Topographically Generated Submesoscale Processes in the Tokara Strait Revealed by a High-Resolution Model

Submesoscale processes (SMPs) in the Tokara Strait where the Kuroshio and complex bottom topographies (many small islands and seamounts) coexist are investigated using a high-resolution (∼0.9 km) model—Japan Coastal Ocean Predictability Experiment configured for the East Asia Sea (JCOPE-T-eas1ks). Our model results show that the Kuroshio–topography interaction generates energetic SMPs on the lee side of the topographies. Variations in the Kuroshio, particularly its path, considerably modulate the SMPs. Specifically, SMPs below the mixed layer are intensified when the Kuroshio axis is located in the central strait during autumn. On the other hand, as the Kuroshio axis shifts northward in spring and summer, a remarkable vortex street is generated on the lee side of Yakushima Island. Additionally, the variation of mixed layer also influences the SMPs, particularly in winter. Energy budget analysis of the SMPs indicates that barotropic instability is the primary source of submesoscale kinetic energy, while baroclinic instability and wind work become nonnegligible in winter. The forward energy cascade is dominant in the Tokara Strait in the upper 350 m, while the inverse energy cascade emerges below the mixed layer. The SMPs disintegrate through different kinds of submesoscale instabilities. The gravitational instability is dominant within the mixed layer, while the centrifugal instability becomes important below the mixed layer. Our findings provide comprehensive insights into SMPs in marginal seas with complex bottom topography, which behave differently from those in the open ocean.