Characteristics of precipitation microphysics during Tropical Cyclone Nisarga (2020) as observed over the orographic region of Western Ghats in the Indian sub-continent

Abstract

The characteristics of precipitation microphysics during various stages of the tropical cyclone (TC) Nisarga (2020) as observed over an orographic station of Western Ghats, India has been highlighted in this paper. The study examines the evolution of convective rain along with the features of surface raindrop size distribution (DSD) within the rainbands and eyewall of the cyclone “Nisarga” based on the observational data of Doppler weather radar and disdrometer during June 02–03, 2020. The cyclone Nisarga, which formed in the Arabian sea, had passed over the Western Ghats after its landfall in the south-western coast of Indian sub-continent. The thermodynamical and microphysical features of the prevailing cloud exhibits strong intensity over the oceanic region than that of over the orographic one along the track of the cyclone. While looking into the impact of rainbands of cyclone as observed by Doppler weather radar over the orographic region, a continuous rise in precipitation is visible when the flow of the cyclone is oriented along the upslope of the terrain. The precipitation intensity and the percentage of occurrences of convective rainfall increased as the primary eyewall of the cyclone reached the orographic station. These are basically due to the presence of the deep convective clouds surrounding the eye of the cyclone, which produces heavy precipitation over the orographic station. Moreover, the orographically generated cloud water along with the shallow convection also plays an important role for the modification of precipitation microphysics over this region of Western Ghats. Thus, these heterogeneous features of rainfall occurrences over the orographic region during the propagation of TC exhibits different radar reflectivity-rain rate (Z-R) relationship which suggests the necessity of a variable relationship for quantitative precipitation estimation (QPE) in different sectors of the TC.