Fields of vorticity, divergence and vertical velocity associated with break and strong monsoon

Abstract

Contrasting rainfall distribution in break and strong monsoon is explained by the fields of vorticity, divergence and vertical motion. (il') Heavy rainfall belt in monsoon, is generally south of the surface position of the monsoon trough. In strong monsoon, the heavy rainfall belt is confined between surface and 700 mb (hPa) monsoon trough position. (iii) The presence of an east- west synoptic scale zonal circulation is observed over the Indian monsoon region similar to the planetary scale 'Walker's circulation'. The synoptic scale east-west zonal circulation is observed over north India and as well as over Peninsular India during the monsoon season, separately and/or simultaneously. During strong monsoon, over north India, there is an ascending motion over northwest India and descending motion over northeast India. And over Peninsular India, there is ascending motion along the west coast of Peninsular India and descending motion over southwest Bay and neighbourhood. During break monsoon, this synoptic scale east-west zonal circulation either weakens or reverses. The strength of monsoon depends upon this synoptic scale east-west zonal circulation.