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

智力价值：本研究首次提出了量化二次循环在推动河口交换流中的作用的实地努力。虽然最近在有限河口参数空间内的数值研究表明，横向平流是潮下沿河道动量平衡的一阶项，但尚未得到观测证实。这一模式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河口环流经典理论有效性的根本性问题。数值和标度结果表明，横向平流的影响几乎总是被内应力平衡，因此基于纵向压力梯度和底部应力之间动量平衡的简单理论可以准确地预测河口残余速度。中心假设是，二次流和界面应力之间的近似抵消是二次循环引起的平流加速度和小规模湍流引起的扩散动量传递之间可能相互作用或反馈的表现。本项目将研究大潮-小潮潮循环中横向平流和界面应力的共变性，并评估它们在河口交换流中的作用。我们计划在詹姆斯河河口进行一系列野外实验，并辅以区域海洋模拟系统（ROMS）和大涡模拟系统（LES）模拟。现场工作包括系泊和船上观察，染料释放实验和微观结构分析。ROMS模拟将重点关注二次环流对河口交换流的影响，而LES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。该项目的研究结果将为二次循环在河口循环中的作用提供一个明确的答案。更广泛的影响：河口色散主要由交换流驱动，预测色散的能力在许多应用问题中至关重要，例如确定河口系统允许的最大每日总负荷（TMDL）。更一般地说，该项目将提供关于河口循环和混合过程的急需信息，并有助于开发最先进的模拟河口流量的数值模型，这是预测水质、污染物和鱼苗运输所必需的。在詹姆斯河的实地考察中，我们将邀请河口附近地区的高中教师和学生参加。通过佛罗里达大学一位研究者的参与，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.