Driving factors of rainfall variability in western equatorial Africa during boreal spring and autumn

We examined the mechanisms controlling the interannual variability of rainfall over western equatorial Africa (WEA) during two rainy seasons of April-May-June (AMJ) and October-November-December (OND). Our results suggest that the remote forcing from the Pacific Ocean modulates the circulation over WEA via an atmospheric bridge, only if either the Atlantic or Indian Ocean is also involved. This is particularly evident in the area stretching along the Atlantic coast wherein both seasons present a similar response to the variability of the global zonal circulation. However, the eastern sector (eastern Zaire Basin) during OND season shows an inverse pattern that is associated with an east-west shift in dynamic variables. Such an opposition is not manifested in AMJ. The role of local factors such as topography appears to be important mainly over the central sector of WEA (i.e., western Zaire Basin). In addition to the impact of the remote oceans, a strong direct relationship between the rainfall in coastal region and local SSTs is apparent. However, we argue that this association may reflect the common remote forcing by the large-scale atmosphere-ocean system. Indicative of this is the stronger association with atmospheric parameters than with SSTs. This is further confirmed with negligible variation of air moisture content corresponding to local SST changes.