Evaluating the impact of topography on the initiation of Nor’westers over eastern India

Abstract

Pre-monsoon thunderstorms are catastrophic and frequent over eastern and north-eastern India. The Chhota Nagpur plateau (CNP) believes to be the triggering platform for thunderstorms over east India. This study attempted to determine the influence of the CNP topography on thunderstorm formation and propagation by observing the changes in the values of thermodynamic indices over eastern India. The work attempted ten cases of thunderstorms in multiple simulations, i.e. each case simulated three times with varying elevations of CNP topography (in total 30 simulations) by Advanced Weather Research and Forecasting (WRF–ARW) model. Our analysis revealed that when the elevation of topography of the CNP changes (increases/decreases), the characteristics of several thermodynamic indices alter considerably (with values changing from negative to the positive side for some indices). We found the Cross Total Index (CTI) shows considerable differences in all the thunderstorm simulations, and the values are higher in the increased CNP topography (∼ −4 to 6 °C). However, the Humidity Index (HI) (∼ −10 to 15 °C) and Convective INhibition (CIN) (∼ −200 to 200 J/Kg) values depict considerable changes in decreased topography. The results are crucial to understanding and quantifying the role of CNP in pre-monsoon thunderstorms over east India.