Orographic and moisture effects on the evolution of the pre-Debby (2006) African easterly waves-mesoscale convective systems over Africa

As a case study on the orographic and moisture effects on the evolution of the African easterly waves-mesoscale convective systems (AEW-MCS), we apply the WRF-ARW model to perform a 32-12-4 km nested simulation in examining the pre-hurricane development period of August 6th through August 22nd, 2006 of Tropical Storm Debby (2006) that primarily formed over the Ethiopian Highlands (EH) region in association with the AEW disturbance and the embedded MCS. Analysis of the numerical simulation data demonstrates that moisture and vertical velocity played a significant role in the maintenance of the convective cycles associated with the pre-tropical cyclone system as it traveled westward across Northern Africa. Both vertical velocity and moisture were initially generated by orographic effects, and were further influenced by environmental factors as the system travels westward. With the mountains in central and western North Africa replaced by flat terrains, we observed that the MCS is somehow weakened and the convective cycles become much less apparent in the coarse domain than in the finer domain. As the system moves further west across Africa, adequate moisture fluxes are guided by the convective development, and the AEW is slightly adjusted by mountainous downstream from the EH region. To further our understanding of orographic and moisture effects on the maintenance of the ARW-MCS, we also use the WRF-ARW model to perform a series of sensitivity tests on TS Debby with mountains being removed and moisture level being modified. Results from both control experiment and sensitivity experiments are then compared with the satellite imagery.