Bottom pressure measurement at Dokdo and its application
이상현; 장경일; 김영호; 박용향; 김구
Bottom pressure which measured at about 23 m depth in Dokdo (DI) was observed to understand the temporal variability of upper ocean circulation around DI. The analysis period spans from May 2000 to September 2003 when both bottom pressure and bottom temperatures at DI are available. In order to compare with the sea level at Ulleungdo (UI), the bottom pressure data at DI are converted into sea level using the hydrostatic relationship. Here, we found that the winter time density structures in winter are nearly homogeneous down to a depth of 30m, thus a simple average of surface and bottom densities represents well the vertical integration over the whole range of density profile. However, in summer the thermocline depth is much shallower and placed at a depth of 10 m to 20 m. Therefore, the vertical density in this area shouldn’t always be considered as homogeneous structures. Especially, the bottom temperature at DI in 2000 is 1℃ lower than that of other years because of disappearance of East Korean Warm Current. The sea level data converted from the bottom pressure at DI could provided useful information on upper ocean currents between UI and DI. Time-series of estimated surface currents using the SLD between UI and DI show a good correlation with the temporal variation which measured data using subsurface current moorings on center of those. Upper currents at mid-point between UI and DI show a dominance of southward currents and then it shows maxima in May or June and minima in September or October in 2001 and 2002, while the seasonal pattern is indistinct in 2003. The surface currents between UI and DI would be a good predictor for temporal variations of surface currents in the Ulleung Interplain Gap. It appears that strong southward flows occur when the East Korea Warm Current (EKWC) meanders cyclonically around DI.