The OQ-Net radar VHF wind profiler network: Comparisons with radiosondes and NWP models
Comparisons between GERB and the Met Office NWP model
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Transcript of Comparisons between GERB and the Met Office NWP model
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Comparisons between GERB and the Met Office NWP model
Richard Allan, Tony Slingo
Environmental Systems Science Centre, University of Reading
Sean Milton, Malcolm Brooks
Met Office, Exeter
Thanks to the GERB International Science Team
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Sinergee project: www.nerc-essc.ac.uk/~rpa/GERB/gerb.html
GERB Model
Harries et al. (2005) BAMS; Allan et al. (2005) JGR
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Objectives
• Improve experience with satellite datasets including GERB
• Timely Model Evaluation– using geostationary data independent of the
assimilation system
• Understanding of physical processes
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Mean model bias: 2006
All-sky Clear-sky
Allan et al. (2007) QJRMS
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Marine stratocumulus
Convective cloud
Radiative biases in the Met Office global model
Convective outflow
Surface albedo
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Mineral dust aerosol
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Dust impact on longwave radiation
• Large perturbation to Met Office model OLR during summer over west Sahara– Consistent with high mineral dust aerosol optical depth
(see also Haywood et al. 2005, JGR)
– Used in planning of GERBILS
Model minus GERB OLR: July 2006, 12-18 UTC
All-sky Clear-sky dust aerosol
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Model-GERB OLR difference time series 15oW-5oE, 15-30oN
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Dust impact on longwave radiationModel minus GERB OLR: 12-18 UTC
All-sky Clear-sky dust aerosol
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Conclusions
• Model evaluation– Satellite data independent of assimilation system– Good feedback for modellers and satellite team– Identified biases relating to cloud and surface
• Mineral dust aerosol over Sahara– Monthly longwave radiative effect up to 50 Wm-2
– Large effect of single events (Slingo et al. 2006, GRL)
– June 18-28 2007: smaller dust events than previous years but detectable OLR bias
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Marine Stratocumulus
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• Curious banding structure– Transition across model
levels (see Lock et al. 2001, MWR)
• Cloud reflectivity bias– Model low-altitude
stratiform clouds are too reflective
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Cloud liquid water path
Bias: model minus GERB; SSM/I; SEVIRI
Albedo Liquid Water Path Cloud
Reduction in model bias from June to July 2006 - relates to cloud liquid water
…but see also Horvath and Davies (2007) JGR
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Convective cloud
5th June 2006
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Convective Decay Time-scale
• Unrealistically low levels of convective cloud
• On-off; common problem in models
• Simple fix…
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Improved shortwave reflectivity
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• Increased convective cloud cover
• But is the physics any better?
• Future work: Comparisons with CloudSat