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Comparisons between GERB and the Met Office NWP model

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. GERB Model.

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Comparisons between GERB and the Met Office NWP model

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  1. 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

  2. GERB Model Sinergee project: www.nerc-essc.ac.uk/~rpa/GERB/gerb.html Harries et al. (2005) BAMS; Allan et al. (2005) JGR

  3. Objectives • Improve experience with satellite datasets including GERB • Timely Model Evaluation • using geostationary data independent of the assimilation system • Understanding of physical processes

  4. All-sky Clear-sky Mean model bias: 2006 Shortwave Longwave Allan et al. (2007) QJRMS

  5. All-sky Clear-sky Radiative biases in the Met Office global model Convective outflow Shortwave Longwave Surface albedo Convective cloud Marine stratocumulus

  6. All-sky Clear-sky Mineral dust aerosol Shortwave Longwave

  7. Dust impact on longwave radiation Model minus GERB OLR: July 2006, 12-18 UTC • 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 All-sky Clear-sky dust aerosol

  8. Model-GERB OLR difference time series 15oW-5oE, 15-30oN 1800 1200 1200 CLEAR 2003 2004 2005 2006 2007

  9. Dust impact on longwave radiation Model minus GERB OLR: 12-18 UTC June 18-28 2007 July 2006 All-sky Clear-sky dust aerosol

  10. 19 June 2007 1800 1500 1200

  11. 21 June 2007 1800 1500 1200

  12. 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

  13. Marine Stratocumulus

  14. Curious banding structure • Transition across model levels (see Lock et al. 2001, MWR) • Cloud reflectivity bias • Model low-altitude stratiform clouds are too reflective

  15. 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

  16. Convective cloud 5th June 2006

  17. Convective Decay Time-scale • Unrealistically low levels of convective cloud • On-off; common problem in models • Simple fix…

  18. Improved shortwave reflectivity

  19. Increased convective cloud cover • But is the physics any better? • Future work: Comparisons with CloudSat

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