Satellite detection of soil moisture impacts on convection at the mesoscale

Understanding of interactions between soil moisture and precipitation is limited by a lack of direct observations at spatial scales on which feedbacks occur. This study identifies a sensitivity of convective cloud to spatial variations in soil moisture, based on analysis of satellite observations from many cases in the Sahel. Patches of wet soil were located using passive microwave data. The patches were composited according to length scale, ranging from 37 to 200 km. The response of the convective cloud field to surface variability along the composite cross-section was studied with thermal infra-red data. A suppression of convective cloud is evident over the wet soil during the afternoon and evening for all but the smallest length scales. Analysis of over 100 individual cases where convection occurred in the vicinity of a patch revealed that the development of cloud systems in their early stages appears to be particularly sensitive to soil moisture.