LAUSR

In situ data suggest that there is a subsurface speed maximum between 70 and 120 m in the Kuroshio, which is first revealed by the directly velocity observation. The subsurface speed maximum can also be advected into the largest marginal sea in the tropics, that is, the South China Sea (SCS). As it enters the SCS, its depth shoals to between 40 and 70 m and then finally disappears in the western northern SCS. Strong subsurface speed maximum intrusion results in strong baroclinic instability, which triggers vigorous baroclinic conversion, consequently the active mesoscale eddy variability in the northern SCS, and vice versa. Our study highlights this intuitive bridge connecting the Kuroshio intrusion and the mesoscale eddy activities in the northern SCS.