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

该项目的目的是利用盐度的变化增进我们对河口物理过程的理解。盐度是定义河口的重要参数之一，盐度在水平方向上的变化为重力环流提供了动力。盐度的垂直变化量化了层化，层化强烈地影响着切变、湍流和混合，并受其影响。盐度方差平衡方程在湍流界被有效地用来量化混合，但令人惊讶的是，在河口动力方面，它几乎没有受到关注，尽管它具有基本的重要性。该项目将使用现实的和理想化的数值模式分析各种河口的盐度差异平衡。从分析中获得的见解将提供对河口动态的更系统的了解，使用一个共同的框架来比较整个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中的交换流动和混合。该项目还将支持这两个机构各有一名研究生，并对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：观察和现实模型”。这门课将包括12-15名对河口过程感兴趣的研究生。学生将获得现场实践经验，他们还将应用和分析现实的模型，从而培养一种将观察和模型结合在一起的挑战和协同性。该项目将建立盐度变化的数学框架，以量化交换流量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。除了这些整体关系外，该分析还将审查通过应变在水平和垂直变化之间的局部交换，并确定层结和混合的时间和空间变化的后果。这里的“混合”被定义为由湍流和分子过程造成的盐度变化的不可逆转的损失。分析将解决这些基本问题：交换流量是由混合控制的，还是相反？混合流和交换流如何对不同河口区域潮汐振幅的变化作出反应？河口几何形状如何影响混合和交换流动？河口应变和潮汐切变如何在不同的区域变化，以及应变如何调节水平和垂直变化之间的交换，从而增强或抑制混合？对这些问题的回答将导致一个关于河口混合和交换流量与河口几何形状和主要强迫参数；河流流量和潮汐有关的可变性的预测框架。

This project aims at advancing our understanding of the physical processes operating in estuaries using the variance of salinity. Salinity is one of the most important quantities defining an estuary and its variance in the horizontal variance provides the driving force for the gravitational circulation. Vertical variance of salinity quantifies stratification, which strongly affects and is affected by the shear, turbulence and mixing. The salinity variance balance equation has been effectively exploited in the turbulence community to quantify mixing, but it has received surprisingly little attention in context with estuarine dynamics, despite its fundamental importance. This project will analyze the salinity variance balance in a variety of estuaries 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.