Characterization of Convective Systems and their Interaction with African Easterly Waves

This study investigates the relationship between African easterly waves (AEWs) and different types of deep convection. It is known that AEWs impact the development of deep convection over tropical North Africa and tropical cyclone formation over the eastern Atlantic. However, the process of how AEWs interact with deep convection is not well understood. Composite analysis based on a 24-year data set of cloud systems (CS) from the International Satellite Cloud Climate Project shows that the relationship changes with various types of convection over this region. This phase change relationship analysis may shed light into the dynamics of AEWs and improve the ability of forecasters to anticipate associated rainfall over the Sahel. Weak and disorganized convective systems (WDCSs; 50 km<radius<100 km) are most common within the southerly phase of the AEWs over East Africa. Mesoscale convective systems (MCSs) with cloud radii >100 km increase in frequency within and to the west of the AEW-trough zone. MCSs are common features of summer in northwestern Africa. Our results indicate that the association between AEWs and deep convection is different and changes across North Africa. Weak AEWs over East Africa have a stronger relationship with WDCSs, while mature AEWs over West Africa have more MCS activity. This evolution suggests that the organization of convection from WDCS to MCS may play a critical role in AEW development. This hypothesis contrasts the traditional view that treats convection uniformly.