Investigating Solar Radiative Forcing by Biomass Burning Aerosols within Clouds Over Southwest Africa Using Satellite Data.

This study investigates the top of atmosphere (TOA) solar radiative forcing induced by the transport of the biomass burning (BB) absorbing aerosol from the African continent over the south-eastern Atlantic Stratocumulus (Sc) region during the longer fire seasons, i.e., the 4 months of June through September.

The evolution, since 2002, of the BB aerosol and the Sc cloud properties from MODIS satellite data, as well as the evolution of the TOA outgoing solar radiative flux in clear and all skies from CERES (Clouds and the Earth’s Radiant Energy System) satellite data are presented and discussed. In clear skies, CERES shows an increasing trend in TOA outgoing shortwave flux (negative TOA forcing) associated to an increasing trend in MODIS aerosol optical thickness (direct effect) over the southeastern Atlantic Sc region. While in the presence of clouds, CERES shows that the negative TOA forcing by BB aerosol in clear skies is converted into a positive forcing, consistent with previous studies.

Further statistical analyzes are performed to determine whether this positive TOA forcing is primarily attributed to the increase in BB aerosols above Sc clouds or to the negative trend in cloud cover and liquid water path observed by MODIS data.