Statistical and Comparative Analysis of Tropical Cyclone Activity over the Arabian Sea and Bay of Bengal (1977–2018)

A statistical comparative analysis of tropical cyclone activity over the Arabian Sea (AS) and Bay of Bengal (BoB) has been conducted using best-track data and wind radii information from 1977 to 2018 issued by the Joint Typhoon Warning Center. Results show that the annual variation in the frequency and duration of tropical cyclones has significantly increased over time over the AS and insignificantly decreased over the BoB. The monthly frequency of tropical cyclones over the AS and the BoB shows a notable bimodal character, with peaks occurring in May and OctoberNovember, respectively. The maximum frequency of tropical cyclones occurs in the second peak as a result of the higher moisture content at mid-levels in the autumn. However, the largest proportion of strong cyclones (H1-H5 grades) occurs in the first peak as a result of the higher sea surface temperatures in early summer. Tropical cyclones over the AS break out later during the first peak and activity ends earlier during the second peak, in contrast with those over the BoB. This is related to the onset and drawback times of the southwest monsoon in the two basins. Tropical cyclones over the AS are mainly generated in the eastern basin, whereas in the BoB the genesis locations are meridionally (zonally) distributed in May-June (October-November) as a result of the seasonal movement of the low-level positive vorticity belt. The Arabian Sea is dominated by tropical cyclones that track west and northwest, accounting for about 74.6% of all the tropical cyclones there, whereas the tropical cyclones with a NE track account for only 25.4%. The proportions of the three types of tracks are similar in the BoB, with each accounting for about 33% of the tropical cyclones. The mean intensity and size of tropical cyclones over the AS are stronger and larger, respectively, than those over the BoB and the size of tropical cyclones over the North Indian Ocean in early summer is larger than that in the autumn. The asymmetrical structure of tropical cyclones over the North Indian Ocean is affected by topography and the longest radius of the 34 kt surface wind often lies in the eastern quadrant of the tropical cyclone circulation in both sea areas.