Response of Atmospheric Thermodynamics to Pre-monsoon Season Thunderstorms over Eastern and North-eastern India

Abstract

Thunderstorm forecasting is necessary to safeguard society from severe damage over different parts of the globe. Forecasting these events is more important in tropical countries like India. Eastern and north-eastern India encounters severe thunderstorms and associated casualties during the pre-monsoon season (March-May). My doctoral research analyses temporal and spatial variation thermodynamic indices and the changing climate scenario impact with respect to pre-monsoon thunderstorms over eastern (Odisha, Jharkhand, and West Bengal) and north-eastern (Assam and Tripura) India. The thermodynamic indices employed for this work are the Lifted Index (LI), K Index (KI), Severe Weather Threat Index (SWEAT), Total Totals Index (TTI), Vertical Totals Index (VTI), Cross Totals Index (CTI), Showalter Index (SHOW), Humidity Index (HI), Boyden Index (BI), Convective INhibition energy (CIN) and Convective Available Potential Energy (CAPE). Thermodynamic indices and their threshold values have been calculated at Kolkata, Bhubaneswar, Ranchi, Agartala and Guwahati stations using the radiosonde data for the past thirty years (1987-2016). The thunderstorm occurrence information has been obtained from the India Meteorological Department (IMD), Pune. The latent and conditional instability indices showed a change in threshold values over these sites. The climatological atlas of various thermodynamic indices was developed using hourly (00 UTC and 12 UTC) ERA-5 re-analysis data to differentiate Thunderstorm and Non-Thunderstorm days (TD and NTD) throughout the study over eastern and north-eastern India. The study also employed Mann-Kendall Trend analysis (MKT) over the spatial domain to find the trends in the spatial variability of thermodynamic indices during TD and NTD. As the Chhota Nagpur Plateau (CNP) and Shillong Plateau (SP) have been identified to provide triggering for thunderstorm development over eastern India and parts of north-eastern India, the study also evaluated the role of CNP and SP in the development and propagation of thunderstorms. Sensitivity experiments are performed (with increasing and decreasing topography of CNP and SP) using state-of-the-art mesoscale model Advanced Weather Research and Forecasting (WRF-ARW) over the eastern and north-eastern India region. The results showed that the characteristics of several thermodynamic indices change substantially with the changes (increases/decreases) in the CNP’s and SP’s topography from its actual topography.