The Enhancement of Precipitation due to Mesoscale Convective Organization

Abstract

In the tropics, extreme precipitation events are often caused by mesoscale systems of organized, spatially clustered deep cumulonimbi, posing a substantial risk to life and property. While the clustering of convective clouds has been thought to strengthen precipitation intensity, no quantitative estimates of this hypothesized enhancement exist. In this study, we use observational data to demonstrate that this enhancement of precipitation intensity does indeed exist. After isolating the effects of mesoscale convective clustering on precipitation, we find that strongly clustered convection precipitates about 47% more intensely than weakly clustered convection. We further show that this enhancement is primarily attributable to an increase in convective precipitation intensity when the environment is less than 70% saturated, with increases in stratiform cloud cover being of equal or greater importance when the environment is closer to saturation. We show that this convective-stratiform transition is a consequence of the invariance of tropical convective and stratiform rain fractions to the degree of mesoscale convective clustering present. Our results are intended to serve as observational constraints for the representation of mesoscale organized convective systems in numerical models, aiding in making more accurate prediction of extreme precipitation events.