The Kuroshio extension low frequency variability : the relative roles of internal and external drivers

Abstract

The Kuroshio Extension (KE) is the inertial meandering jet formed by the convergence of the Kuroshio and Oyashio currents in the Northern Pacific. It is widely mentioned in the literature that the KE variability is bimodal on interannual to decadal time scales. The nature of this low frequency variability (LFV) is still under debate; some authors suggest that internal oceanic mechanisms play a fundamental role in the phenomenon but there is also evidence from the observations that the KE LFV is connected with changes in broader patterns of variability such as the Pacific Decadal Oscillation (PDO). In this thesis we first inspect the interplay between the ocean and the atmosphere in the KE, taking advantage of a large ensemble of global hindcasts and finally, we examine the role of the atmosphere in the KE’s total variability in the context of a fully coupled system. We show in agreement with previous studies that the KE LFV is an intrinsic oceanic mechanism paced by atmospheric forcings and that changes in the horizontal resolution of the atmospheric model have not a relevant impact on the KE’s degree of realism. In this context, we highlight that the PDO acts as a pacemaker of the KE LFV, suggesting this pattern as a predictor. With this study we have made some progress in the state-of-the-art and the current scientific knowledge, understanding both the nature of the KE LFV and the impacts of the atmospheric horizontal resolution on the KE system, which is important to identify the needs of the next generation models to capture and predict the KE LFV.