Submesoscale instabilities in the ocean bottom boundary layer: A new pathway for energy dissipation

海底边界层的亚尺度不稳定性：能量耗散的新途径

基本信息

批准号：
1948953
负责人：
Jacob Wenegrat
金额：
$ 38.27万
依托单位：
University of Maryland, College Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-06-15 至 2023-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948953&HistoricalAwards=false
关键词：
Submesoscale instabilities ocean bottom boundary

项目摘要

One of the long standing questions in physical oceanography is how the energy input to the ocean circulation is eventually dissipated, a problem with far-reaching implications for both our basic understanding of ocean circulation and for developing accurate ocean models. Recently it has been suggested that instabilities in the bottom layer and topographic wakes provide an important source of turbulent mixing, however the dynamics and energetics of these instabilities remain largely unexplored. At relatively small scales, where the rotation of the Earth is no longer the dominant factor, called submesoscales, instabilities in the ocean bottom layer modify the extraction, and dissipation of energy from the flow, and hence may alter classic conceptions of bottom turbulence. This research will use theory and idealized high-resolution numerical models to determine how submesoscale instabilities near the bottom, over and downstream of topography, modify turbulent mixing. These instabilities are believed to be common feature near the bottom, but are poorly understood in this setting relative to the surface layers. Likewise, these processes are currently absent in most large-scale ocean models, underscoring the need to develop a quantitative understanding of their impact and dependence on controlling parameters. This understanding is central to problems such as how dense water is brought to the surface in the abyssal overturning circulation, and the exchange of nutrients and other biogeochemical tracers between the bottom and interior layers. Results of this work will improve our understanding, and eventual parameterization, of dynamics along topography, and in particular how these boundary layer processes modify the larger-scale ocean circulation and energetics. This project will also enable the training of a postdoctoral researcher, and support the establishment of the initial research group of a junior faculty member.Preliminary results suggest that submesoscale instabilities in the bottom boundary layer (BBL) open a new pathway for dissipating kinetic energy, and further modify the turbulent mixing of buoyancy near topography, believed to be a key aspect of how dense water is brought back to the surface in the abyssal overturning circulation. These results suggest that classic conceptions of how flow-topography interaction generates turbulence are incomplete, and the role of submesoscale instabilities needs to be considered. This project will investigate the energetics of baroclinic, symmetric, and centrifugal instabilities generated by flow along topography. Large-Eddy Simulation (LES) will be used to examine how these instabilities modify the partitioning and flux of energy between eddy and mean kinetic and potential energy terms, and the irreversible dissipation of kinetic energy and mixing of buoyancy. Reynolds-averaged simulations with variable topography will also be used, in conjunction with the LES, to determine how the upstream BBL evolution influences the energetics of topographic wakes. This work will provide a more complete description of the physical processes, and parameter dependencies, which determine how submesoscale instabilities affect the energetics of the ocean circulation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

物理海洋学中长期存在的问题之一是如何最终消散了海洋循环的能量输入，这对我们对海洋循环的基本理解和开发准确的海洋模型具有深远的影响。最近，有人提出，底层和地形唤醒中的不稳定性提供了湍流混合的重要来源，但是这些不稳定性的动力学和能量学在很大程度上尚未探索。在相对较小的尺度下，地球的旋转不再是主要因素，称为子镜，海洋底层的不稳定性会改变提取的提取，而从流量中耗散了能量，因此可能会改变底部湍流的经典概念。这项研究将使用理论和理想化的高分辨率数值模型来确定底部，上游和下游的尺度尺度不稳定性如何修改湍流混合。这些不稳定性被认为是底部附近的常见特征，但是在这种情况下相对于表面层，人们对此有些了解。同样，这些过程目前在大多数大型海洋模型中都不存在，这突显了对它们的影响和对控制参数的依赖性的定量理解的必要性。这种理解对于诸如如何在深渊倾覆的循环中将密集的水以及营养素和其他生物地球化学示踪剂的交换在底部和内部层之间的交换中至关重要。这项工作的结果将改善我们对地形沿线动力学的理解，最终的参数化，尤其是这些边界层过程如何修饰大规模的海洋循环和能量学。该项目还将能够对博士后研究人员进行培训，并支持建立初级教师成员的初始研究小组。预定结果表明，在底部边界层（BBL）中，在底部边界层（BBL）开辟了一个新的途径，以开放一个新的途径，以散发出近距离的效果，使水面的繁殖力逐渐变化，以使水的动荡构成了多余的层次，而又一张大的方面是一定的，而dises the to dises teposect of dose则是多义的，那么多义的层面是造成的。循环。这些结果表明，关于流程图相互作用如何产生湍流的经典概念不完整，需要考虑集合不稳定性的作用。该项目将研究由地形沿着流量产生的斜压，对称和离心不稳定性的能量。大型模拟（LES）将用于检查这些不稳定性如何改变涡流和平均动能和势能项之间的能量分配和通量，以及动能的不可逆转耗散以及浮力的混合。雷诺平均具有可变地形的模拟也将与LES结合使用，以确定上游BBL演化如何影响地形唤醒的能量学。这项工作将为物理过程和参数依赖性提供更完整的描述，这些过程决定了子级的不稳定性如何影响海洋循环的能量学。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的智力优点和更广泛的影响审查标准通过评估来进行评估的。