Turbulent mixing by nearshore internal bores

近岸内孔的湍流混合

• 批准号: 1235552
• 负责人: Stephen Monismith
• 金额: $ 23.11万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-15 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1235552&HistoricalAwards=false
• 关键词: Turbulent; mixing; nearshore; internal; bores

Intellectual Merit: The overall understanding of the larger-scale physics of the inner shelf has advanced notably in the past few years, but there has been little work on the shallow nearshore regions where stratified inner shelf waters interact with the shore. Limited observations to date, including work in Monterey Bay and Mamala Bay, suggest that transient mixing and stratification events, presumably associated with the shoaling and breaking of internal wave fields present offshore, dramatically alter the physical environment in this ecologically important part of the ocean.In this project, detailed observations of periodic turbulent bores and fronts will be conducted in 10 to 30 m water in southern Monterey Bay using a set of Acoustic Doppler Velocimeters (ADV) and fast Conductivity/Temperature sensors to describe the behavior of nearshore turbulent mixing and stratification events. The ADVs will be mounted on an 8m high tower and cabled to shore, to measure turbulence variables including Reynolds stresses, turbulence dissipation and buoyancy fluxes. This tower will be supplemented by an array of Acoustic Doppler Current Profilers and thermistor chains centered on it to provide a detailed spatial and temporal view of these flows, including diagnosing their dynamics. An Automated Underwater Vehicle will be used to map larger-scale variations in temperature and salinity. The project is designed to accomplish two related goals that could substantially advance current understanding of flows in the nearshore: (1) Show how these bore-like features interact with topography and other (e.g. tidal) flows, and (2) Examine the turbulence produced during this interaction in light of existing dynamical frameworks of boundary layer and stratified shear turbulence.Broader Impacts: The local dynamics of the bore/relaxation front pattern that has been often reported in the literature can be the dominant source of variability in an ecologically important class of physical environments. This is significant for several reasons: (1) The bores/fronts appears to be an important mechanism by which deeper offshore waters are supplied to nearshore environments in shelf regions of coastal upwelling systems. Because of the interaction between these bottom derived waters and surface process affected waters in nearshore ecosystems, this is important for understanding how climate change will affect these ecosystems since these waters are low in dissolved oxygen and have high acidity. (2) These bores/fronts are thought to be an important mechanism for the exchange of organisms between the nearshore and the outermost regions of the inner shelf. (3) Vertical turbulent mixing is critical to many ecological processes such as benthic grazing and primary production by phytoplankton.The project's investigators will be experimenting with how to best use coastal ocean observing systems and, through their participation in Stanford's Center for Ocean Solutions, how to connect their use with the data and information needs of policy makers as well as those of other marine ecologists and geochemists.From an educational standpoint, the proposed work will be labor intensive and thus will engage a number of Stanford graduate and undergraduate students. Besides the two students directly involved in the project, at least four other graduate students will likely be involved in the field work, including two women Ph.D. students working with the investigators. As part of this project, a graduate field methods class that will be built around the May 2013 experiment will be taught. Finally, the investigators will also develop a microdocumentary (see http://microdocs.org/) on the importance of internal bores to nutrient fluxes, and nearshore ecosystem production. In conjunction with this video, they will visit several local area high schools in largely underrepresented districts to make short (30 min) presentations on oceanography, ocean health, and ocean career opportunities during which the microdocumentary will be presented to the classroom.

智力优势：在过去的几年里，对内大陆架的大尺度物理学的全面了解有了显著的进展，但在分层的内大陆架沃茨与海岸相互作用的浅水近岸区域，却鲜有研究。迄今为止的有限观测，包括在蒙特雷湾和马马拉湾的工作，表明可能与近海内波场的变浅和破碎有关的瞬时混合和分层事件，极大地改变了海洋这一生态重要部分的物理环境。将使用一套声学多普勒测速仪（ADV）和快速电导率/对蒙特利湾南部10至30 m水中的周期性湍流孔和锋面进行详细观察描述近岸湍流混合和分层事件行为的温度传感器。ADV将安装在一个8米高的塔上，并通过电缆连接到海岸，以测量湍流变量，包括雷诺应力、湍流耗散和浮力通量。这个塔将由一系列声学多普勒海流剖面仪和热敏电阻链补充，以提供这些流动的详细空间和时间视图，包括诊断其动态。将使用一个自动水下航行器来绘制温度和盐度的大规模变化。该项目旨在实现两个相关的目标，可以大大提高目前对近岸水流的理解：（1）显示这些孔状特征如何与地形和其他因素相互作用。（2）根据现有的边界层和分层剪切湍流的动力学框架，研究这种相互作用过程中产生的湍流。在文献中经常报道的孔/松弛前模式的本地动态可以是在生态上重要的一类物理环境的变异性的主要来源。这是重要的几个原因：（1）孔/锋似乎是一个重要的机制，更深的离岸沃茨供应到近岸环境中的陆架区的沿海上升流系统。由于这些底层沃茨与近岸生态系统中受地表过程影响的沃茨之间的相互作用，这对于了解气候变化将如何影响这些生态系统非常重要，因为这些沃茨溶解氧低，酸度高。(2)这些孔/前线被认为是一个重要的机制，生物之间的近岸和最外层地区的内大陆架的交流。(3)垂直湍流混合对许多生态过程至关重要，如底栖动物放牧和浮游植物的初级生产。该项目的研究人员将试验如何最好地利用沿海海洋观测系统，并通过参与斯坦福大学的海洋解决方案中心，如何将其使用与决策者以及其他海洋生态学家和地球化学家的数据和信息需求联系起来。从这个角度来看，这项工作将是劳动密集型的，因此将吸引一些斯坦福大学的研究生和本科生。除了两名直接参与该项目的学生外，至少还有四名其他研究生可能参与实地工作，其中包括两名女博士。学生与调查人员合作。作为该项目的一部分，将在2013年5月实验前后开设一个研究生实地方法课程。最后，研究人员还将制作一部微纪录片（见http：//microdocs.org/），介绍内孔对营养通量和近岸生态系统生产的重要性。结合这段视频，他们将访问几个当地的高中在很大程度上代表性不足的地区，使海洋学，海洋健康和海洋职业机会的简短（30分钟）介绍，在此期间，微纪录片将呈现给教室。