Abstract
Abstract. The Kuroshio Current System in the North Pacific displays path transitions on a decadal timescale. It is known that both internal variability involving barotropic and baroclinic instabilities and remote Rossby waves induced by North Pacific wind stress anomalies are involved in these path transitions. However, the precise coupling of both processes and its consequences for the dominant decadal transition timescale are still under discussion. Here, we analyse the output of a multi-centennial high-resolution global climate model simulation and study phase synchronisation between Pacific zonal wind stress anomalies and Kuroshio Current System path variability. We apply the Hilbert transform technique to determine the phase and find epochs where such phase synchronisation appears. The physics of this synchronisation are shown to occur through the effect of the vertical motion of isopycnals, as induced by the propagating Rossby waves, on the instabilities of the Kuroshio Current System.
Highlights
The Kuroshio Current System (KCS) in the North Pacific plays an important role in climate through its meridional heat transport (Hu et al, 2015)
reconstructed components (RCs) resulting from the singular-spectrum analysis (SSA) applied to the first principal component (PC) of the zonal wind stress and the Kuroshio Extension (KE) path length are used in the phase synchronisation analysis which is described in the following
By performing an SSA, oscillatory components on decadal scales of the Kuroshio Extension (KE) path length and the first PC of the zonal wind stress field were chosen as representative observables for the proposed oscillators
Summary
The Kuroshio Current System (KCS) in the North Pacific plays an important role in climate through its meridional heat transport (Hu et al, 2015). In models which capture baroclinic instabilities, a collective interaction of the mesoscale eddies eventually leads to a so-called turbulent oscillator (Berloff et al, 2007) in which the KCS displays low-frequency variability Approaches on combining both forced and internal views have been made as an attempt to develop a more detailed theory explaining the path transitions of the KCS and its dominant decadal timescale in terms of the interaction between forced Rossby waves and the internal variability (including the mesoscale eddies). When a baroclinic Rossby wave model (based on the linear vorticity equation under longwave approximation) is subjected to non-stationary wind stress forcing, no path transitions are found due to the interaction of the Rossby waves and the western boundary current (Qiu and Chen, 2010), so internal variability appears essential for KCS path variability.
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