On the interaction of mesoscale eddies and a tropical cyclone in the Bay of Bengal

Oceanic eddies span over a wide range of sizes and affect the thermodynamic properties of water column. By modifying the thermal structure of the upper ocean, these eddies influence the air-sea heat exchange and, therefore, the strength of a tropical cyclone (TC) that passes over the eddy zone. To understand the interaction of tropical cyclone with different types of eddies (cyclonic and anticyclonic) over the Bay of Bengal (BoB) region, three idealized numerical experiments are performed using an atmosphere–ocean–wave coupled model. In these experiments, the atmospheric and wave models are forced by the realistic surface forcing (i.e. wind, pressure, heat and momentum fluxes) of the Vardah cyclone period (10–15 December 2016) in the BoB. The ocean model is initialized with three idealized conditions, i.e. horizontally constant profile of temperature and salinity throughout the model domain, idealized three-dimensional (3-D) temperature and salinity profiles in the area of 2° radius for cyclonic eddy and anticyclonic eddy. The 3-D eddy profile is placed in the path of TC Vardah track. The strength and radius of both idealized cyclonic and anticyclonic eddies are kept same. The model-simulated results of these three experiments were intercompared and it is found that the tropical cyclone interaction with an anticyclonic eddy had provided an ancillary strength to the TC by raising the tropical cyclone heat potential (TCHP) in comparison with other experiments. The utilization of coupled ocean–atmosphere–wave model had also provided a better representation of ocean–atmosphere coupled feedback processes during TC interaction with different eddies. The analysis of feedback processes depicted that the TC interaction with an anticyclonic eddy has raised the magnitude of its existing moist-static-energy comparative to the cyclonic eddy interaction case which resulted into an increase in the strength of the TC.