Subseasonal rainfall variability in the tropical eastern Atlantic-West African region

Mean rainfall band in the tropical eastern Atlantic-West African region shows an evident seasonal cycle. Major rainfall events, however tend to be concentrated in two regions and appear in two different seasons, manifesting an abrupt shift of the mean rainfall zone during June-July. (i) Near the Gulf of Guinea (about 5N), intense convection and rainfall are seen during April-June and roughly following the seasonality of SST in the tropical eastern Atlantic. (ii) Along the latitudes of about 10N over the interior West African continent, a second intense rainfall belt begins to develop from July and remains there during the later summer season.

In this study, we investigate the subseasonal variations within this seasonal variation in both surface precipitation and its associated large-scale processes. The 8-yr (1998-2005) high-quality TRMM rainfall, TRMM Microwave Imager (TMI) sea surface temperature (SST), water vapor and cloud liquid water observations are applied along with the 6-yr (2000-2005) QuikSCAT satellite-observed oceanic winds. Particularly, we will focus on various waves and/or oscillations which shape surface rainfall patterns, and their possible contributions to the seasonal migration of the mean rainfall band, i.e., the ITCZ. Both intraseasonal modes (including the possible local amplification of the MJO) and synoptic-scale perturbations will be quantified, specifically their spatial distributions and temporal variations. Variations in surface winds and SST on subseasonal time scales will also be examined.