A nonlinear theory of the Kuroshio Extension low-frequency variability

The Kuroshio Extension is a highly stratified, eastward-flowing free inertial meandering jet formed by the confluence of the Kuroshio and Oyashio western boundary currents which is well known to display a decadal variability of bimodal character, connecting a zonally elongated meandering jet and a much weaker jet with a reduced zonal penetration. In this context, modeling results of an ocean circulation model suggest that the Kuroshio Extension low-frequency variability may be basically due to nonlinear intrinsic oceanic mechanisms. These modeling results, their validation with altimeter data and the interpretation of the variability in terms of dynamical systems theory are discussed. Moreover, the role played by the basin geometry in shaping the variability, the occurrence of the mechanism of coherence resonance, the results of a companion low-order QG model, and the application of sequential importance sampling techniques are outlined