| In this communication the observed synchronization between the Kuroshio-Oyashio Extension (KOE) decadal bimodality and the Pacific Decadal Oscillation-North Pacific Oscillation (PDO-NPO) is investigated through a process study (Pierini, J. Climate, 27, 448-454, 2014). A circulation model of the North Pacific Ocean is forced by a wind field composed of a climatological component and of a schematic NPO, representing here the atmospheric decadal time-scale mode of variability (NPO and PDO are virtually linearly correlated in the period of interest).
During 1990-2012 the NPO forcing is found to efficiently excite the KOE oscillations, whose timing and teleconnection with the NPO are in good agreement with altimeter observations (e.g., Qiu and Chen, Deep-Sea Res. II, 57, 1098-1110, 2010). The analysis is developed in the framework of nonlinear dynamical systems theory: several sensitivity experiments are therefore carried out. The emerged dynamical mechanism is explained as a case of excitable dynamical system in which an intrinsic mode of variability is paced by an external forcing (a behavior likely to be fairly common in climate dynamics). |