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

Abstract

Previous studies have indicated that internal tides (ITs) in the South China Sea (SCS) are dominated by the M2, K1, and O1, among which intense nonlinear interaction occurs. In this study, the impact of multiple tidal forcing on the simulation of the M2 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 M2 individually yields larger M2 tidal currents and baroclinic energy fluxes than observations and the run forced by the M2, K1, and O1 together, although the M2 barotropic tidal forcing is the same in the two runs. The M2 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 M2 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 M2 to tri-diurnal ITs in the SCS Basin. In addition, the nonlinear interaction enhances the energy loss of the M2 ITs in the LS.