Inferring microphysical processes occurring in mesoscale convective systems from radar measurements and isotopic analysis

Abstract

An attempt has been made, for the first time, to effectively utilize the synergy of various approaches providing microphysical information of precipitation to study short term variations in a Mesoscale Convective System (MCS). A campaign has been conducted wherein rain samples are collected during the passage of MCSs over Gadanki, India, and simultaneously a powerful VHF radar and disdrometer have been operated to infer the characteristics of the vertical structure and rain drop size distribution (DSD) of precipitation. Besides the convection and transition rain, two distinctly different phases of the stratiform rain are identified. Evaporation of rain drops seems to be significant in both convection and stratiform portions of MCS. Observed changes in the temporal variation of the stable oxygen isotope ratios (δ18O) of precipitation are interpreted in terms of microphysical processes leading to isotopic fractionation. The pattern of variability in isotopic abundance is found to be different from convection to transition and to stratiform rain. The present analysis clearly shows that the height (or temperature) and the rain regime of condensation are of paramount importance in determining δ18O. Correlations of δ18O with rainfall integral parameters stress the need for caution in interpreting the depleted isotopic ratios are due to high rainfall and/or bigger drops.