Long‐Range Radiation and Interference Pattern of Multisource M₂ Internal Tides in the Philippine Sea

Abstract

Long‐range radiation and interference of M2 internal tides from multiple sources in the Philippine Sea are examined by driving a high‐resolution numerical model. The M2 internal tides are effectively generated around the boundary area, which includes the Luzon Strait, Ryukyu Island chain, Bonin Ridge, Mariana Arc, and Izu Ridge, favoring the occurrence of complex interference patterns. The local sources (mainly Daito Islands and Palau Ridge) inside the basin contribute to a small portion (~5%) of total energy but enhance the geographical inhomogeneity of the baroclinic field. The mode‐1 and mode‐2 M2 tidal beams from boundary sources radiate a long distance into the basin but exhibit different interference‐modulated geography variations. A 2‐D line source model characterizing interference can reproduce the general baroclinic field. Two notable interference cases are investigated: (1) the superposition of internal tides from Luzon Strait and Miyako Strait bifurcates into several southeastward beams, consistent with previous numerical simulations and altimeter measurements, and (2) the interference between Tokara Strait and Bonin Ridge exhibits a multiscale spatial pattern, which is modulated by the local generated energy and bathymetry features. Energetic dissipation occurs both near the boundary sources and in the basin. A locally dissipated fraction q of ~0.4 is estimated at the Luzon Strait and Bonin Ridge with continuous bathymetry features, while q of ~0.6 is estimated at the Ryukyu Island chain and Mariana Arc with discrete topographic variability. A lower locally dissipated fraction indicates a stronger energy flux radiating into the basin, where enhanced dissipation coincides closely with the interference‐modulated flux field.

Southward Internal Tides in the Northeastern South China Sea

“…The largest flux may be two times the lowest value. Similar features have been observed using field measurements in other regions (Johnston et al, 2015;Martini et al, 2007;Nash et al, 2006;Rainville et al, 2010;Wang et al, 2018;Zhao et al, 2010). In other words, the dominant northwestward internal tides from the Luzon Strait are significantly modulated by the much weaker southward internal tides.…”

Parametric Subharmonic Instability of the Semidiurnal Internal Tides at the East China Sea Shelf Slope

“…As predicted in Yang et al (2018), with the presence of strong negative vorticity, PSI can even occur poleward of the critical latitude, which is unlikely in the classical theory. At the northeast of ECS, there is a Tokara strait which is mainly located poleward of the M 1 critical latitude and is characterized by both intense Kuroshio and strong semidiurnal ITs (Wang et al 2018). Possible occurrence of PSI at the Tokara strait is expected, which awaits further exploration.…”

Seasonal and Spatial Features of Barotropic and Baroclinic Tides in the Northwestern South China Sea

“…Remotely generated baroclinic tides can interfere with locally generated baroclinic tides and then complicate the wave field, increase the dissipation and modulate the local conversion rate from barotropic to baroclinic tide. Hence, it is essential to correctly understand the horizontal pathways of energy flux beams, which are important for estimations of the local conversion and ocean mixing (Wang et al, ; Xu, Chen, et al, et al, ). The vast baroclinic tide generated in the LS can reach and influence nearly everywhere in the SCS (supporting information).…”