The Role of Local Wind Stress Curl in Modulating Kuroshio Extension Latitudinal Variability

Abstract

The Kuroshio Extension (KE) exhibits a typical interannual to decadal latitudinal shift. Previous studies have proposed that eastern/central North Pacific wind and oceanic intrinsic variability are responsible for the KE variability. In this study, we define a KE index using Empirical Orthogonal Function analysis based on subsurface temperature to quantify the variability of the KE shift caused by thermocline migration. The KE region exhibits positive (negative) temperature anomalies and clockwise (anti-clockwise) circulation anomalies in the north (south) phase of the KE. A lead correlation analysis indicates that, in addition to a 3–4 years leading correlation between the eastern/central North Pacific wind stress curl anomalies and the KE index, a significant linear correlation is revealed in the local region when the wind stress curl anomalies lead the KE index 0–1 year. By conducting a series of sensitivity experiments using both a global circulation model and a reduced gravity model, we suggest that both local wind and (broad) remote wind are responsible for the interannual to decadal variability of the KE, with their contributions being comparable. Regarding the local wind forcing process, when the wind stress curl anomalies are positive (negative) in the western North Pacific, they generate negative (positive) local Sea Surface Height anomalies and temperature anomalies through Ekman divergence (convergence), resulting in the southward (northward) shift of the KE.