Internal Processes within African Easterly Waves

The internal processes within African Easterly Waves (AEWs) involving mass, dynamic and water vapor fields are investigated using ERA-I reanalysis, in order to highlight the interactions between convection and AEWs. The budgets of heat, moisture and momemtum are analysed along the different phases of AEWs detected using synoptic- scale precipitable water anomalies as proposed by Poan et al (2013). The strong climatological meridional gradient of moisture present in the Sahel impacts the shape of the apparent heat source and humidity sink. AEW events over the Sahel are associated with a meridional shift of the Intertropical Convergence Zone (ITCZ). Large exchanges of momentum by small scales convective transport is also highlighted between the low and mid levels, contributing to the reinforcement of the AEW circulation at 600 hPa and the damping of the monsoon flow. This also appears as a possible mechanism for the vertical tilt of the meridional wind associated with AEWs. Heat budgets in the southern flank of the West African Heat Low (HL) region reveal that the HL thickness synoptic variability is mainly driven by the horizontal advection of heat. However, the turbulent mixing participates to its development and the vertical circulation acts as a precursor which initiates the heat transport in lower layers. These budgets as well the Q vector formulation of the vertical circulation ultimately allow to determine the distinct contributions of diabatic and adiabatic processes.