Seasonal Variation of Submesoscale Ageostrophic Motion and Geostrophic Energy Cascade in the Kuroshio

Abstract

The study of submesoscale ageostrophic motion is crucial for enhancing our comprehension of ocean dynamics. This paper employs global sea surface velocity reanalysis data and mixed layer depth data to examine the factors influencing submesoscale ageostrophic energy in the Kuroshio region as well as the energy transition between ageostrophic and geostrophic energy. The findings indicate that submesoscale ageostrophic kinetic energy in the Kuroshio region peaks during winter and spring. Mixed layer depth and geostrophic strain significantly boost ageostrophic kinetic energy, especially in strong current area. Analysis of kinetic energy spectral density reveals how energy distribution and transition scale vary across strong and slow current zones during different seasons, highlighting that submesoscale kinetic energy is susceptible to seasonal variations. In summer and autumn, the transition scale of kinetic energy is generally larger compared to those in spring and winter. Submesoscale ageostrophic motion predominantly gains kinetic energy from the release of available potential energy (APE) and horizontal shear production (HSP) while losing a small portion of its kinetic energy through vertical shear production (VSP) in the Kuroshio.