Orientation of coastal-zone Langmuir cells forced by wind, wave and mean current at variable obliquity
Orientation of coastal-zone Langmuir cells forced by wind, wave and mean current at variable obliquity
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DOI：
10.1017/jfm.2019.683
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发表时间：
2019-10
影响因子：
3.7
通讯作者：
K. Shrestha;W. Anderson;A. Tejada-Martínez;J. Kuehl
中科院分区：
文献类型：
--
作者：
K. Shrestha;W. Anderson;A. Tejada-Martínez;J. Kuehl
朗缪尔环流是上层海洋中的一个重要湍流过程，受大气风应力和表面波漂移的机械驱动和维持。此外，特别是在沿海地区，平均流的存在--无论是与潮汐流或大尺度涡流相关--产生底部边界层剪切，这进一步调节了沿海地区朗缪尔湍流的物理属性。我们发现，平均流、大气阻力和单色波场方向之间的倾斜强迫所产生的底边界层切变的存在改变了所产生的大尺度朗缪尔环流的方向。提出了一个基于定义强迫倾角的显著参数来预测这一合成取向的模式。我们还进行了系统的参数研究，以分离显著参数的“转向”影响，这表明所产生的朗缪尔细胞的方向总是位于外力的中间。为了给结果提供严格的基础，我们研究了影响流向涡度维持的项，并为观测结果提供了理论依据。
Langmuir circulation, a key turbulent process in the upper ocean, is mechanistically driven and sustained by imposed atmospheric wind stress and surface wave drift. In addition, and specifically in coastal zones, the presence of a mean current – whether associated with tidal currents or large-scale eddies – generates bottom-boundary-layer shear, which further modulates the physical attributes of coastal-zone Langmuir turbulence. We show that the presence of bottom-boundary-layer shear generated by oblique forcing between the mean current, atmospheric drag, and monochromatic wave field direction changes the orientation of the resultant, large-scale Langmuir cells. A model to predict this resultant orientation, based on salient parameters defining the forcing obliquity, is proposed. We also perform a systematic parametric study to isolate the ‘turning’ influence of salient parameters, which reveals that the resultant Langmuir cell orientation is always intermediate to the imposed forces. In order to provide a rigorous basis for the results, we study terms responsible for sustenance of streamwise vorticity, and provide a theoretical justification for the observed results.