450 / 2024-09-17 11:01:19

The near-inertial waves observed in the Southern Bay of Bengal

near-inertial waves, Bay of Bengal, reflection,anticyclonic eddy

Two consecutive strong near-inertial waves (NIWs) events were clearly observed through the subsurface mooring in the southern Bay of Bengal (BoB). The first was triggered by the consecutive tropical cyclones, exhibiting a distinct upward phase that indicated the downward propagation of near-inertial energy driven by wind. The second occurred after the passage of tropical cyclones, and characterized by predominant downward phase propagation, reaching a maximum value of about 11.2 cm/s at a depth of 120 m. The rotational spectrum shows that the near-inertial energy propagates upward at this time, indicating that the NIWs have undergo reflection during the downward propagation process. The Ray-Tracing model results indicate that when the mooring is situated within the influence of an anticyclonic eddy, the buoyancy frequency weakened and vertical shear intensified, leading to the reflection of NIWs. Furthermore, local NIWs may be induced by parameter subharmonic instability mechanism associated with semi-diurnal tides, resulting in a significant enhancement of near-inertial energy and promoting strong self-interaction of NIWs (f+f=2f). This observation reveals the influence of anticyclonic eddy on the vertical propagation of NIWs and improves understanding of upper layer mixing in the southern BoB.