Using Composite Analysis and Cloud Type Switching to Describe the Interaction between African Easterly Waves and Convective Activities

The development of deep convection over tropical North Africa is often associated with African Easterly Waves (AEWs). The process of how AEWs interact with deep convection is not well understood. This study shows that this relationship changes with various types of convection across tropical North Africa. This study also tests a hypothesis that weak and disorganized types of convection organize into a mesoscale convective system, triggering AEWs. This hypothesis is in contrast with the traditional view that convection is of a single type. It was investigated using composite analysis of satellite cloud, precipitation and reanalysis datasets. Results show that enhanced weak and disorganized convective systems propagate westward from the Arabian Sea and western Indian Ocean, appear to transition to a more organized or mesoscale convective system west of the Ethiopian highlands, and AEWs were initiated farther west around 15°E. This phase relationship analysis may shed light onto the dynamics of AEWs and improve the ability of forecasters to anticipate their associated rainfall.