Coastal cape and canyon effects on wind-driven upwelling in northern Taiwan Strait
Coastal cape and canyon effects on wind-driven upwelling in northern Taiwan Strait
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DOI：
10.1002/2014jc009831
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发表时间：
2014-07
影响因子：
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通讯作者：
Zhaoyun Chen;Xiao‐Hai Yan;Yuwu Jiang
中科院分区：
文献类型：
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作者：
Zhaoyun Chen;Xiao‐Hai Yan;Yuwu Jiang
利用观测资料和数值模式相结合的方法，揭示了夏季台湾海峡北部的上升流特征和机制。现场数据提供了上升流以温跃层的形式向岸上倾斜的证据。遥感数据显示，沿海地区有一条上升流带，这种情况在半个多夏天都会发生。上升流概率图显示出两个上升流岩心，一个位于平潭岛下游，形成角效应，另一个位于三沙湾沿岸峡谷上方。遥感数据和数值模拟结果表明，南风对平潭岛浅水区上升流带的形成起着关键作用，而潮汐通过潮汐混合效应调节上升流位置，尤其是平潭岛背风区。利用理想岬角和海岸峡谷地形进行的进一步数值实验表明，垂直速度在岬角和峡谷下游增强。涡度方程表明，相对涡度沿流线的变化和涡度的摩擦扩散是导致岬外、峡谷内和峡谷周围垂直速度的主要原因。根据位涡量守恒，相对涡量在不规则地形（如岬角和峡谷）上沿流线的变化是台湾海峡北部两个上升流核的主要机制。
A combination of observations and numerical model is used to reveal the upwelling features and mechanisms in the northern Taiwan Strait during summer. In situ data give evidence of the upwelling in the form of thermocline tilting upward onshore. The remote sensing data show a strip of upwelling in the coastal region, which occurs more than half a summer. The upwelling probability map indicates there are two upwelling cores, one located downstream of Pingtan Island formed as cape effect and the other over the coastal canyon off the Sansha Bay. Remote sensing data and numerical model results suggest that the southerly wind plays a key role in shaping this upwelling strip, while the tides regulate the upwelling location through tidal mixing effect in the shallow water region, especially lee of Pingtan Island. Further numerical experiments using idealized cape and coastal canyon topography show that vertical velocity is intensified downstream of the cape and canyon. The vorticity equation shows that relative vorticity change along a streamline and frictional diffusion of vorticity are responsible for the vertical velocity off the cape and within and around the canyon. According to the conservation of potential vorticity, the variation of relative vorticity along a streamline over irregular topography, e.g., cape and canyon, is the main mechanism for the two upwelling cores in the northern Taiwan Strait.