Direct estimation of relative vorticity of the Kuroshio off Boso Peninsula

The horizontal structure of current velocity and relative vorticity of the Kuroshio were precisely investigated by analyzing shipmounted acoustic Doppler current profiler (ADCP) data repeatedly collected off Boso Peninsula in October-November, 2003. In previous studies, the horizontal velocity shear of the Kuroshio was estimated only with the vorticity component A (dv/dx: cross-stream shear of down-stream velocity), assuming that the vorticity component B (-du/dy: down-stream shear of cross-stream velocity) is small. And the used coordinate is usually stream coordinate, which consists in streamline and curvature direction. This coordinate has one problem, strictly speaking. If the measured velocity is not along the streamline of the current, and it is not suitable to evaluate relative vorticity. In the present study, the vorticity component B is estimated directly by measuring the velocity structure along multiple cross-sections of the Kuroshio repeatedly, and it is very accurate to evaluate relative vorticity , since the present coordinate is not stream coordinate but Cartesian coordinate. The vorticity component A of the Kuroshio on the coastal side of the main path is larger than that on the offshore side off Boso Peninsula. The cross-stream velocity changes locally and the vorticity component B cannot be ignored. The relative vorticity on the coastal side of the Kuroshio main path is high (>0.6 times 10^-4 [1/s]) and cannot be neglected in comparison with the planetary vorticity (~0.8 times 10^-4 [1/s]), which means that the Rossby number cannot be assumed to be small and nonlinearity may be effective in local dynamics on the coastal side of the Kuroshio main path. The vorticity component B cannot be neglected, which not vorticity component A but also vorticity component B is necessary to evaluate relative vorticity. Potential vorticity (PV) investigating relative vorticity data and expendable-CTD data is investigated. The distribution of- PV is shown the vortex stretching of the parcel in Kuroshio current