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

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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
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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

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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?

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Global variability
ERA40 NCEP SRB
Ts CIWV LWc SFC
1980 1985 1990 1995 2000 2005
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Global variability
ERA40 NCEP SRB
Surface Net LWc Clear-sky OLR Clear-sky Atmos
LW cooling QLWc
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Surface LWc and CIWV
dSNLc/dCIWV 1.5 Wkg-1
ERA40 NCEP
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Atmospheric LWc and Ts
dQLWc/dTs 3 Wm-2K-1
ERA40 NCEP
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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

SNLces(SDLc-sTs4)
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Tropical Oceans
ERA40 NCEP SRB OBS
1980 1985 1990 1995
2000 2005
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Tropical Oceans OLRc and QLWc
ERA40 NCEP SRB OBS
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Clear-sky LW and CIWV scatter with Ts SRB and OBS
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Tropical Oceans descent QLWc
ERA40 NCEP SRB OBS
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Linear least squares fit

• Tropical ocean descending regime
• Dataset dQLWc/dTs Slope
• ERA-40 3.70.5 Wm-2K-1
• NCEP 4.20.3 Wm-2K-1
• SRB 3.60.5 Wm-2K-1
• OBS 4.60.5 Wm-2K-1

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

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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
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July 2004 monthly-diurnal mean GERB prelim
version CERES FM1FM4
See Jacqui Russells talk for more detailed
analysis
OLR
Albedo
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Global, 1200 UTC, GERB vs UKMO forecast model
Model change
GERB change
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CLEAR-SKY differences (model minus GERB) Global
Ocean, 1200 UTC data
Clear-sky OLR Clear-sky Albedo
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Current activities at UK Met Office
Alejandro Bodas Mark Ringer
HadGAM1 SRB2
HadGAM1-ISCCP D2 Cloud HadGAM1- 4D DAO CIWV
SW LW