Multiwave Interference Characteristics of Semidiurnal Internal Tides in the Northern South China Sea: Perspective of Energetics From Mooring Array Observations

Abstract Multiwave interference fundamentally shapes the spatial inhomogeneity of internal tides, yet its impact on vertical structure and its modulation by seasons and eddies in the deep ocean remain poorly constrained by direct observations. Using a cross‐shaped mooring array (∼50‐km resolution) deployed in the northern South China Sea from June 2018 to April 2019, this study quantifies the interference dynamics of mode‐1 semidiurnal internal tides (SITs). Observations show that both the horizontal distribution and vertical structure of SIT energy and flux are largely shaped by the superposition of a primary northwestward beam from the Luzon Strait and a secondary southward beam from the continental slope. A refraction‐modified line source model successfully reproduces the observed heterogeneous patterns. Furthermore, the SIT interference field exhibits significant non‐stationarity. The observed ratio of horizontal kinetic energy to available potential energy exhibits opposite seasonal variations between summer and winter, with larger anomalies near the two source regions and smaller anomalies elsewhere. Further analysis reveals that this pattern stems from the combined effect of reversed seasonal circulation and stratification, which drives opposite and spatially inhomogeneous shifts in the interference pattern. Eddy‐induced currents and stratification also drive opposite interference pattern changes in anticyclonic versus cyclonic eddies, but currents overwhelmingly prevail. Consequently, the interference pattern rotates clockwise in anticyclonic eddies and counterclockwise in cyclonic eddies. The observed energy and flux exhibit pronounced responses to the deflection of the interference pattern. These findings highlight that multiwave interference is a dynamically evolving process that spatiotemporally redistributes tidal energy in the deep ocean.