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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, UK. Introduction. Clear-sky radiative cooling: radiative convective balance atmospheric circulation Earth’s radiation budget
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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, UK
Introduction • Clear-sky radiative cooling: • radiative convective balance • atmospheric circulation • Earth’s 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
Datasets used • Surface and Top of Atmosphere clear-sky LW fluxes • Column integrated water vapour (CIWV) • Reanalyses: • ERA-40 (1979-2001) • NCEP-1 (1979-2004) • Satellite data • ERBS, ScaRaB, CERES (clear-sky OLR) • SMMR, SSM/I V5 (CIWV) • Combination datasets: • SRB Rel. 2(1983-1994)…reanalysis?
ERA40 NCEP SRB Global variability Ts CIWV LWc SFC 1980 1985 1990 1995 2000 2005
ERA40 NCEP SRB Global variability Surface Net LWc Clear-sky OLR Clear-sky Atmos LW cooling QLWc
Surface LWc and CIWV dSNLc/dCIWV ~ 1.5 Wkg-1 ERA40 NCEP
Atmospheric LWc and Ts dQLWc/dTs ~ 3 Wm-2K-1 ERA40 NCEP
Clear-sky net LW over oceans • SMMR and SSM/I to prescribe CWV • HadISST SST and da Silva climatology to estimate T0 • Prata (1996) clear-sky LW formula: SNLc=εs(SDLc-σTs4)
Tropical Oceans ERA40 NCEP SRB OBS 1980 1985 1990 1995 2000 2005
Tropical Oceans: OLRc and QLWc ERA40 NCEP SRB OBS
Tropical Oceans: descent QLWc ERA40 NCEP SRB OBS
Linear least squares fit • Tropical ocean: descending regime • Dataset dQLWc/dTs Slope • ERA-40 3.7±0.5 Wm-2K-1 • NCEP 4.2±0.3 Wm-2K-1 • SRB 3.6±0.5 Wm-2K-1 • OBS 4.6±0.5 Wm-2K-1
Implications for tropical precipitation (GPCP)? GPCP P ERA40 QLWc OBS QLWc
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-2K-1 • All-sky changes? Models?
Initial comparisons of GERB data with UK Met Office global forecast model http://www.nerc-essc.ac.uk/~rpa/GERB With thanks to GERB International Science Team including Jacqui Russell (Imperial College, London), Nicolas Clerbaux (RMIB, Belgium) Harries et al.(2005) BAMS 86 p.945 Allan et al. (2005) JGR 110, D14111
July 2004 monthly-diurnal mean GERB prelim version CERES FM1+FM4 See Jacqui Russell’s talk for more detailed analysis OLR Albedo
“Global”, 1200 UTC, GERB vs UKMO forecast model Model change GERB change
CLEAR-SKY differences (model minus GERB) “Global” Ocean, 1200 UTC data Clear-sky OLR Clear-sky Albedo
Current activities at UK Met Office Alejandro Bodas Mark Ringer HadGAM1 – SRB2 HadGAM1-ISCCP D2 Cloud HadGAM1- 4D DAO CIWV SW LW