Radiation Path of Diurnal Internal Tide in the Northwestern Pacific Controlled by Refraction and Interference

The diurnal internal tides contribute nearly a quarter of global baroclinic tidal energy, while their roles in shaping spatiotemporal inhomogeneity of tidal energy field are not well known. Here, based on a combination of observation-supported numerical simulation and theoretical analyses, we clarify the combined and relative contributions of β refraction, subtidal circulation refraction and multi-wave interference to the long-range radiation and dissipation maps of diurnal internal tides in the northwestern Pacific. The diurnal tidal beams are primarily emanated from the Luzon Strait (LS) and Talaud-Halmahera Passage (THP). The β refraction effect, which is more pronounced at higher latitudes, refracts the mean path of LS tidal beam equatorward by ~40° when it arrives at the deep basin, consistent with previous altimeter observations. A second refraction effect by subtidal circulation with seasonal variability deflects the mean beam path by ~10°. Multi-wave interference of tidal beams from the LS and THP further enhances the inhomogeneous pattern, resulting in enhanced and reduced energy flux beam branches with distinct vertical structures in the west Mariana basin. A modified line-source model and theoretical ray-tracing analysis can well explain the effects of refraction and interference. Internal tidal dissipation map in the deep basin coincides well with the inhomogeneous and spreading radiation paths. The mechanism characterization of the world’s most energetic diurnal internal tides in the northwestern Pacific could improve our understanding of global baroclinic tidal energy redistribution and associated tidal mixing parameterization in climate-scale ocean models.