Dust variability over Northern Africa and rainfall in the Sahel

The Infra-Red Difference Dust Index (IDDI) is a new dataset that uses reductions in atmospheric brightness temperature (derived from METEOSAT IR-channel measurements) to map the distribution of mineral aerosols over continental Africa. The IDDI dataset is described, and the IDDI data are used to identify the major African dust sources, located in the Sahel-Sahara zone. The seasonal variations in these sources are discussed. Annual, seasonal and monthly dust indices are constructed from the IDDI data for different latitudinal zones in the Sahel-Sahara zone. The temporal and spatial variability of dust production in the Sahel and Sahara is inferred from these indices and the latitudes of maximum dust production are identified. Interannual variability of dust production is described in conjunction with a consideration of variations in annual rainfall over the Sahel. Relationships between rainfall and subsequent dust production in the Sahel are investigated by correlating zonally averaged rainfall and IDDI values at lags of one and two years. The spatial and temporal patterns of dust production suggest that spring and summer deflation is associated with the passage of convective disturbances across the Sahel. There is evidence that wet-season rainfall totals have an impact on dust production in the later part of the following dry season. The results also suggest a cumulative impact of rainfall on December dust production. However, there is no evidence from this study that dust production is associated with widespread land degradation.