The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

Intense flow-topography interactions occur in the Kuroshio region where complex bottom topography exists, leading to the generation of multiscale dynamical processes, including internal waves and submesoscale eddies. In this study, focusing on the Tokara Strait where dozens of small islands and seamounts as well as strong Kuroshio and tidal currents coexist, we investigate the generation and evolution of submesoscale eddies and internal waves using high-resolution models. The Kuroshio generates energetic submesoscale eddies on the lee side of the topographies. Variations in the Kuroshio, particularly its path, considerably modulate the submesoscale eddies. Energy budget analysis indicates that barotropic instability is the primary source of submesoscale kinetic energy, while baroclinic instability and wind work become non-negligible in winter. The submesoscale eddies disintegrate through different kinds of instabilities and thereby contribute to turbulent mixing. In addition to the Kuroshio, semidiurnal tidal currents excite semidiurnal internal tides, which further generate high-wavenumber near-inertial waves via parametric subharmonic instability (PSI). Although the Kuroshio suppresses the PSI along its main path, the PSI majorly contributes to mixing in and around the Tokara Strait in most of the areas outside the Kuroshio path.