Why Did the 2017 Kuroshio Large Meander Event Become the Longest in the Past 70 Years?

The Kuroshio south of Japan is known to vacillate between a straight and a large meander (LM) path. Since 1950, eight LM events have been observed with different durations. The most recent/on-going LM started in August 2017 and has become the longest event in record. By analyzing eddy-resolving sea surface height data and by adopting a wind-forced linear vorticity model, we demonstrate that the on-going LM is maintained by an exceptionally stable dynamic state of the Kuroshio Extension (KE) forced by wind stresses across the Pacific basin. The highly-stable KE system not only minimizes westward eddy perturbations from disrupting the upstream Kuroshio path, its strengthened southern recirculation gyre further helps to anchor the Kuroshio across the Izu Ridge. By contrasting the on-going event to the 2004-2005 event, we argue that the LM duration is more sensitive to the wind-forced KE dynamic state than the eastward Kuroshio transport south of Japan.