West Africa can be divided into three climatic zones (Guinea, Soudan, Sahel) about 5 degrees in width. Within and between these zones, there are significant differences in topography and land cover. Observations of West African convective systems from the TRMM satellite's microwave imager during the wet seasons since 1998 have provided key insights into the characteristics of these convective systems such as frequency, distribution, sizes, and intensities. With the exception of frequency, the variability of these characteristics was much greater regionally and intraseasonally than interannually. To test the potential links between the regional monsoon dynamics and local land/atmosphere interaction, we conducted numerical studies using the Goddard Cumulus Ensemble/Parameterization for Land-Atmosphere-Cloud Exchange (GCE-PLACE) a coupled cloud-resolving/land surface process model. We created scenarios of boundary layer growth and convective development using land cover and soils representative of each of the three climatic zones.

The strength of the monsoon moisture flux was the most important factor in determining fair or convective weather in each zone. However, the local land/atmosphere interaction influenced the timing, precipitation efficiency, and size of convective systems, consistent with the general trends of each zone observed in the TRMM data. It seems likely that the similarity of the physical characteristics of convective systems through wet and dry years can be attributed to the influence of the land cover, specifically vegetation types and densities, on boundary layer growth.