LEAVE OF THE KUROSHIO CURRENT ZONE FROM THE COAST TO THE EAST OF CAPE SHIONOMISAKI
The temperature field in Fig.3 and the current field in Fig.5 indicate that the current zone of the Kuroshio extends due eastward from the tip of the Kii Peninsula (Cape Shionomisaki), and leaves the shelf and continental slope. It is curious as a geostrophic flow which touches the bottom is generally forced to follow bottom contours due to the vorticity conservation law.
The coastline in the vicinity of Cape Shionomisaki is shown together with 200 m bottom contour in Fig.6. The bottom contour to the west of the cape is straight, but that to the east has a large curvature. The 200 m bottom contour to the east of the cape is approximated by a circle arc as shown in the figure. The radius of the circle is 25.9 km. If we assume the current velocity just above the bottom is 1.0 m/s or the vertically averaged velocity is 1.5 m/s as estimated in the previous section, the centrifugal force would become 0.39 × 10-4 m/s2 or 0.87 × 10-4 m/s2 when the current is trapped by bottom contours to the east of the cape. The corresponding Coriolis forces at 35.5°N (the pressure gradient force is hardly estimated without the knowledge of bottom pressure field, but it would be comparative to the Coriolis force due to the geostrophic nature of the Kuroshio) for these velocity values are 0.77 × 10-4 m/s2 or 1.15 × 10-4 m/s2 respectively. Thus, if the current follows the bottom contours, the centrifugal force becomes comparative to Coriolis force for the observed range of current speeds, and the current is hardly to able to follow the bottom contours. This gives the reason why the Kuroshio leaves the shelf and slope regions to the east of Cape Shionomisaki.
