Modulation of Inverse Kinetic Energy Transfer by Eddy Current Feedback and Its Underlying Dynamics in the Kuroshio Extension

Abstract

The eddy current feedback (ECFB), an important sink for eddy kinetic energy (EKE), deflects the oceanic EKE to the atmosphere and is also found to influence the oceanic cross-scale kinetic energy (KE) transfer. However, the underlying dynamics of ECFB modulating KE transfer still lack thorough investigation. In this study, the ECFB is found to substantially reduce the inverse KE transfer, with this reduction extending to a depth of 500 m in the Kuroshio Extension. Within the surface boundary layer (SBL), the weakened inverse KE transfer is attributed to the enhanced EKE loss to the atmosphere and reduced conversion from eddy available potential energy (EAPE) to EKE. Below the SBL, conversion from EAPE to EKE becomes the sole dominant driver of the reduced inverse KE transfer. On the one hand, the negative wind work induced by ECFB enhances EKE loss within the SBL. On the other hand, the weakened meander fronts and the consequent suppressed baroclinic instability are responsible for the weakened conversion from EAPE to EKE under ECFB. Under ECFB, the growth rate of the baroclinic instability decreases by 12%. The reduction in meander fronts is caused by the diminished meander KE and the associated weakening of the strain rate, which is due to the pressure work divergence resulting from Ekman pumping under ECFB.