WP2.5 – Coupled error covariances and bias

correc7on (1)XiangboFeng,KeithHaines,DavidMulholland

(2)EricdeBoisseson,Pa<rckLaloyaux

(1)  DepartmentofMeteorology,UniversityofReading,UK(2)  ECMWF,Reading,UK

18/01/17 ERA-CLIM23rdGeneralAssembly

UREAD: Deliverables

• D2.8ReportonstrengthsandweaknessesofweaklycoupledDAmethodsforEarthsystemreanalysis.UREAD18• D2.9Reportontechniquesforcalcula<ngcouplederrorcovariancesfromoutputsofaweaklycoupledDAexperiment.METO+UREAD18

18/01/17 ERA-CLIM23rdGeneralAssembly

• D2.10Reportonassessmentofcoupled-modeldri[andapproachesforobtainingconsistentoceanandatmosphericbiascorrec<ons.

UREAD34+12=46

Outline

1.  Calcula<onofcrosserrorcovariancesatvarying<mescalesfromCERA-20C(D2.9)

2.  StrengthsofCERA-20CoverERA-20C:SST-Prela<onship(D2.8)

3.  TemporalvariabilityofoceanbiasinCERA-20C(D2.10)

18/01/17 ERA-CLIM23rdGeneralAssembly

1. Calcula7ng cross error covariances based on CERA-20C

•  Method:CERA-20C=>10memberensembleproductEnsemblemean<>=Bestes<mateEnsemblespread=Uncertaintyes<mate(errors)Ensemblesavailableforboth24hourbackgroundfieldsxbandtheanalysesxaBackgrounderrorcovarianceprovidesbackgrounderrorinforma<onforassimila<onofsubsequentobserva<onsleadingtoanalysis•  DataSST,T2m,Mixedlayerdepths,u10,v10andprecipita<onhavebeenstudied3-hourfieldsusedforJanuary2006monthlyfieldsusedfor1900-2010Mostanalysesbasedonanalysisensemblesxa•  PaperSubmieedtoQJRMS

18/01/17 ERA-CLIM23rdGeneralAssembly

High-frequency varia7ons

ERA-CLIM23rdGeneralAssembly

3-hourfieldsfor1st-31stJanuary2006

•  T2mspread>SSTSpread•  T2mspreadlargeinITCZandinareas

withwesternboundarycurrents•  SSTspreadislargeinsummerandin

upwellingregions•  T2m-SSTerrorcorrela<onsarestronger

insummer(SH)andupwellingregions.•  Small-scaledailyanomaliesanddiurnal

cyclesarealsoseen

T2mspread

SSTspread

SST-T2mcorrela1on

1Jananom.

1Jananom.

1Jananom.

DiurnalcyclesofspreadsT2m,SST,SST-T2mCorrel.

1

0E 180E 0W

18/01/17 ERA-CLIM23rdGeneralAssembly

Time mean of monthly 7mescale varia7ons Data:Monthlyaverageofeachensemblemember,2006-2010

•  T2mandSSThavesimilarlarge-scalevaria<ons•  T2m<SSTspread,exceptinITCZ•  Correla<onsmostlysmallerwhereT2mspreadlarger•  Note:TAOmooringisposi<oned

T2mspread

SSTspread

T2mspread/SSTspread

T2m-SSTcorrela1on

18/01/17 ERA-CLIM23rdGeneralAssembly

Seasonal cycles

•  BothT2mandSSTspreadsexhibitaclearlarge-scaleseasonalcycle,0.02°C(10-20%ofthe<memean),withlargervaluesinsummerhemisphere.

•  SSTspreadhas±1-2month<melag.

•  AnnualamplitudeofT2m-SSTensemblecorrela<onis>0.1(15%ofthe<memean).

•  MLDandatmosphericconvec<onaredis<nguishedtobethecausesforsuchseasonalvariability.

AmplitudeofT2mspread

AmplitudeofSSTspread

AmplitudeofT2m-SSTcorrel.

PhaseofT2mspread

PhaseofSSTspread

PhaseofT2m-SSTcorrel.

Data:Monthlyaverageofeachensemblemember,2006-2010

18/01/17 ERA-CLIM23rdGeneralAssembly

Long-term changes Data:Monthlyaveragesofeachensemblemember,1900-2010

•  Spreadsdecreaseasobserva<onsincrease•  ChangesaroundWWs,1980and2008correspondingtoabruptdatachanges•  T2mspreadregulatedbywinduncertain<esinearlyyears•  Correla<onssteadilyincreasethenleveloffa[er1980•  Inter-annualvariabilitystronginNino3.4duetothedeepconvec<onmovement

SSTandT2mmean

SST,T2mand10mwindspreads

T2mandSSTensemblespreadra1oandcorrela1on

2. Strengths of weakly coupled DA for CERA-20C

18/01/17 ERA-CLIM23rdGeneralAssembly

SST-precipita<onrela<onship

•  AimToevaluatetheimprovementsofCERA-20Cinrepresen<ngatmosphere-oceanfeedbacks•  MethodLinearcorrela<onbetweenSSTandPrecipita1onmonthlyvariability•  DataCERA-20Cmember0ERA-20CObserva<ons:HadISST2ensemblemean,GPCPobserva<onsMonthlyfieldswithseasonalcycleremovedfor1979-2010

18/01/17 ERA-CLIM23rdGeneralAssembly

SST-P monthly variability correla7ons

ERA-20C CERA-20C

Observa1ons

•  ERA-20Chaswiderspreadofposi<vecorrela<ons•  CERA-20Cmoreconsistentwithobserva<ons

18/01/17 ERA-CLIM23rdGeneralAssembly

BlackcontourishighPregionsClimatologicalP>12cm/month

SST-P correla7ons: High Precip. P > 12cm/month

ERA-20C CERA-20C

Observa1ons

•  CERA-20Cespeciallyimprovestherela<onshipforhighPregions,whereair-seacouplingisstrong

18/01/17 ERA-CLIM23rdGeneralAssembly

ERA-20C CERA-20C

Observa1ons

•  CERA-20Calsogreatlyimprovestherela<onshipforthehigh-frequency(sub-seasonal)variability.

•  Obs.andCERA-20C:nega<vecorrela<on=>Precip.iscoolingSSTs.

SST-P correla7ons: Sub-seasonal variability (3-month running mean removed)

18/01/17 ERA-CLIM23rdGeneralAssembly

Monthly precipita7on differences for 7me mean GPCP-ERA-20C GPCP-CERA-20C

Errorreduc1oninCERA-20CcomparedtoERA-20C(posi1veforimprovement)

•  CERA-20Cprovidesabeeeres<mateofPrateoveroceansthanERA-20C,presumablyasaresultofthebeeersimulatedSST-Prela<onship.

RedcontourishighPregionsClimatologicalP>12cm/month

18/01/17 14

GlobalP.average,60°N-60°S

ERA-20CCERA-20CGPCP

Oceans Lands

Monthly varia7ons

UREAD: Deliverables • D2.8ReportonstrengthsandweaknessesofweaklycoupledDAmethodsforEarthsystemreanalysis.UREAD18• D2.9Reportontechniquesforcalcula<ngcouplederrorcovariancesfromoutputsofaweaklycoupledDAexperiment.METO+UREAD18• D2.10Reportonassessmentofcoupled-modeldri[andapproachesforobtainingconsistentoceanandatmosphericbiascorrec<ons.

UREAD34+12=46

18/01/17 ERA-CLIM23rdGeneralAssembly

18/01/17 ERA-CLIM23rdGeneralAssembly

3.1 Bias in Seasonal Forecas7ng system 4

•  ReportedatlastERACLIM2mee<ng•  Publ.Mulhollandetal2016

•  OceanAssimila<onBiascorrec<ons(T,S)maintainedintocoupledforecastruns

•  Correc<onsDampedover20days•  Equatorialwavenoisereduced•  Manyhindcastini<alcondi<onstested1980’sonwards

•  Nino3.4SSTforecastskillincreasedin4-7months

•  Availablefortes<ngatECMWF(alsoMetO)

Mulholland,HainesandBalmaseda2016QJRMS

18/01/17 ERA-CLIM23rdGeneralAssembly

3.2 Ocean bias in CERA-20C

SSTincrement

•  SSTinCERA-20Chasregionalbiasesw.r.tHadISST2by±0.5°C,andis~0.05°Cwarmeronglobalaverage

•  SSTincrementisusuallynega<ve,andisoneorderofmagnitudesmallerthan∆SST•  SSTbiasisconsiderablyconstantwith<me

∆SST

∆SST = CERA_an - HadISST2, and CERA_an- CERA_fc, 1900-2010

18/01/17 ERA-CLIM23rdGeneralAssembly

Mean subsurface T increment along tropics (5°N-5°S), 1990-2010

•  Modelzonalheatredistribu<oninerrorneardateline•  Errorsclearlyan<-correlated•  Nobiascorrec<onscurrentlybeingappliedwhichcouldreducethesemean

incrementscf.Mulholland

Time mean

Temporal variability

18/01/17 ERA-CLIM23rdGeneralAssembly

Associa7on with ver7cal thermocline advec7on

•  Monthlytemporalvaria<onsareassociatedwithlocalver<calvelocity,by~66.6deg.C/daypercm/s.

•  NoteTAOmooringsites

Correla<onbetweenTincrementandWvelocityvariability,1990-2010

Further bias correc7on work •  Oceanbiascorrec<onmethodshave(a)Climatologicalcorrec<on(needinglongpriorrun)+(b)Onlinecorrec<on•  TestwhetherOnlinecorrec<onscancompensatefor“approximate”climatologicalcorrec<one.g.useORAS4pre-processedclimatologicalcorrec<onsinCERA-20C?•  Inves<gateapplyingbiascorrec<oninCERA-20C(shortrunstotestimpact)•  Inves<gatebiascorrec<onsinCERA-SAT?Shortrunse.g.usingCERA-20CorORAP/S5climatologicalcorrec<ons•  Inves<gateotherapproachesforcorrec<ngoceanbiasinthetropicalthermocline,e.g.parametrizedwithver<calvelocity.

18/01/17 ERA-CLIM23rdGeneralAssembly

18/01/17 ERA-CLIM23rdGeneralAssembly

Thanks!