Numerical Studies of Submesoscale Island Wakes in the Kuroshio

Abstract

AbstractSubmesoscale wake formation at Green Island (∼7 km) in the Kuroshio is examined by the three‐dimensional numerical simulations, which are validated by field observations. On the basis of geophysical (rotating and stratified) flow, the wake exhibits sequentially detached recirculation, containing upwelling of cold water, propagates downstream via advection, forming an along‐stream oscillating wake, resembling to the von K rm n vortex streets (VKVS). Evidence includes (1) the shedding frequency as a function of the horizontal eddy viscosity shows a trend analogous with classical wakes; (2) the wake behaviors depend on the Reynolds number (Re), where the turbulent transition regime is determined; and (3) the aspect ratio of the island wakes is similar to the ratio of the VKVS. Unlike classical wakes, the vortex street features are adapted by inertial and barotropic instabilities. The inertial instability has large growth rate and tends to slightly destabilize the anticyclonic recirculation. The barotropic instability could be a secondary process to generate eddy kinetic energy at downstream. Finally, our model suggests the hotspot of the turbulent mixing in the wake is located at the plane free shear layer as a result of the vertical shear instability, which is induced by the island‐shelf effect and the tilting of the vertical vorticity.