On the Mixing of Waters at a Northern Offshore Area of Taiwan

Abstract

Previous hydrographic surveys show that there exists a permanent upwelling center of Kuroshio subsurface water above the shelf break at the northeast offshore area of Taiwan. The water type of this cold dome is quite different from its Kuroshio origin. This indicates that the upwelling water is being mixed with shelf water and that the mixing is mainly in a vertical direction. The energy source of the mixing is partially supported by the internal tidal motion. A typical example was observed during December 3-4, 1989 from the CTD and ADCP surveys at an anchored station. During the survey period, the Kuroshio intruded onto the shelf and both the hydrographic and current profile data indicated a strong internal tide. The gradient Richardson number is smaller than 1 below 80 m and is about 4-10 in the thermocline, which is in the 40-80 m depth range. This indicates that the flow is generally unstable and thus the turbulent mixing is enhanced.

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