Abstract The Kuroshio Extension (KE) exhibits significant decadal variations, particularly following the 1976/77 Pacific climate regime shift. Robust ocean-atmosphere interactions over the KE imply a potential key role in basin-scale climate variability. Recent studies suggest that North Pacific Oscillation (NPO)-like atmospheric teleconnections from the central tropical Pacific dominantly influence KE decadal variability through oceanic Rossby waves. However, this relationship varies on interdecadal timescales and only achieves statistical significance after the regime shift. This study utilizes outputs from an unprecedented 500-year pre-industrial control simulation conducted with an eddy-resolving coupled general circulation model to explore the potential and mechanisms of natural variability-induced interdecadal modulation. When the entire simulation period is divided into five segments, a relationship between the KE and the central tropical Pacific, resembling that after the regime shift, is found during the segment marked by the strongest decadal variability in the central tropical Pacific and the NPO. These variability enhance each other by positive feedback on decadal timescale via the Pacific meridional mode triggered by air-sea interaction. As the westerly jet migrates southward over the eastern North Pacific during this period, the southern lobe of the NPO also expands southward, likely providing a favorable background condition for its active interaction with the tropics. In contrast, the relationship is absent in other periods, likely due to weaker and less persistent tropical variability, differences in the location of atmospheric teleconnections, and/or influences of the Kuroshio large meander. These findings suggest that the interdecadal modulation of the KE may occur independently of anthropogenic forcing.
Tamura et al. (2025) studied this question.