PNNL

Abstract

For this report, West Africa refers to the region between 17.5°W (eastern Atlantic coast) and approximately 15°E (along the western border of Chad) and 5°N north of the equator (near the Guinean coast) to 20°N. It is typically divided into two climatically distinct sub-regions: the semi-arid Sahel region (north of about 12°N) and the relatively wet coast of Guinea to the south. The rainy period over this region is associated with the latitudinal movement of the zone of convection, or the West African monsoon, and typically occurs in boreal summer (June–September). The inter-annual and decadal variabilities of this monsoon movement are controlled by the north–south SST gradient across the tropical Atlantic, ENSO, and SSTs over the Indian Ocean (Giannini et al. 2003; Hagos et al. 2008).