2005년 7월 LADCP를 이용하여 관측한 울릉분지의 심층해류

Abstract

Deep currents in the Ulleung Basin were observed by a LADCP (Lowered acoustic Doppler current profiler) in July 2005. As a first step, current speeds measured by bottom tracking mode near sea-bed were analyzed. Mean and standard deviation were calculated and bad data that deviations from the mean were larger than the mean plus minus two standard deviations were excluded to average at every 10 m interval. The averaged data were compared with the data observed by SADCP (ship mounted ADCP) at three stations that bottom depths were shallow enough to detect by SADCP. The correlation between the velocities by LADCP and SADCP was good. At the two stations (D02, D04), the currents were observed twice to examine time variance. The maximum difference of current was 8 cm/s at station D02 with the time difference of 19 hours. On the other hand, the difference of current speeds was nearly same within 2 cm/s with 13 hours time difference at station D04. This result indicates that the bottom current varies actively dependent on space and time. The mean current was calculated by average the current form 30 m to 130 m over the sea-bed. Although the dominant surface current structure was determined by a warm eddy in the Ulleung Basin, the deep current did not show the warm eddy structure. Deep cold current from the Japan Basin to the Ulleung Basin through a trough between Ulleung-do and Dok-do was observed about 12 cm/s. However, the outflow was 4.6 cm/s at the eastern station in the trough. To estimate transport of the deep current in the trough, it is required to observe detail more than this survey. The strongest current was observed with 23 cm/s southeastward in station D05 located in south of Dok-do. In the Ulleung Basin, it was difficult to find dominant feature. The southward current flowed in the continental shelf. This observation result is expected to use to search a reference layer in geostrophic current calculation.