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Dust and biomass aerosols in HiGAM Presentation for RADAGAST meeting, Reading 19-20 July 2007

Dust and biomass aerosols in HiGAM Presentation for RADAGAST meeting, Reading 19-20 July 2007. Margaret Woodage Environmental Systems Science Centre University of Reading, U.K. UK-HiGEM Project.

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Dust and biomass aerosols in HiGAM Presentation for RADAGAST meeting, Reading 19-20 July 2007

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  1. Dust and biomass aerosols in HiGAM Presentation for RADAGAST meeting, Reading19-20 July 2007 Margaret Woodage Environmental Systems Science Centre University of Reading, U.K.

  2. UK-HiGEM Project • Started Jan 2004, collaborative project (involving HC, NCAS, BAS, CEH, ESSC, NOCS, UEA) aiming to build a High-resolution Global Environmental Model for the NERC community. • Based on new UKMO Hadley Centre climate model HadGEM1, with resolution increased to N144 (atmos) and 1/3 deg (ocean) • Run on the HPCx computer, Edinburgh and also by the UJCC on the Earth Simulator, Yokohama • Latest coupled experiment (run by Len Shaffrey) has completed 60 model years on HPCx and several papers are in preparation.

  3. UK-HiGEM Project • I have run atmos-only (HiGAM) experiments with interactive dust modelling included (not in coupled runs due to expense!) aiming to see how dust behaves in model at higher resolution: • What does model do with dust? Can horizontal and vertical distributions be modelled realistically, and time and space scales of dust storms be accurately represented? • How does dust feed back on model climatology? How are monsoons, Easterly waves and tropical cyclones affected by dust? • 4 expts run for 18yrs each with amip SSTs 1982-2000, 2 including dust radiative FX, 2 excluding FX (but with double rad call to diagnose radiative ‘forcing’ of dust)

  4. UK-HiGEM model: atmospheric component • Grid point model with 38 vertical levels, horizontal res 0.875 deg lat x 1.25 deg lon • Non-hydrostatic with Semi-Lagrangian advection • Prognostic cloud physics, shallow and deep convection parameterisations • Land surface exchange scheme, boundary layer mixing of surface fluxes • Edwards-Slingo 2-stream radiation code

  5. Interactive aerosol modelling in HiGEM All aerosols tracers are: • advected via semi-Lagrangian advection scheme • mixed in boundary layer and by convection • subject to dry and wet deposition. • Feedback on the model is via the radiative effects: direct (scattering and absorption) and indirect (cloud albedo and lifetime effects)

  6. Aerosols species modelled in HiGAM: • Sulphate: 6 tracers (3 SO4 modes), direct and indirect FX • Soot: 3 tracers, direct FX • Biomass: 3 tracers, direct and indirect FX • Dust: 6 tracers, direct FX • Sea-salt: 0 tracers, direct and indirect FX Cost: expt takes 30% longer to run with dust included (~1.5 hr per model month for N144 atmos-only) Time-dependent emissions for Sulphur cycle, soot and biomass are specified via ancillary files from various data sources, but sea-salt and dust are generated internally within the model

  7. Outline of HC dust scheme (from Steph Woodward, HadCM3 version, JGR 106, 2001) 6 particle size bins 0.03 – 30 um radius: N.B. Typical sizes: Clay 0-1, Silt 1-25, Sand 25 – 2000um (larger sand particles not modelled as too big to be mobilised as dust) Dust produced when friction velocity U*> threshold U*t (fn of particle size and soil moisture content) Availability determined from dust parent soil ancillary file (Wilson & Henderson-Sellers, J Clim,1985) Dust flux : fn of U*3, U*t3, Veg fraction, rel mass in size division,,%Clay… (broadly based on Marticorena & Bergametti, JGR 100, 1995) Wet deposition from below cloud scavenging Dry deposition due to gravitational settling and turbulent mixing in BL “Globally representative” refractive indices from data from various deserts determine spectral properties

  8. Model Dependence and Tuning of Dust Dust code is strongly model dependent (also “real world” dust is very sensitive to meteorological conditions, hence very episodic, spatially and temporally variable) • Tuningis required to produce realistic dust burdens whenever model changes are made Dust generation equn: U_thresh=0.2log10(Drep) + BW + C where Drep is representative particle diameter, W is soil moisture, B and C are tunable parameters. Need to look at: total annual mean burdens (20-30 Tg) season of max and min burdens (JJA max) regional distributions and ‘background’ loading in remote areas size division containing peak mass (div 4, ~1-3 micron)

  9. 10yr mean seasonal dust loadings

  10. Seasonal and annual mean global dust burdens

  11. Ann mean dust loadings and SSTs

  12. Sulphate (mean 0.5 Tg ), soot (mean 0.3 Tg) and biomass (mean 1.6 Tg)DJF JJA

  13. 5yrmn JJA xcdfr+dustFX

  14. 5yrmn JJA xcdfg-dustFX

  15. 5yrmn JJA zonal mean xcdfr+dustFX

  16. 5yrmn JJA dust radiative forcing xcdfg

  17. 5yrmn DJF xcdfr+dust FX

  18. 5yrmn DJF zonal mean xcdfr+dustFX

  19. 5yrmn DJF dust radiative forcing xcdfg

  20. DJF JJA

  21. JAN 5yrmn aerosol loading and AODDUST BIOM

  22. Comparison of DUST aerosol extinction from DABEX flight data, HadGEM and HiGAM

  23. Comparison of BIOMASS aerosol extinction from DABEX flight data, HadGEM and HiGAM for Niamey in January

  24. Niamey 13N 2E5yrmn JAN DJF JJA loading (mg/m2) AOD BIOM 124 0.6 DUST 519 0.2 515 0.2 264 0.08 In Salah 27N 2E BIOM 6 0.03 DUST 1731 0.82 1614 0.51 5035 0.59 Aerosol loadings and AODs

  25. DJF and JJA dust and biomass profiles over Africa

  26. Climate Model Challenge: Washington et al JGR 111, 2006: Dust and low-level circulation over the Bodele Depression, Chad: Observations from BoDEx 2005 “Surface wind speeds are characterised by a pronounced diurnal cycle, with a maximum during the midmorning and a minimum throughout the night….. …The LLJ also has a pronounced diurnal cycle but the phase leads the surface winds by up to 8 hours…. What the BoDEx data has shown is that efforts to simulate dust emission will require models to resolve an important mesoscale feature in the LLJ as well as the modulation of the wind in a pronounced diurnal cycle. For global climate models this represents quite a challenge.”

  27. Jan 3hrly 10m and 925 mb winds

  28. Feb 3hrly 10m and 925mb winds

  29. Feb 3hrly 10m wind and dust emiss

  30. Model March dust storm6hrly dust, 925mb wind17 18 19 20

  31. March 6hrly model dust loadings

  32. End of presentation(Go to dust_12fps movie)

  33. HiGAM orography over Africa

  34. N144 dust parent soil ancil file

  35. BIOM loading and AOD 3yrmnDJF JJA

  36. Longitudinal XS JJA xcdfr+dustFX

  37. 5yrmn DJF longitudinal XS xcdfr+dustFX

  38. Comparison of dust forcings (W/m2) HiGAM xbxab xcdfg HADAM3 Surface SW -0.47 -1.69 -1.22 LW +0.21 +0.43 +0.4 Total surf -0.25 -1.27 -0.82 TOA SW +0.07 -0.35 -0.16 LW +0.1 +0.31 +0.23 Total TOA +0.17 -0.04 +0.07

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