Low-frequency current observations in the Korea/Tsushima Strait

Abstract

High resolution, continuous current measurements made in the Korea/Tsushima Strait between May 1999 and March 2000 are used to examine current variations having time periods longer than 2 days. Twelve bottom-mounted acoustic Doppler current profilers provide velocity profiles along two sections: one section at the strait entrance southwest of Tsushima Island and the second section at the strait exit northeast of Tsushima Island. Additional measurements are provided by single moorings located between Korea and Tsushima Island and just north of Cheju Island in Cheju Strait. The two sections contain markedly different mean flow regimes. A high velocity current core exists at the southwestern section along the western slope of the strait for the entire recording period. The flow directly downstream of Tsushima Island contains large variability, and the flow is disrupted to such an extent by the island that a countercurrent commonly exists in the lee of the island. The northeastern section is marked by strong spatial variability and a large seasonal signal but in the mean consists of two localized intense flows concentrated near the Korea and Japan coasts. Peak nontidal currents exceed 70 cm s-1 while total currents exceed 120 cm s-1. The estimated mean transport calculated from the southwest line is 2.7 (Sv ≡ 106 m3 s-1). EOF analyses indicate total transport variations in summer are due mainly to transport variations near the Korea coast. In winter, contributions to total transport variations are more uniformly distributed across the strait.