Tides and Turbulent Mixing in the North of Taiwan Island
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Microstructure and hydrological profiles were collected along two cross-shelf sections from the deep slope to the shallow water in the north of Taiwan Island in the summer of 2006. While the tidal currents on the shelf were dominated by the barotropic tide with the current ellipse stretched across the shelf, significant internal tides were observed on the slope. The depth-mean turbulent kinetic energy (TKE) dissipation rate on the shelf was 10−6 W kg−1, corresponding to a diapycnal diffusivity of 10−2 m2 s−1. The depth-mean TKE dissipation rate on the slope was 1×10−7 Wkg−1, with diapycnal diffusivity of 3.4×10−4 m2 s−1. The shear instability associated with internal tides largely contributed to the TKE dissipation rate on the slope from the surface to 150 m, while the enhanced turbulence on the shelf was dominated by tidal or residual current dissipations caused by friction in the thick bottom boundary layer (BBL). In the BBL, the Ekman currents associated with the northeastward Taiwan Warm Current were identified, showing a near-bottom velocity spiral, which agreed well with the analytical bottom Ekman solution.
Key wordsmicrostructure observations turbulent mixing internal tides bottom boundary layer bottom Ekman spiral
本文基于2006年夏季在台湾岛东北部海域从陆坡至陆架的湍流和水文断面观测,揭示了该海域的湍流量级及相关水文特征.研究发现:陆架上潮流以正压潮为主,在地形的作用下,潮汐椭圆被压缩,而在陆坡上以显著的内潮信号为主.在陆架上,深度平均的湍动能耗散率量级为 10-6 W kg-1, 对应的湍流混合率量级为10-2 m2 s-1.在陆坡上,深度平均的湍动能耗散率为10-7 W kg-1,平均湍流混合率为3.4×10-4 m2 s-1.陆坡上层垂向水文观测显示:由内潮引起的剪切不稳定极大的贡献于湍动能耗散率,而在陆架上增强的湍动能耗散率则主要由潮流和定常流在厚底边界层内的底摩擦作用下产生.
关键词微尺度观测 湍流混合 内潮 底边界层 底Ekman螺旋
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Special thanks to the crew of the R/V Dong Fang Hong 2, particularly Professor Xianwen BAO (Ocean University of China) who chaired the cruise in the ECS. The survey was sponsored by the National Basic Research Program of China (Ministry of Science and Technology). The authors extend their thanks to Professor Martin VISBECK for the LADCP data processing. Dr. Jim PRICE was generous to share his bottom Ekman solution program during the MIT–WHOI joint program class in fall of 2009. Discussions with Professor Fangli QIAO, Xuejun XIONG, Zhiyu LIU and Dr. Guansuo WANG were helpful. Mr. Changsan XU helped improve the quality of the figures. The research was also granted by the National Natural Science Foundation of China (Grant Nos. 41306003 and 41430963), the Fundamental Research Funds for the Central Universities (Grant Nos. 0905–841313038, 1100–841262028 and 0905–201462003), the China Postdoctoral Science Foundation (Grant No. 2013M531647) and the Natural Science Foundation of Shandong (Grant No. BS2013HZ015). The GEBCO and AVISO data were downloaded from https://doi.org/www.gebco.net and https://doi.org/www.aviso.altimetry.fr, respectively. The authors appreciate the constructive comments and suggestions from the two anonymous reviewers, which greatly improved the quality of the manuscript.
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