Local impacts of Saharan dust on convection and on the monsoon circulation during the pre-onset and the established monsoon periods

The aim of this study is to analyze the local impacts of dust on the West African monsoon circulation. Using different regional models (Meso-NH and WRF), dust schemes have been used to quantify the impacts of dust on convection and on the main components of the West African monsoon, such as the West African Heat Low (WAHL), African Easterly Waves (AEWs), monsoon and Harmatan winds. Two different periods have been simulated, one in 2006, during the AMMA campaign, investigated a 6-day pulsation of the West African heat low (WAHL) in summertime (14 to 20 July), with convective rainfall and dust bursts being observed over the Sahel at the beginning and end of the episode. Three Meso-NH simulations were designed which differed in their dust representation. This study highlights two effects of dust on the WAHL over the Sahara: a so-called direct effect associated with dust radiative heating, which increases the WAHL thickness, and a so called indirect effect that intensifies both the African easterly jet and a related African easterly wave. Using the observation provided by the FENNEC international project in June 2011, a second study has been done to better understand the local impacts of the dust during the pre-onset period, when the dust load in the mid-troposphere appears large. Using WRF simulations in an ensemble system, the sensitivity of the monsoon circulation to direct and indirect effects of the dust have been compared to the sensitivity of the large-scale forcings