Role of mesoscale circulations on monsoon rainfall over the west coast of India

Sensitivity of monsoon rainfall to different ambient wind speeds, orography and wind shear was studied using a two-dimensional mesoscale model. Three numerical experiments were performed with different initial uniform ambient wind speeds (U = 0.1 ms−1, 5 ms−1 and 10 ms−1) for a typical summer day. It was found that the rainfall increased over the mountain slopes as the initial ambient wind increased. As expected, sheared flow produced increased amounts of precipitation as compared to the uniform ambient flow. Effect of sea/land temperature difference on monsoon rainfall was also investigated. Incorporation of diurnal heating caused the surface pressure gradient to increase, leading to local accelerations of winds, increased mesoscale circulations and more rainfall. The model did not predict precipitation when the orography was not considered.