Characteristics and mechanisms of the upwelling in the southern Taiwan Strait: a three-dimensional numerical model study

Using a nested circulation model based on the Princeton Ocean Model, we investigate the characteristics and mechanisms of two main upwellings in the southern Taiwan Strait: the Southwest upwelling and the Taiwan Bank upwelling. The Southwest upwelling exists in summer when the southwesterly monsoon dominates, and the Taiwan Bank upwelling occurs over a longer period from May to September. The upslope current over a distinctly widened shelf transports the cold water on-shoreward at the lower layer and the southwesterly monsoon wind drives the cold water to the surface layer, forming the Southwest upwelling, while tidal residual current weakens the upslope advection. For the Taiwan Bank upwelling, the upward transport of the South China Sea water due to the Bank topography carries the cold water from the subsurface layer to the depth of approximately 25 m near the Taiwan Bank, then the strong tidal mixing forces this upwelled water further upward to the surface layer.