Propagation Features of Diurnal Internal Tides West of the Luzon Strait Revealed by a Large PIES Array

Abstract Energetic internal tides (ITs) are generated from the Luzon Strait (LS) and propagate westward into the South China Sea (SCS). Owing to the lack of large-scale synchronous measurements, the propagation features and seasonal variations of diurnal ITs remain unclear. From 2018 to 2019, mode-1 diurnal ITs west of the LS were continuously observed using a large-scale moored array of 27 pressure inverted echo sounders (PIESs) and a thermistor chain. Measurements confirmed that diurnal ITs radiate from the LS with a north–south asymmetrical pattern, with the most energetic channel located in the middle and south of the LS. The total energy radiated into the SCS across 120°E is 2.67 GW for the K 1 and 1.54 GW for O 1 ITs, approximately two times larger than those inferred from satellite observations. K 1 dominates among the diurnal ITs, with its maximum isopycnal displacement (amplitude) and energy input to the SCS being the strongest in summer (i.e., 16.3 m and 2.81 GW, respectively). The propagation speed of K 1 is higher in summer and autumn along the main channel (i.e., 4.33 and 4.36 m s −1 , respectively). Seasonal stratification and circulation play important roles in the seasonal variation of amplitude and propagation speed of the K 1 ITs. The seasonal variability of diurnal-band ITs, which includes all diurnal constituents, is location-dependent and primarily results from the superposition of the K 1 and P 1 ITs. In particular, vertical displacement is strong in summer and winter along the main channel of the K 1 and P 1 ITs. The seasonal amplitude of K 1 can modulate this seasonal feature.