Convective-to-Stratiform Transition of MCSs off Western Africa and its Relationship to the Diurnal Offshore Precipitation Maximum

Satellite-based climatological analyses show a sharp contrast between the fractional convective and stratiform rainfall over Africa and its neighboring eastern Atlantic water. While convective rainfall dominates over continental Africa, stratiform precipitation dominates the rainfall totals over the eastern Atlantic. The convective maximum over land is mainly contributed by numerous mesoscale convective systems (MCSs). At the same time, the diurnal peak of precipitation exhibits a maximum just offshore from western Africa. To this end, the objective of this study is to use a phenomenon-based approach to investigate the sharp rainfall morphology contrast between continental Africa and the eastern Atlantic while also relating that contrast to the climatological precipitation maximum off western Africa. We hypothesize that MCSs coming off Africa structurally change as they move off continental Africa and into the maritime environment over the Atlantic. To test this hypothesis, we use primarily hindcasts produced during NASA’s Convective Processes Experiment - Cabo Verde (CPEX-CV) field campaign using the Model for Prediction Across Scales - Atmosphere (MPAS-A). This model was configured with a convection-permitting mesh extending from eastern Africa to the western Atlantic, thus covering the extensive tracks of multiple MCSs as they propagated offshore into the Atlantic. Results show that MCSs in MPAS-A transition from mature trailing stratiform systems over land to decaying stratiform systems over water. Further analysis will investigate if shear-cold pool dynamics can explain this behavior, and how such dynamics change with the time of day.