The Tsushima Warm Current through Tsushima Straits Estimated from Ferryboat ADCP Data

Abstract

Abstract Current structures across the Tsushima Straits are studied using results from long-term acoustic Doppler current profiler (ADCP) observations by a ferryboat between Hakata and Pusan conducted since February 1997. Two maxima of the northeastward current are observed in the central parts of the eastern and western channels, and the maximum velocity in the western channel is stronger than that of the eastern channel. Downstream of the Tsushima Islands, a southwestward countercurrent is observed associated with a pair of cyclonic and anticyclonic eddies. In the western channel, the deep countercurrent is observed pronouncedly on the bottom slope of the Korean side from summer to winter. The volume transport of the Tsushima Warm Current through the straits has strong seasonal variation with a minimum in January and two maxima from spring to autumn (double peaks). The spring peak of the volume transport through the eastern channel is more pronounced than the autumn peak, and the autumn peak of the western channel is more pronounced than the spring peak. The inflow volume transport into the Japan Sea through the western channel significantly increases in autumn because of an incrementation of the freshwater transport. The total volume transport averaged over the observation period (5.5 yr) is 2.64 Sv (Sv ≡ 106 m3 s−1). The average volume transports through the eastern and western channels are 1.10 and 1.54 Sv, respectively.