Modulation of the Kuroshio Current on the M2 Internal Tide Energetics at the Luzon Strait

Abstract Previous studies have demonstrated that the internal tides (ITs) near the Luzon Strait (LS) are significantly modulated by the Kuroshio Current (KC). However, the modulation, particularly the contributions of the KC’s velocity and stratification to the modulation, remains incompletely understood. Based on the interaction theory between subtidal motions and ITs, and 9-month numerical simulation results, this study investigates the KC’s modulation on the M 2 IT energetics at the LS, with a focus on quantifying the contributions of the KC’s velocity and stratification to the modulation. The KC directly modulates the IT energy budget through buoyancy production, shear production, and advection. Among them, the buoyancy production, associated with the KC’s stratification, dominates over the shear production and advection, which are related to the KC’s velocity. Furthermore, the KC influences the tidal conversion and energy flux of ITs by changing the pressure perturbation as well as barotropic and baroclinic tidal currents through nonlinear interaction with ITs. Sensitivity analysis indicates that the bottom pressure perturbation plays a more important role in the tidal conversion, whereas the baroclinic tidal currents are more crucial in the energy flux. Further analysis shows that the contributions of KC’s velocity and stratification to the buoyancy and pressure perturbation are generally comparable. Moreover, the KC’s velocity plays a more important role than the stratification in determining the phase speed of ITs, which leads to different energy flux patterns under different KC paths.