African Easterly Waves in Convection Permitting Simulations: The Role of Moist Convection

African easterly waves (AEWs) are synoptic-scale disturbances that are active within the North African Monsoon. Their growth has been linked to barotropic and baroclinic instability of the African Easterly Jet (AEJ). It has also been shown that moist convection may have an important role in their maintenance. However, details of their interaction with convection have not yet been sufficiently understood. This study tests a range of hypotheses from AEWs being driven entirely through diabatic processes---as in a Diabatic Rossby Wave (DRW)---to entirely by adiabatic hydrodynamic instability. Preliminary results using reanalysis data suggest that the AEWs fall somewhere in the middle of this spectrum.

To investigate these hypotheses, this study will utilize a set of convection permitting Weather Research and Forecasting model (WRF) simulations. The control simulations will be analyzed using eddy kinetic energy (EKE) and potential vorticity (PV) budgets to assess where and how various processes are active. Next, by modifying a microphysics scheme to limit latent heating in the WRF simulations, sensitivity studies will allow for the examination of the structure, dynamics, and evolution of AEWs with limited latent heating, while maintaining as similar of an environment as possible to the control simulation.

Our preliminary results from a simulation of a single AEW show that the DRW mechanism generates PV in the low- and mid-levels of AEWs while the Rossby Wave mechanism is more important aloft. Further, by limiting the moisture in sensitivity studies, convection and diabatic effects were limited, and the AEW was increasingly limited to the upper levels with decreasing moisture. These results suggest that the AEW is very different without diabatic processes but they are not a requirement for the AEWs continued propagation and maintenance.