Statistical Characteristics and Interdecadal Variation of Tropical Cyclones in the North Indian Ocean

Based on the ADT-HURSAT cyclone dataset produced by the unified satellite observation and identification scheme, the general characteristics of tropical cyclones in the North Indian Ocean (NIO) during the 40-year period of 1978–2017 were statistically investigated. The results reveal that spring and autumn were the peak seasons for tropical cyclones in the NIO, and the peak number of cyclones in the Bay of Bengal was about one month earlier than that in the Arabian Sea in both peak seasons. Cyclones in the NIO occurred mainly in the eastern waters of the Arabian Sea and the west-central waters of the Bay of Bengal. Cyclones of the cyclone storm class were more common in the north, whereas all cyclones above (including) the extremely severe cyclone storm class occurred within the 5°N–15°N latitude. For interdecadal changes, the number of tropical cyclones in the NIO increased by an average of 5 per decade in the autumn for the decadal change, and the region was characterized as moving northwestward in the next two decades, with tropical cyclones in the Arabian Sea moved 1.3° and 3.2° (p<0.01), more significant than the Bay of Bengal cyclones, with an average intensification rate of about 20% over the Bay of Bengal. Compared with the previous 10 years (1998–2007), their number decreased, and their maximum intensity increased to 120 kt; meanwhile, their number has remained stable since 1998, but their maximum intensity decreased. These conclusions differed from studies using other datasets, indicating that dataset quality is important for the analysis of cyclonic characteristics. Further analysis exhibited that decadal variation in latent heat flux is the main factor controlling the interdecadal change in a tropical cyclone generation area in the NIO.