Effects of Wind, Tide, and the Kuroshio on Cold Water Upwelling Along the Southeastern Margin of the Taiwan Bank in Summer

Abstract

To understand the effects of wind, tides, and the Kuroshio on cold-water upwelling around the Taiwan Bank, a series of experiments-including in situ observations, satellite remote sensing, and numerical modeling-was designed and conducted to address these scientific questions. This study employs a numerical model to identify the dominant forcing mechanisms, specifically, winds, tides, and the Kuroshio Current, and to evaluate how they individually and collectively drive this upwelling. Through a series of sensitivity experiments (Experiments A-G), we isolated each physical forcing to examine its impact on the modeled surface temperature fields, time-series variations at specified temperature sites, and vertical thermal profiles. The model results demonstrate that the Kuroshio Current plays a crucial role in the cold-water upwelling; in scenarios where the Kuroshio acts as the sole forcing (Exp. C), a distinct cold-water band forms along the southeastern edge of the bank, lifting the 26.5 degrees C isotherm to within approximately 2.5 m below the sea surface. Tidal forcing is found to play a critical enhancing role; the combination of the Kuroshio and tides (Exp. F) produces the most intense upwelling recorded, causing cold-water isotherms (26.5 degrees C) to protrude through the sea surface. Conversely, wind stress suppresses the cold band; in all cases where wind is included (Exps. D, E, and G), the intensity of the upwelling decreases, and the vertical rise of the 26.5 degrees C isotherm is reduced. The fully integrated model (Exp. G), incorporating all three forces, successfully reproduces the prominent banana-shaped cold-water band (akin to observations in nature), confirming that while the Kuroshio and tides provide the primary upward energy, wind stress weakens the strength of cold-water upwelling.