Sloping boundary layers in the deep ocean: using three-dimensional numerical simulations to help interpret one-dimensional observations

通过主动混合，斜坡地形上的边界层保持了稳定的分层，这意味着与分层海洋内部的持续交换和影响。估计表明，这些边界层的混合与海洋盆地内部的混合相当，甚至超过。最近的研究认为，这种底流混合维持了沿斜坡地形的上升流，这是大规模海洋翻转环流的普遍特征，对深海的通气率具有重要意义。在这项工作中，PI建议研究这些深海地层的动力学和影响。在高分辨率野外观测的背景下，通过进行高分辨率的三维数值模拟，研究了斜坡测深之上的湍流边界层。它的目的是提高对大规模撞击关键过程的物理理解，从而提高我们对有限观测的解释和参数化这些边界层的方法。这一努力将加强和扩大PI与他过去曾合作过的两个小组之间的国际合作。它将允许PI在进一步进行建模合作的同时，为研究提供独特合适的数据集。研究结果将通过在科学会议上的介绍和同行评议文献中的出版物广泛传播。带有相应叙述的流程可视化也将作为外联开发和传播。这些视频可以在YouTube上观看，也可以通过关注流体动力学的博客观看，但重点是科学传播和推广。该项目的科学目标是更好地了解这些边界层的动力学，以及它们如何与相对静止的盆地内部相互作用和影响。PI和他的合作者还试图了解如何在实际采样限制下最好地解释系泊温度测量，并考虑到最近使用索普尺度估计湍流强度对这些流动的挑战。初步结果与观测结果相当吻合，表明基本的动态正在定量准确地捕捉到，集中模拟和实地观测的重新分析的综合将比单独使用任何一种方法更能全面地了解潜在的动态。拟模拟的观测包括靠近东北大西洋的三个地点，它们具有亚临界、临界和超临界地形坡度，并估计近底耗散率随坡度系统地变化两个数量级。所提出的研究将增加我们对潮汐驱动的边界层以及它们如何与相对静止的内部盆地相互作用和影响的理解。拟议的工作还将为从一维系泊或垂直剖面获得的现场测量结果的解释提供见解和指导。特别是，假设这些边界层中的索普尺度与奥兹米多夫尺度密切相关，并且在解释观测结果时可以忽略非局部产生的湍流的水平平流，这些假设的后果和含义将被解决。这种见解可以形成在更大规模模型中改进这些过程的参数化的基础。

Though active mixing, the boundary layers above sloping topography maintain their stable stratification, implying a continuous exchange with, and impact on, the stratified ocean interior. Estimates suggest that the mixing in these boundary layers is comparable to, or exceeds, the mixing in the interior of the ocean basins. Recent work argues that such diapycnal mixing sustains upwelling along sloped topography that is a pervasive characteristic of the large-scale ocean overturning circulation with important implication for the ventilation rate of the abyssal ocean. In this work, PI proposes to examine the dynamics and impacts of these deep-ocean stratified, turbulent boundary layers above sloping bathymetry by conducting high-resolution, three-dimensional numerical simulations in the context of high-resolution field observations. It aims to improve physical understanding of a key process with large-scale impacts and thereby improve our interpretation of limited observations and approaches to parameterizing these boundary layers. The effort will enhance and extend international collaborations between the PI and two groups with which he has worked in the past. It will allow the PI to work first hand with uniquely appropriate data sets for the study while furthering ongoing modeling collaborations. Findings will be broadly disseminated through presentation at scientific conferences and through publications in the peer reviewed literature. Flow visualizations with corresponding narratives will also be developed and disseminated as outreach. These will be available on YouTube and via blogs focusing on fluid dynamics but specializing in scientific communication and outreach.The scientific objective of the project is to better understand the dynamics of these boundary layers and how they interact with and influence the comparatively quiescent interior basin. PI and his collaborators also seek to understand how to best interpret moored temperature measurements given practical sampling limitations and in light of recent challenges to the use of Thorpe scale estimates of turbulence intensity for these flows in particular. Preliminary results compare remarkably well with observations, suggesting that the essential dynamics are being captured with quantitative accuracy and that a synthesis of focused simulation and re-analysis of field observations will lead to a more complete picture of the underlying dynamics than either approach alone. The observations to be simulated include three sites in close proximity in the Northeast Atlantic with subcritical, critical, and supercritical topographic slopes and with estimates of near-bottom dissipation rates that vary systematically with slope by two orders of magnitude. The proposed research will add to our understanding of tidally-driven boundary layers and how they interact with, and influence, the comparatively quiescent interior basin. The proposed work will also provide insight and guidance for the interpretation of field measurements obtained from one-dimensional moorings or vertical profiles. In particular, the consequences and implications of assuming that Thorpe scales are closely related to Ozmidov scales in these boundary layers and that horizontal advection of non-locally produced turbulence can be neglected in interpreting the observations will be addressed. This insight can form the basis for improved parameterizations of these processes in larger-scale models.