Interaction between the M2 internal tides and typhoon-induced near-inertial waves near the Luzon Strait

Abstract

The South China Sea is abundant with intense internal tides (ITs) and typhoon-induced near-inertial waves (NIWs), which inevitably interact with each other. Based on the numerical simulation results, the interaction between the M₂ ITs and typhoon Megi-induced NIWs in the deep ocean near the Luzon Strait is studied. The interaction gives rise to sum- and difference-frequency waves, denoted as the fM₂ and M₂-f waves. Results of this study highlight the contribution of the M₂-f waves to shear enhancement: The kinetic energy of the M₂-f waves is one order of magnitude smaller than that of the M₂ ITs, but the domain-averaged vertical shear squared caused by the M₂-f waves is comparable to that of the M₂ ITs. The IT-NIW interaction is dominated by the product of vertical internal tidal velocity and vertical shear of horizontal near-inertial velocity, which is followed by the product of horizontal near-inertial velocity and horizontal shear of horizontal internal tidal velocity. The IT-NIW interaction influences the evolution of near-inertial kinetic energy through modulating the energy exchange and near-inertial energy flux, which are site-dependent. In the modulation of energy exchange, the terms associated with horizontal shear of horizontal internal tidal velocity play crucial roles. Whereas in the modulation of near-inertial energy flux, the terms associated with vertical shear of horizontal near-inertial velocity are dominant.