On Reset of the Wind-Forced Decadal Kuroshio Extension Variability in Late 2017

Abstract

Decadal modulations of the Kuroshio Extension (KE) system between a stable and an unstable dynamic state in the western North Pacific have prevailed in the past three decades. This dominance of decadal variations is controlled by the negative feedback loop involving the wind-forced KE variability and its feedback onto the overlying extratropical stormtracks and the basin-scale surface wind field. The wind-forced decadal KE modulations were disrupted in August 2017 due to the development of the Kuroshio large meander south of Japan. By forcing the inow KE paths northward and by avoiding override the shallow Izu Ridge, the Kuroshio large meander was able to compel rapidly the KE from the wind-forced, pre-existing, unstable state to a stable state. Following the large meander occurrence in late 2017, the stabilized KE change is found to affect the overlying stormtracks and the basin-scale wind field the same way as those generated by the wind-forced KE change prior to 2017. Given the consistent atmospheric response to both the large-meander-induced and wind-forced KE variability, we expect that the KE dynamic state will resume its decadal modulation after the phase reset relating to the 2017 large meander event.