STUDY ON DEEP CIRCULATION IN JAPAN SEA BASED ON LAGRANGIAN CURRENT MEASUREMENT.

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The Japan Sea Proper Water with temperature of about 1ﾟC occupies below 100m layr in the Sea of Japan. The proper Water is formed off Siberian Coast by the winter cooling, but transport and migration of it was not clarified. The marine environment of Japan Sea is of great importance in these days partly by damping of radio active wastes or by oil spill caused by wreck of an oil tanker. Direct measurements of currents are requisite for circulation study. Moored current meters, of Eulerian measurement, are affected by topographic control, especially at deep layrs. On the other hand, tracking of neutral floats, of Lagrangian measurement, is most effective to show the transport of sea water. In August 1995, we deployed two ALACE (Autonomous Lagrangian Current Explorer) floats to drift at 300 m in the Sea of Japan. The float comes to the sea surface every 10 days ot twenty days, ant its position is fixed by a satellite tracking system, ARGOS.One float, deployed at 40ﾟ 43'N and 136ﾟ 18'E,showed an anti-clockwise eddy of 100 km in deiameter, and then moved about 300 km to northeast until December 1996. The other float, deployed at 40ﾟ 54'N and 132ﾟ 24'E,showed a clockwise eddy of about 300 km in diameter, and moved about 100 km to southwest. An average drifting speed at 300 m is of about 5 cm/sec. These trajectories indicate that the convected water off Siberia reaches to off the west coats of Hokkaido within one year and that the water does not come to off the San-in coast or south of Yamoto Rise. The positioning by the ARGOS System are made about ten times a day, and we estimated surface current to be about 100 cm/sec and a dominant tidal current is shown.