Turbulence Closure for Energetic, low-Ri Stratified Shear Flows

层状低理查森数剪切流在科学和实际应用中具有重要意义，对湍流闭合提出了很高的要求。一个可以真实模拟这种流动的湍流闭合模型将通过采用现有的闭合模型并在必要时对其进行修改，并对其进行三步筛选过程来开发。步骤0是要求闭合具有均匀、分层剪切流的实际稳定状态，例如在Van Atta小组的实验室实验中。在第一步中，在模拟和观测到的湍流耗散率和长度尺度的严格定量比较中，隔离测试关闭件。第一步的观测基础是潮汐驱动的哈德逊河河口的大量微结构测量。在步骤1中，对闭合的要求是，在给定观测到的切变和浮力频率的情况下，闭合产生与所观察到的湍流混合的水平和潮汐深度-时间结构密切匹配的结果。在步骤2中，将封闭物嵌入到红海咸水外流的2D和3D数值模型中。这里对闭合的要求是，它允许数值模式再现外流的特殊结构，它结合了底部的核心层，在100多公里的距离内经历了很少的夹带和稀释，而核心层上方的厚剪切带经历了高度高能的湍流混合。我们将探讨非静力2D模型和较粗分辨率、静压3D模型中关闭件性能的差异。3D模型允许研究旋转和流出通道地形的可能影响。将考虑的关闭计划包括鲍姆特和彼得斯以及Canuto等人的新关闭计划。修改后通过步骤0的闭包，这是彼得斯等人以前使用的另一个闭包。拟议研究的更广泛影响将是通过改善沿海和河口水域的管理，以及研究由于改进了最广泛使用的模式中嵌入的湍流封闭而导致的气候和气候变化。一个教育部分是通过研究生的拟议参与来提供的。

ABSTRACTOCE-0352047Stratified, low-Richardson number shear flows, which are of crucial importance in scientific and practical contexts, place high demands on turbulence closures. A turbulence closure model that can realistically simulate such flows will be developed by taking, and if necessary modifying, existing closures and to subjecting them to a three-step screening process. Step 0 is a demand that the closures have a realistic steady state for homogeneous, stratified shear flows such as in the laboratory experiments of Van Atta's group. In Step 1 the closures are tested in isolation in a strict quantitative comparison of simulated and observed turbulent dissipation rates and length scales. The observational basis of Step 1 are extensive microstructure measurements from the tidally driven Hudson River estuary. The demand on the closures in Step 1 is that, given the observed shear and buoyancy frequency, the closures produce a close match of the levels and tidal depth-time structure of the observed turbulent mixing. In Step 2 the closures are embedded in 2D and 3D numerical models of the outflow of saline water from the Red Sea. The demand on the closure here is that it allow the numerical models to reproduce the peculiar structure of the outflow which combines a core layer at the bottom that undergoes little entrainment and dilution over a distance of over 100 km while a thick shear zone above the core layer undergoes highly energetic turbulent mixing. The difference in performance of the closures in a non-hydrostatic 2D model and a coarser-resolution, hydrostatic 3D model will be explored. The 3D model allows investigating possible effects of rotation and of the outflow channel topography. The closure schemes which will be considered include the new closure by Baumert and Peters, the Canuto et al. closure which passes Step 0 after modification, another closure previously employed by Peters et al. and Mellor/Yamada which is being used ubiquitously.The broader impacts of the proposed research will be through improved management of coastal and estuarine waters as well as research into climate and climate change as a result of improvement of turbulence closures embedded in most widely used models. An educational component is given through the proposed participation of a graduate student.