TheCross-CalibratedMulti-Platform(CCMP)OceanVectorWindAnalysis
(V2.0)CarlA.Mears,L.Ricciardulli,J.ScottandF.J.Wentz
RemoteSensingSystems
RossHoffman, S.MarkLeidnerAtmosphericandEnvironmentalResearch
RobertAtlasNOAA/AOML
Outline
1. WhatisCCMP?2. What’snewinVersion2.03. LimitationsandFuturePlans
WhatisCCMP?
BackgroundField
SatelliteMeasurementsBuoyWinds Speedsconsistent
withmeasurementswheretheyexist.
DirectioninformationandgapfillingfromBackground
CCMPVectorWindsOriginallyDevelopedbyAtlas,Hoffman,
VariationalAnalysis• CCMPisconstructedbyminimizingacostfunction.• Thisfunctionhas2parts:
• Agreementwithmeasurements.
• Agreementwiththebackgroundfield.Disagreementwiththebackgroundmustbebothsmall,andsmooth.Enforcedbyconstraintsonthevectormagnitude,divergence,vorticity,andLaplacianoftheBackgroundminusAnalysisdifference.
• ThesetermsareweightedbyempiricallydeterminedweightsthataffectthebehavioroftheVAM.• ForCCMP,thesearechosensothatobservationsaremuchmoreimportantthanthebackground.
( ) ( )22 or A O A OV V V V- -å å
VariationalAnalysis:EffectoftheWeights
• So:• Whenanobservationexists(andiscloseintime),CCMPwindspeedisveryclose(0.5m/srms)totheobservations.• Whennonearbyobservationsexists,CCMPyieldsthebackgroundfield.• Thesmoothnessconstraintsmakethetransitionfromthesetworegimessmooth,withlowvorticityanddivergence.ThishelpstheVAMassignwinddirectiontowindspeedmeasurementsfromsatellites.
ERA-Int BackgroundField
CCMPV2.0
DifferencesBetweenV1.0andV2.0Version1.0 Version2.0Background:
ERA-40(before1999)ECMWF OperationalAnalysis
Background:ERA-Interim
Satellite RadiometerWindsUsedwhateverRSSversionwasavailable,sodifferentversionsusedovertime.
SatelliteRadiometerWindsUsesRSS Version7only,sointercalibrationbetweensatellitedataismuchimproved.
Uses SSM/I,AMSRE,QuikScat SSMIS, Windsat,AMSR2,GMI,andASCATadded
1987-2011 1987-2016, updatedevery6monthsorso.
RunatNASA GSFC RunatRemoteSensing Systems.(thisiscurrentlydonewithzerofunding)
AvailableviaFTPatftp2.remss.com/ccmp/v02.0/
Buoys:TAO,Triton,PIRATA,NDBC,RAMA
HowImportantaretheBuoys?Experiment:RemovemostoftheTAOArrayat5degreesand8Degrees
MonthlyMeanZonalWind,AllBuoys
MonthlyMeanZonalWind,BuoysRemoved
Difference,BuoysRemoved- Baseline
ProsandLimitations….
Pros:• SpatiallyComplete(nogapsbetweenswaths,nearland,inrain)• Onedatasetspansentiretimeperiod.• WindsinbetteragreementwithobservationsthanReanalysis(butseelimitationsbelow.)• Additionalinformationonintermediate(~200km)lengthscalesascomparedtoreanalysis.
ThesefeatureshavemadetheproductVERYpopular.>350PeerreviewedpapershaveusedCCMPV1andV2.
Limitations:
• Notsogoodforlong-termtrends.• Problemsoverregionsofanomalousstability.• Problemsinregionsofhighspeedoceancurrents.
• Notsogoodforsmallscalefeatures(<200km).
Sourcesoftheselimitations
• MuchoftheseproblemsarecausedbydifferencesbetweenERA-InterimandtheSatellitewinds.• Satellitewindsare10mEquivalentNeutralStabilityWinds• ButERA-Int windsareactual10mwinds.• Satellitesmeasurerelativewinds(i.e.relativetotheoceansurface,whichmightbemoving)• ERA-Interimwindsarebiasedlowrelativetosatellitesatwindsaboveabout15m/s.
CCMPLong-TermTrendLargerthaninitsSources
Why?
Overtime,moreandmoresatelliteobservationsareincluded.
Thusagreaterproportionofthewindsareadjustedupwardtomatchthehighersatellitewinds
Thisresultsinaspuriousupwardtrend.
ERA-Int isbiasedlowvs.satellitesathighwindspeed
AMSR2– ERA-Interim10mWindsJJA2013 RegionsofWarmAiroverColdWater
HighStability->10mwindsdon’tmixdownwell.Surfaceroughnesslessthanusual…
ERA-Interim– AMSR2(m/s)Neartheequator,differencearelikelyduetoacombinationofstability,oceancurrents,andraineffects.
ERA-Interimconvertedto10mNeutralEquivalentWinds(LiuandTang,1996)
ERA-Interim– AMSR2(m/s)
AddedhighwindadjustmenttoERA-Interim.
ERA-Interim– AMSR2(m/s)
Improvements
• AdjusttheBackgroundforBackground/ObservationBiases,whichshouldreducespuriousglobaltrends.• Convertbackgroundto10mneutralstabilitywindsbeforeusing.Thisshouldreduceproblemswithregionsofhigh/lowstability.• Accountforoceancurrents,particularlyintropics.• (Long-Term)generateastressproductusingsimilarmethods.
CCMPLives!
