Shear dispersion from near-inertial internal Poincaré waves in large lakes: Shear dispersion in stratified large lakes
Shear dispersion from near-inertial internal Poincaré waves in large lakes: Shear dispersion in stratified large lakes
复制标题
大型湖泊中近惯性庞加莱内波的剪切色散：分层大型湖泊中的剪切色散
DOI：
10.1002/lno.10163
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发表时间：
2015
影响因子：
4.5
通讯作者：
Hawley, Nathan
中科院分区：
文献类型：
--
作者：
Choi, Jun M.;Troy, Cary D.;Hawley, Nathan
在这项工作中，我们研究了混合层的横向分散，增强了近惯性内部庞加莱波在近海地区的一个大型分层湖，密歇根湖。我们研究的假设，近惯性内部庞加莱波产生的垂直剪切不仅是一个能源的垂直混合在温跃层和混合层，但也通过非定常剪切流分散机制增强水平分散。复杂的经验正交函数分析表明，占主导地位的剪切结构被观察到的热结构的镜像，与最大剪切的位置逐渐降低的混合层加深。这种剪切和垂直混合结构的变化在层化的早期和晚期之间产生了不同的剪切流弥散特征。估计的深度平均表面层垂直湍流扩散系数从 到 在分层期间，相关的横向色散系数估计为0.140。庞加莱波被发现大大提高横向分散的时间小于惯性周期后释放。相比之下，亚惯性剪切是导致剪切分散的主要机制，其时间大于惯性周期。本文提出了一个简单的横向弥散系数的近似计算方法，它是表面流速（或风摩擦速度）和混合层深度的乘积。计算出的分散系数同意与大久保的扩散图的时间长达一个星期，这表明，不稳定的剪切分散是一个合理的机制来解释观察到的分散率在混合层释放后的早期。
In this work, we study mixed layer lateral dispersion that is enhanced by near‐inertial internal Poincaré waves in the offshore region of a large stratified lake, Lake Michigan. We examine the hypothesis that the vertical shear created by near‐inertial internal Poincaré waves is not only an energy source for vertical mixing in the thermocline and mixed layer, but also enhances horizontal dispersion via an unsteady shear flow dispersion mechanism. Complex empirical orthogonal function analysis reveals that the dominant shear structure is observed to mirror the thermal structure, with the location of maximum shear gradually lowered as the mixed layer deepens. This changing structure of shear and vertical mixing produces different characteristics in shear flow dispersion between the early and later stratified periods. The estimated depth‐averaged surface layer vertical turbulent diffusivity grows from to over the stratified period, and the associated lateral dispersion coefficients are estimated as 0.1 40 . The Poincaré waves are found to enhance greatly lateral dispersion for times less than the inertial period following release. In contrast, sub‐inertial shear is the dominant mechanism responsible for shear dispersion for times greater than the inertial period. A simple approximation of the dispersion coefficient for lateral dispersion is developed, which scales as the product of surface current velocity (or wind friction velocity) and mixed layer depth. The calculated dispersion coefficients agree well with Okubo's diffusion diagram for times up to a week, which suggests that unsteady shear dispersion is a plausible mechanism to explain observed dispersion rates in the mixed layer for early times after release.