A coupled modeling approach to understand ocean coupling and energetics of tropical cyclones in the Bay of Bengal basin

In this study, a coupled model is implemented in the Bay of Bengal basin for simulating tropical cyclones Phailin and Hudhud, with the latter experiencing strong vertical wind shear (VWS). The experiments conducted include a control run (CTL) with the WRF model and a coupled run (CPL) with the COAWST model. Validations prove that the coupled simulations perform better in terms of intensity, track error and equitable threat score. CPL_Hudhud shows enhanced atmosphere-ocean coupling with respect to CTL_Hudhud, while the effect is minute in the case of Phailin. The peak VWS period of tropical cyclone Hudhud shows that high low-level theta(e) gets advected cyclonically from the downshear-right of the storm into the cyclone's inflow layer located in the downshear-left half and is marked by strong radar echoes. Storm energetics reveal that bulk kinetic energy and bulk latent energy have opposite trends during the bulk-energetically growing stage of the storm, and kinetic energy increases at the expense of total potential energy through cross-isobaric flows because of rapid moisture consumption by deep convection. SST and VWS are the crucial factors that determine the atmosphere-ocean coupling, but CPL_Hudhud intensified even in the presence of strong VWS due to enhanced moisture consumption through deep convection, enhanced surface fluxes of moisture and kinetic energy generation. The thermodynamic efficiency of tropical cyclones prove to be quite low as most of the latent heat released is used to warm the atmosphere. In short, this study highlights the importance of a coupled model in simulating extreme weather events and the significance of VWS along with SST in dictating the storm energetics.