Collaborative Research: Multiscale modeling of internal tides at topographic generation sites: turbulence and wave energetics:

与内潮生成地点或附近发生的内波有关的湍流过程是维持和调节全球海洋环流的关键因素，而全球海洋环流是气候系统的一个关键组成部分，同时影响海洋吸收二氧化碳和热量的纬向输送。湍流耗散的大小和空间分布的精确计算是必要的物理为基础的参数化的转换和耗散率在近场的发展。当几何形状、正压强迫和环境参数改变时，湍流会发生质的变化。内波产生期间驱动湍流能量耗散的物理过程的空间和时间尺度跨越几个数量级。为了解决这些知识差距，多尺度的方法是必要的，跨越尺度之间的差距：从外向低模式内潮的尺度（垂直尺度是一公里的顺序，水平尺度是几十公里，时间是小时的顺序），通过非线性形成更高的波数模式，最后，湍流事件（米的空间尺度和分钟的时间尺度）。不同尺度模型的整合不仅与海洋科学有关，而且在科学和工程的许多领域也有很大的意义，例如，湍流边界层过程在中长期天气预报中的表现。对开发或应用参数化感兴趣的更广泛的社区将能够获得模拟数据和数值模型代码。两名研究生将接受培训，并获得将尖端数值工具应用于复杂海洋问题的宝贵经验。本文将对正压潮流在孤立地形上产生内波的过程进行数值研究。驱动的假设是，只有列入湍流在一个现实的方式可以提供一个正确的描述的耗散率在这些网站的生成和近场传播的内波。尺度分离将通过一种新的分层方法来处理，该方法将小尺度的大涡模拟（LES）与大尺度的分层海洋模型（SOMAR）相结合。LES模型，配备了一个复杂的亚网格尺度模型，能够提供一个忠实的描述湍流，而不需要可调的参数。非静力SOMAR是专门优化，以处理各向异性的内波问题。我们的目标是实现一个双向嵌套SOMAR-LES模型，使LES驱动与现实的强迫，SOMAR接收现实的湍流反馈。我们将这样做的一个模型的三角形脊在海洋尺度上的一个广泛的关键无量纲参数：整体的游览数，障碍物的临界性，内部游览数和长度的临界斜率。模拟将进行分析，以确定（i）内波能量对无量纲参数的依赖性，以及（ii）更好地了解近场的稳定性，湍流和相关的耗散率。

Turbulent processes associated with internal waves occurring at or near the generation sites of internal tides are key ingredients in maintaining and regulating the global ocean circulation which is a crucial component of the climate system affecting simultaneously the uptake of carbon dioxide into the ocean and the meridional transport of heat. Accurate computation of the magnitude and spatial distribution of turbulent dissipation is necessary for the development of physically based parameterizations of conversion and dissipation rates in the near-field. Qualitative changes in turbulence occur when geometry, barotropic forcing and environmental parameters change. The spatial and temporal scales of the physical processes that drive the turbulent energy dissipation during the generation of internal waves span several orders of magnitude. To address these knowledge gaps, a multi-scale approach is necessary to span the disparity between scales: from the scale of the outgoing low-mode internal tide (vertical scale is of order one kilometer, horizontal scale is of order tens of kilometers, time is of order hours) through the nonlinear formation of higher wave number modes to, finally, the turbulence events (spatial scale of meters and time scale of minutes). The integration of models across disparate scales is not only relevant to ocean sciences but also of great interest in many areas of science and engineering, e.g., the representation of turbulent boundary layer processes in medium- and long-term weather forecasting. The broader community interested in developing or applying parameterizations will have access to the simulation data and the numerical model code. Two graduate students will be trained and gain valuable experience in applying cutting edge numerical tools to a complex ocean problem. A numerical investigation of the generation process of internal waves by barotropic tidal flow over an isolated topographic feature scales with the relevant non-dimensional parameters will be conducted. The driving hypothesis is that only the inclusion of turbulence in a realistic way can provide a correct description of the dissipation rates during generation and near-field propagation of internal waves at these sites. The scale-separation will be handled through a novel hierarchical approach that combines Large Eddy Simulation (LES) at small scales with the Stratified Ocean Model with Adaptive Refinement (SOMAR) for the large scales. The LES model, equipped with a sophisticated subgrid-scale model, is capable of providing a faithful description of turbulence, without the need of tunable parameters. The non-hydrostatic SOMAR is specifically optimized to deal with the anisotropy of the internal wave problem. The goal is to implement a two-way nested SOMAR-LES model so that the LES is driven with realistic forcing, and SOMAR receives realistic turbulent feedbacks. We will do so for a model triangular ridge at oceanic scales over a wide range of key non-dimensional parameters: overall Excursion number, obstacle criticality, inner Excursion number and length of critical slope. The simulations will be analyzed to ascertain (i) the dependence of internal wave energetics on the non-dimensional parameters, and (ii) a better understanding of stabilities, turbulence and associated dissipation rates in the near-field.