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V. Buchard , A. da Silva, P. Colarco , R. Spurr

GEOS-5 Simulations of Aerosol Index and Aerosol Absorption Optical Depth with Comparison to OMI retrievals. V. Buchard , A. da Silva, P. Colarco , R. Spurr. GMAO meeting – 03/31/2011. GEOS-5 Aerosols and VLIDORT interface (1). 1) AEROSOL MODEL :.

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V. Buchard , A. da Silva, P. Colarco , R. Spurr

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  1. GEOS-5 Simulations of Aerosol Index and Aerosol Absorption Optical Depthwith Comparison to OMI retrievals. V. Buchard, A. daSilva, P. Colarco, R. Spurr GMAO meeting – 03/31/2011

  2. GEOS-5 Aerosols and VLIDORT interface (1) 1) AEROSOL MODEL : • Aerosol transport module GOCART implemented in the GEOS-5 climate model. • Driven by assimilated meteorological fields, radiative feedbacks • Simulates 5 aerosol types : (dust, sea salt, black and organic carbon and sulfate) • Horizontal resolution : 0.5°x 0.65° • 72 vertical levels from surface to 85 km • Aerosol Mass Concentration : • for each grid cell • for each layer • Mie calculations Assimilation of MODIS/ MISR aerosol data AOD • Updates • Aerosol Mass Concentration

  3. GEOS-5 Aerosols and VLIDORT interface (2) 2) Vertical profiles of optical properties at OMI lat/long: OMI (Ozone Monitoring Instrument)/ AURA • Aerosol Mass Concentration : • for each layer • geolocation at OMI lat/long • Mie calculations • AOD, SSA, g, P(θ) • at OMI lat/long and λ • for each layer 354 nm 388 nm 471 nm Vertical profiles of AOD, SSA and g at OMI λ

  4. GEOS-5 Aerosols and VLIDORT interface (3) 3) Radiative transfer calculation : • Input parameters from OMI file : • -Geometry angles : • Solar Zenith Angle • Relative Azimuth Angle • Sensor Zenith Angle - Surface albedo at 3 λ • AOD, SSA, g, P(θ) • at OMI lat/long and λ • for each layer Model Pressure & Temperature VLIDORT Radiative transfer code : • Discrete Ordinate Method • Scalar or Vector mode • Several options for surface specification (Lambertian surface used here) • TOA radiances • Aerosol Index

  5. Aerosol Index • Qualitative indicator of the presence of absorbing aerosol ( AI > 0 ). • AI is derived from the change in the spectral dependence of the back-scattered UV radiances induced by aerosols relative to the Rayleigh scattering between 354 and 388 nm (Torres et al., 2007) : • AI depends on : -aerosol concentration - aerosol layer height - aerosol optical properties

  6. Comparison of monthly mean TOA Radiances (1) Globally, good agreement but : A 388 nm 388 nm 388 nm 388 nm Difference OMI – GEOS-5 GEOS-5 Free running model OMI • Overestimation of the modeled radiances over land, • Underestimation of the modeled radiances over ocean in the southern hemisphere. 388 nm GEOS-5 with assimilation of MODIS/MISR AOD

  7. Comparison of the monthly mean • TOA Radiances (2) A 354 & 471 nm 354 nm 354 nm 354 nm GEOS-5 Free running model OMI Difference OMI – GEOS-5 471 nm 471 nm 471 nm GEOS-5 Free running model OMI Difference OMI – GEOS-5 • Same conclusions as 388nm

  8. UVAerosol Index (AI) Comparison GEOS-5 Free running model OMI Difference OMI – GEOS-5 • GEOS-5 simulated AI captures major features, but is not perfect… • too much dust in Northwest Africa, • not enough dust in Arabia Peninsula, • not enough biomass burning (Southwest Africa). => Assimilation of AOD from MODIS/MISR have small impact on AI. GEOS-5 with assimilation of MODIS/MISR AOD Difference OMI – GEOS-5

  9. Absorption AOD Comparison A 388 nm • OMI and modeled - AAOD capture both : • African dust • Biomass plumes in Southwest Africa • Dust in Arabia Peninsula OMI - AAOD GEOS-5 - AAOD • Model has some absorption in China, not observed by OMI • AI – AAOD : • Biomass plume too low • In Africa : dust plume or concentration too high in the model ? • In Arabia Peninsula : the model places the dust plumes too low ? GEOS-5 - AI OMI - AI

  10. GEOS-5 Dust Vertical Distribution

  11. Aerosol layer altitude : Use of CALIPSO data In Africa Modeled Mass Mixing ratio for Dust • Modeled dust plume height seems to be well placed

  12. Aerosol layer altitude : Use of CALIPSO data In Arabia Peninsula Modeled Mass Mixing ratio for Dust • Large amount of aerosol close to the surface

  13. Conclusions – Future work Conclusions : • VLIDORT simulated Radiances and AI agree well with OMI. • Altitude of the aerosol layer can explain differences in AI (ex : Arabia Peninsula). Plume height in the model or Planetary Boundary Layer Process ?. • MODIS/MISR AOD assimilation have marginal impact on the comparison between AI products (MISR/MODIS do not contain absorption information). Future work : • Recompute the AI with the new model (New Biomass emissions, optical tables) • Include clouds in the radiative transfer calculation and assessing their impact on AI . • Inclusion of water leaving radiances using MODIS assimilated chlorophyll dataset (from Watson Gregg).

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