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

Abstract

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.