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.

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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!