Collaborative Research: Investigating Tidal Influences on Subtidal Estuary-Coast Exchange Using Observations and Numerical Simulations

该项目将调查潮汐对潮下动量动力学的影响，以及在受旋转影响的分层河口系统与沿海海洋之间的界面上的交换。潮汐过程的重要性挑战了传统的观点，即环流和交换是由重力环流主导的。重点是辨别产生余流的三种潮汐机制的重要性和性质：(A)轴向流垂直切变和垂直涡旋粘性之间的潮汐关系，与垂直切变的轴向潮流引起的轴向密度梯度的应变有关；(B)落潮引起的潮汐平均次级环流；(C)轴向和侧向潮流相关的侧向结构造成的轴向密度梯度差平流的差异。将使用观测和数值模拟来研究出现在潮汐下轴向动量方程中的每种机制的诊断项。该遗址位于长岛海湾东部(LIS)，这是一个复杂的系统，但通常代表着宽广、深厚的河口。将利用一套广泛的存档观测，包括几年来每天8次的渡口声学多普勒海流剖面仪(ADCP)断面、系泊CTD剖面仪的水文投射时间序列，以及过去约15年的全年双周/每月CTD调查。新的实地工作包括额外两年的渡轮采样，以及识别潮汐过程所需的小型船舶拖曳波浪器/ADCP调查。这些调查将描述湍流、切变和层结的三维空间结构和潮汐循环，从而填补了增进对河口物理了解的公认需要。数值模拟强调真实的强迫函数和湍流参数和系数值的校准，以便捕捉测量的速度切变、层化和湍流的总体观测特征(横向和垂直结构；潮汐周期的幅度和相位)。实际配置的模型的面向过程的运行将用于研究潮汐机制的作用。模型将使用欧拉和拉格朗日分析方法来研究标量通量和输送路径。了解河口海岸交换在水质管理中的应用。研究结果将与研究地点的决策者相关，该地点是一个城市河口，受到周围沿海人口的严重影响。作为新观察平台的渡轮客运区现有的面向公众的教育展示，将与URI海洋项目办公室和部门合作进行评估和重新设计。环境与自然资源经济学。这次展览提高了每年约30万渡轮乘客对河口物理海洋学及其与水质的联系的认识。另外两年的速度和水文网格数据产品将张贴在渡轮项目网站(www.gso.uri.edu/foster)上。一名URI本科生和一名康涅狄格大学研究生将接受培训。结果将被纳入康涅狄格大学本科生和研究生的海洋学课程。

The project will investigate tidal influences on sub-tidal momentum dynamics and exchange at the interface between a rotation-influenced, stratified estuarine system and the coastal ocean. Prominence of tidal processes challenges the conventional view that circulation and exchange are dominated by gravitational circulation. Emphasis is on discerning the importance and nature of three tidal mechanisms for residual flow generation: (a) tidal correlations between axial current vertical shear and vertical eddy viscosity, associated with strain of the axial density gradient by vertically sheared axial tidal currents; (b) tidal-mean secondary circulation from ebb-flood differences in differential advection of the axial density gradient by laterally sheared axial tidal flow; and (c) lateral tidal rectification due to lateral structure in correlations between axial and lateral tidal currents. Diagnostic terms that appear in the sub-tidal axial momentum equation for each mechanism will be investigated using observations and numerical simulations. The site is eastern Long Island Sound (LIS), a complex system, but one that is generally representative of wide, deep estuaries. An extensive suite of archived observations will be exploited, including several years of 8-times daily ferry-based acoustic Doppler current profiler (ADCP) transects, time series of hydrographic casts from moored CTD profilers, and year-round biweekly/monthly CTD surveys over the past ~15 years. New fieldwork includes two additional years of ferry sampling, and small vessel towed-undulator/ADCP surveys needed for tidal process identification. The surveys will characterize the three-dimensional spatial structure and tidal cycles of turbulence, shear, and stratification, so filling a recognized need to advance understanding of estuarine physics. Numerical modeling emphasizes realistic forcing functions and calibration of turbulence parameterization and coefficient values such that gross observed features (lateral and vertical structure; amplitudes and phases of tidal cycles) of measured velocity shear, stratification, and turbulence are captured. Process-oriented runs of the realistically configured model will be used to investigate the roles of tidal mechanisms. Scalar fluxes and transport pathways will be investigated with the model using both Eulerian and Lagrangian analysis methods. Understanding of estuary-coast exchange has applications to water quality management. Findings will be relevant to decision makers at the study site, an urban estuary heavily impacted by surrounding coastal populations. An existing public-oriented educational display, in the passenger area of the ferry serving as one platform for new observations, will be assessed and redesigned by collaboration with URI Office of Marine Programs and Dept. of Environmental and Natural Resource Economics. The display raises awareness of estuarine physical oceanography, and its connection to water quality, among ~300,000 ferry riders per year. Two additional years of velocity and hydrographical grid data products will be posted at the ferry project website (www.gso.uri.edu/foster). A URI undergraduate and a University of Connecticut graduate student will be trained. Results will be incorporated in University of Connecticut oceanography courses for undergraduate and graduate classes.