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

与发生在内潮发生地或附近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重要组成部分，同时影响着二氧化碳进入海洋的吸收和经向热量的输送。准确计算湍流耗散的大小和空间分布对于发展基于物理的近场转换和耗散率的参数化是必要的。当几何形状、正压强迫和环境参数改变时，湍流中会发生质的变化。在内波产生过程中，推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。为了弥补这些认识空白，需要采取多尺度办法来跨越不同尺度之间的差距：从流出的低模内部潮汐的尺度(垂直尺度约为一公里，水平尺度约为数十公里，时间约为几小时)，到高波数模的非线性形成，再到最终的湍流事件(空间尺度为米，时间尺度为分钟)。不同尺度上的模式集成不仅与海洋科学有关，而且在许多科学和工程领域也引起极大兴趣，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，并获得在应用尖端数值工具解决复杂海洋问题方面的宝贵经验。利用相关的无量纲参数，数值研究了正压潮流在孤立地形尺度上产生内波的过程。驱动假设是，只有以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过程中的耗散率。尺度分离将通过一种新的分层方法来处理，该方法结合了小尺度上的大涡模拟(LES)和大尺度上的自适应细化分层海洋模型(Somar)。LES模式配备了一个复杂的亚网格尺度模式，能够提供对湍流的真实描述，而不需要可调的参数。针对内波问题的各向异性，对非静力SOMAR进行了专门的优化。我们的目标是实现一个双向嵌套的Somar-LES模式，以便LES以现实的强迫驱动，Somar收到现实的湍流反馈。我们将对一个海洋尺度的三角山脊模型进行这项工作，该模型涵盖了一系列关键的无量纲参数：总漂移数、障碍物临界程度、内漂移数和临界坡长。这些模拟将被分析以确定(I)内波能量对无量纲参数的依赖，以及(Ii)更好地理解近场中的稳定性、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.