Asymmetric modulation of winter mixed layer depth induced by mesoscale eddies alongside the Kuroshio Extension jet

Abstract

Ocean mesoscale eddies are observed to influence mixed layer depth (MLD) with a deepening by anticyclonic eddies (AEs) and a shoaling by cyclonic eddies (CEs). By using Argo profiles, satellite altimeter data and eddy-resolving model data, this study investigates how the AEs and CEs alongside the Kuroshio Extension jet (KEJ) modulate the winter MLD. Results show that although the modulations by the AEs and CEs are roughly symmetric over the whole region on the winter MLD, their impacts are strongly asymmetric to the north and south of the KEJ. The deepening effect by the AEs is much more than the shoaling effect by the CEs to the north of the KEJ, while the shoaling effect by the CEs is much more than the deepening effect by the AEs to the south of the KEJ. Therefore, their overall effect results in a net deepening to the north and a net shoaling to the south of the KEJ. A further analysis finds that this asymmetric feature is closely related to the distribution of eddy amplitudes which implies more energetic AEs to the north but CEs to the south of the KEJ. This study highlights the importance of the distribution of energetic eddies on the modulation of MLD.