Detailed current structures over the continental shelf off the San'in Coast in summer

We discussed the detailed current structures over the continental shelf off the San'in Coast in June 1988 and June 1989, using ADCP (acoustic Doppler current profiler) data, which were taken by the quadrireciprocal method (Katoh, 1988) for removing tidal currents from observed currents. In waters northwest of Hagi (Yamaguchi Pref.) and Hamada (Shimane Pref.), two mainly northeastward current cores were observed on each of transects. The offshore current core is baroclinic in relation to the bottom cold water with temperature below 10°C, and has velocities mostly between 0.5 and 0.8kt (26 and 41 cm s^–1) at 20 m depth. The onshore current core, which is barotropic, has velocities between 0.3 and 0.5 kt (15 and 26 cm s^–1) at 20 m depth. In waters northwest of Izumo (Shimane Pref.), where the width of the continental shelf is narrow, it is difficult to distinguish between the two current cores, because the offshore core tends to join the onshore one. Estimating the magnitude of each term in the diurnally averaged equation of motion for about 3.3 nautical miles (6.1 km), we found that the orders of the inertia term and the gradient of tidal stress were 10^–4 cm s^–2, and the order of the Coriolis force was 10^–3 cm s^–2. Near the bottom northwest of Hagi and Hamada, two bands of countercurrents were found; one was slightly offshore of the intersection between the continental shelf and permanent thermocline, and the other was in the water colder than 5°C ridging on the continental shelf.