Fakultät für Geowissenschaften, Geographie und Astronomie

Institut für Meteorologie und Geophysik

Homogenization of TEMP data with innovations from reanalyses

3rd WCRP Conference on Reanalyses, 31 Jan 2008

Leopold HaimbergerChristine Gruber, Stefan Sperka, Christina Tavolato

FWF, EC6FP, ECMWF, MetOffice

3rd WCRP Conference on Reanalyses, 31.1.2008

Wind direction biases

Gruber & Haimberger, 2008, MetZ, accepted

Wrong northdirection

y-H(xb)

100 hPa

3rd WCRP Conference on Reanalyses, 31.1.2008

RAOBCORE, RICH• RAdiosonde OBservation COrrection using REanalyses

• 1) Basic idea:– Analysis of time series of innovations y-H(xb) (obs-bg)

– Break detection with modified Standard Normal Homogeneity Test

• 2) Adjustment of detected breaks with:– mean innovations before/after breaks (Haimberger, 2007 J.Climate)

• Bg used as reference for homogenization

• depends on homogeneity of bg

– or anomaly/innovation differences from neighboring RS stations• independent of bg (RICH, Haimberger et al. 2008, J. Climate)

• Reference built from homogeneous pieces of neighboring time series

• Automatic adjustment schemes for both T and Wind

• Full RS dataset homogenized -> Suitable for reanalyses!

3rd WCRP Conference on Reanalyses, 31.1.2008

A classicalexample

Gruber & Haimberger 2008, MetZ, accepted

Marion Island

South Africa

12 degree wind direction error

1986, MWR

3rd WCRP Conference on Reanalyses, 31.1.2008

Global RS-Wind homogenization

Gruber & Haimberger, MetZ, 2008, accepted

Grey=anyinhomogeneity

Black=wind directionerror >3deg

3rd WCRP Conference on Reanalyses, 31.1.2008

12h-00h-T-difference, 50 hPa

• This trend is spurious, can be removed• Day-night differences – Yes, but daily means?• Compare with MSU data, ERA-40 BG, HadAT• Compare RICH/RAOBCORE

Composite30W-40EEurope/Africa

3rd WCRP Conference on Reanalyses, 31.1.2008

MSU anomaly differences at Yap

Haimberger et al.2008, J. Clim

MSU4

MSU3

3rd WCRP Conference on Reanalyses, 31.1.2008

RICH: Anomalies vs. Innovations

Smaller variance with innovations!

3rd WCRP Conference on Reanalyses, 31.1.2008

Tropical LS and TS comparison

Haimbergeret al. 2008,J. Climate

MSU4

MSU3

1K

3rd WCRP Conference on Reanalyses, 31.1.2008

Santer et al., in prep.together with P. Thorne

3rd WCRP Conference on Reanalyses, 31.1.2008

Impact of RAOBCORE adj. in ERA-Interim

0.4K

Difference of assimilation experimentswith/without adjustments

3rd WCRP Conference on Reanalyses, 31.1.2008

Adjustments of US Vaisala RS (Redder et al. 2004)

IFS CY29Unadj RS

IFS CY30Unadj RS

IFS CY29NASA-ADJ

IFS CY30NASA-ADJ

•Error of VRS 80 operated by NCEP. •Biases removed with physical model(Redder et al., 2004) used in MERRA

•RAOBCORE can be applied on top•Improves bias estimates further in the past(Haimberger, special project report 2007)

3rd WCRP Conference on Reanalyses, 31.1.2008

Arguez (2007), BAMSAgreement in pre-satellite ERA?

Arguez et al.2007, BAMS

3rd WCRP Conference on Reanalyses, 31.1.2008

Historical upperair data & pilot

reanalyses

Brönnimann, 2008

SLP basedReanalysisfrom G. Compo

1933-1944

1943/44

3rd WCRP Conference on Reanalyses, 31.1.2008

Conclusions• Advances made:.

– Improved radiosonde TEMPERATURES and WINDS– Large breaks clearly identifiable– Better agreement with MSU, surface temperatures, GCMs

• Key: Availability of innovations in ERA-40

• RAOBCORE data used in ERA-Interim, MERRA– Positive impact in innovation statistics– Physically based adjustments can be added

• To-do list for ERA-75 reanalysis– Uncertainty estimates with background from JRA25, ERA-Interim– Pre-1979 RS T- data need more attention– Preparation of pre-1958 data c.f. S. Brönnimann– Use surface data reanalysis output for homogenization?

3rd WCRP Conference on Reanalyses, 31.1.2008

ΔFa=0.3PWATM

OCEAN

Does the energyexport from thetropics change?

AOGCMs:Atmosphere: +3%Ocean: -20%

Held&Soden (2006), J. Climate

Can we find thiswith reanalyses?

3rd WCRP Conference on Reanalyses, 31.1.2008

12h-00h RS-T differences, 50 hPa

3rd WCRP Conference on Reanalyses, 31.1.2008

Adjusted 12-00GMT Difference, 50hPa

3rd WCRP Conference on Reanalyses, 31.1.2008

Tropical MT and LT comparisonMSU2

MSU2LT

3rd WCRP Conference on Reanalyses, 31.1.2008

Independence of bg

Trappes(France) 12GMT

Stuttgart 00 GMTNo sign of break in bg

Rapa(South Pacific) 00GMT

3rd WCRP Conference on Reanalyses, 31.1.2008

Station climatology adjustment

bgT

x,y

Mean T of neighbouringhomogenized „reliable“series

Mean T of most recentpart of tested series

Bg used for interpolation

(bg-obs)iobsi

Expected(bg-obs)

actual(bg-obs)

3rd WCRP Conference on Reanalyses, 31.1.2008

Adjusted 12h-00h T-Difference, 50 hPa

Composite30W-40EEurope/Africa

Composite120E-120WFar East/Pacific/Alaska

T-Difference

T-Difference

3rd WCRP Conference on Reanalyses, 31.1.2008

RAOBCORE v1.3 – no BG adj.

3rd WCRP Conference on Reanalyses, 31.1.2008

12GMT-00GMT-Difference, 50 hPa

• This trend had nonclimatic reasons, can beremoved

• Day-night differences – Yes but daily means?• Compare with MSU data, ERA-40 BG, HadAT• Compare RICH/RAOBCORE

Composite30W-40EEurope/Africa

3rd WCRP Conference on Reanalyses, 31.1.2008

Effect of bg adjustment on bgtrends

V1.4v1,.2, v1.3

3rd WCRP Conference on Reanalyses, 31.1.2008