The Impact of El-Nino and La-Nina on the Pre-Monsoon Convective Systems over Eastern India

El-Nino and La-Nina are believed to change the intensity and frequencies of extreme weather events globally. The present study aims to analyse the impact of El-Nino and La-Nina on the lightning activities of cloud systems and their associated precipitation and thermodynamic indices over the Eastern India regions (Odisha, Jharkhand, and West Bengal) during the pre-monsoon season (March-May). Eastern India receives catastrophic thunderstorm events during the pre-monsoon season. The results suggest that the number of lightning flashes was higher in the El-Nino years than in the La-Nina periods, which helps convective activities to be developed over the study region. The precipitation variations showed similar patterns during El-Nino and La-Nina periods, but the magnitudes were higher in the latter. Results from the analysis of thermodynamic indices show that, during the La-Nina phase, the convective available potential energy (CAPE), convective inhibition (CIN), severe weather threat index (SWEAT), humidity index (HI), and total totals index (TTI) values increased, while the cross total index (CTI) and K index (KI) decreased. In contrast, the vertical total index (VTI) and Boyden index (BI) values showed less significant changes in both El-Nino and La-Nina periods. The anomalies of flash rate densities over most parts of our domain were positive during the El-Nino years and negative during the La-Nina years. Precipitation anomalies had a higher positive magnitude during the La-Nina phase, but had spatial variability similar to the El-Nino phase. The anomalies of most of the thermodynamic indices also showed noticeable differences between El-Nino and La-Nina periods, except for the HI index. El-Nino periods showed higher lightning and increased values of associated thermodynamic indices over eastern India, indicating more pronounced convective systems.