Impact of multiple tidal forcing on the simulation of the M2 internal tides in the northern South China Sea

Previous studies have indicated that internal tides (ITs) in the South China Sea (SCS) are dominated by the M-2, K-1, and O-1, among which intense nonlinear interaction occurs. In this study, the impact of multiple tidal forcing on the simulation of the M-2 ITs in the northern SCS is investigated based on a primitive equation model. Under the same model settings except the forcing at open boundaries, the run forced by the M-2 individually yields larger M-2 tidal currents and baroclinic energy fluxes than observations and the run forced by the M-2, K-1, and O-1 together, although the M-2 barotropic tidal forcing is the same in the two runs. The M-2 barotropic to baroclinic energy conversion in the Luzon Strait (LS) is almost comparable in the two runs, suggesting that it is not the cause for the differences between the two runs. Indeed, the intense nonlinear interaction between the M-2 and diurnal ITs should account for the differences. Results show that the nonlinear interaction is more intense in the SCS Basin than the western Pacific. Therefore, more energy is transferred from the M-2 to tri-diurnal ITs in the SCS Basin. In addition, the nonlinear interaction enhances the energy loss of the M-2 ITs in the LS.