Kuroshio water intrusion into the subarctic region in the western North Pacific Ocean and analyses of the Lagrangian coherent structure

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.

Automated summary

Previous studies have shown that quasi-stationary jets, known as Isoguchi jets, play a role in regulating the warm and salty conditions in the transition zone between the Subarctic Boundary and the Subarctic Front. However, this study reveals that mesoscale eddies and interannual/decadal variations are responsible for the intrusion of Kuroshio water into this transition zone. A case study using the Lagrangian coherent structure indicates that the northward shift of the Kuroshio Extension creates a favorable velocity field for the intrusion, while the geometric structure of the Isoguchi jet remains quasi-permanent.