Program

The Kuroshio Extension is an eastward-flowing, inertial jet in the subtropical western North Pacific Ocean after the Kuroshio separates from the coast of Japan. Being the extension of a wind-driven western boundary current, the KE has long been recognized as a turbulent current system rich in large-amplitude meanders and energetic pinched-off eddies. An important feature emerging from recent high-precision satellite altimeter measurements and eddy-resolving ocean model simulations, is that the KE system exhibits clearly-defined decadal modulations between a stable and an unstable dynamic state. The decadally-modulating KE dynamic state not only exerts a great impact on the regional sea surface temperature, heat content and water mass properties, it also brings about significant changes in marine ecosystems and fisheries in the western North Pacific Ocean. Here we show that the time-varying KE dynamic state can be predicted at lead times of up to 5~6 years. The long-term predictability rests on two dynamic processes: (1) the oceanic adjustment is via baroclinic Rossby waves that carry interior wind-forced anomalies westward into the KE region, and (2) the KE variability induces a negative feedback response in the overlying atmosphere that enhances the oceanic variance with a preferred timescale of ~10 years.

This second process is a novel addition and is at the heart of the prolonged multi-year predictability of the KE dynamic state.