Impact of Earth's Rotation on the Nonlinear Evolution of Internal Tide Beams: Insights From Laboratory Experiments

The Coriolis force, arising from the Earth's rotation, plays a critical role in shaping the nonlinear evolution of internal tides (ITs) in the stratified ocean. This study employs laboratory experiments to investigate the impact of Earth's rotation on the instability and energy redistribution of IT beams generated by ridge topography. The results confirm that, within a specific range of the Coriolis parameter, IT beams transfer energy to two secondary waves (SWs) with smaller spatial scales via triadic resonance instability (TRI) and near-inertial parametric subharmonic instability. The weakly nonlinear theory is applied to analyze the spatiotemporal scales of these SWs, with their frequencies and wavenumbers governed by the highest theoretical instability growth rate. Strong TRI markedly alters the spatial distribution of energy dissipation, shifting intense dissipation from along the IT beams to regions closer to the ridge. Furthermore, the self-interaction of ITs induces mean flows near the ridge crest and along IT beams. The generation of intense SWs, combined with enhanced rotation, reshapes the structure and magnitude of mean flows by modifying the divergence of Reynolds stress, which is linearly related to velocity of mean flows near the ridge. These findings provide new insights into the instability mechanisms and energy cascading processes of IT beams.