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Published byEmery Newman Modified over 8 years ago
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Evaluating the Met Office global forecast model using GERB data Richard Allan, Tony Slingo Environmental Systems Science Centre, University of Reading Sean Milton, Malcolm Brooks Met Office, Exeter
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Objectives Improve experience with satellite datasets including GERB Timely Model Evaluation Understanding of physical processes
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Sinergee project: www.nerc-essc.ac.uk/~rpa/GERB/gerb.html GERB April 2007 OLR Animation Model
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ShortwaveLongwave Mean model bias: 2006 All-sky Clear-sky
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ShortwaveLongwave Convective cloud Surface albedo Mineral dust aerosol Marine stratocumulus Cirrus outflow
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All-sky Clear-sky ShortwaveLongwave Mineral dust aerosol
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Dust impact on longwave radiation Large perturbation to Met Office model OLR during summer over west Sahara Correlates with high mineral dust aerosol optical depth Model minus GERB OLR: July 2006, 12-18 UTC
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18 UTC model-GERB OLR over West Sahara GERBILGERBIL – aircraft campaign (Jim Haywood) GERB Intercomparison of Longwave Radiation: June 2007 http://www.faam.ac.uk/public/campaigns/index.html#gerbil
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Consistent with calculations of dust longwave radiative effect Clear-sky OLR bias (Wm-2) in 2003 Calculations: Direct radiative effect Direct plus shortwave feedback effect Haywood et al. (2005) JGR 110, D05105
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- Major dust source for Amazon - Large component from March 2004 dust storms
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March 2004: an interesting month Loeb et al. (2007) J. Climate, 20, p.582 March 2006 was interesting too…
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All-sky Clear-sky ShortwaveLongwave Marine stratocumulus Convective cloud Cirrus outflow Radiative biases in the Met Office global model
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Marine Stratocumulus
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Curious banding structure –Transition across model levels Cloud reflectivity bias –Model low-altitude stratiform clouds are too reflective
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Changes in albedo bias (ocean) Model upgrade (March 2006) reduced but did not remove albedo bias –Compensating errors: ITCZ/stratocumulus
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Stratocumulus composites
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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
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LWP Wentz : overestimate for low cloud fraction? TMI Wentz /MODIS LWP Overcast boundary layer clouds: good agreement Horváth and Davies (2007) JGR 112, D01202
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Convective cloud 5 th June 2006
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Model evaluation: near-real time Change in model minus GERB flux differences Relate to change in model physics implementation 13 th March | 14 th March Model SW albedo 2005 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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Increased convective cloud cover But is the physics any better? Future work: Comparisons with CloudSat
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Improved shortwave reflectivity
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Gulf of Guinea ModelCloudSat 19 th July 2006 5 th July 2006
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Conclusions Top down-bottom up approach –Good for feedback to modellers Mineral dust aerosol –Shortwave absorption; longwave radiative effect –Large effect of single events Marine stratocumulus –Reflectivity and seasonal variability: issues Deep convection –Intermittent in models; issues with detrainment
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