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。水平盐度方差为重力环流提供驱动力，垂直方差量化分层，分层强烈影响剪切、湍流和混合，也受到剪切、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。该方程已在湍流领域被有效地利用来量化混合，但令人惊讶的是，尽管它具有根本重要性，但在河口动力学方面却很少受到关注。该项目将使用现实和理想化的数值模型来分析跨越广泛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对河口动力学的更系统的理解，使用通用框架来比较河口参数空间的速率和机制。该分析方法还将应用于沿海和全球海洋的交换流和混合。该项目还将支持两个机构各一名研究生，并为其培训做出贡献。 PI 还计划为研究生开设为期 5 周的暑期课程，题为“河口动力学：观测和现实模型”。该课程将有 12-15 名对河口过程感兴趣的研究生参加。学生将获得实践现场经验，他们还将应用和分析现实模型，从而培养将观测结果和模型结合起来的挑战感和协同作用。该项目将开发盐度方差的数学框架，以量化交换流和混合之间的积分关系，然后将这些关系应用于不同的河口环境。除了这些积分关系之外，分析还将通过应变检查水平和垂直方差之间的局部交换，并确定分层和混合的时间和空间变化的后果。这里“混合”被定义为由湍流和分子过程导致的盐度变化的不可逆损失。该分析将解决以下基本问题：交换流量是由混合控制的，还是反之亦然？混合流和交换流如何响应不同河口状况下潮汐幅度的变化？河口几何形状如何影响混合和交换流？河口和潮汐切变造成的应变在不同情况下如何变化，应变如何调节水平和垂直方差之间的交换，从而增强或抑制混合？这些问题的答案将形成一个预测框架，用于预测与河口几何形状和主要强迫参数有关的河口混合和交换流的变化；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.