Global variable resolution simulations of Mississippi River basin rains of summer 1993

A variable resolution global model is used to simulate a 13 day period of heavy rainfall during the 1993 Mississippi River basin floods. The model allows interaction between the atmosphere of the inner, fine resolution region that covers most of the United States and the outer global domain. We describe the impact of flow generated by latent heating over the central United States and its interaction with the global atmosphere. For this case, global constraints on the divergent flow impose substantial modifications upon the rainfall evolution within the central region. The most accurate simulations of rainfall occur when both local divergence and local thermal modifications interact with their global counterparts. The moisture budget is strongly influenced by the imposition of both divergence and thermal fields, and the temporal and spatial distribution of horizontal moisture flux and rainfall change substantially with the degree of outer state prespecification.