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Changes in clear-sky longwave radiative cooling in the atmosphere 1979-2004 Richard Allan Environmental Systems Science Centre, University of Reading,

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Presentation on theme: "Changes in clear-sky longwave radiative cooling in the atmosphere 1979-2004 Richard Allan Environmental Systems Science Centre, University of Reading,"— Presentation transcript:

1 Changes in clear-sky longwave radiative cooling in the atmosphere Richard Allan Environmental Systems Science Centre, University of Reading, UK

2 Introduction Clear-sky radiative cooling: –radiative convective balance –atmospheric circulation Earths radiation budget –Understand clear-sky budget to understand cloud radiative effect Datasets: –Reanalyses – observing system –Satellites – calibration and sampling GERB comparisons with UKMO forecast model Met Office modelling activities

3 Datasets used Surface and Top of Atmosphere clear-sky LW fluxes Column integrated water vapour (CIWV) Reanalyses: –ERA-40 ( ) –NCEP-1 ( ) Satellite data –ERBS, ScaRaB, CERES (clear-sky OLR) –SMMR, SSM/I V5 (CIWV) Combination datasets: –SRB Rel. 2( )…reanalysis?

4 Global variability Ts CIWV LWc SFC ERA40 NCEP SRB

5 Global variability ERA40 NCEP SRB Surface Net LWc Clear-sky OLR Clear-sky Atmos LW cooling Q LWc

6 Surface LWc and CIWV dSNLc/dCIWV ~ 1.5 Wkg -1 ERA40 NCEP

7 Atmospheric LWc and Ts dQ LWc /dTs ~ 3 Wm -2 K -1 ERA40 NCEP

8 Clear-sky net LW over oceans SMMR and SSM/I to prescribe CWV HadISST SST and da Silva climatology to estimate T 0 Prata (1996) clear-sky LW formula: SNLc=ε s (SDLc- σT s 4 )

9 Tropical Oceans ERA40 NCEP SRB OBS

10 Tropical Oceans: OLRc and Q LWc ERA40 NCEP SRB OBS

11 Clear-sky LW and CIWV scatter with Ts: SRB and OBS

12 Tropical Oceans: descent Q LWc ERA40 NCEP SRB OBS

13 Linear least squares fit Tropical ocean: descending regime DatasetdQ LWc /dTs Slope ERA-403.7±0.5Wm -2 K -1 NCEP4.2±0.3Wm -2 K -1 SRB3.6±0.5Wm -2 K -1 OBS4.6±0.5Wm -2 K -1

14 Implications for tropical precipitation (GPCP)? ERA40 Q LWc GPCP P OBS Q LWc

15 Conclusions Intercomparisons of datasets: clear-sky LW at SFC, TOA, ATM Reanalyses: observing system changes Satellites: calibration, sampling Increase in clear-sky LW cooling of atmosphere of ~3-5 Wm -2 K -1 All-sky changes? Models?

16 Initial comparisons of GERB data with UK Met Office global forecast model Harries et al.(2005) BAMS 86 p.945 Allan et al. (2005) JGR 110, D With thanks to GERB International Science Team including Jacqui Russell (Imperial College, London), Nicolas Clerbaux (RMIB, Belgium)

17 July 2004 monthly-diurnal mean GERB prelim versionCERES FM1+FM4 OLR Albedo See Jacqui Russells talk for more detailed analysis

18 Global, 1200 UTC, GERB vs UKMO forecast model Model change GERB change

19 CLEAR-SKY differences (model minus GERB) Global Ocean, 1200 UTC data Clear-sky OLR Clear-sky Albedo

20 Current activities at UK Met Office Alejandro Bodas Mark Ringer HadGAM1 – SRB2 SW LW HadGAM1- ISCCP D2 Cloud HadGAM1- 4D DAO CIWV


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