Deep flow field in the Japan/East Sea as deduced from direct current measurements

Abstract

The mean flows and variability in the abyssal Japan/East Sea are investigated on the basis of direct current observation data. The distribution of the mean flow vectors indicates relatively strong cyclonic circulations along the basin periphery and sluggish flows in the interior region. Strong mean flows of faster than 6.0 cm s−1 are found at the western edge in the Yamato and Ulleung Basins, considered to be the western boundary currents in each basin. The similarity between the distributions of the mean flow vectors in the upper (400–1000 m) and lower layers (1000 m-bottom) indicates common circulation patterns throughout the water column of the Proper Water. Progressive vector diagrams show meandering curves with clockwise and anticlockwise turns due to the passing of mesoscale eddies. Since a dominant background flow is absent in the basin interior, the ratio of eddy kinetic energy to the mean-flow kinetic energy reaches more than 50 in the interior region. This indicates that the flows observed in the interior region are comparable to those in the basin periphery, even though the mean flow is generally weak. Spectral analysis has revealed that tidal fluctuations are prevailing in the Ulleung Basin, while they are absent in the Yamato and Japan Basins, though the inertial oscillation is dominant in all of the basins. This indicates that the tidal energy from the East China Sea is confined within the Ulleung Basin, suggesting the barrier effect of the Yamato Rise and the Oki Spur. Significant energy peaks are also found in the 2–5 and 5–10 day period bands in the Yamato Basin. The former variation represents the shelf-wave activity trapped on the basin edge and the latter is due to eddy migrations associated with the Tsushima Current.