Abstract
Previous studies have suggested that the quasi-stationary jets, sometimes called the “Isoguchi jets” in the western North Pacific Ocean, regulate the warm and salty conditions in the transition domain between the Subarctic Boundary and the Subarctic Front. Here, we show that mesoscale eddies and interannual/decadal modulations are responsible for the Kuroshio water intrusion into the transition domain. A case study using the Lagrangian coherent structure suggests that the northward shift of the Kuroshio Extension forms a favorable velocity field for the Kuroshio water intrusion around the Subarctic Boundary, while the geometric structure inside the Isoguchi jet is quasi-permanent.