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Evaluation of clouds and radiation in the Met Office global forecast model using GERB/SEVIRI data

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.

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Evaluation of clouds and radiation in the Met Office global forecast model using GERB/SEVIRI data

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  1. 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

  2. Objectives • Validation of new datasets (GERB/SEVIRI) • Timely Model Evaluation • Understanding of physical processes

  3. GERB Model Recent Comparison SEVIRI Channels: WV (top) and IR (bottom) OLR: SW Albedo:

  4. Evaluation of clear-sky fluxes Allan et al. (2005) JGR, 110, D14111, 10.1029/2004JD005698

  5. Model evaluation: near-real time Model-GERB: tropical land OLR • Change in model minus GERB flux differences • Relate to change in model physics implemented Model SW albedo ALB 2005 2006 13th March | 14th March

  6. Model evaluation: near-real time Model-GERB: tropical land ΔOLR • Change in model minus GERB flux differences • Relate to change in model physics implemented Model SW albedo ΔALB 2005 2006 13th March | 14th March

  7. Time-series: 1200 UTC data OLR (Wm-2) SW Albedo

  8. July 2006 mean OLR α Model GERB (Edition 1) CERES

  9. Systematic biases LW Model minus GERB1200 UTC SW All-sky: ITCZ Convectivecloud Low cloud Desert dust aerosol Clear-sky: Surface albedo Water vapour

  10. Model Evaluation: Namibian Stratocumulus region31st March 2004 Model Level

  11. More recent example5th June 2006 Model Level

  12. Stratocumulus: composites (Edition 1 data) Model overestimates cloud albedo Reasonable simulation of cloud fraction

  13. Composites: April-July 2006 LWCF (Wm-2) • Sample only where stratocumulus identified • Model: reasonable simulation of cloud cover and longwave radiative effects • Underestimation of SW albedo ALB CF: Frequency of Sc:

  14. Diurnal Cycle

  15. Time series

  16. 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

  17. 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…

  18. Time-series: Model-GERB ∆OLR (Wm-2) ∆SW Albedo

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