Synoptic fluctuation of the Taiwan Warm Current in winter on the East China Sea shelf

Abstract

Abstract. 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 100 m isobaths and an offshore branch between the 100 and 200 m 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 100 m 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.

Modulation of Shelf Circulations Under Multiple River Discharges in the East China Sea

“…Lee & Chao, 2003;Lie & Cho, 2016;J. Wang et al, 2019;Xuan et al, 2016;Xuan et al, 2017;Zhu et al, 2004). Such a feature was significant in autumn and winter, when the majority of the Changjiang River plume extended along the coastal area of the East China Sea (Figure 10).…”

“…Su et al, 1994). Especially in winter seasons, the TWC is bottom-intensified (D. Huang et al, 2016;Xuan et al, 2017;Zhu et al, 2004). Near 28.5°N, the TWC bifurcates into two branches, with one continues flowing northward toward the Changjiang River Estuary, the other is diverted eastward first, and then turns to the north toward the Tsushima/Korea (T/K) Strait (Lian et al, 2016;Qi et al, 2017;J.…”

Advances on Coastal and Estuarine Circulations Around the Changjiang Estuary in the Recent Decades (2000–2020)

“…The variations of coastal circulation in the ECS are jointly driven by monsoons, tides, and the buoyancy forcing from the extensive Changjiang River discharge (Lie and Cho, 2016;Wu et al, 2018b). In general, coastal circulation over the shelf shallower than 50 m generally flows northeastward in summer and southwestward in winter (Lee and Chao, 2003;Ge et al, 2013;Gan et al, 2016), although extensive synoptic variation has also been observed (Xuan et al, 2016a). The instabilities associated with this current may stimulate notable cross-shelf water exchange in both seasons (Yuan et al, 2005He et al, 2010).…”

Sea Surface Height and Current Responses to Synoptic Winter Wind in the Bohai, Yellow, and East China Seas: Two Leading Coastal Trapped Waves

“…Huang et al () showed that the synoptic fluctuations of the TWC are related to the winter monsoon. The spatial distribution and dynamics of the synoptic fluctuations were also investigated with numerical models (Oey et al, ; Xuan et al, ). In our study, the synoptic variations in the TWC on the ECS shelf are shown in Figure c, with large σ u values (>15 cm/s) near the coast and decaying in the offshore direction.…”