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Changes in clear-sky longwave radiative cooling in the atmosphere 1979-2004

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

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

  2. 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

  3. 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?

  4. ERA40 NCEP SRB Global variability Ts CIWV LWc SFC 1980 1985 1990 1995 2000 2005

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

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

  7. Atmospheric LWc and Ts dQLWc/dTs ~ 3 Wm-2K-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 T0 • Prata (1996) clear-sky LW formula: SNLc=εs(SDLc-σTs4)

  9. Tropical Oceans ERA40 NCEP SRB OBS 1980 1985 1990 1995 2000 2005

  10. Tropical Oceans: OLRc and QLWc ERA40 NCEP SRB OBS

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

  12. Tropical Oceans: descent QLWc ERA40 NCEP SRB OBS

  13. 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

  14. Implications for tropical precipitation (GPCP)? GPCP P ERA40 QLWc OBS QLWc

  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-2K-1 • All-sky changes? Models?

  16. 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

  17. July 2004 monthly-diurnal mean GERB prelim version CERES FM1+FM4 See Jacqui Russell’s talk for more detailed analysis OLR Albedo

  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 HadGAM1-ISCCP D2 Cloud HadGAM1- 4D DAO CIWV SW LW

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