Tidal force increasing the upwelling intensity off the northeastern coast of Taiwan

Most historical research and observations have revealed the presence of a cold dome associated with a cyclonic eddy off the northeastern coast of Taiwan. The phenomenon could be derived from the interaction between the Kuroshio and the complex terrain of the local continental slopes. Also, the monthly average SST (sea surface temperature) of satellite image data indicates the prominent features of this cold water mass in the region during the summer. In spite of experiencing long-term investigations, some specific factors contributing to the formation of this cold eddy still need to be clarified. Consequently, a three-dimensional general circulation model (MITgcm) was employed to explore the underlying physical mechanisms of the cold dome formation. In considering some particular factors, the model results at a depth of 50 m reveal that as the Kuroshio passes over the North Mian-Hwa Canyon, it generates a cold water mass with temperatures approximately 4-5 ^oC lower than that of the Kuroshio water. However, the temperature decrease in the model's surface layer deviates from observational data, such as satellite image information, showing a modest decrease of around 1 ^oC. The subsequent inclusion of wind effects imposed on the model indicates that the summer monsoon enhances the strength of the cold water mass. However, the impact on surface temperature drop is insignificant, decreasing by only 0.2 ^oC compared with the no-wind model case. Finally, the tidal force imposition in the model leads to a substantial temperature reduction, dropping from 1 ^oC (without tides ) to 5-6 ^oC (with tides), more closely aligning with field observations and satellite mages. Additionally, temperature time-series analysis reveals the periodic oscillations, including daily and longer 15-day tidal cycles.

Key words: Cold dome; Kuroshio; MITgcm; Tide