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

Abstract

AbstractThe diurnal internal tides contribute nearly a quarter of global baroclinic tidal energy. However, their roles in shaping the spatiotemporal inhomogeneity of the tidal energy field are not well known. Based on observation‐supported numerical simulation and theoretical analyses, we clarify the combined and relative contributions of β refraction, subtidal circulation refraction and multiwave interference to the long‐range radiation and dissipation maps of diurnal internal tides in the northwestern Pacific. The diurnal tidal beams primarily emanate from the Luzon Strait (LS) and Talaud‐Halmahera Passage (THP). The β refraction shifts the mean path of the LS tidal beam equatorward by ∼40° when it arrives at the deep basin. This is consistent with previous altimetric observations. A second refraction effect by subtidal circulation with seasonal variability deflects the mean beam path by ∼10°. Multiwave interference of the tidal beams from the LS and THP further enhances the inhomogeneous pattern. It enhances or reduces the energy fluxes of the tidal beams with distinct vertical structures in the western Mariana basin. A modified line‐source model and theoretical ray‐tracing analysis explain the effects of refraction and interference well. The internal tidal dissipation map in the deep basin coincides well with the inhomogeneous and spreading radiation paths. The 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 tidal mixing geography.