenotbeenwellunderstood.Inthisletter,wereportaninterestingcaseinwhichbackgroundplasmadensityloweredthelowercutofffrequencyofchorusemissionsfromabove0.1fce(typicalordinarychorus)to0.02fce(extremelylow-frequencychorus).Thoseextremelylow-frequencychoruswaveswereobservedinaratherdenseplasma,wherethenumberdensityNewasfoundtobeseveraltimeslargerthanhasbeenassociatedwithobservationsofordinarychoruswaves.Forsuprathermalelectronswhosefreeenergyissuppliedbyanisotropictemperatures,lineargrowthrates(calculatedusingin-situplasmaparametersmeasuredbytheVanAllenProbes)showthatwhistlermodeinstabilitycanoccuratfrequenciesbelow0.1fcewhenthebackgroundplasmadensityNeincreases.EspeciallywhenNereaches90cm^-3ormore,thelowestunstablefrequencycanextendto0.02fceorevenless,whichisconsistentwithsatelliteobservations.Therefore,ourresultsdemonstratethatadensebackgroundplasmacouldplayanessentialroleintheexcitationofextremelylowfrequencychoruswavesbycontrollingthewavegrowthrates.

  • 标签: LOW-FREQUENCY CHORUS EMISSIONS anisotropic temperature instability
  • 简介:AtUTC2018-01-1002:51:31,anMw7.6earthquakeoccurred44kmeastofGreatSwanIsland,Honduras(location17.469°N,83.520°W,depth10km,accordingtotheUnitedStatesGeologicalSurvey).Wecarriedoutstudiesofthefocalmechanismandruptureprocessoftheearthquake,usingseismicdatafromtheIRISdatacenter.Forthefocalmechanismsolution,apointsourcemodelwasusedtoinvert26far-fieldP-waveformsand26SHwaveformswithhighS/Nratioandrelativelyevenazimuthcoverage(epicentraldistance30°<△<90°);thentheresult(Figure1)wasusedtoconstructafinitefaultmodelforruptureprocessinversion(YaoZXandJiC,1997;WangWMetal.,2008),resultinginapreliminarymodeloftheslipdistributionofthisearthquake(Figures2–4).Thecalculatedseismicmomentis2.41×10^20N·mandtheestimatedearthquakemagnitudeMw=7.5.Themaximumslipisabout1900cm.

  • 标签: EAST of GREAT SWAN ISLAND EARTHQUAKE