Role of deep convection in regulating the Indian summer monsoon dynamics: a regional scale modelling study

Abstract

The deep convection and associated moist processes have a major role in regulating the circulation and precipitation characteristics of the Indian summer monsoon. This aspect is examined by conducting sensitivity experiments with the Weather Research and Forecast model. Three active monsoon cases during the periods 16-25 June 2015, 20-29 July 2010 and 1-9 August 2007 are selected for the study. Control simulations using reanalysis data as initial and lateral boundary conditions reveal that the model could simulate mean features of the precipitation and circulation pattern during those active monsoon periods. In sensitivity experiments, microphysical latent heat release in the model is switched off and all other conditions are kept same as that of control simulations. The removal of latent heat release in the model suppresses development of deep convection over the monsoon domain and causes substantial reduction in precipitation. A large-scale descending motion appears in the mid-troposphere and vertical growth of clouds is hampered. As a result, thick cloud bands form in the lower atmosphere, which reduces the short-wave radiation reaching the surface and leading to a reduction in land surface temperature over the Indian region. The cessation of deep convection also affects the strength and position of monsoon low-level circulation. The lack of convective heating shifts the low-level jet core over the Arabian Sea towards north. Consequently, the low-level jet gets strengthened over the north-west India and weakens over the peninsular India. The present study unambiguously established the fact that organized deep convection and concomitant vertical heating over the monsoon domain have a prominent role in regulating monsoon dynamics.