Based on the 1/48° MIT LLC-4320 model data, the ageostrophic kinetic energy in the Kuroshio region south of Japan is decomposed using a localized multiscale energetics formalism with three scale windows:a large scale window (>128 days), a mesoscale window (8-128 days), and a submesoscale window (1-8 days). The intrinsic nonlinear interactions between the three scale windows are explored using canonical transfer theory. The results show that the submesoscale ageostrophic kinetic energy in the Kuroshio region south of Japan is significantly distributed along the Izu-Ogasawara Ridge, particularly pronounced in the summer.
In the region influenced by this topography, submesoscale ageostrophic kinetic energy primarily originates from forward energy transfer due to ageostrophic motions and the interactions between geostrophic and ageostrophic motions. Subsequently, it cascades forward from the large scale to the submesoscale as ageostrophic kinetic energy and the kinetic energy of the geostrophic-ageostrophic interaction term. The contributions of both are roughly equivalent, while the contribution from baroclinic instability is relatively small. In contrast, in region without topographic influence, submesoscale ageostrophic kinetic energy is relatively lower, and the process of canonical energy transfer is comparatively weaker.

 

Oceanic submesoscale processes,ageostrophic kinetic energy