Changes in clear-sky longwave radiative cooling in the atmosphere 1979-2004 Richard Allan...
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Transcript of Changes in clear-sky longwave radiative cooling in the atmosphere 1979-2004 Richard Allan...
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?
Global variability
1980 1985 1990 1995 2000 2005
Ts
CIWV
LWc
SFC
ERA40
NCEP
SRB
Global variabilityERA40
NCEP
SRB
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
Clear-sky LW and CIWV scatter with Ts: SRB and 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)?
ERA40 QLWc
GPCP P
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
Harries et al.(2005) BAMS 86 p.945
Allan et al. (2005) JGR 110, D14111
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)
July 2004 monthly-diurnal mean
GERB prelim version CERES FM1+FM4
OLR
Albedo
See Jacqui Russell’s talk for more detailed analysis
“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
SW
LW
HadGAM1-ISCCP D2
Cloud
HadGAM1- 4D DAO CIWV