Moored Instrument Observation in the Tsushima Current Southwest of the Tsugaru Strait.

Warm water of the Tsushima Current converges southwest of the Tsugaru Strait and flows relatively stable northward with most narrow cross section in the Japan Sea. Therefore, many Japanese oceanographers have evaluated the volume transport in this region to monitor the interannual or seasonal variation of the Tsushima Current system. However, the description on the water movements by the past studies have been only inferred from the dynamic caluclation on the basis of hydrographic data. From April 1992 to March 1993, we carried out the direct current measurement southwest of the Tsugaru Strait by using of a moored instrument at the depth of 130m (Apr.∼Oct.1992) and 180m (Oct.1992∼Mar.1993) to investigate the dynamical variability of the Tsushima Current. The large baroclinic events appear to be dominated mainly by passing through the seaward meander of the coastal current in May 1992 and by merging a warm eddy with the spatial scale of several hundred kilometers within the coastal curent in January 1993. Moreover, about one month-periodical fluctuations observed in the temparature and the on-offshore current corresponded with a Tsushima Current frontal eddy event that could be identified in the NOAA/AVHRR images. From a comparison between the current velocities observed by the current meter and the geostrophic ones, it is suggested that the Tsushima Current includes the evidence as the barotoropic northward flow with about 10 cm s-1 tobe unrelated with the seasonal changes of stratification. This implies that the actual Tsushima Current transports are likely to be larger than those estimated by the past.