Influence of Mesoscale Convective Systems on the Diurnal Cycle of Rainfall over Central Sub-Saharan Northern Africa

While mesoscale convective systems (MCSs) including squall lines and African wave disturbances are frequently observed over the Africa Sahel, it is unclear how their development directly relates to the observed diurnal cycle of daily rainfall over this region and what their relationship is to the underlying land surface. In this study observational rainfall data from TRMM, circulation and moisture fields from various atmospheric reanalyses, and high resolution regional modeling simulations are examined to better understand the role MCSs play in the maintenance of the diurnal cycle of rainfall for this region.

Results indicate that MCSs play a significant role in the total amount of daily rainfall over the central Sahel, ranging from 40 – 90% of the total daily rainfall, depending on the criteria used define an MCS and the time of year. Regional topographic features such as the Jos Plateau, the Cameroon Highlands, Massif du Tondu of Central African Republic, and the Marrah Mountains of Sudan are found to play an important role in the initiation/reinvigoration of MCSs over central sub-Saharan Northern Africa in the afternoon. Case studies utilizing convection permitting resolution WRF regional modeling simulations demonstrate the roles of cold pool outflow boundaries in the apparent westward movement of convective systems across this region and highlight some of the limitations of the observational datasets for this type of study.