Wind-driven and intrinsic interannual-to-decadal variability in the Kuroshio Extension

The Kuroshio Extension and its variability affect the atmosphere aloft through its large oceanic heat transport that is released to the atmosphere. It is therefore important to explore variability in the current to improve our understanding of air-sea interactions over the North Pacific region. While interannual-to-decadal variability in the Kuroshio Extension is primarily driven by atmospheric variability over the central/eastern North Pacific, the nonlinear jet has also intrinsic variability independent from the atmospheric forcing. To separate the wind-driven and intrinsic components of the Kuroshio Extension variability under realistic conditions, we analyze a ten-member ensemble, of fifty-year integration of an eddy-resolving OGCM driven by time-varying JRA55 reanalysis data. We consider the ensemble mean as the wind-driven, and the spread of ensemble members from their average as the intrinsic components. Filtering out effects of mesoscale eddies by the 13-month running mean, magnitudes of the wind-driven (4.7 cm/sec) and intrinsic (4.0 cm/sec) components are comparable. Meanwhile, the time series of the ensemble mean and spread show clearly different time scales: the former is dominated by decadal, and the latter by interannual variability. While possibly model dependent, thus result implies that the observed Kuroshio Extension may have a significant intrinsic component, which limit predictability of the jet on the interannual time scale.