Collaborative Research: Using Salinity Variance to Link Estuarine Mixing and Exchange Flow

盐度的变化是定义河口的最重要的量之一。水平盐度变化为重力环流提供了驱动力，垂直变化量化了层化，层化强烈影响剪切、湍流和混合，并受剪切、湍流和混合的影响。盐度方差平衡作为理解河口混合流和交换流相互作用的一种方法，具有很大的前景。这个方程已被有效地利用在湍流社区量化混合，但令人惊讶的是，它很少受到关注的背景下与河口动力学，尽管其根本的重要性。本项目将使用现实和理想化的数值模型，分析跨越参数空间的各种河口的盐度方差平衡。从分析中获得的见解将提供一个更系统的了解河口动力学，使用一个共同的框架，比较率和机制在河口参数空间。该分析方法也将应用于沿海和全球海洋的交换流和混合。该项目还将在这两个机构各支助一名研究生，并为他们的培训作出贡献。PI还计划为研究生开设一个为期5周的暑期课程，名为“河口动力学：观测和现实模型”。“这门课将涉及12-15名对河口过程感兴趣的研究生。学生们将获得实地实践经验，并将应用和分析现实模型，从而培养将观测和模型结合在一起的挑战感和协同感。本项目将开发盐度变化的数学框架，以量化交换流和混合之间的整体关系，然后将这些关系应用于不同的河口环境。除了这些积分关系，分析将检查水平和垂直方差之间的本地交换通过应变，并确定分层和混合的时间和空间变化的后果。在这里，“混合”被定义为湍流和分子过程造成的盐度变化的不可逆损失。分析将解决这些基本问题：是交换流量控制的混合，反之亦然？在不同的河口区，混合和交换流如何响应潮汐振幅的变化？河口几何形状如何影响混合和交换流？如何应变河口和潮汐剪切在不同的制度，以及应变如何调制水平和垂直方差之间的交换，从而增强或抑制混合？这些问题的答案将导致一个预测框架的河口混合和交换流量的变化关系到河口的几何形状和占主导地位的强迫参数，河流流量和潮汐。

The variance of salinity is one of the most important quantities defining an estuary. Horizontal salinity variance provides the driving force for the gravitational circulation, and vertical variance quantifies stratification, which strongly affects and is affected by the shear, turbulence and mixing. The salinity variance balance has great promise as an approach to understanding the interaction of mixing and exchange flow in estuaries. This equation has been effectively exploited in the turbulence community to quantify mixing, but it has received surprisingly little attention in context with estuarine dynamics, in spite of its fundamental importance. This project will analyze the salinity variance balance in a variety of estuaries that span a broad swath of parameter space, using realistic and idealized numerical models. The insights gained from the analysis will provide a more systematic understanding of estuarine dynamics, using a common framework to compare rates and mechanisms across the estuarine parameter space. The analysis approach will also have application to exchange flows and mixing in the coastal and global ocean. This project will also support a graduate student at each of the two institutions and contribute to their training. The PIs also plan to teach a 5-week summer class for graduate students entitled "Estuarine Dynamics: Observations and Realistic Models." The class will involve 12-15 graduate students interested in estuarine processes. The students will gain hands-on field experience, and they will also apply and analyze realistic models, thereby developing a sense of the challenge and synergy that comes from bringing together observations and models.This project will develop the mathematical framework of the salinity variance to quantify the integral relationships between exchange flow and mixing, and then apply those relationships to diverse estuarine settings. In addition to these integral relationships, the analysis will examine the local exchange between horizontal and vertical variance via straining, and determine the consequences for temporal and spatial variations of stratification and mixing. Here "mixing" is defined as the irreversible loss of salinity variance by turbulent and molecular processes. The analysis will address these fundamental questions: Is exchange flow controlled by mixing, or vice versa? How do mixing and exchange flow respond to variations in tidal amplitude in different estuarine regimes? How does estuarine geometry affect mixing and exchange flow? How does straining by estuarine and tidal shear vary in different regimes, and how does straining modulate the exchange between horizontal and vertical variance and thereby enhance or suppress mixing? The answers to these questions will lead to a predictive framework for the variability of estuarine mixing and exchange flow in relation to the estuarine geometry and the dominant forcing parameters; river discharge and tides.