Warm-rain-process-convection暖雨过程对流课件

HeavyrainfallandflashfloodHeavyrainfallandflashflood1Warm-rain-process-convection暖雨过程对流课件2FlashFloodsFlashfloodsarethenumberoneweather-relatedkillerinovermuchoftheglobeNearlyhalfofallflashfloodfatalitiesareautorelatedFlashFloodsFlashfloodsaret3Warm-rain-process-convection暖雨过程对流课件4FlashFloodDefinitionIntensePrecipitationSmallfast-responsebasins“Asituationwherethecausativeprecipitationandthesubsequentrunoffareoccurringonthesamescales.”

NATOAdvancedStudyInstitute(1999)FlashFloodDefinitionIntense5FlashfloodforecastingTheflashflood-aprototypicalhydro-meteorologicaltopicAmeteorologicalevent:rainfallAhydrologicalsettingBasinresponsetimesRunoffcharacteristicsWorkingwithhydrologists?Flashflood“guidance”isanestimateoftherainfallneededforflashfloodingtooccurFlashfloodforecastingThefla6FloodconsiderationsLargeriversliketheYangtzerespondtotherainfalloveraperiodofdaysFlashfloods-responsetorainfallisveryrapid:periodofperhaps10sofminutesSmallbasinsincomplexterrainarethosemostlikelytohaveflashfloodsUrbanfloodingcanhaveimportantimpacts-highrunoff.FloodconsiderationsLargerive720070718JinanFlashFloodingEventJinanisthecapitalcityofShandongprovince.During12hperiodfrom14:00BST(BeijingStandardTime)18Julyto02:00BST19July2007,theaveragerainfallfrom123weatherstationsforwholeShandongprovinceis62mm.Itscapitalcity,Jinan,hasexperiencedmostsevererainfall.The12hrainfallindowntownareais140mm,mostoftherainfallwasprecipitatedduring3hperiodfrom17:20to20:20BSTon18July2007.25peoplewerekilledbytheflashfloodinginJinancity.20070718JinanFlashFlooding8AFFForecastingstrategyObtainflashfloodguidancefromhydrologists:theminimumrainfallperunittimeneededfortheoccurrenceofaflashfloodBeginwiththequestion:“Whatistheprobabilityofrainfallapproachingthatvaluetoday?”AFFForecastingstrategyObtai9Precipitationin

FlashFloodsAccumulation5-50cmover1-12hoursDurationMostlylessthan3hoursIntensity

Arid/semi-aridclimates7.5-20cm/hour(avg.11.5cm/hour)Humidclimates12.5-30cm/hour(avg.19cm/hour)CourtesyMattKelschPrecipitationin

FlashFloods10Precipitationin

FlashFloodsEnhancedIntensityPrecipitationefficiencyTropical,maritimeconnectionDeep,above-freezinglayerLow-leveljet,rapidmoisturereplenishmentLow-levelfocus(terrainandboundary)/class/FLOAT_2001/index.htmPrecipitationin

FlashFloods11ThelowleverjetThelowleverjet12ThelowleveljetThelowleveljet13ThelowleveljetfromsouthwestThelowleveljetfromsouthwe14LowleveljetfromeastandmiddleleveljetfromsouthwestLowleveljetfromeastandmi15BasinCharacteristics

inFlashFloodsSmall9-150km2(avg.55km2)70%mountainouswatersheds>50%alteredUrbanizationDeforestation,firescarsThin/impermeablesurfacelayer,Clay,rocks(lowinfiltration)Pavement(noinfiltration)Or,thick,saturatedsoillayersCourtesyMattKelschBasinCharacteristics

inFlash16FlashFloodForecastingInsomecasesthehydrologyisthedrivingforce,andsignificantflashfloodscanhappenwithunimpressiverainfall.“FlashFloodforecastingrequiresmorethanaccurateforecastsofexcessiveaccumulation.”

-MattKelsch(2000)FlashFloodForecastingInsome17FlashFloodForecastingKnowrunoffcharacteristicsSmall,fast-responsebasinsUrbanbasinsDeforestationandfirescarareas.HailremainingonedayafterCheyenne,WYflashfloodof

1August1984FlashFloodForecastingKnowru18FlashFloodForecastingKnowledgeofrelationshipofstormspeedanddirectiontostreamflowcanbecriticalFlashFloodForecastingKnowled19FlashfloodforecastingWhathappenstothewateronthegroundisjustasimportant,andinsomecasesmoreimportant.Knowyourbasins!Flashfloodforecasting20RainfallAmountBasically,theamountofrainfallthatfallsoveranareadependson:TheINTENSITYoftherainfallTheSIZEoftherainfallareaThePROPAGATIONoftherainfallareaRainfallAmountBasically,the21RainfallAmount(cont.)Additionalconsiderationsdetermininghowmuchrainwillfallinclude:Howmuchmoistureisavailable?Willtheprecipitationbeconvectiveornot?Willcellstrainoverthesameareaornot?Willnewstormsformorcontinuetoformupstream?(regeneration)Willaboundaryorlocaltopographyprovidelocalenhancement?RainfallAmount(cont.)Additio22FlashFloodThreatfromWeaklyshearedCellsRainfallcontributionstotheflashfloodthreatare:therainfallrate,anditsduration.Rainfallrateisdependenton:theupwardmoistureflux,andespecially,precipitationefficiencyFlashFloodThreatfromWeakly23FlashfloodthreatfromweaklyshearedcellsUpwardmoisturefluxdependsonUpdraftstrengthMoisturecontentofairenteringupdraftPrecipitationefficiencyisthefractionoftotalmoistureingestedbytheupdraftthatfallsbacktothegroundasrainfall.Environmentsfavoringhighprecipitationefficiencyaremostlikelyassociatedwithflashfloodreports Flashfloodthreatfromweakly24FlashfloodthreatfromweaklyshearedcellsFavorableconditionsforhighprecipitationefficiency:Highmid-levelrelativehumidity(littledryentrainment)Deepwarmcloudlayer(increasewarmcollisioncoalescencemicrophysics)Wideupdrafts(reducedryentrainment)SeedingFlashfloodthreatfromweakly25BasicprinciplesChappell’sLaw-Part1Rainfallrate,R

EwqE=precipitationefficiencyw=ascentrateq=watervapormixingratioBasicprinciplesChappell’sLaw26EffiencyschematicEffiencyschematic27Whatcontrolsefficiency?EvaporationofcondensedwaterEnvironmentalhumidityWindshearExportationofcondensedwaterintoanvil,typicallyintheformoficeMultiplecellsEarlycellsmaybeinefficientLatercellsdevelopinanewenvironmentspectrumofclouddropletsizesLargerarealcoverageofMPSWhatcontrolsefficiency?Evapo28FlashfloodthreatfromweaklyshearedcellsWarmclouddepthincreasescollisioncoalescenceresultinginexcessiverainfallratesStormtopmaynotbehighFlashfloodthreatfromweakly29FlashfloodthreatfromweaklyshearedcellsAsignatureofadeepwarmcloudLookforsignificantincreaseinreflectivityfromthefreezingleveldowntotheLCLRadarwillunderestimaterainfallpotentialofthesestormsifbeamrisesabovetheLCLFlashfloodthreatfromweakly30Warm-rain-process-convection暖雨过程对流课件3117:53BST0.5°reflectivity(yellowthinlinerepresentthepositionofverticalcrosssection)17:53BST0.5°reflect3217:53BST17:53BST33Thesooneryoucankeyinonwarmrainprocessdominatedconvection,thequickeryoucanswitchtotropicalZ/Randhelpdetectflashflood-producingrainAnticipatingDominantWarmRainProcessConvectionEnvironmentalassessmentismostimportant,thensupplementwithreal-timedatasignaturesThesooneryoucankeyinonw34AssesstheenvironmentAssesstheenvironment35Jinan2007071808Jinan200707180836Jinan2007071814Jinan200707181437Jinan2007071820Jinan200707182038Xintai2007071808Xintai200707180839Zhengzhou2007071808Zhengzhou200707180840ComparisonofwarmrainconvectionwithintenseconvectionComparisonofwarmrainconvec41WarmRainProcesses

Real-TimeDataSignaturesLookforreflectivitystructures,satellite,andlightningdataHighreflectivityconcentratedbelowthein-cloudfreezinglevel(lowechocentroid)IRSatellite:Cloudtops“warm”LackofsignificantlightningWarmRainProcesses

Real-Time42WarmRainProcesses

RadarSignaturesKansasTurnpikeFlashFloodAug30,2003LECWarmRainProcesses

RadarSign4317:53BST0.5°reflectivity(yellowthinlinerepresentthepositionofverticalcrosssection)17:53BST0.5°reflect4417:53BST17:53BST45Warm-rain-process-convection暖雨过程对流课件46对流单体6时04分和6时10分剖面图对流单体6时04分和6时10分剖面图47Warm-rain-process-convection暖雨过程对流课件48Warm-rain-process-convection暖雨过程对流课件49Warm-rain-process-convection暖雨过程对流课件50Warm-rain-process-convection暖雨过程对流课件51WarmRainProcesses

ARecentExampleWarmRainProcesses

ARecentE52CrossSectionthroughWarm-RainSupercellCrossSectionthroughWarm-Rai53Warm-rain-process-convection暖雨过程对流课件54Warm-rain-process-convection暖雨过程对流课件55Warm-rain-process-convection暖雨过程对流课件56BasicprincipleChappell’sLaw-Part2DurationoftherainfallSizeoftherainfall“footprint”SpeedofmovementoftherainfallareaNotthesameasstormmovement!IndividualconvectivecellscanmovethroughaconvectivesystemBasicprincipleChappell’sLaw57DurationandintensityofrainDurationandintensityofrain58Warm-rain-process-convection暖雨过程对流课件591.0度速度图1.0度速度图60FlashfloodthreatfromweaklyshearedcellsFF-typedurationscanresultfromindividualstormsthathave:Slowmovement(<10kts)Largeareasofhighrainfallratesalongthemotionvector,celltraining,orAlloftheseFlashfloodthreatfromweakly61Rainfalldurationsfromindividualstormsdependon;(1)slowmovementand(2)largeareaofhighrainfallrates.Rainfalldurationsfromindivi62Warm-rain-process-convection暖雨过程对流课件63Warm-rain-process-convection暖雨过程对流课件64070021.01.27.591070021.02.27.591070021.01.19.591070021.02.19.591070021.03.27.591070021.03.19.591070021.00.37.591070021.00.41.591070021.00.57.591070021.01.27.591070021.02.27.565072422.01.27.591072422.02.27.591072422.01.19.591072422.02.19.591072422.03.27.591072422.03.19.591072422.00.37.591072422.00.41.591072422.00.57.591072422.01.27.591072422.02.27.566074206.01.27.591074206.02.27.591074206.01.19.591074206.02.19.591074206.03.27.591074206.03.19.591074206.00.37.591074206.00.41.591074206.00.57.591074206.01.27.591074206.02.27.567075355.01.27.591075355.02.27.591075355.01.19.591075355.02.19.591075355.03.27.591075355.03.19.591075355.00.37.591075355.00.41.591075355.00.57.591075355.01.27.591075355.02.27.568081703.01.27.591081703.02.27.591081703.01.19.591081703.02.19.591081703.03.27.591081703.03.19.591081703.00.37.591081703.00.41.591081703.00.57.591081703.01.27.591081703.02.27.569Warm-rain-process-convection暖雨过程对流课件70Warm-rain-process-convection暖雨过程对流课件71FlashfloodproducingconvectionSustainedconvectionisalwaysmulticellularSupercellstypicallyarenotefficientOftenmoverapidlySheared,highkineticenergyenvironments,oftenwithdeeplayersoflowhumidityabovetheboundarylayerNonsupercellstorms-bothdiscreteandlinearlyorganizedFlashfloodproducingconvecti72“CellTraining”PRODUCESASEQUENCEOFCELLS,REPEATEDLYPASSINGOVERTHESAMEAREA“CellTraining”PRODUCESASEQU73CellTrainingorRegenerationFactorsthatcanleadtoechotrainingorregenerationinthesameareainclude:Aslowmovinglow-levelboundaryorfrontAquasi-stationaryLLJAquasi-stationaryareaofupper-leveldivergenceAlow-levelboundaryalmostparalleltothemeanflow(sourceofmoistureconvergence)AlackofstrongverticalwindshearCellTrainingorRegenerationF74Warm-rain-process-convection暖雨过程对流课件75Trainingecho

76Warm-rain-process-convection暖雨过程对流课件77Warm-rain-process-convection暖雨过程对流课件78Warm-rain-process-convection暖雨过程对流课件79Warm-rain-process-convection暖雨过程对流课件80Warm-rain-process-convection暖雨过程对流课件81Warm-rain-process-convection暖雨过程对流课件82Warm-rain-process-convection暖雨过程对流课件83Warm-rain-process-convection暖雨过程对流课件84Warm-rain-process-convection暖雨过程对流课件85Warm-rain-process-convection暖雨过程对流课件86Warm-rain-process-convection暖雨过程对流课件87Warm-rain-process-convection暖雨过程对流课件88Warm-rain-process-convection暖雨过程对流课件89Warm-rain-process-convection暖雨过程对流课件90Warm-rain-process-convection暖雨过程对流课件91TrainingechoTrainingecho92SystemMovementNotsurprisingly,slowmovingsystemsusuallyproducetheheaviestrainfall!Forveryshort-termforecasts,extrapolationbasedonradarandsatelliteprovideprimaryguidanceForlongertermforecasts,modelsprovidedecentguidanceButyoustillneedtoconsidermodelcharacteristicsandlimitationsSystemMovementNotsurprisingl93CellMovementandPropagationSystemmovementdependsoncellmovementandpropagationIndividualconvectivecellsusuallymoveataround90%ofthemeanwindwithaslightdeviationtotherightPropagationisaffectedbyhowfastnewcellsformalongsomeflankofthesystemCellMovementandPropagationS94UsingRadarImagery(cont.)AnimatingimageryisusefulforDeterminingcell/systemmovementDeterminingifcellsaretrainingUsingRadarImagery(cont.)Ani95Warm-rain-process-convection暖雨过程对流课件96DiscussionQuestion

Whataresomeoftheradarlimitationsthatcanadverselyimpactyourdecisionmakingduringaheavyprecipitationevent?

AttenuationAnomalousPropagation(AP)–beampropagationRange–radarhorizonGroundclutterPoorcalibrationBeamblockageImproperZ/Rrelationship(algorithm)Hailcontamination(algorithm)BelowbeamaffectsBrightbandcontaminationPowerfailure,equipmentfailure

DiscussionQuestion Whatare97RainfallEstimationLimitationsBrightbandContaminationRadarCenteredArchofHigherRainfallAccumulationsonprouduct.OverestimaterainfallBut