Upper circulation patterns in the Ulleung Basin

Continuous acoustic travel-time measurements from a two-dimensional array of pressure-gauge-equipped inverted echo sounders spanning the entire Ulleung Basin of the southwestern Japan/East Sea between June 1999 and July 2001 are used to examine the upper temperature and current patterns. A new method, referred to as the Residual GEM Technique, interprets the travel-time data into a three-dimensional ( x , y , p ) time-series of daily, synoptically mapped current and temperature fields. During the two-year measurement period, at least five non-repeating persistent flow patterns are found. The patterns during the first year coincide with changes in the total volume transport through the Korea/Tsushima Strait, while the patterns of the second year do not. The mean temperature of the basin displays strong interannual variability and is correlated with the total Korea/Tsushima Strait transport, with a higher mean temperature in the first year when total volume transport was higher. In addition, a new framework for describing the flow patterns is presented. A newly described cold-core eddy, referred to as the Dok Cold Eddy, is about 60 km in diameter and typically forms southwest of Dok Island when the Subpolar Front loops southward between Ulleung and Dok (Takeshima) Islands and sheds an eddy. The Dok Cold Eddy is highly variable in space and time, and it tends to propagate westward towards the coast of Korea, where it merges with cold waters from the north. Three such propagation events preceed the disappearance of the East Korean Warm Current, which then remains absent between June and November 2000. The Offshore Branch forms by branching in the Korea/Tsushima Strait and is present during much of our two-year observation period.