Effect of Boundary Layer Dynamics on the Profiles of Rain Drop Size Distribution During Convective Rain

Abstract

The profiles of rain microstructures have been investigated for different types of precipitation using microrain radar observations at a tropical location Kolkata (22.57° N, 88.37° E). A prominent dip in radar reflectivity ($Z$ ) profile has been observed near the boundary layer at high rain rates. This phenomenon is due to the break-up of raindrops into smaller sizes at around 2 km height during intense convective events. The boundary layer dynamics decides the dominance of one of the two processes, namely, coalescence and break-up of rain drops, and determines the drop size distribution profile near the boundary layer. A sharp gradient of vertical velocity at 1-2 km heights is responsible for enhanced drop break-up resulting in an increase in the small drop number density.