The circulation in the upper and middle layers of the Luzon Strait during spring 2002

On the basis of current measurements at the mooring station and hydrographic and wind data obtained in the Luzon Strait during spring 2002, the numerical calculation and comparison of circulation were implemented by the aid of a diagnostic model with a modified inverse method. During the observation period, the directions of subtidal current at the mooring station are mostly northwestward or northward at depths of 200 and 500 m, different from those at a depth of 800 m. At depths above 400 m, most of the Kuroshio bypasses the South China Sea (SCS) near the Luzon Strait. However, both the observed and modeled results show part of the Kuroshio flows westward to intrude into the area around the continental slope south of China, and the net westward volume transport across the longitudinal section of 120°33′E is about 0.82 × 106 m3 s−1 in the upper layers from the sea surface to 400 m level. At depths below 400 m, the directions of flow east of 120°57′E are mostly eastward, and the net eastward volume transport across the longitudinal sections of 121°09′E and 121°15′E both are about 2.4 × 106 m3 s−1 in the middle layers between 500 m and 1200 m. This indicates the SCS water with a higher oxygen concentration flows eastward into the eastern side of the Luzon Strait in the middle layer. Comparison between the observed and modeled results shows they agree basically with each other.