Modeling the transport and optical properties of smoke aerosols from African savanna fires during the Southern African Regional Science Initiative campaign (SAFARI 2000)

Abstract

We investigate the transport and optical properties of smoke aerosols from southern Africa using an offline three‐dimensional aerosol transport model. We use Sun photometer retrieved particle size distributions and monthly mean satellite‐derived smoke emissions as input parameters. We find that using these observations in our model allows us to reproduce the measured optical properties collected during the Southern African Regional Science Initiative campaign (SAFARI 2000). In particular, we find day‐to‐day oscillations in the simulated aerosol optical thickness (AOT) similar to Aerosol Robotic Network (AERONET) retrievals, suggesting that variations in aerosol loading are controlled more by transport processes than fluctuations in smoke emissions. We also find that the simulated AOT, Ångström exponent, and single scattering albedo compare well to AERONET. The model and satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multiangle Imaging Spectroradiometer (MISR) also show that the dominant transport of smoke plumes over Africa was westward during September 2000. However, the satellite observations show higher AOT values than our model over the Atlantic Ocean. These higher values observed by the satellites may be a result of poor single scattering assumptions and the contamination by subpixel clouds in the retrievals. However, the monthly mean smoke emissions may also be too low, resulting in low simulated AOT values. We also find discrepancies between MODIS and MISR, which limit our ability to use the satellite data to validate our model. Our work suggests strategies for improving the treatment of smoke aerosols from African biomass burning in climate and microphysical models.