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Generation Mechanisms of Nonlinear Internal Waves in Coastal Plain Estuaries

滨海平原河口非线性内波的产生机制

基本信息

批准号：
1756155
负责人：
Ming Li
金额：
$ 34.11万
依托单位：
University of Maryland Center for Environmental Sciences
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-04-15 至 2023-03-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1756155&HistoricalAwards=false
关键词：
Generation Mechanisms Nonlinear Internal Waves

项目摘要

This research aims at significantly advancing our understanding of estuarine mixing processes and improving the predictions of water-quality and biogeochemical cycling in estuaries. Numerical models used in predicting environmental conditions in estuaries often have difficulties in reproducing stratification affecting our ability to accurately predict various biogeochemical processes, including bottom water hypoxia. This may be related to the lack of proper parameterizations for wave-induced mixing in the pycnocline. Nonlinear internal waves are ubiquitous in the stratified coastal ocean and play an important role in generating turbulent mixing and transporting biochemically important materials. However, nonlinear internal waves have been rarely studied in stratified estuaries, except for flows over sills at the entrance to deep fjords. Turbulence and mixing in estuaries has been mainly attributed to bottom boundary layer turbulence whereas little attention has been paid to breaking internal waves. This project will re-analyze experimental data and use numerical models to examine the role of internal waves in estuarine mixing. It will provide educational opportunities for one Ph.D. graduate student who will be trained in numerical ocean modeling, and advanced data analysis techniques. In addition, undergraduate students will be involved in this project during the summer months.Tidal currents in coastal plain estuaries primarily move in the along isobath direction and are thought to be no-conducive to internal wave generation. On the other hand, most coastal plain estuaries feature a deep channel flanked by shallow shoals, with steep bathymetric changes in the cross-channel direction. Moreover, lateral circulation has been observed in many estuaries. It is hypothesized that when the internal Froude number exceeds 1, the interaction between the lateral circulation and channel-shoal bathymetry leads to the generation of an internal lee wave. The latter evolves into a train of nonlinear internal waves through nonlinear steepening and dispersion. It is also hypothesized that under strong tidal or wind forcing conditions the lateral circulation generates frontogenesis and a bottom gravity current which excites upstream propagating nonlinear internal waves. These hypotheses are based on the recent observations of internal lee waves and internal solitary waves in Chesapeake Bay and will be tested using process-oriented and realistic modeling. The previously collected mooring data will be re-analyzed to better quantify the relationship between nonlinear internal waves and estuarine turbulent mixing. A realistic 3-D hydrostatic model of Chesapeake Bay will be run to conduct hindcast simulations and interpret the observational data. The generation, propagation and transformation of internal waves in estuaries will be investigated using hydrostatic and non-hydrostatic models configured over an idealized estuarine channel. The wave generation mechanisms will be explored under a wide range of river flow, tidal and wind forcing conditions. These model runs will be complemented by data analysis to identify the connection between nonlinear internal waves and mixing in the estuary.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

本研究旨在显著提高我们对河口混合过程的理解，并改善河口水质和水地球化学循环的预测。用于预测河口环境条件的数值模型往往难以再现分层，影响我们准确预测各种海洋地球化学过程的能力，包括底层水缺氧。这可能与缺乏适当的参数化波诱导的混合密度跃层。非线性内波在近岸分层海洋中普遍存在，在产生湍流混合和输送重要的生物化学物质方面起着重要作用。然而，在分层河口，除了在深峡湾的入口处的窗台流的非线性内波很少被研究。河口的湍流和混合主要归因于底部边界层湍流，而很少注意到破碎的内波。这个项目将重新分析实验数据，并使用数值模型来研究内波在河口混合中的作用。它将为一个博士提供教育机会。研究生谁将在数值海洋建模和先进的数据分析技术的培训。此外，本科生将在夏季参与该项目。沿海平原河口的潮流主要沿等深线方向运动，被认为不利于内波的产生。另一方面，大多数沿海平原河口的特点是两侧是浅浅滩的深水道，在跨水道方向上水深变化很大。此外，在许多河口还观察到了侧向环流。据推测，当内部弗劳德数超过1，横向环流和渠道浅滩水深之间的相互作用，导致内部背风波的产生。后者通过非线性变陡和色散演化成一列非线性内波。它还假设，在强潮汐或风强迫条件下的横向环流产生锋生和底部重力流，激发上游传播的非线性内波。这些假设是基于最近在切萨皮克湾的内部背风波和内部孤立波的观测，并将使用面向过程的和现实的建模进行测试。将重新分析先前收集的系泊数据，以更好地量化非线性内波和河口湍流混合之间的关系。将运行一个切萨皮克湾的现实三维流体静力学模型，以进行后报模拟和解释观测数据。本研究将利用理想化河口水道之流体静力学及非流体静力学模式，探讨河口内波之产生、传播及转换。波浪生成机制将在广泛的河流流量，潮汐和风强迫条件下进行探索。这些模型运行将通过数据分析来补充，以确定非线性内波和河口混合之间的联系。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。