利用步长模拟对青藏高原涡度方差测量法的质量评价

2112200612ADVANCESINEARTHSCIENCEVol.21No.12Dec.20061001-8166200612-1260-08QualityAssessmentofTibetanPlateauEddyCovarianceMeasurementsUtilizingFootprintModelingS.Metzger1MAYao-ming2T.Markkanen1M.Gckede3LIMaoshan2T.Foken11.UniversityofBayreuthDepartmentofMicrometeorologyBayreuthGermany2.ChineseAcademyofSciencesInstituteofTibetanPlateauResearchBeijing100085China3.OregonStateUniversityDepartmentofForestScienceCorvallisUSAAbstractAqualityanalysisincludingfootprintmodellinghasrevealedspatialandtemporalstructuresinthequalityofEddyCovariancemeasurementsfortwohighlandsiteslocatedontheTibetanplateau.Fetchanalysishasshownthatupto1/3ofthemeasurementsdonotfulfillassumptionsnecessaryforaphysi-callycorrectdataprocessing.Despitethisfactmeasurementsoflatentheat-CO2-andmomentumfluxingeneralfulfillthequalitytestcriteriatoanextendthattheresultscanberegardedassuitableforfunda-mentalresearchwherebyusuallycertainwindsectorshavebeenfoundviolatingbasicassumptions.Measurementsofthesensibleheatfluxallowfortheusageincontinuouslyrunningmeasurementwhilestillfewindicationsofthequalityassessmentcannotbeexplainedduetolocaltopographybutindicateorganizedstructuresandleadtothehypothesisofmesoscaleflowpatternsintheboundarylayer.KeywordsAlpineECFootprintClimatologyGCMMesoscaleTibetQAQCClCnumberP412P463DocumentcodeA1IntroductionLandsurface-atmosphereinteractionprocessesplayanimportantroleintheenergyandmattercyclessuchasthatofCO2andwateroverawidemagnitudeofscales.Considerabledeficitexistsconcerningthea-bilitytoproperlydescribetheseprocessesespeciallyinhighelevationenvironmentswhichamongothersleadstosystematicallybiasedassessmentofclimatea-nomaliesbyGlobalClimateModelsGCMs.TheEddyCovarianceECmethodisthebestmeasurementtechniquecurrentlyavailableforthede-terminationofmatterandenergyfluxesbetweentheat-mosphereandtheunderlyingsurface.ThereforeECmethodhasbecomeawidelyacceptedtoolforthede-terminationofmatterandenergyfluxesappliedbyseveralfluxnetworkssuchasAmerifluxEUROFLUXandAsiaFluxoverallcoordinatedwithinFLUX-NET1.HowevertheadoptionoftheECmethodisbasedontheassumptionthatcertainstatisticalandme-teorologicalrequirementsarefulfilledandtheequip-mentisworkingreliably.Thedevelopmentofanauto-matedqualitycontrolandsitecharacterizationproce-dure23hasshownthatnon-idealconditionsarecom-monforawiderangeofsites.Theprocedureconsistsofqualitytests45incombinationwithaforwardLa-grangianfootprintmodel6usingdetailedterraindatagatheredbyremotesensingmethods.Qualitytestscov-ere.g.steadystateanddevelopedturbulenceassump-tionsandleadtoanoverallflaggingofthefluxdataReceivedate2006-10-11.BiographyS.MetzgerE-mailstefan.metzgeruni-bayreuth.dequality.Footprintmodelingdefinesthespatialcontextofthesefluxestherebythequalityflagscanbealloca-tedtodifferentwinddirectionsundervaryingmeteoro-logicalconditions.Thusthisprocedureenablesthecollectionofhigh-qualitydatasetsfortheassignmentofthesefluxestodifferentlandusetypesonlandscapescalewhichleadstorepresentativetrainingareasfortheamendmentofremotesensebasedGCMs.ECmethodisrarelyusedatalpineresearchsta-tionsmostofthemdominatedbyforestse.g.RenonItaly89andNiwotRidgeUSA8atelevationsupto3050m.ThisstudyaimstoevaluatetowhatextenttheECmethodcanbeappliedtotheconditionsofshal-lowandoftenverystableplanetaryboundarylayerlowpressureandextremedailyandseasonalcyclesoftem-peratureandstratificationoftheatmosphereovertheTibetanplateau.ThereforeresultsofthequalitycontrolprocedurefortwoTibetanplateaugrasslandsitesatele-vationsupto4745marepresented.2MaterialsandmethodsTheanalysiswascarriedoutfortwositesinTibetChinawithNaMuCuositelyingontheSEbanksofLakeNaMuCuolocated150kmNofLhasaandtheEverestsitelocatedinreachofthe1mountEverestbasecamp.ExactlocationsandmeasurementperiodsarelistedinTable1.LandusedataoftheChineseAcademyofSciencesCASwitharesolutionof50mwasused.LanduseclasseshadbeendistinguishedduetounsupervisedclassificationofLandsatTM/ETMimagesverifiedduringon-the-spotinvestigationsin2000.Forrefine-mentandevaluationthedirectsurroundingofthefluxtowerwasremappedin2006witharesolutionof20mduetoon-the-spotinvestigationscoveringareasof0.3km2Everestand1.6km2NaMuCuorespectively.SpatialReferencewasobtainedusingtheGarmineMapGPS.Measurementswerecarriedoutreceiving5-9sat-ellitescausingaspatialprecisionof57m.Intotal6landuseclassesweredistinguishedwhereasthereofthetargetlandusetypegrasslandwasdividedintwoclasseswithvegetationcoveringdegreesexceedingorundercutting50laterreferredtoasMeadow50andMeadow50.Coveringdegreeslessthan5areincludedinclassGravel.Elevationdatawitharesolutionof90mfromShuttleRadartopogra-phymeasurementSRTMprovidedbytheGlobalLandCoverFacilityGLCFhasbeenutilized.TheNaMuCuositeislocatedbetweentheLakeNaMuCuoin1kmdistanceNWandaNEE-SWWori-entedmountainrangepeaking5700mabovesealevelaslin15kmdistanceSSEseeFig.1aPlate.ThemeasurementitselfislocatedonalevelplanedominatinglanduseclassisMeadow50.Anothersmalllakeislocated150mNWofthetowerstretchingNE-SWfor2kmFig.3aPlate.80mWofthemeasurementthestationbuilding40mand80mNEa30mprofiletowerandacontainerfortracegasmeas-urementsaree