Sub-basinal and sub-seasonal TC activities over NIO during 1980-2021

Abstract

Tropical Cyclones (TCs) bring strong winds, heavy rainfall, and storm surges upon landfall, causing significant social and economic damages, including a high number of casualties. Especially, In the Asian region, including the western-North Pacific (WNP) where TCs are most frequent and the North Indian Ocean (NIO), which represents over 30% of global disaster indicators, TCs were responsible for 21% of occurrences, 70% of fatalities, and 30% of losses. In this study, we examined the temporal and spatial relationships between TC activities and environmental variables in the NIO, focusing on the pre- and post-monsoon periods and dividing the region into the Arabian Sea and the Bay of Bengal. Regardless of the region, there was a close relationship between TC intensity and inner-core rainfall. However, the rainfall area of TC showed different characteristics: in the Arabian Sea, latent heat flux over ocean (LHFLX) and vertical wind shear (VWS) were identified as key factors, while in the Bay of Bengal, relative humidity at 600 hPa (RH600) played a significant role. It was observed that the frequency of TCs in the Arabian Sea increased during post-monsoon, which can be attributed to favorable conditions for TC activity, such as increased LHFLX, weakened tropical zonal circulation and VWS, and increased RH600, associated with an Indian Ocean Dipole-like uneven warming pattern caused by global warming. These findings suggest an increased risk due to the higher frequency and intense RS associated with TCs in the Arabian Sea, highlighting the need for appropriate measures.