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

在内潮产生地点或附近发生的与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，同时影响海洋对二氧化碳的吸收和热量的经向输送。湍流耗散的大小和空间分布的精确计算对于发展基于物理的近场转换和耗散率参数化是必要的。当几何形状、正压强迫和环境参数发生变化时，湍流会发生质的变化。在内波产生过程中，驱动湍流能量耗散的物理过程的时空尺度跨越了几个数量级。为了解决这些知识差距，需要一种多尺度的方法来跨越尺度之间的差异：从流出的低模态内部潮的尺度（垂直尺度为一公里级，水平尺度为几十公里级，时间为几小时级）到高波数模态的非线性形成，最后是湍流事件（米的空间尺度和分钟的时间尺度）。跨不同尺度模式的整合不仅与海洋科学有关，而且在许多科学和工程领域也有很大的兴趣，例如，在中长期天气预报中湍流边界层过程的表示。对开发或应用参数化感兴趣的更广泛的社区将可以访问模拟数据和数值模型代码。两名研究生将接受培训，并获得应用尖端数值工具解决复杂海洋问题的宝贵经验。在孤立的地形特征尺度上对正压潮汐流产生内波的过程进行了数值研究，并考虑了相关的无量纲参数。驱动假设是，只有以一种现实的方式包含湍流，才能正确描述这些地点内波产生和近场传播期间的耗散率。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与自适应改进（SOMAR）相结合。LES模型配备了复杂的子网格尺度模型，能够提供对湍流的忠实描述，而不需要可调参数。对非流体静力SOMAR进行了专门优化，以处理内波的各向异性问题。目标是实现双向嵌套的SOMAR-LES模型，使LES受到真实的强迫驱动，SOMAR接收真实的湍流反馈。我们将对一个海洋尺度的三角脊模型进行这样的研究，该模型包含了一系列关键的非量纲参数：总体偏移数、障碍临界性、内部偏移数和临界斜率长度。将对模拟进行分析，以确定(i)内波能量学对无量纲参数的依赖，以及（ii）更好地理解近场的稳定性、湍流和相关耗散率。

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.