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

虽然活跃的混合，倾斜地形上的边界层保持其稳定的分层，这意味着一个连续的交换，并影响，分层的海洋内部。估计表明，这些边界层的混合相当于或超过了海洋盆地内部的混合。最近的工作认为，这种底辟混合维持上升流沿着倾斜地形，这是一个普遍的特点，大规模的海洋翻转环流与深海的通风率的重要影响。在这项工作中，PI建议检查这些深海地层的动力学和影响fi艾德，湍流边界层以上倾斜水深进行高分辨率，三维数值模拟的背景下，高分辨率的现场观测。它的目的是提高物理理解的一个关键过程与大规模的影响，从而提高我们的解释有限的观测和方法参数化这些边界层。这一努力将加强和扩大PI与他过去曾合作过的两个团体之间的国际合作。它将使PI能够直接使用研究中唯一合适的数据集，同时进一步进行建模合作。研究结果将通过在科学会议上的介绍和通过同行评审文献中的出版物广泛传播。还将编制和传播具有相应叙述的流程可视化，作为外联活动。这些内容将在YouTube上发布，并通过专注于流体动力学但专门从事科学交流和推广的博客提供。该项目的科学目标是更好地了解这些边界层的动态，以及它们如何与相对静止的内部盆地相互作用并影响它们。PI和他的合作者还试图了解如何最好地解释锚定温度测量给定的实际采样限制，并在最近的挑战，特别是使用索普尺度的湍流强度估计这些流。初步结果与观测结果相比非常好，这表明基本动态正在以定量的准确性被捕获，并且将重点模拟和对实地观测的重新分析相结合，将比单独采用任何一种方法更全面地了解基本动态。要模拟的观测包括三个地点在靠近东北大西洋亚临界，临界和超临界地形坡度和估计的近底耗散率，系统地随坡度变化的两个数量级。拟议中的研究将增加我们对潮汐驱动边界层的理解，以及它们如何与相对静止的内部盆地相互作用和影响。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结果提供见解和指导。特别是，假设索普尺度密切相关的Ozmidov尺度在这些边界层和水平平流的非本地产生的湍流可以忽略不计的解释观测的后果和影响将得到解决。这一见解可以形成在更大规模的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.