Understanding the post‐monsoon tropical cyclone variability and trend over the Bay of Bengal during the satellite era

An effort is made to investigate the tropical cyclone (TC) variability over the Bay of Bengal in the warming climate scenario during the satellite era (1979–2018). In this study, the authors investigate interannual variations in the overall capacity of the Bay of Bengal (BoB) basin in the post‐monsoon season to produce either intense or moderate TCs. Globally accepted and widely used metrics accumulated cyclone energy (ACE) and power dissipation index (PDI) are used to examine the energy and damage generated by TCs. A statistical change‐point analysis is conducted to detect the shift in the tropical cyclone frequency and ACE during the study period, indicating the year 1999 as a change point. The results show the increasing trend in ACE in the BoB during the post‐monsoon season with a statistical significance of 95%. On the contrary, the overall frequency is almost unchanged but has shown an increasing trend in the last decade of the study period. Additionally, atmospheric and ocean factors influencing the TC intensity are investigated by applying principal component analysis for three categories of TCs, viz. the very severe cyclonic storm, severe cyclonic storm, and cyclonic storm. Implementation of principal component analysis and correlations of maximum sustained wind speed (MSW2; intensity) with relative vorticity, minimum sea‐level pressure (MSLP), sea‐surface temperature (SST), specific rainwater content, and vertical wind shear revealed relative vorticity as the most dominating parameter amongst all governing factors which determine the final intensity of the BoB TCs. On the contrary, SST shows the different nature of the relationship with different TC categories. This study indicates an increase in the Bay of Bengal post‐monsoon accumulated cyclone energy over 1979–2018 in the warming climate scenario; however, the overall frequency of the tropical cyclone has not changed much. Still, a partially upward trend has been seen in the tropical cyclone in the recent two decades.