Upload
barbra-carter
View
215
Download
0
Tags:
Embed Size (px)
Citation preview
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)
• 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
Assimilation of MODIS/ MISR aerosol data
1) AEROSOL MODEL :
Mie calculations
Aerosol Mass Concentration
AOD
Updates
GEOS-5 Aerosols and VLIDORT interface (2)2) Vertical profiles of optical properties at OMI lat/long:
AOD, SSA, g, P(θ)• at OMI lat/long and λ• for each layer
Mie calculations
354 nm388 nm471 nm
Vertical profiles of AOD, SSA and g at OMI λ
Aerosol Mass Concentration :• for each layer• geolocation at OMI lat/long
OMI (Ozone Monitoring Instrument)/ AURA
VLIDORT Radiative transfer code :– Discrete Ordinate Method– Scalar or Vector mode– Several options for surface specification (Lambertian surface used here)
AOD, SSA, g, P(θ)• at OMI lat/long and λ• for each layer
Input parameters from OMI file :- Geometry angles :
• Solar Zenith Angle• Relative Azimuth Angle• Sensor Zenith Angle
- Surface albedo at 3 λ
Model Pressure & Temperature
3) Radiative transfer calculation :
• TOA radiances• Aerosol Index
GEOS-5 Aerosols and VLIDORT interface (3)
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
⇒ Globally, good agreement but :
A 388 nm
Comparison of monthly mean TOA Radiances (1)
Overestimation of the modeled radiances over land,
Underestimation of the modeled radiances over ocean in the southern hemisphere.
388 nm 388 nm 388 nm
GEOS-5 Free running model OMI Difference OMI – GEOS-5
GEOS-5 with assimilation of MODIS/MISR AOD
388 nm
Comparison of the monthly mean TOA Radiances (2)
A 354 & 471 nm
⇒ Same conclusions as 388nm
354 nm 354 nm 354 nm
471 nm 471 nm471 nm
GEOS-5 Free running model
GEOS-5 Free running model
OMI
OMI
Difference OMI – GEOS-5
Difference OMI – GEOS-5
UV Aerosol Index (AI) Comparison
⇒ 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 Free running model OMI Difference OMI – GEOS-5
GEOS-5 with assimilation of MODIS/MISR AOD Difference OMI – GEOS-5
Absorption AOD Comparison
OMI and modeled - AAOD capture both :• African dust • Biomass plumes in
Southwest Africa• Dust in Arabia Peninsula
A 388 nm
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 ?
OMI - AAOD
OMI - AI
GEOS-5 - AAOD
GEOS-5 - AI
Model has some absorption in China, not observed by OMI
GEOS-5 Dust Vertical Distribution
Aerosol layer altitude : Use of CALIPSO dataIn Africa
Modeled dust plume height seems to be well placed
Modeled Mass Mixing ratio for Dust
Aerosol layer altitude : Use of CALIPSO dataIn Arabia Peninsula
Modeled Mass Mixing ratio for Dust
Large amount of aerosol close to the surface
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).
Conclusions – Future work