Variability of Propagating Diurnal Internal Tides in the South China Sea Radiated From the Luzon Strait

Internal tides drive heterogeneous diapycnal mixing, modulating ocean circulation, and biogeochemical processes, yet their spatiotemporal variability remains largely unknown. This study combines mooring observations and numerical simulations to investigate the propagation of diurnal internal tides (DITs) from the Luzon Strait (LS) into the SCS and their responses to dynamic background fields—including the Kuroshio, mesoscale eddies, and seasonal circulation—during the 2015/2016 super El Niño. Results reveal that the looping Kuroshio diverted DIT energy northeastward, reducing southwestward energy flux into the mid-southern SCS by 14% compared with stationary conditions. Conversely, the leaking Kuroshio, paired with cyclonic eddies, enhanced this flux by 33%. Wintertime cyclonic circulation facilitated the southwestward DITs and resulted in about 200-km westward migration of the main DIT beam in the middle SCS. In response to the super El Niño event, the summertime SCS circulation was characterized by a 120-km-wide northeastward jet in the middle SCS, which ducted the southwestward DITs and strengthened them into the middle and southern SCS by 30%. These findings underscore the critical role of rapidly evolving background motions in shaping internal tide dynamics, offering insights for improving climate models and turbulent mixing parameterizations.