The effect of variations in surface moisture on mesoscale circulations

The model contains prognostic equations for water vapor, cloud water, and rain water, with a simple parameterization of cloud microphysical processes. For convectively unstable initial conditions with a relative humidity of 50%, lifting associated with the sea-breeze front induces a precipitation system which propagates inland from the coast. The sea-breeze circulation associated with dry land is considerably stronger than that produced by moist land; however, the evaporation over land in the sea-breze simulation with moist land results in increased rainfall in spite of the weaker circulation. When moist land is located adjacent to dry land, an "inland sea breeze' is generated which is almost as strong as the dry-land sea breeze, and significant precipitation is produced. The results indicate that inhomogeneities in land moisture on a horizontal scale of 100-200 km can, in a convectively unstable environment with weak environmental flow and sufficient moisture, initiate convective rainfall. They support Anthes' hypothesis that planting bands of vegetation with widths of order 100 km in semiarid regions could, under favorable large-scale conditions, produce increases in convective precipitation. -from Authors