A New Dynamic Regime in the Kuroshio/Kuroshio Extension and the North Pacific Climate System after 2018

Abstract Over the four decades following the 1976/77 climate regime shift, the Kuroshio Extension (KE) in the North Pacific subtropical gyre exhibited quasi-decadal oscillations between stable and unstable dynamic states. These oscillations were facilitated by a delayed negative feedback loop involving wind-forced interior ocean adjustment, its modulation on the KE dynamic state, and the KE’s feedback on atmospheric storm tracks and the wind stress field. However, this feedback loop ceased functioning after 2018, giving rise to a new dynamic regime. In this new regime, the Kuroshio south of Japan assumes a persistent large-meander (LM) path, while the stabilized KE jet migrates poleward. This study identifies three key processes responsible for the emergence of this regime: 1) a shift in the external forcing field, characterized by intensified wind forcing over the northern subtropical gyre and weakened forcing over the southern gyre; 2) nonlinear reinforcement between the Kuroshio LM and the poleward-migrated KE jet; and 3) altered storm-track and wind stress responses to the KE’s new stable dynamic state. The establishment of this regime has played a critical role in the recent upper-ocean warming—manifested as frequent marine heat waves—along the 35°–45°N band of the western North Pacific. An upper-ocean temperature budget analysis reveals that this cumulative warming is primarily driven by lateral advection associated with the migrating KE jet, while the net surface heat flux forcing acts to dampen the advection-induced temperature anomalies.