Collaborative Research: Entrainment in Dense Currents Over a Rough Bottom

合作研究：粗糙底部浓密水流的夹带

• 批准号: 1333174
• 负责人: Claudia Cenedese
• 金额: $ 47.74万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-15 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1333174&HistoricalAwards=false
• 关键词: Collaborative; Research; Entrainment; Dense; Currents

Overview:The dynamics controlling the entrainment in dense currents are fundamental to the formation, movement, and distribution of the densest water in the ocean; a cornerstone of the thermohaline circulation. However, the entrainment and mixing in these currents occurs at such small scales, and the flows are so rapid that full resolution of the dynamics is presently very difficult, if not impossible, in global ocean circulation and climate models. Consequently, the entrainment, and often the overflows themselves are not resolved and need to be parameterized.Intellectual Merit :The existing parameterizations for entrainment in dense currents account primarily for the shear-induced entrainment at the interface between the dense flow and the ambient fluid. However, the turbulence generated by roughness elements at the bottom boundary, which produces an enhanced drag, is intense and cannot be ignored. In this project, it is hypothesized that for dense currents having a height much larger than the bottom boundary layer thickness, the turbulent eddies generated by the bottom roughness will play a role in homogenizing the dense current but will not contribute to entrainment of ambient waters within the dense current (i.e. will not contribute to changes in the water properties). Conversely, for dense currents having a height comparable to or smaller than the bottom boundary layer thickness, the turbulent eddies near the bottom should be large enough to entrain the ambient water lying above the dense current and should significantly influence the dense water properties. The effect of entrainment due to bottom roughness should therefore be included in the entrainment parameterizations, and the parameter regime in which bottom roughness is important be identified.This project will address this shortcoming with a combined laboratory and numerical study focused on entrainment and dense currents dynamics over a wide range of rough bottoms, in which the shape (circular, square, and triangular cross section), vertical extent, spacing (sparse vs. dense configuration), and spatial distribution (regular vs. irregular) of the roughness elements will be varied. The investigators will: (i) quantify the relationship between entrainment and the ratio of the dense current height to the bottom boundary layer thickness; (ii) determine the influence of the shape, vertical extent, spacing, and spatial distribution of the roughness elements on the thickness of the bottom boundary layer in which turbulent eddies are expected to develop; (iii) establish a new universal entrainment parameterization which takes into account the bottom roughness.Broader Impacts :Overflows and dense currents are important aspects of the deep ocean circulation. As such, improved understanding of the dynamics of these currents when they flow over a rough bottom bathymetry, and the development of relationships between the entrainment and roughness parameters has the potential to change the way mixing is parameterized in these flows. In practice, results from this project could lead to advanced entrainment parameterizations, a more realistic location in the water column of important water masses in climate models, and hence, an improved prognostic power of these models.This project will support the Ph.D. thesis work of a graduate student at UT San Antonio. The student will gain experience in collaborative research involving numerical models and laboratory experiments. Both PIs are deeply involved in teaching and advising and the results from this project will quickly find their way into graduate education. Cenedese is also on the faculty of the Geophysical Fluid Dynamics (GFD) Summer Program at WHOI. Over the course of this grant, it is expected that one or more GFD fellows will work on related projects under her guidance. Finally, the investigators plan to attract graduate and undergraduate guest students to work at WHOI on ~ 4 month projects in support of the proposed study. The experimental work at WHOI will also utilize the Geophysical Fluid Dynamics Laboratory, which has a long tradition of providing facilities, and assisting students and scientists from around the US and world to conduct fluid dynamics experiments in the areas of physical oceanography, geology, and bio-physical interactions. Videos of experiments and related numerical models will be presented on the web with associated explanations suitable for classroom use.

概述：控制稠密水流夹带的动力学对于海洋中最稠密的水的形成、运动和分布至关重要；温盐环流的基石。然而，这些洋流的夹带和混合发生在如此小的尺度上，而且流动速度如此之快，以至于在全球海洋环流和气候模型中，目前完全解决动力学问题即使不是不可能，也是非常困难的。因此，夹带，通常是溢流本身没有得到解决，需要进行参数化。 智力优点：现有的密流中夹带的参数化主要考虑了密流和环境流体之间界面处的剪切引起的夹带。然而，底部边界处的粗糙单元产生的湍流会产生增强的阻力，并且是强烈的且不容忽视。在本项目中，假设对于高度远大于底部边界层厚度的稠密水流，底部粗糙度产生的湍流涡流将起到均匀化稠密水流的作用，但不会有助于夹带周围的水体。密集的水流（即不会导致水特性的变化）。相反，对于高度等于或小于底部边界层厚度的稠密水流，底部附近的湍流涡旋应足够大以夹带位于稠密水流上方的环境水，并且应显着影响稠密水特性。因此，底部粗糙度引起的夹带效应应包含在夹带参数化中，并确定底部粗糙度重要的参数范围。该项目将通过针对夹带和密集电流动力学的实验室和数值研究相结合来解决这一缺点在各种粗糙底部上，其中粗糙度元素的形状（圆形、方形和三角形横截面）、垂直范围、间距（稀疏与密集配置）和空间分布（规则与不规则）将会多种多样。研究人员将：（i）量化夹带与密流高度与底部边界层厚度之比之间的关系； (ii) 确定粗糙度元素的形状、垂直范围、间距和空间分布对预计会形成湍流涡流的底部边界层厚度的影响； (iii) 建立一种新的通用夹带参数化，其中考虑了底部粗糙度。更广泛的影响：溢流和密集洋流是深海环流的重要方面。因此，提高对这些水流流过粗糙底部测深时的动力学的理解，以及夹带和粗糙度参数之间关系的发展，有可能改变这些水流中混合参数化的方式。在实践中，该项目的结果可能会带来先进的夹带参数化，在气候模型中重要水团的水柱中具有更真实的位置，从而提高这些模型的预测能力。该项目将支持博士生项目。德克萨斯大学圣安东尼奥分校研究生的论文工作。学生将获得涉及数值模型和实验室实验的合作研究经验。两位 PI 都深入参与教学和咨询工作，该项目的成果将很快应用于研究生教育。 Cenedese 也是 WHOI 地球物理流体动力学 (GFD) 夏季项目的教员。在这笔赠款的过程中，预计一名或多名 GFD 研究员将在她的指导下从事相关项目。最后，研究人员计划吸引研究生和本科生客座学生在 WHOI 开展为期约 4 个月的项目，以支持拟议的研究。 WHOI 的实验工作还将利用地球物理流体动力学实验室，该实验室具有提供设施的悠久传统，并协助来自美国和世界各地的学生和科学家在物理海洋学、地质学和生物领域进行流体动力学实验。 - 身体互动。实验和相关数值模型的视频将在网络上发布，并附有适合课堂使用的相关解释。