Revisiting the Kuroshio Frontal Eddies in the East China Sea: Insights From the Eddy Energy Budget

Abstract

Kuroshio frontal eddies in the East China Sea (ECS) have been observed and investigated for a long time; however, the energetics of frontal eddy-mean flow interactions remain unclear. In this study, we revisit the Kuroshio frontal eddies in the ECS from the perspective of the eddy energy budget using an eddy-resolving ocean general circulation model (OGCM) named OFES2. By decomposing the variables into frontal eddy (5 < T < 20 days) and background components (T > 20 days), we diagnose each term in the eddy energy budget equation to examine their contributions and spatiotemporal variations. The results demonstrate that the frontal eddy energy increases downstream along the Kuroshio in the ECS, with high values in the upper 500 m. Baroclinic instability is the primary source of frontal eddy energy in the entire ECS Kuroshio region, while barotropic and shear instabilities also contribute to one-third of the total energy conversion. In contrast, the work done by wind to eddy energy is insignificant. Further instability analysis suggests that these eddies can be generated either locally within the ECS or come from the upstream region east of Taiwan Island, with a faster growth rate in the ECS. The temporal variation of the frontal eddy energy is largely controlled by baroclinic instability, which is further modulated by the Kuroshio volume transport. The results of this study provide new insights into the Kuroshio frontal eddies, which may be extended to other western boundary current regions where the frontal eddies exist.