Tsushima Warm Current paths in the southwestern part of the Japan Sea

• We compiled a long-term record of monthly mean sea surface currents in the Japan Sea.
• We investigated the Tsushima Warm Current (TWC) paths by using degree of stability.
• We showed a schematic view of the TWC paths in the southwestern part of the Japan Sea.

We compiled a long-term record of monthly mean sea surface currents in the Japan Sea from satellite altimetry and satellite-tracked drifter data. The record covers the entire Japan Sea for the period from May 1995 through January 2009. Using these data, we examined the path of the Tsushima Warm Current in the southwestern part of the Japan Sea. The mean sea surface current field revealed a “triple-branch” pattern. The first branch through the eastern channel of the Tsushima Strait flows along the coast of Japan with a mean current velocity of 20 cm s−1. The second branch flows along the continental shelf edge at around the 200-m isobath with a mean current velocity of 12 cm s−1. The third branch flows along the east coast of the Korean peninsula with a mean current velocity of 25 cm s−1. We investigated seasonal variation in the path of each branch. The first branch flowing along the Japanese coast throughout the year is highly stable. The second branch is stable throughout the year except in November. The third branch flowing along the east coast of Korea is highly stable until 38°N. Downstream of the third branch around 38°N, the current bifurcates into northeastward and southeastward currents. The northeastward current exhibits stable flow from June to February except in January. This current joins an eastward current originating around 39°N, 128.5°E. The southeastward current flows stably in June, September, and December. There were two current paths east of 131°E over the continental shelf off the San’in coast of Japan. The nearshore current flows along the Japanese coast with a mean current velocity of 23 cm s−1, and the offshore current flows around the continental shelf area with a mean current velocity of 19 cm s−1. These two currents are highly stable throughout the year. A current flows to the west of Oki Island to around 38.5°N and is highly stable in all months except March to July. These results provide a schematic view of the paths of the Tsushima Warm Current in the southwestern part of the Japan Sea.