The seasonal mean and synoptic fluctuation of the wintertime Taiwan Warm Current (TWC) were investigated using a well-validated finite volume community ocean model. The spatial distribution and dynamics of the synoptic fluctuation were highlighted. The seasonal mean of the wintertime TWC has two branches: an inshore branch between the 30 and 100m isobaths and an offshore branch between the 100 and 200m isobaths. The Coriolis term is much larger than the inertia term and is almost balanced by the pressure gradient term in both branches, indicating geostrophic balance of the mean current. Two areas with significant fluctuations of the TWC were identified during wintertime. One of the areas is located to the north of Taiwan with velocities varying in the cross-shore direction. These significant crossshore fluctuations are driven by barotropic pressure gradients associated with the intrusion of the Taiwan Strait Current (TSC). When a strong TSC intrudes to the north of Taiwan, the isobaric slope tilts downward from south to north, leading to a cross-shore current from the coastal area to the offshore area. When the TSC intrusion is weak, the crossshore current to the north of Taiwan is directed from offshore to inshore. The other area of significant fluctuation is located in the inshore area between the 30 and 100m isobaths. The fluctuations are generally strong both in the alongshore and cross-shore directions, in particular at the latitudes 26.5 and 28_ N.Wind affects the synoptic fluctuation through episodic events. When the northeasterly monsoon prevails, the southwestward Zhe-Min coastal current dominates the inshore area associated with a deepening of the mixed layer. When the winter monsoon is weakened or the southwesterly wind prevails, the northeastward TWC dominates in the inshore area.

Citation：Xuan, J., D. Huang, T. Pohlmann, J. Su, B. Mayer, R. Ding and F. Zhou. Synoptic fluctuation of the Taiwan Warm Current in winter on the East China Sea shelf. Ocean Sci., 2017, 13(1): 105-122.

Current standard deviation in the layer of the VMV. The black arrows indicate the major axis of the ellipse, which represent the standard deviation of the current. The color shading shows the respective magnitude. The two blue arrows indicate the two TWC branches. The red curve indicates the area where the current standard deviation is larger than 0.1ms-1 and the branches’ representative points (P1 and P2) are selected for later analysis.