Shoaling Internal Tides Propagating From a Shallow Ridge Modulated by the Kuroshio

This study presents remotely generated internal tides that propagate into shallow regions and are modulated by background flows using numerical simulations and field observation data. Numerical results indicate that strongly enhanced semi-diurnal (similar to M2) internal tide energy is generated over a shallow ridge, the Izu-Ogasawara Ridge. The generated internal tides propagates toward the Kuroshio upstream and shoal toward shallow regions near Cape Shiono-Misaki. The intensified internal tide energy flux toward the cape is explained by two mechanisms: (a) intensified internal tide generation over the ridge due to the interaction between tides and the Kuroshio and (b) wave energy convergence along the Kuroshio due to wave refractions. A 13-year field data set obtained from the cape was used to investigate shoaling internal tides influenced by the Kuroshio. The observed results reveal a significant positive correlation between the kinetic energy of semi-diurnal internal tides and the background flows caused by the Kuroshio, which evidently supports the intensified internal tides attributed to the interaction between background flows and tides, as proposed by recent studies. The intensity of shoaling internal tides is also largely influenced by the path of the Kuroshio and seasonal effects. The magnitude of shoaling internal tides is clearly weaken as the Kuroshio meander occurs. Shoaling internal tides modulated by the Kuroshio can provide new insights into energy transport and mixing processes in coastal oceans. Oceans worldwide have internal waves that significantly contribute to the transport of mass and heat within the oceans. In particular, internal waves propagating into shallow coastal regions result in enhanced energy dissipation accompanied by strong mixing and transport, similar to ocean surface waves. Internal waves at tidal frequencies are called internal tides and energetically dominate other internal waves in coastal regions. However, difficulties in observing the physical processes associated with internal tides have hindered the comprehensive elucidation of internal tides. This study presents shoaling internal tides generated by the combined effects of the Kuroshio and tides over a shallow ridge using numerical simulations and field observations. The numerical results show clear processes of shoaling internal tides propagating toward the Cape, generated by the interaction between the Kuroshio and the tides. Long-term (13-year) field observation data obtained from the Cape show that the magnitude of internal tides is significantly intensified by the magnitude of the Kuroshio, clearly indicating that the Kuroshio path/meander modulates shoaling internal tides. The shoaling internal tides observed in this study are anticipated to contribute to mixing and transport in coastal oceans. Shoaling internal tide are investigated with a numerical model and a long-term field data set The Kuroshio intensifies generation of internal tides over a shallow ridge resulting in shoaling internal tides The Kuroshio meander greatly influences the magnitude of shoaling internal tides