Observation of the Soya warm current using HF ocean radar

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. Frequency of the HF radar is 13.9 MHz, and range and azimuth resolutions are 3 km and 5 deg., respectively. It covers a range of about 70 km from the coast. Surface current velocity observed by the radars is compared with data from drifting buoys and shipboard ADCPs (Acoustic Doppler Current Profilers). The current velocity derived from the HF radars shows good agreement with that observed by the drifting buoys. The rms (root-mean-squared) differences are about 15 cm/s for the zonal and meridional components. The observed current velocity also exhibits a reasonable agreement with the shipboard ADCP data. It is shown that the HF radars clearly capture seasonal and short-term variations of the Soya Warm Current. The velocity of Soya Warm Current reaches its maximum, which is about 1 m/s, in summer, and becomes weak in winter. The current axis is located at a distance from 20 to 30 km from the coast, and the width is about 40 km. The surface transport across the strait shows a significant correlation with the sea level difference along the strait derived from coastal tide gauge records