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Observation of the Soya Warm Current combining HF Ocean Radar with Coastal Tide Gauges and Satellite Altimetry


Naoto Ebuchi, Yasushi Fukamachi, Kay I. Ohshima, Kunio Shirasawa, and Masaaki Wakatsuchi
Institute of Low Temperature Science, Hokkaido University
N19-W8, Kita-ku, Sapporo 060-0819, JAPAN
Phone: +81-11-706-5470, Fax: +81-11-706-7142


Three HF ocean radar stations were installed at the Soya/La Perouse Strait in the Sea of Okhotsk in order to monitor the Soya Warm Current (SWC), which enters the Sea of Okhotsk from the Sea of Japan through the strait and flows along the coast of Hokkaido as a coastal boundary current. The frequency of the HF radar is 13.9 MHz, and the range and azimuth resolutions are 3 km and 5 deg., respectively. The radar covers a range of approximately 70 km from the coast. The surface current velocity observed by the HF radars exhibits good agreement with that observed using drifting buoys and shipboard and bottom-mounted Acoustic Doppler Current Profilers (ADCPs). It is shown that the HF radars clearly capture seasonal and short-term variations of the SWC. The velocity of the SWC reaches its maximum, approximately 1 m/s, in summer, and weakens in winter. The velocity core is located 20 to 30 km from the coast, and its width is approximately 50 km. The surface transport by the SWC shows a significant correlation with the sea level difference along the strait, as derived from coastal tide gauge records. The cross-current sea level difference, which is estimated from the sea level anomalies observed by the Jason-1 satellite altimeter and a coastal tide gauge, also exhibits variation in concert with the surface transport and along-current sea level difference. Analysis of the vertical current velocity profiles observed by the bottom-mounted ADCP suggests a possibility estimating the volume transport of the SWC from the surface current measurements by the HF radars.

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