Intraseasonal Variability of the West African Monsoon in a Regional Climate Model

The West African monsoon exhibits significant intraseasonal variability that leads to periods of increased or decreased African easterly wave (AEW) activity during boreal summer. The variability of AEWs is important for precipitation variability in the Sahel and tropical North Africa, as well as cyclogenesis variations in the North Atlantic. This study investigates the extent to which the intraseasonal variability in North Africa is modulated by external forcings, including the Madden-Julian oscillation (MJO). The Weather Research and Forecasting (WRF) model is used to simulate several boreal summers that exhibit significant West African intraseasonal variability in precipitation and AEW activity. In sensitivity tests, eastward and westward propagating intraseasonal variability is filtered from the WRF lateral boundaries to examine if North African precipitation and AEW activity differ in the absence of the MJO and other large-scale phenomena, including equatorial Kelvin and Rossby waves. Sensitivity and control experiments are compared, with a particular emphasis placed on the relationship between convection triggered in East Africa and AEW activity in West Africa. Previous work has suggested that a moistening and convective signal in East Africa associated with the MJO precedes periods of increased AEW activity. The exploration of East African moistening and other potential mechanisms will shed light on how increases in AEW activity are initiated on intraseasonal timescales.