TRACER REDISTRIBUTION BY CLOUDS IN WEST-AFRICA - NUMERICAL MODELING FOR DRY AND WET SEASONS

The vertical transport by clouds of an inert tracer and its redistribu tion by complex West African circulations are examined using a two-dim ensional mesoscale meteorological model with explicit microphysics. Th e model reproduces the tropical distribution of clouds and precipitati on along a meridional cross section over West Africa, corresponding to the position of the Intertropical Convergence Zone (ITCZ) during the dry and rainy seasons. The resulting redistribution of the inert trace r is therefore closely related to the northward migration of the ITCZ between January and July. The occurrence of biomass burning during the dry season is shown to be an important source of tracer enrichment at upper levels in the atmosphere.