Collaborative Proposal: Impact of secondary circulation and mixing of estuarine exchange flows.

智力价值：这项研究是首次提出的现场工作，以量化次级环流在驱动河口交换流动中的作用。虽然最近在有限河口参数空间的数值研究表明，侧向平流是潮下沿航道动量平衡的先导阶项，但这一点尚未得到观测证实。对这一模型结果的观测检验对河口海洋学领域至关重要，因为它提出了一个关于经典河口环流理论有效性的根本问题。数值结果和尺度结果表明，横向平流的影响几乎总是被内应力平衡的，因此，基于纵向压力梯度和底应力之间的动量平衡的简单理论可以提供对河口残余速度的准确预测。中心假设是，二次流与界面应力之间的接近抵消是二次环流引起的平流加速与小尺度湍流引起的扩散动量传递之间可能存在相互作用或反馈的表现。该项目将研究大潮周期中侧向平流和界面应力之间的协变性，并评估它们在河口交换流动中的作用。我们计划在詹姆斯河河口进行一系列现场试验，并辅之以ROMS(区域海洋模拟系统)和LES(大涡模拟)模拟。实地工作包括系泊和船上观察，以及染料释放实验和微观结构分析。ROMS模拟将重点研究二次环流对该宽阔河口河口交换流动的影响，而大涡模拟将研究二次流与小尺度湍流之间的相互作用和可能的耦合。这项研究的结果将为次级环流在河口环流中的作用提供一个明确的答案。更广泛的影响：河口扩散在很大程度上是由交换流量驱动的，预测扩散的能力在许多应用问题中是至关重要的，例如确定河口系统允许的最大日总负荷(TMDL)。更广泛地说，该项目将提供关于河口环流和混合过程的迫切需要的信息，并有助于开发模拟河口流动的最先进的数值模型，这是预测水质、污染物和鱼苗迁移所必需的。对于詹姆斯河的实地考察，我们将邀请来自河口附近地区的高中教师和学生参与。通过佛罗里达大学一名研究人员的参与，该项目加强了少数群体对科学的参与。该项目还将为三名研究生和本科生实习生提供培训。

Intellectual Merit: This study is the first proposed field effort to quantify the role of secondary circulation in driving the estuarine exchange flow. Although recent numerical studies in a limited estuarine parameter space suggest that the lateral advection is a leading-order term in the subtidal along-channel momentum balance, it has not been confirmed by observations. Observational test of this model result is critical to the field of estuarine oceanography because it raises a fundamental question regarding the validity of the classic theory of estuarine circulation. Numerical and scaling results have suggested that the effects of lateral advection are nearly always balanced by internal stresses so that a simple theory based on the momentum balance between longitudinal pressure gradient and bottom stress provides an accurate prediction for the estuarine residual velocity. The central hypothesis is that the near cancellation between secondary flows and interfacial stress is a manifestation for a possible interaction or feedback between the advective accelerations due to secondary circulation and diffusive momentum transfer due to small-scale turbulent flows. This project will investigate the co-variability between the lateral advection and interfacial stress over the spring-neap tidal cycle and assess their roles in the estuarine exchange flow. We plan to conduct a series of field experiments in the James River estuary, complemented by ROMS (Regional Ocean Modeling System) and LES (Large Eddy Simulations) modeling simulations. Field efforts include moored and shipboard observations as well as dye-release experiments and microstructure profiling. ROMS modeling will focus on the effects of secondary circulation on the estuarine exchange flows in this wide estuary, while LES modeling will examine the interactions and possible coupling between secondary flows and small scale turbulent flows. Results obtained from this project will provide a definitive answer on the role of secondary circulation in estuarine circulation. Broader Impacts: Estuarine dispersion is largely driven by the exchange flow and the ability to predict dispersion is critical in many applied problems such as determining the Maximum Total Daily Load (TMDL) permissible to an estuarine system. More generally, this project will yield much-needed information regarding the circulation and mixing processes in estuaries and help develop state-of-the-art numerical models for simulating estuarine flows, which are required for predicting water quality, contaminant and fish larvae transport. For the field work in the James River, we will involve participation of high school teachers and students from the areas near the estuary. Through the participation of one of the investigator at the University of Florida, this project enhances the involvement of minority groups in science. This project will also provide training to three graduate students and undergraduate interns.