gerb/ceres meeting 2006 exeter evaluation of clouds and radiation in the met office global forecast...
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GERB/CERES Meeting 2006 Exeter
Evaluation of clouds and radiation in the Met Office global forecast model using GERB/SEVIRI data
Richard Allan, Tony Slingo
Environmental Systems Science Centre University of Reading, UK
Sean Milton, Malcolm Brooks
Met Office, Exeter, UK
With thanks to the GERB International Science Team including colleagues at Imperial College and the Royal Meteorological Institute of Belgium
GERB/CERES Meeting 2006 Exeter
Objectives
• Validation of new datasets (GERB/SEVIRI)
• Timely Model Evaluation• Understanding of physical processes
GERB/CERES Meeting 2006 Exeter
Recent ComparisonGERB Model
OLR:
SW Albedo:
SEVIRI Channels: WV (top) and IR (bottom)
GERB/CERES Meeting 2006 Exeter
Evaluation of clear-sky fluxes
Allan et al. (2005) JGR, 110, D14111, 10.1029/2004JD005698
GERB/CERES Meeting 2006 Exeter
Model evaluation: near-real time
• Change in model minus GERB flux differences
• Relate to change in model physics implemented
13th March | 14th March
Model SW albedo
2005 2006
OLR
ALB
Model-GERB: tropical land
GERB/CERES Meeting 2006 Exeter
Model evaluation: near-real time
• Change in model minus GERB flux differences
• Relate to change in model physics implemented
13th March | 14th March
Model SW albedo
2005 2006
Model-GERB: tropical land
ΔOLR
ΔALB
GERB/CERES Meeting 2006 Exeter
Time-series: 1200 UTC data
OLR
(Wm-2)
SW Albedo
GERB/CERES Meeting 2006 Exeter
July 2006 mean
Model GERB (Edition 1) CERES
OLR
α
GERB/CERES Meeting 2006 Exeter
Systematic biases
All-sky:
Clear-sky:
Desert dust aerosol
ITCZ
Low cloud
Surface albedo
Convective
cloud
Water vapour
LW Model minus GERB 1200 UTC SW
GERB/CERES Meeting 2006 Exeter
Model Evaluation: Namibian Stratocumulus region
31st March 2004
Mod
el
Leve
l
GERB/CERES Meeting 2006 Exeter
More recent example5th June 2006
Mod
el
Leve
l
GERB/CERES Meeting 2006 Exeter
Stratocumulus: composites
(Edition 1 data)
Model overestimates cloud albedo
Reasonable simulation of cloud fraction
GERB/CERES Meeting 2006 Exeter
Composites: April-July 2006
• Sample only where stratocumulus identified
• Model: reasonable simulation of cloud cover and longwave radiative effects
• Underestimation of SW albedo
LWCF (Wm-2)
ALB CF:
Frequency of Sc:
GERB/CERES Meeting 2006 Exeter
Diurnal Cycle
GERB/CERES Meeting 2006 Exeter
Time series
GERB/CERES Meeting 2006 Exeter
Large error in model simulated clear-sky OLR over west Sahara identified in July 2003 also present in 2006 for Edition 1 GERB data
Partially explained by large mineral dust aerosol optical depth
See RADAGAST project: http://radagast.nerc-essc.ac.uk and also: Haywood, Allan, Slingo et al. (2005) J. Geophys. Res. 110
GERB/CERES Meeting 2006 Exeter
Summary
• Ongoing near-real time comparisons of GERB/SEVIRI and Model
• Validation of new datasets– GERB/SEVIRI, surface observations
• Timely model evaluation– e.g. new physical parametrizations
• Process studies– e.g., stratocumulus, surface properties, mineral dust,
radiative flux divergence…
GERB/CERES Meeting 2006 Exeter
Time-series: Model-GERB∆OLR
(Wm-2)
∆SW Albedo
GERB/CERES Meeting 2006 Exeter