Rapid intensification of the Super Cyclone Amphan: Environmental drivers and its future projections

Abstract

Tropical cyclones are intense weather systems that originate over warm tropical oceans and they alter the dynamical, chemical, and biological state of the oceans. Here, the reasons for the rapid intensification of Super cyclone Amphan that occurred in May 2020 in the Bay of Bengal (BoB) are thoroughly investigated. One of the main causes for the intensification of Amphan into a super cyclone is the rise in sea surface temperature (SST). Additionally, the warm-core eddies present in the track of cyclones also contributed to its rapid intensification. The Tropical Cyclone Heat Potential (TCHP) and Upper Ocean Heat Content (OHC) were consistent and remained high throughout the cyclone period to maintain its high intensity. Although there were greater cyclone-induced cold wakes during the period, the background SST conditions were still higher and were favourable for the cyclone to intensify further. The vertical wind shear in both shallow and deep layers was minimal, which further helped the formation of a stable and strong cyclonic vortex, and thus contributed to its rapid intensification. The behaviour of cyclone Amphan in future scenarios is analysed using a coupled atmosphere-ocean model. Compared to the current scenario, the severity of cyclones is expected to increase in the future (RCP 8.5). Early landfall is observed in the case of RCP 4.5. As a result of elevated UOHC, Amphan attains more strength in the RCP 8.5 than it does in the present scenario. The translational speed increases in the future, which makes the cyclone move faster. Due to the passage of Amphan, there is a reduction in UOHC, which is higher in the case of a future warm climate. This suggests that additional energy from the ocean is transferred to the atmosphere, causing the cyclone to intensify further. According to the results from the coupled atmosphere-ocean model, the future warm atmospheric and oceanic conditions will be more favourable for the genesis and development of stronger cyclones.