摘要：We investigated the large-scale connection between African aerosol and precipitation in the
West African Monsoon (WAM) region using 8-year (2000–2007) monthly and daily
Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products (aerosol
optical depth, fine mode fraction) and Tropical Rainfall Measuring Mission (TRMM)
precipitation and rain type. These high-quality data further confirmed our previous results
that the large-scale link between aerosol and precipitation in this region undergoes distinct
seasonal and spatial variability. Previously detected suppression of precipitation during
months of high aerosol concentration occurs in both convective and stratiform rain, but not
systematically in shallow rain. This suggests the suppression of deep convection due to the
aerosol. Based on the seasonal cycle of dust and smoke and their geographical
distribution, our data suggest that both dust (coarse mode aerosol) and smoke (fine
mode aerosol) contribute to the precipitation suppression. However, the dust
effect is evident over the Gulf of Guinea while the smoke effect is evident over
both land and ocean. A back trajectory analysis further demonstrates that the
precipitation reduction is statistically linked to the upwind aerosol concentration. This
study suggests that African aerosol outbreaks in the WAM region can influence
precipitation in the local monsoon system which has direct societal impact on
the local community. It calls for more systematic investigations to determine
the modulating mechanisms using both observational and modeling approaches.
