A three-dimensional high-resolution internal tidal model was constructed based on MITgcm and used to simulate the internal tide in the northern SCS. The simulated internal tides reproduce the magnitude and variation characteristics of the isotherm fluctuations and velocity observed by two subsurface buoys. The generation, propagation and dissipation of the simulated internal tide are analyzed. The conversion rate of K1 tide and M2 tide in the Luzon Strait area is nearly 8.91 GW and 13.72 GW, respectively. The baroclinic tidal energy flux presents a clockwise spiral structure between the two ridges in the Luzon Strait, due to the supercritical topography.
Internal tides are internal waves with tidal frequency and are generated by the interaction of barotropic tides with rough terrain, such as continental shelf and sea ridge, in stratified oceans. Compared with the surface tide, the internal tide has stronger vertical disturbance and baroclinic velocity, and the horizontal wavelength can reach hundreds of kilometers (Kang et al., 2000). As an important intermediate link in the process from surface tide to mixing (Rudnick et al., 2003), internal tide play a very important role in the dissipation of barotropic tide (Munk, 1997; Egbert and Ray, 2000) and the strengthening of mixing (Rudnick et al., 2003), influencing the global large-scale circulation (Munk and Wunsch, 1998). The global energy conversion from barotropic tide to internal tide is about 1TW, which is about half of the energy required to maintain the thermohaline circulation (Munk and Wunsch, 1998; Egbert and Ray, 2000).
The South China Sea (SCS) is one of the major areas of internal tide generation, drawing extensive attention. Conducting internal tide research based on observational data is the most direct approach. In addition, numerical simulations also play a crucial role in investigating internal tide. Wu et al. (2013) used the MITgcm model to study the seasonal variations of the M2 and K1 internal tides at the 21°N section. The results indicated that the K1 internal tide is trapped in the SCS Basin, while the M2 internal tide propagates to the continental shelf and essentially does not reflect into the basin. Utilizing data from multiple satellite altimeters, Wang et al. (2016) conducted internal tide simulations using a high-resolution three-dimensional non-hydrostatic model driven by the four major tidal components, studying tidal mixing phenomena in the Luzon Strait and the SCS. Li et al. (2021) studied the regulation of turbulence mixing on internal tides in the SCS through numerical simulations, including the balance of slope tide energy, incoherence, and nonlinear interactions among different tidal components. Guo et al. (2023) explored the role of anticyclonic and cyclonic eddies in regulating M2 internal tides based on numerical simulations.
