Rain microphysical properties over the rain shadow region of India

Abstract

The variability in the microphysical properties of raindrop size distribution (DSD) over the rain shadow region of Indian peninsula is investigated in this study. Simultaneous in-situ measurements of precipitating cloud systems by an impact disdrometer, Micro Rain Radar (24 GHz), and wind profiler (1.28 GHz) are used in this study. The normalized Gamma distribution parameters for five DSD clusters of precipitating systems, corresponding to the non-convective, deep convective, shallow convective, mixed-type, and stratiform rain types were obtained using the k-means clustering algorithm. Four DSDs are nearly bounded by shape parameters, −3 < μ < 25, except for stratiform DSDs (−3 < μ < 45) indicating a wide variation in DSD shape. Bimodal (mono-modal) distributions in terms of frequency of occurrence of Nw are observed in the non-convective, deep convective and shallow convective (stratiform and mixed) clouds. The bimodality is attributed to the large raindrops formed by the collision and coalescence (CC) process, and the small raindrops due to breakup that survive evaporation and reach the ground. The mono-modality of stratiform rain is attributed to the in-efficient CC and CC-breakup process. These rain microphysical processes are further characterized using the radar reflectivity factor (Z)-Rainfall Intensity (R) relationships of the form Z = aRb. Finally, we found that the convective DSDs over the region appear to be a composite of both maritime and continental characteristics.