Dispersion and Mixing Caused By Near-Inertial Internal Waves in Lake Michigan

近惯性内波是海洋和大型湖泊中普遍存在的特征。在沿海海洋中，近惯性内波通常以水平传播的垂直模式存在，但它们的存在和重要性通常被更有活力的内潮所掩盖。然而，在大型湖泊中，分层的海岸环境主要是模态近惯性波，因为没有高能潮汐。因此，在大型湖泊中研究这些特征是有动机的，因为湖泊环境提供了一个独特的实验室，人们可以在没有其他能量过程干扰的情况下研究惯性内波。此外，在大型湖泊中，惯性内波对海岸混合和色散具有一级重要性，因为没有其他机制，分层作用很强。智力优势：该项目基于一个假设，即近惯性内波在密歇根湖和其他五大湖在严重分层、弱强迫夏季期间的垂直混合和水平弥散中起重要作用。许多大湖环流和扩散研究在惯性周期或更小的时间尺度上过滤掉了过程，并且进一步假设这种过滤可以对热、生物群和污染物的垂直混合和水平扩散的推断产生重要影响。这项研究的目的是双重的。首先，该项目将量化分层期间沿海密歇根湖的垂直混合，以确定基线湍流混合的强度和由偶发性近惯性波引起的跨温跃层混合的强度；将测试这些波浪的新开发的海洋混合参数化。其次，该项目将通过染料释放研究和静态和惯性波主导条件下的数值模拟直接测量水平色散，以明确解决近惯性波在所谓的高水平色散中的作用。将进行两类实验。在第一组以垂直混合为目标的实验中，预定的微观结构测量将补充固定系泊的速度和温度，以确定湍流耗散的垂直和跨大陆架变异性及其与可解析内波参数的关系。在惯性波事件期间的幕式微观结构测量将试图量化这种湍流在惯性波周期中的可变性。在第二类实验中，以水平色散为目标，在惯性波事件期间在分层水中进行染料释放实验。染料分散将由普渡大学的自主水下航行器（AUV）进行量化，该航行器将由船只支持。额外的色散工作将使用经过验证的密歇根湖高分辨率数值模型进行，并基于沿海环境中近惯性波的理想化表示进行分析。更广泛的影响：这个项目的更广泛的影响集中在与国家公园管理局的印第安纳沙丘国家湖岸的合作上。普渡大学的自主水下航行器是一种天然的、经过验证的推广工具，将用于与国家公园管理局组织的一系列基于海滩的推广活动，包括演示和教育研讨会。教育工作者讲习班将重点培训K-12教育工作者如何将大湖湖沼学的要素纳入其中，以激励未来的科学家。此外，研究者通过普渡大学夏季本科生研究奖学金（SURF）项目指导本科生研究人员，该项目将支持几名本科生研究人员。最后，该项目将成为研究生博士论文的基础，并支持早期职业教师。

Near-inertial internal waves are ubiquitous features in the ocean and large lakes. In the coastal ocean, near-inertial internal waves often exist as horizontally-propagating vertical modes, but their presence and importance is usually overshadowed by more energetic internal tides. However, in large lakes, the stratified coastal environment is dominated by modal near-inertial waves because energetic tides are absent. The study of these features in large lakes is therefore motivated because the lake setting provides a unique laboratory in which one can study inertial internal waves without interference from other energetic processes. Additionally, in large lakes, inertial internal waves are of first order importance for coastal mixing and dispersion because other mechanisms are absent and stratification is strong.Intellectual Merit: This project is based on the hypothesis that near-inertial internal waves play a significant role in vertical mixing and horizontal dispersion in Lake Michigan and other Great Lakes during the heavily stratified, weakly-forced summer period. Many Great Lakes circulation and dispersion studies filter out processes on timescales of inertial period or smaller, and it is further hypothesized that this filtering can have important consequences for inferences drawn about vertical mixing and horizontal dispersion of heat, biota, and pollutants. The objectives of this study are twofold. First, the project will quantify vertical mixing in coastal Lake Michigan during the stratified period, in order to determine the magnitudes of baseline turbulent mixing and the magnitudes of cross-thermocline mixing caused by episodic near-inertial waves; newly-developed oceanic mixing parameterizations for these waves will be tested. Secondly, the project will directly measure horizontal dispersion with dye release studies and numerical modeling for both quiescent and inertial-wave dominated conditions to explicitly resolve the role of near-inertial waves in supposedly heightened horizontal dispersion.Two types of experiments will be conducted. In the first set of experiments, which target vertical mixing, scheduled microstructure measurements will complement fixed moorings of velocity and temperature to determine the vertical and cross-shelf variability of turbulent dissipation and its relationship to resolvable internal wave parameters. Episodic microstructure measurements during inertial wave events will attempt to quantify the variability of this turbulence over the inertial wave cycle. In the second type of experiment, which targets horizontal dispersion, dye release experiments will be performed in stratified waters during inertial wave events. The dye dispersion will be quantified by Purdue's autonomous underwater vehicle (AUV), which will be vessel-supported. Additional dispersion work will be performed using a validated, high-resolution numerical model of Lake Michigan and analysis based on idealized representations of near-inertial waves in the coastal environment.Broader Impacts: The broader impacts of this project are centered on collaboration with the National Parks Service's Indiana Dunes National Lakeshore. Purdue's autonomous underwater vehicle is a natural, proven outreach tool that will be utilized in a set of beach-based outreach activities organized with the National Parks Service, including demonstrations and an educator workshop. The educator workshop will focus on training K-12 educators on how to incorporate elements of Great Lakes limnology to inspire future scientists. Additionally, the investigator has an established record of mentoring undergraduate researchers through the Purdue Summer Undergraduate Research Fellowship (SURF) program, and this project will support several undergraduate researchers. Finally, the project will form the basis of a graduate student's Ph.D. dissertation, and support an early-career faculty member.