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vortex.pdf

vortex.pdf

李家的某某 2013-12-13 评分 0 浏览量 0 0 0 0 暂无简介 简介 举报

简介:本文档为《vortexpdf》,可适用于人文社科领域,主题内容包含VORTEXisthelargest,mostambitiousstudyfocusedonimprovingourunderstandingoft符等。

VORTEXisthelargest,mostambitiousstudyfocusedonimprovingourunderstandingoftornadoes,includingtornadogenesis,tornadostructure,andimprovingforecastsTHESECONDVERIFICATIONOFTHEORIGINSOFROTATIONINTORNADOESEXPERIMENTVORTEXbyJoshuaWurman,DaviDDoWell,yvettericharDson,PaulmarkoWski,erikrasmussen,DonalDburgess,louisWicker,anDhoWarDbbluesteinFigHistoryofleadtimes,probabilityofdetection,andfalsealarmratesfortornadowarningsImprovementsinwarningperformancearerelatedtointroductionsofnewtechnologyandforecastingmethodsNearlyallofthemostintensetornadoes,thosecapableofcausingthemostwidespreaddamageandlargestnumberoffatalities,arespawnedbysupercellthunderstormsRecently,computermodelsandobservingtechnologyusedtostudysupercellshavebecomemoreaccessibleandincreasinglysophisticated,enablingdetailedscientificexplorationofsupercellsandtornadoesImprovementstotornadoforecastsandwarningsinrecentdecadesmaybelinkedtoimprovementsinobservingtechnologyandunderstandingofprocessesrelatedtotornadoformation(Fig)Althoughtheseadvanceshaveledtoanincreaseinknowledgeandimprovementstoconceptualmodelsoftheprocessesgoverningtornadicstorms,theyalsohaveilluminatedgapsinourunderstandingoftornadogenesisandevolution,particularlythoseaspectsoftheproblemthatrequirecontemporaneousknowledgeofaugusTaMERICaNMETEOROLOgICaLsOCIETY|thewind,thermodynamic,andprecipitationfieldsinandaroundsupercellsThesegapsinourknowledge,andimprovementsinobservingcapabilities,motivatedthesecondVerificationoftheOriginsofRotationinTornadoesExperiment(VORTEX)asasuccessortotheoriginalVORTEX(VORTEX)andothersmallerfollowonprogramsUsingthelatestdevelopmentsinquicklydeployableobservingtechnology,theprimaryobjectivesofVORTEXweretoobtainsimultaneouswind,precipitation(p),andthermodynamicdatatoi)betterunderstandanddocumenttheprocessesunderlyingtornadogenesis,intensification,maintenance,anddemiseii)identifypropertiesofthelocalenvironmentthatareinfluentialinthetornadolifecycleiii)improvecomputermodelingandpredictionofsupercellthunderstormsandtornadoesandiv)improveourunderstandingofthenearsurfacestructureoftornadoesandtherelationshipbetweentornadicwindsanddamageTheoverarchinggoalofVORTEXwastoimprovetheunderstandingoftheprocessesthoughtessentialtoimprovingtheaccuracy,leadtime,andfalsealarmratesoftornadowarningsDelineatingthesubtle,poorlyunderstood,andordifficulttoobservedifferencesamongnontornadicsupercells,weaklytornadicsupercells,andviolentlytornadicsupercellswouldfurtherthisimprovementAdditionalobjectivesofVORTEX,thoughttobeimportantforimprovingforecastskill,weretodeterminehowstormsinteractwitheachotherandwiththeirlocalenvironmentandhowtheseinteractionsaffecttornadogenesis,maintenance,anddemiseDatacollectedbyVORTEXalsowillbeusedforthedevelopmentofstormscalenumericalweatherprediction(NWP)systemsFinally,becausemanyofthedetailsconcerningtornadostructurearenotwellunderstood,suchastheverticaldistributionofwindsandtheintensityandvariabilityofwindsnearthesurface,VORTEXsoughtdetaileddocumentationoftornadostructureanditsrelationshiptodamageRECENTOBSERVATIONALSTUDIESOFSUPERCELLSANDTORNADOESOurknowledgeoftornadoesandsupercellstormsprogressedsubstantiallyduringthelatterportionofthepreviouscentury(eg,LudlamLemonandDoswellDoswellandBurgessDaviesJonesetalMarkowskiandRichardson)However,untilthemids,muchofthisunderstandingarosefromtheoretical,laboratory,andnumericalmodelsaswellasfromlowresolutionobservationalstudiesMajorportionsoftheconceptualunderstandingoftornadogenesiswereunverifiedbyactualobservationsVORTEX:–Apivotalmomentoccurredin–,whenVORTEXestablishedanewexperimentalparadigmandpioneeredadecadeoftargeted,mobileexperimentsthatfocusedontornadicstormsandgreatlyenhancedourunderstandingofsupercellthunderstorms(Rasmussenetal)Potentiallytornadicstormsweretargetedbyanarrayofinstrumentation,includingaquicklyscanningmobileDopplerradar(WurmanetalWurman,),FMCWandWbandradars(Bluesteinetal,),anarrayofinstrumentedvehicles(themobilemesonetStrakaetal),severalmobileballoonsoundingsystems(Rustetal),severalmobilephotogrammetricteams,deployableinsituinstrumentation(Winnetal),andanaircraftfittedwithapseudodualDopplerradarsystem(WakimotoandAtkins)ThistargetablearrayofcuttingedgeinstrumentationpermittedthestudyoftornadoesandsupercellswithadegreeofdetailandbreadthneverbeforeachievedVORTEXestablishedtheviabilityofemployingalarge,fullyadaptablearrayoflandandairbasedinstrumentationtosampleshortlived,rare,andnonstationaryphenomenasuchastornadoesData,techniques,andknowledgefromVORTEXwereusedbymanyresearchers(eg,WakimotoandAtkinsWurmanetala,b,DowellandBluestein,a,bMarkowskietala,b,c,,,WakimotoetalWakimotoandAFFILIATIONS:WurmanCenterforSevereWeatherResearch,Boulder,ColoradoDoWellEarthSystemResearchLaboratory,NationalOceanicandAtmosphericAdministration,Boulder,ColoradoricharDsonanDmarkoWskiThePennsylvaniaStateUniversity,UniversityPark,PennsylvaniarasmussenRasmussenSystems,Mesa,ColoradoburgessCooperativeInstituteforMesoscaleMeteorologicalStudies,UniversityofOklahoma,Norman,OklahomaWickerNationalSevereStormsLaboratory,NationalOceanicandAtmosphericAdministration,Norman,OklahomabluesteinUniversityofOklahoma,Norman,OklahomaCORRESPONDINGAUTHOR:JoshuaWurman,CenterforSevereWeatherResearch,VassarCircle,Boulder,COEmail:jwurmancswrorgTheabstractforthisarticlecanbefoundinthisissue,followingthetableofcontentsDOI:BAMSDInfinalformFebruaryAmericanMeteorologicalSocietyaugust|LiuTrappRasmussenetal,WurmanandGillZiegleretalGilmoreandWickerFierroetalRichardsonetalStrakaetal)toadvanceourknowledgeoftornadicstormsVORTEXresultedinaqualitativechangeinourunderstandingoftornadicstormsObservationsrevealedstrikingkinematicsimilaritiesbetweentornadicandnontornadicsupercellsatscalesjustlargerthanthetornado,suggestingthattornadogenesisisaperhapsfragileprocessthatmaydependonsubtle,unobserveddifferencesinmorphologiesandprocesseswithinsupercellsandtheirambientenvironmentsAssuch,itisnowknownthatbothtornadicandnontornadicsupercellstormscancontainstronglowlevelmesocyclones(TrappMarkowskietal)ThoughtheimportanceofdowndraftsintornadogenesiswashypothesizedbeforeVORTEX(eg,LudlamDaviesJonesa,b),VORTEXfieldobservationsandrecentidealizedsimulationssuggestthatthethermodynamicpropertiesofthedowndraftmayplayanimportantroleinmodulatingtornadoformationandintensity(Markowskietal,)Ourawarenessoftheprevalenceofmesoscaleheterogeneities,suchasthoseassociatedwitholowboundariesandanvilshadowsinthesupercellenvironment,hasbeenheightened,leadingtonumericalsimulationstostudytheireffectsontheevolutionofconvectivestorms(AtkinsetalGilmoreandWickerFierroetalRichardsonetalFrameandMarkowski)Strongandviolenttornadoesoftenwerefoundtobeassociatedwithpreexistingmesoscaleboundaries(Markowskietalc)Additionally,finescaleobservationsoftornadostructureandevolutionwerefirstobtainedduringVORTEXThefirstdetailedthreedimensionalmapsofthewindsintornadoeswereobtainedbytheprototypeDoppleronWheels(DOW)mobileradarThesethreedimensionalmapsofthecoreflowandsurroundingregionswithfinetemporalandspatialresolutionpermittedthedocumentationofthehorizontal(H)andvertical(V)distributionofintensewindsandtheirevolution,centraldowndrafts,rapidchangesintornadostructure,andtheverticalandhorizontaldistributionofdebris(Wurmanetala,bWurmanandGillRasmussenandStraka)PostVORTEXfieldprojectsBuildingontheadaptive,targetedexperimentaldesignofVORTEX,severalsmallerfieldprogramsfocusingontornadoesandsupercellthunderstormswereundertakenduringthe–periodSeveralprograms,suchassubVORTEXwithrearflankdowndraft(RFD(MarkowskietalShabbottandMarkowski)andAnalysisoftheNearSurfaceWindandEnvironmentalongtheRearFlankofSupercells(ANSWERS)concentratedonthermodynamicobservations,primarilyusingmobilemesonetvehiclestostudythepropertiesofdowndraftsandtheirrelationshiptotornadogenesis(eg,LeeetalLeeetal)OtherfieldprojectsincludingtheRadarObservationofThunderstormsandTornadoesExperiment(ROTATEWurman,,,),utilizedmobileorquicklydeployablehighresolutionradarstostudytornadogenesisandmaintenance(DowelletalBluesteinetalaWurmanetalb,cMarquisetalWurmanetalMarquisetal)tornadostructure(WurmanBluesteinetalb,AlexanderandWurmanLeeandWurmanBluesteinetala,bTanamachietalKosibaetalKosibaandWurman)stormscaleprocessescoincidentwithtornadogenesis(WurmanetalcBiggerstaffetalBykoetal)therelationshipbetweentornadicwinds,debris,anddamage(BurgessetalWurmanandAlexanderDowelletalWurmanetala)andsupercellsthatdidnotproducetornadoes(BecketalFrameetalMarkowskietal)ROTATEoperatedofthepostVORTEXyears(–and–)andutilizeduptothreeDOWs,includingarapidscanDOW(Wurmanetal),mobilemesonetvehicles,andinstrumentedinsitutornadopodsItcollectedsingleandordualDopplerdatainapproximatelydifferenttornadoesandinmanynontornadicsupercells,allowingfortheconstructionofaradarbasedclimatologyoftornadocharacteristicsandkinematics(AlexanderandWurmanAlexander)MAJOROUTSTANDINGQUESTIONSINTORNADOSCIENCEAlthoughtheaforementionedstudieshavecontinuedtoadvanceourunderstandingoftornadoesandsupercellstorms,thelackofcontemporaneousthermodynamicdataandhighresolution,radarderivedwindfieldshaslimitedtheabilityofthesestudiestofullydiagnosetheprocessesinvolvedwithtornadogenesis,evolution,andstructure,becausethedevelopmentoflowlevelrotationislikelytodependonboththevorticitypresentintheenvironmentaswellasthatdevelopedbaroclinicallywithinthestorm’scoldpoolEvaluatingthecontributionsofeachoftheserequiresknowledgeofboththewindandthermodynamicaugustaMERICaNMEtEOROLOgICaLsOCIEtY|fieldsovermultiplespatialscalesandovertemporalperiodsextendingfarenoughbeforetornadogenesisthatparcelsparticipatinginthegenesisprocesscanbetracedbackthroughthestorm,revealingthesourceofrotationRecently,severaldataassimilationtechniquesforconvectivescalemodelshavebeenutilizedtoretrievethethreedimensionalthermodynamicandhydrometeorfieldsfromsingleDopplerdata(eg,DowelletalMarquisetal)but,withoutobservationstoverifyorrefutemodelgeneratedoutput,theveracityofthesecomputergeneratedfieldsremainslargelyuntestedSeveralkeyfocusareasrequiringadditionalstudywereidentifiedTornadogenesisThemostpressingproblemsintornadosciencearecenteredonpredictingtheoccurrenceofsignificanttornadoesie,tornadoescapableofinflictingdamagecorrespondingtoanenhancedFujita(EF)scaleratingoforhigherIdentifyingthosestormsthatwillproducesignificanttornadoesiscriticalbecausemostfatalitiesandcatastrophicdamageareassociatedwiththesmallfractionoftornadoesthatexhibitthemostintensewindspeeds(afractionthatmaybelargerthanpreviouslythought(AlexanderandWurmanAlexander)andtheevensmallerfractionthatimpactsdenselypopulatedareas(BrooksandDoswellWurmanetala)However,thisidentificationiscomplicatedbythefollowingobservations:•althoughmostsignificanttornadoesarespawnedfromsupercellthunderstorms,mostsupercellthunderstormsdonotproducetornadoesandanevensmallerfractionproducesignificanttornadoes(Trappetal)•ifatornadodoesoccur,itonlyoccursduringasmallportionofthelifetimeofthesupercellthunderstormand•mosttornadicsupercellthunderstorms,evenwhenproducingtornadoes,donotproducesignificanttornadoes(Verboutetal)AbriefreviewofourcurrentknowledgeoftornadogenesisispresentedhereThereaderisreferredtoDaviesJonesetal()andMarkowskiandRichardson()formoredetailedreviewsIntheabsenceofpreexistingenvironmentalverticalvorticity,supercellthunderstormsacquiremidlevelrotationthroughthetiltingofenvironmentalhorizontalvorticitybyanupdraftandthesubsequentstretchingofthisnowverticalvorticitybythehorizontalconvergenceassociatedwiththeupdraft(RotunnoLillyDaviesJones)AlthoughthetiltingofhorizontalvorticitysolelybyanupdraftcanproduceFigEvolutionofthevorticityvector(thinblackarrowsthesenseofrotationisindicatedbythebroad,curledblackarrows)alongtrajectories(blue)inthreesituationsTheupstreamvorticityisstreamwiseineachcase(a)Inthecaseofairrisingthroughupdraft,tiltingofhorizontalvorticitybytheupdraftalonecannotproduceverticalvorticityatthesurfacebecauseairisrisingawayfromthesurfaceasverticalvorticityisacquired(b)Inthecaseofairsubsidingthroughadowndraftinwhichbaroclinicvorticitygenerationisneglected,thehorizontalvorticityistilteddownwardduringdescentandreturnstoahorizontalorientationatthesurface(c)Inthecaseofairsubsidingthroughadowndraftinwhichhorizontalvorticityisgeneratedbaroclinicallybyahorizontalbuoyancy(B)gradient,suchthatwarmairisintothepage(thedirectionofvorticitygenerationistowardtherightandindicatedbythemagentaarrow),thebaroclinicvorticitygenerationintroduces,inthewordsofDaviesJonesandBrooks(,p),a“slippagebetweenthedescendingfluidandvortexlines”SubsequenttiltingofthevorticityvectorallowsairparcelstoreachthesurfacehavingcyclonicvorticityIntensestretchingcanfurtheramplifytheverticalvorticitynearthesurface(suchstretchingprobablyrequiresthatthedowndraftparcelsnotbetoonegativelybuoyant,lesttheycannotascendandbeassociatedwithlargedwdz)Here,(c)isadaptedfromDaviesJonesandBrooks()august|intenserotationatmidlevels,nonearsurfacerotationisgeneratedbecauseverticalvorticityonlydevelopsasparcelsriseawayfromthesurface(Fig)Therefore,downdraftsarecriticalintransportingandorgenerating(throughbarocliniceffectsandsubsequenttilting)lowlevelverticalvorticity(eg,DaviesJonesa,bRotunnoandKlempWalkoDaviesJonesandBrooksStrakaetal)Indeed,dualDoppleranalyses(eg,BrandesDowellandBluesteinWakimotoandCaiDowellandBluesteina)andnumericalsimulationsindicatethatatleastsomeairparcelspassthroughtheRFDbeforeenteringthetornado(WickerandWilhelmson)Downdraftshavelongbeenobservedintherearflanksofbothtornadicandnontornadicsupercells(eg,LudlamFujitaBurgessetalLemonandDoswell)SurfaceobservationsoftheRFDsuggestthatdifferentcombinationsofmicrophysicalanddynamicalprocessesmaybeimportantindifferentsupercells,atdifferentlocationswithinindividualRFDs,andatdifferenttimesinthesamesupercell(MarkowskietalGrzychetalHirthetal)Sometornadicsupercellscontainmultiplerearflankgustfronts(RFGFsWurmanetalcMarquisetalWurmanetalMarquisetal),suggestingthatsomeforcingmechanismsmaybetransientandthatRFDairreachingthegroundnearlycontemporaneouslywithinthesamesupercellmayreachthegroundwithsubstantiallydifferentthermodynamicproperties(FinleyandLee,Grzychetal)TherelativeimportanceoftheseprocessesintornadogenesisispoorlyunderstoodSupercellsandtheirenvironmentsUnderstandinghowtheenvironmentsofsupercellthunderstormsaffecttheirpropensitytocausetornadoesiscriticaltoourabilitytoforecasttornadogenesisStudieshaveshownthatenvironmentalvariabilityandsurfaceboundariescanaffectstormstructureandmayinstigatetornadogenesis(eg,MaddoxetalMarwitzandBurgessBrooksetal,WeckwerthetalMarkowskietalcRasmussenetalRichardsonetal)Althoughmanynumericalstudieshavebeenconductedonisolatedsupercellthunderstorms(eg,RotunnoandKlemp),supercellsinnaturearerarelyisolatedandtheirenvironmentsarefrequentlycomplex(eg,Ziegleretal)Supercellscandevelopfrommultiplesmallercells(BluesteinandParker),andrapidchangescanoccurafterinteractionwithanothercell(eg,LemonLeeetalBluesteinandGaddyHastingsandRichardson)Tornadogenesismayoccurafterstormmergers(LeeetalHoustonandWilhelmsonDowellandBluesteina,bMagsigandDowell)Wurmanetal(c)hypothesizedthattornadoesresultingfromcellmergersmighttendtobeweakandshortlivedItisnotclearwhichinteractionspromotetornadogenesisandwhicharedetrimentalLowlevelwindsintornadoesComputer,laboratory,andconceptualmodelsoftornadovorticesforamoredetailedreview,seeDaviesJonesetal()remainlargelyunsubstantiatedbyreliablequantitativeobservationsofactualtornadoesInordertohaveconfidenceinconceptualmodelsandtheoriesdevelopedfromlaboratoryandnumericalexperiments,quantitativeobservationsareneededinavarietyofactualtornadoeshavingavarietyofobservedstructuresAlthoughobservationalstudiesofthelowlevelandcoreflowregionsarechallenging,observationsbyradarandinsituinstrumentsoccasionallyhavebeenobtainedThemostfrequentobservationshavebeenbymobileradarsatcloserangetotornadoes(eg,Wurmanetala,b,WurmanandGillBluesteinandPazmanyWurmanLeeandWurmanBluesteinetalWur

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