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Evaluating Radiative & Energy Balance in Met Office NWP Models over Africa.

Evaluating Radiative & Energy Balance in Met Office NWP Models over Africa. Sean Milton, Glenn Greed, Malcolm Brooks, J.Haywood,R.Allan* & A. Slingo* Met Office, Exeter, UK *ESSC, Reading University. RADAGAST Meeting 19 July 2007. Outline Introduction – NWP models

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Evaluating Radiative & Energy Balance in Met Office NWP Models over Africa.

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  1. Evaluating Radiative & Energy Balance in Met Office NWP Models over Africa. Sean Milton, Glenn Greed, Malcolm Brooks, J.Haywood,R.Allan* & A. Slingo* Met Office, Exeter, UK *ESSC, Reading University RADAGAST Meeting 19 July 2007

  2. Outline • Introduction – NWP models • Global Model evaluation of 12-36 hour forecasts vs ARM (Niamey) & GERB. • Dry Season - Dec 05 to Mar 06 • Wet Season – JJA 2006 • Aims • Improved understanding of radiative forcing due to aerosol and cloud • Interaction of land surface & convection in hydrological cycle & WAM. • Improve parametrizations & weather predictability

  3. NWP Forecast Systems – Unified Model Africa LAM ~ 20km UK 4km Regional 12km Saharan Regional Model 20km • Global 40km/50L • 60 hour forecast twice/day • 144 hour forecast twice/day • +EPS 24member, 90km • HadGEM1a physics. • 3hr Radiation call • Simple aerosol climatology

  4. SOP3 SOP1&2 Jan-Feb 2006 DABEX/DODO Aug 2006 DODO2 ARM mobile facility - Niamey Observations available over Africa during 2006 RADAGAST

  5. Atmospheric Seasonal Radiation Balance13 Jan – 16 Mar 2006

  6. SW Radiation Balance – SurfaceMidDec 2005 – mid Apr 2006 Overestimate SW down ~ 50-100 Wm-2 Underestimate SW up Accuracy ARM Measurements +/- 9Wm-2

  7. Surface Energy Balance & Near surface Temperatures – Model vs ARM

  8. Improving UM Surface Albedo UM Old UM + MODIS Bare Soil Too Dark Too Bright

  9. Global UM - ARM AOT 440nm Banizoumbou Importance of Aerosols for NWP 8 Mar Dust Event AOT 440nm

  10. Dust Parametrization – Woodward 2001 Six dust sizes 0.03 -30 microns Conv BL mixing • Threshold friction velocity defined for particles from .06 to 2000 microns (previously .06 to 60) • 9 Bins in Horizontal Flux (3 sand) • Inhibition of dust from steep slopes – numerical issues • Use of IGBP (1km) soil source data in place of Wilson-Henderson-Sellers (1985) 1 deg data (NWP only). • Reduce threshold friction velocity by 0.15 m/s in NWP • Use global “nudged” soil moisture to initialise Saharan CAMM. Transport Deposition Gravitational Settling Uplift (v*, soil moisture) Wet Soils Data

  11. Major Saharan Dust Outbreak6-9 March 2006

  12. 12Z 8 Mar 2006 500m Day 4 Forecast 12Z 9 Mar 2006 500m Day 5 Forecast

  13. Global Model 5 day forecast - Dust 8 March – T+96 MODIS 1-5 day global model forecast N216 L38 Initialised 12UTC 4 March 2006

  14. Impact of Dust on Radiation balance – Day 4 Forecasts 12 UTC 8th March

  15. ARM 200 Wm-2 Reduction SW Model 100 Wm-2 Reduction In SW due to inclusion of dust Net SW Net LW

  16. AERONET vs CAMM during DODO2 Dakar Andreas Keil Glenn Greed

  17. Model vs GERB – West Africa (Land Only) Routine monitoring of global model against GERB allowed us to quickly spot weak cloud (SW and LW) radiative forcing over land following change to convection scheme in March 2006 and implement correction in Dec 2006. JJA 2006 period has been re-run with corrected physics

  18. Impact of new physics – day 2 forecasts Stronger cloud radiative forcing – decrease in OLR and Downward SW at surface => smaller latent heat flux => less precipitation

  19. Summary • Aerosols • Used ARM and GERB radiative fluxes to quantify role played by Dust (& biomass) in NWP model errors in radiative TOA and surface energy balance. • Surface albedo • Systematic underestimates of reflected SW in Sahel, overestimates in other regions (e.g.Sahara, Saudi Arabia). • Dust Parametrization • performs well in both Global UM and Saharan Model. • AOD agree well with AERONET measurements. • Monsoon • Marked spin up in precipitation – W. Africa • Poor cloud radiative forcing in model recently improved – rerun JJA2006 with new physics.

  20. Future • Aerosols • Further comparison of Dust in model with aircraft data from DODO/DABEX and GERBIL - dust radiative properties • More work on dust uplift (PDRA Reading D.Ackerley) • Dust operational in Southern Asia Model by 2008. • Global NWP Model? – simplified dust parametrization. • Experiments with predicting biomass burning. • Implement final MODIS surface albedo changes – Autumn 2007. • Analysis of “wet season” JJA06 reruns in collaboration with RADAGAST and AMMA-UK community • Soil moisture & hydrological cycle • Resolution & convection

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