Tides enhance the intensity of upwelling and water temperature oscillations in the cold dome region off northeastern Taiwan

Abstract

As the western boundary current in the North Pacific Ocean, the Kuroshio plays a key role in the marine environment around Taiwan. Over the past decades, extensive research and in situ observations have identified a cold dome and cold eddy off the northeastern coast of Taiwan, presumably influenced by the interaction between the Kuroshio and the complex topography. Satellite images of monthly sea surface temperature have revealed a prominent cold water mass in summer. Previous studies have not yet explained clearly the formation mechanism of this cold dome. In this study, we used the Massachusetts Institute of Technology General Circulation Model to identify the mechanisms underlying the formation of this cold dome off the northeastern coast of Taiwan. Various scenarios were simulated to determine the primary causes of cold water upwelling in the cold dome region. Model results at 50-m depth revealed that a cold dome, 4 degrees C-5 degrees C cooler than the Kuroshio, was formed off the northeastern coast of Taiwan where the Kuroshio impinged. However, the model's temperature drop 1 degrees C in the surface layer falls short of field observations and satellite images, 5 degrees C. Including effects of wind stress in the model showed that the summer monsoon may increase the cold-dome area, but not the surface temperature drops. Including tides in the model accurately simulates the observed near surface temperature drop of 5 degrees C-6 degrees C. Model temperature exhibits periodic variations. Spectral analysis of model temperature revealed spectral peaks at diurnal, semidiurnal tidal and 14-day periods.