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

该项目将调查潮汐对受旋转影响的分层河口系统与沿海海洋交界面的潮下动量动力学和交换的影响。潮汐过程的突出挑战了环流和交换由重力环流主导的传统观点。重点指出了三种潮汐机制对剩余流产生的重要性和性质：(a)轴流垂直剪切和垂直涡动黏度之间的潮汐相关性，以及轴流垂直剪切引起的轴向密度梯度应变；(b)侧向剪切轴向潮汐流对轴向密度梯度差平流的影响；(c)由于侧向结构引起的轴向和侧向潮流相关性的侧向潮流整流。在每个机制的潮汐下轴向动量方程中出现的诊断术语将使用观测和数值模拟进行研究。该地点位于长岛海湾（LIS）东部，这是一个复杂的系统，但通常是宽而深的河口的代表。将利用一套广泛的存档观测资料，包括几年来每天8次的基于渡轮的声学多普勒电流剖面仪（ADCP）样条，系泊CTD剖面仪的水文剖面时间序列，以及过去~15年的全年两周/每月CTD调查。新的实地工作包括额外两年的渡轮采样，以及潮汐过程识别所需的小型拖曳起伏船/ADCP调查。这些调查将描绘三维空间结构和湍流、切变和分层的潮汐循环，因此填补了公认的需要，以促进对河口物理的理解。数值模拟强调实际强迫函数和湍流参数化和系数值的校准，以便捕获测量的速度切变、分层和湍流的总体观测特征（横向和垂直结构；潮汐周期的振幅和相位）。实际配置模型的面向过程运行将用于研究潮汐机制的作用。标量通量和输运路径将使用欧拉和拉格朗日分析方法与模型进行研究。对河口-海岸交换的理解可以应用于水质管理。研究结果将与研究地点的决策者相关，这是一个受到周围沿海人口严重影响的城市河口。现有的面向公众的教育展示，在客轮的乘客区作为一个新的观察平台，将与URI海洋项目办公室和环境与自然资源经济部门合作进行评估和重新设计。该展览提高了每年约30万名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发布在渡轮项目网站（www.gso.uri.edu/foster）上。一名URI本科生和一名康涅狄格大学的研究生将接受培训。结果将被纳入康涅狄格大学的本科和研究生海洋学课程。

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.