Generation of diurnal K₁ internal tide in the Luzon Strait and its influence on surface tide in the South China Sea

Abstract

The predominance of diurnal surface tides over semidiurnal surface tides in the South China Sea (SCS) has been attributed to the near‐resonance response of the former in the SCS. Recent observations further revealed vigorous internal tides in the northern SCS. Conceivably, internal tides generated in the Luzon Strait could modify the surface tide in the SCS. We use a three‐dimensional tide model of the East Asian seas to address this issue. With a typical summertime stratification of the SCS as the initial condition, energy budget indicates that one third of the incident K 1 surface tide energy is converted to the baroclinic energy over topographic ridges in the Luzon Strait. In comparison with a global tidal model [Matsumoto et al., 2000], our numerical experiments that annihilated or reduced the K 1 internal tide in the Luzon Strait led to up to 50% amplification of the simulated K 1 surface tide in the SCS. This suggests that the baroclinic energy conversion substantially reduces the amplitude of K 1 surface tide in the SCS. The simulated phases in the SCS differ little from those calculated from Matsumoto’s tide model, suggesting that the modification is primarily on the amplitude. Two‐dimensional surface tidal models lack baroclinic energy conversion in the Luzon Strait; the consequent overestimation of surface K 1 tide can be reduced only through precise prescription of sea levels in the Luzon Strait or assimilation of sea level data.