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

通过活跃的混合，坡面以上的边界层保持了稳定的层结，这意味着与层化海洋内部的持续交换和影响。估计表明，这些边界层中的混合与洋盆内部的混合相当或超过。最近的工作认为，这种昼夜混合支持沿倾斜地形的上升流，这是大尺度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建议通过在高分辨率野外观测的背景下进行高分辨率的三维数值模拟来研究这些深海层状、倾斜水深上方的湍流边界层的动力学和影响。它的目的是增进对一个具有大规模影响的关键过程的物理理解，从而改进我们对有限观测的解释和对这些边界层进行参数化的方法。这一努力将加强和扩大国际和平协会与他过去合作过的两个组织之间的国际合作。它将允许PI与研究的唯一合适的数据集进行第一手工作，同时促进正在进行的建模协作。研究结果将通过在科学会议上的陈述和同行评议文献中的出版物广泛传播。还将开发带有相应叙述的流动可视化，并将其作为外联进行传播。这些将在YouTube和博客上提供，重点是流体动力学，但专门从事科学交流和对外交流。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平静的内盆地相互作用和影响。Pi和他的合作者还试图了解如何在给定实际采样限制的情况下最好地解释系泊温度测量，并考虑到最近使用Thorpe Scale估计这些流动的湍流强度的挑战。初步结果与观测结果相比非常好，这表明正在以定量的准确性捕捉到基本动力学，综合重点模拟和实地观察的重新分析将比单独使用任何一种方法更全面地了解基本动力学。要模拟的观测包括东北大西洋的三个地点，这些地点非常接近，具有亚临界、临界和超临界地形坡度，估计的近底耗散率随坡度系统地变化两个数量级。这项拟议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平静的内陆盆地相互作用和影响的理解。拟议的工作还将为解释从一维系泊或垂直剖面获得的现场测量提供洞察力和指导。特别是，假设索普尺度与这些边界层中的厄兹米多夫尺度密切相关，以及在解释观测时可以忽略非局部产生的湍流的水平平流的后果和影响将被讨论。这一见解可以为在更大规模的模型中改进这些过程的参数化奠定基础。

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.