Seasonal variation of the current in the Tsushima Strait deduced from ADCP data of ship-of-opportunity

The ADCP data obtained in the Tsushima Strait in the period from February 1987 to November 1990 on board twelve patrol vessels and one research vessel belonging to Maritime Safety Agency was analyzed. Total amount of the data is 200,053, but after quality check, we used 158,401 data for the analysis of the current field and its variability in the strait. The seasonal variation of the currents had been believed to be large. However, no direct current observation throughout the season had been made, and the knowledge on the seasonal variation was derived indirectly from the data of the sea level difference across the strait and of the density field given by hydrographic observations. ADCP data indicates that the seasonal variation of the current field is considerably small in all sub-regions. In the relatively strong current region to the west of the Tsushima Island, the northeast current component has maximum value in the early winter season.