The Role of Convection in African Easterly Wave Dynamics

African easterly waves (AEWs) are synoptic-scale disturbances associated with the African Easterly Jet (AEJ) that move westward across sub-Saharan Africa during the West African Monsoon season. It has been shown that the barotropic and baroclinic extraction of energy from the AEJ is not sufficient to sustain AEWs, and that moist convection may have an important role in their maintenance. Therefore, this study aims to investigate the role of convection in the propagation and growth of AEWs. More specifically, this study tests the hypothesis that convection and AEWs interact through the Diabatic Rossby Wave (DRW) mechanism.

To investigate how convection (and diabatic heating) affect the structure and evolution of AEWs, this study examines a potential vorticity (PV) budget. Data for this PV budget is obtained through two different approaches. First a composite average AEW from the ERA-Interim analysis is examined. Second, an AEW case study is simulated using the Weather Research and Forecasting model (WRF) at convection permitting resolution. Sensitivity tests are also carried out using WRF that eliminate convective diabatic heating.

Early results show that diabatic processes generate PV in the low- and mid-levels of AEWs. Further, without diabatic effects, the PV structure of the AEW is limited to the upper-levels and the low-level structure of AEWs, important for Hurricane genesis, is weak or not present. These results suggest that AEWs grow through the DRW mechanism although the propagation of the wave is dominated by advection by the AEJ.