Estimation of wind drift current in the Soya Strait

Three high-frequency (HF) ocean radars were deployed around the Soya (La Pérouse) Strait in 2003 to monitor the Soya Warm Current (SWC). Surface current observed by the HF radars contains a wind drift component, which must be removed in order to estimate the interior SWC. The wind drift parameters, speed factor and turning angle were derived from the surface current measured by the HF radars, the vertical current profile measured by a bottom-mounted acoustic Doppler current profiler (ADCP), and wind data from the numerical weather analysis system operated by the Japan Meteorological Agency (JMA) from October 1, 2006 to July 24, 2008. The ensemble-mean turning angle and speed factor from the entire dataset (excluding August 2007) were estimated to be 28° and 0.66 %, respectively. No significant seasonal variations were discernible in the wind drift parameters. After removal of the wind drift current estimated from the wind with the ensemble-mean drift parameters, the correlation coefficient between the along-shore current speed and sea level difference between the Sea of Japan and Sea of Okhotsk improved from 0.791 to 0.825. It was revealed that the magnitude of wind drift current reaches 45 % of that of the interior current in winter and approximately 20 % in summer, indicating the importance of wind drift current estimation in this region.