PNNL

Abstract

This study examines the cloud and precipitation features associated with mesoscale convective systems (MCSs) over the Indian monsoon zone using 6-years of satellite observations and an objective MCS-tracking method. MCSs exhibit distinct regional and seasonal variations, peaking during the summer monsoon (June-September). The majority of MCSs are positioned along a southeast-northwest stretch of the monsoon trough, accounting for 40-70% of total precipitation and moving at an average speed of 6.3 m s?1, with westward motion being more common. Although the frequency of long-lived MCSs (> 40 hours) is ten-times lower than that of short-lived MCSs (5-20 hours), they produce two to three times as much rain as short-lived ones. Composites of environmental properties at MCS initiation are most prominent for the longest-lived MCSs. A bulk of land (Bay of Bengal- BoB) MCSs initiates at 16 LT (04-06 LT) and reaches peak maturity at 18 LT (14 LT). The frequency of convective precipitation from MCSs is much higher than that of non-MCS precipitation, indicating that MCSs play a key role in contributing to monsoon intense precipitation events. Short- and long-lived MCSs showed distinct lifecycle evolution, as well as a strong land-ocean contrast. Particularly, long-lived MCSs over BoB have larger cold-cloud shield (37%) and precipitation feature (44%) areas, higher rain-rates (33%) and produce more total rainfall (67%) than those over land. They show higher rates of area-growth and more cloud mergers in the early-half of their lifespan. These results on monsoonal-MCSs and their lifecycle evolution provide observational constrains for model simulations.