Monsoon onset over Sudan-Sahel: Simulation by the regional scale model MM5

The Mesoscale Model MM5 is used to study the regional features of the West African Monsoon onset. In order to increase the results, simulations are carried out for eight consecutive seasons ( March to September) of the years 1994 to 2001. The results show that the model can reproduce the dynamical features of the monsoon in a reasonably good manner but the seasonal cycle seems enhanced. It is hypothesized that overestimated rainfall amounts could be related to a poor representation of the land surface characteristics. Nevertheless, the mean simulated monsoon onset dates are similar to those find in the CMAP data set. The onset is characterized by an apparent increase in zonal flow that could bring moisture from the eastern Atlantic ocean, in conjunction with a deepening of the Saharan heat low. These results show that the model can be used to detail the basic processes linked to the monsoon onset and to perform dynamical downscaling.