Atmosphere-upper-ocean interactions during three rare cases of rapidly intensified tropical cyclones over North Indian Oceans

The present study investigates the evolution of ocean thermal parameters during the intensification of three rare cases of rapidly intensified long-duration tropical cyclones (TCs) formed over the North Indian Ocean (NIO). TCs consume energy from the underlying warm ocean for their development. The movement of TC towards warmer sea surface temperature (SST) fueled the TCs during rapid intensification (RI). Though, the ultimate storm intensities of the TCs were significantly impacted by ocean mean temperature up to 26 ºC isotherm (OMT) rather than the SST. This is an important factor to be considered in studying the impact of ocean thermal energy on TCs. The passage of TCs after RI causes cooling in SST by 1–2 °C. Though, the reduction in OMT was about 0.5 °C because more ocean thermal energy is available in the upper layers. The maximum intensification of the TC Fani to the category-4 stage was much contributed by the OMT rather than SST. The energy input to the ocean due to wind stress is higher at the lower translational speed of TCs. The total (average) of mechanical energy transferred to the ocean by TCs Fani, Luban, and Ockhi are 6019 (35.8), 3460 (16.9), and 5449 (36.3) TW, respectively, during their lifecycle. The study suggests that the interaction of TCs and OMT (upper layer ocean thermal energy) rather than SST (only ocean skin temperature) has to be understood in greater detail to address the research problem of TC prediction.