Title: The eddy-dipole mode interaction and the decadal variability of the Kuroshio Extension system

Journal: Ocean Dynamics, doi: 10.1007/s10236-016-0991-6

Authors: LUO D. -H.*, S. -H. Feng, and L. -X. Wu

Abstract:In this paper, the physical cause of why the eddy kinetic energy (EKE) in the upstream Kuroshio Extension (KE) region is strong (weak) during a large (small) jet meandering period is studied by using the satellite altimeter data and constructing an eddy-dipole mode interaction theory from a reduced gravity shallow water wave quasi-geostrophic vorticity equation. It is found that the large KE jet meander corresponds to a large-scale positive-over-negative dipole SSH anomaly (KED− mode, hereafter), a double-branch jet with a weak strength and a strong EKE in the upstream KE region, while the small jet meander corresponds to a negative-over-positive dipole anomaly (KED+ mode, hereafter), a strong single-branch jet, and a weak EKE. Further diagnostics using this new eddy-dipole mode interaction theory reveals that the horizontal advection and KED deformation field can change the eddy activity in the upstream KE region. When the KED− mode is amplified by mesoscale eddies, the EKE grows by extracting energy from the KED− deformation (shearing and stretching) field and due to a reduced eastward advection, thus showing a high EKE level during the KED− mode (large jet meander) episode. In contrast, when the KED+ mode is intensified, the kinetic energy of the eddy weakens by losing its energy to the KED+ deformation field and by an enhanced eastward advection, thus showing a low EKE level during the KED+ mode (small jet meander) episode. Because the KED mode shows a clear decadal variation due to the modulation of the Pacific Decadal Oscillation, both the KE jet and EKE exhibit inevitably a distinct decadal variability.