Investigation of the contrasting influence of air–sea interactions on the intensification process of pre-and post-monsoon tropical cyclones over the Bay of Bengal in a coupled model framework

This study investigates the role of air–sea interactions in the intensification of tropical cyclones (TC) during two peak cyclone seasons over the Bay of Bengal (BoB), that is, pre-, and post-monsoon, utilizing the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) model. Two TCs, that is, Phailin (post-monsoon) and Mocha (pre-monsoon), are considered for this study. Results indicate that COAWST successfully replicated the basic features of TCs, but underestimated (overestimated) the intensity of Phailin (Mocha). Mocha’s asymmetric intensification is influenced by strong vertical wind shear (VWS), while Phailin’s intensification is aided by a post-monsoon conducive atmosphere in the absence of VWS. Interestingly, the energetics analysis demonstrates that Mocha’s intensity was strongly regulated by a high Tropical Cyclone Heat Potential (TCHP) (>120 kJ·cm−2) area located far away (˜300 km) from the core regions by increasing lateral moisture flux (43% in six hours) through primary circulation. Furthermore, this has also helped to counter the influence of the cold core eddy (CCE) below the storm central circulation. The moisture flux and bulk kinetic energy are two prominent indicators for TC intensification during the pre-monsoon season. Phailin steadily intensified into an Extremely Severe Cyclonic Storm (ESCS) despite having lower TCHP during the post-monsoon season. It is found that the negative influence of the ocean was less prominent during the post-monsoon season due to the presence of a thick barrier layer (BL) resulting in reduced sea surface temperature cooling compared to the pre-monsoon, leading to steady intensification of Phailin. In general, it is noted that pre-monsoon TCs exhibit a stronger dependency on ocean thermal structures compared to the post-monsoon.

Recommended citation: Chakraborty, S., Pattnaik, S., Banerjee, A., & Chakraborty, T. (2025b). Investigation of the contrasting influence of air–sea interactions on the intensification process of pre‐ and post‐monsoon tropical cyclones over the Bay of Bengal in a coupled model framework. Quarterly Journal of the Royal Meteorological Society. https://doi.org/10.1002/qj.4957
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