Analysis of TRMM-identified extreme precipitation systems in Africa: Storm characteristics and contributions to the total rainfall

The TRMM (Tropical Rainfall Measuring Mission) satellite was designed to both measure spatial and temporal variation of tropical rainfall around the globe and to understand the factors controlling precipitation. While extreme deep convection tends to form in the vicinity of mountain ranges, an investigation of TRMM Precipitation Radar (PR) data from 1999-2012 reveals the role of the easterly wave in producing extreme precipitation systems in Africa. The easterly wave flows over Africa along the tropical belt and TRMM-identified storms that typically manifest as mesoscale convective systems (MCSs) are located in correspondence to the easterly wave's location. This study shows that extreme precipitation in Africa is not topography dependent, but rather dependent on the placement of the easterly wave.

For a complete understanding of the impact of these intense precipitation systems on the hydrologic cycle in Africa, it is necessary to assess the contribution from various forms of extreme systems to the climatological rainfall. The TRMM-identified storms were separated into four categories based on different characteristics of radar echo intensities and rain types. Previous studies have demonstrated that the TRMM PR algorithm underestimates heavy precipitation, thus a more traditional Z-R method was used to mitigate the algorithm bias. Precipitation totals were calculated to create a rainfall climatology for Africa. An estimate of how much of the climatological rainfall in Africa is accounted for by extreme storms will be presented. Wide convective echoes tend to have the largest contribution to the total rainfall amounts, with locations focusing along the tropical belt and the Congo rainforest. A seasonal investigation of storm contributions displays a modulation that corresponds with the easterly wave placement. An analysis of the diurnal cycle of rainfall for various extreme storm types will be presented.