Reflections of tropical cyclone-generated near-inertial internal waves within an anticyclonic eddy in the southern Bay of Bengal

Abstract

Two consecutive strong near-inertial waves (NIWs) events were observed by a subsurface mooring in the southern Bay of Bengal (BoB). The first event, directly triggered by two consecutive tropical cyclones, displayed a pronounced upward (downward) phase (energy) propagation. The second event, occurring approximately 14 days post-tropical cyclones, featured predominant downward phase propagation with a peak velocity of 11.2 cm/s at 120 m depth. Despite weak wind-generated near-inertial energy flux (WNEF) during the second event, stronger energy reflection was observed in the upper layer of an anticyclonic eddy (ACE). Analyses using rotary wavenumber and ray-tracing models revealed upward propagating energy, reduced buoyancy frequency, and enhanced vertical shear, suggesting NIW reflection within the ACE. Nonlinear internal wave interactions were identified as the mechanism behind the generation of 2f = f + f waves. In the second NIWs event, increased near-inertial energy and 2f wave formation were possibly linked to local NIWs, driven by wind stress input and the radiation of NIWs during the adjustment process induced by anticyclonic eddy instability. These results highlight the influence of ACEs on the vertical propagation of NIWs and enhance the understanding of the upper-layer mixing process in the southern BoB.