Internal Tide and Waves on the Oregon Continental Shelf

本研究项目的目的是提高我们对大陆架上海洋内潮的产生、传播和消散的认识。内潮是正压潮汐迫使分层的海洋超过水深起伏时产生的内波。穿过大陆架向海岸传播的内潮可能会变得非常复杂，通常会发展成非线性内波。内潮是世界各地大陆架变化的主要来源，也可能是产生混合标量和动量的湍流的重要能量来源。重要的是要确定内潮在能量和动量收支中所起的作用，以便更好地理解和模拟沿海海洋环流。同样重要的是要知道内潮对导致物质跨陆架运输的过程的贡献，这些物质包括营养物质、幼虫和沉积物。该项目的具体科学目标是：描述大陆架上潮汐频率附近内响应的幅度、能量通量和垂直结构，描述非线性内潮在大陆架上传播时的垂直结构和传播特征，量化大陆架上的内波背景频率连续体，并评估内潮对生物群和沉积物跨陆架运输的潜在影响，以及当前海岸环流数值模式中使用的混合参数。实现这些目标的方法是分析在1999年夏季、2001年夏季和2003年冬季进行的三次综合实验期间在俄勒冈海岸进行的大量观测。此前资助的分析主要集中在低频风强迫环流上。这个项目关注的是内潮和更高的频率。内潮的二维原始方程数值模式将被用作指导分析的工具。该模型的目的是帮助我们了解与观测结果相一致的基本物理平衡。更广泛的影响：内部潮汐有助于能量的耗散和混合，然而，潮汐通常不明确地包括在环流模型中。研究，如这里提出的，将有助于确定内部潮汐的潜在重要性，最终导致将潮汐直接纳入模型，或修改用于混合的现有参数。非线性内波包在传输生物群，如幼虫、岸上和近海沉积物方面可能很重要。这项研究将对这些过程提供一些见解，包括关于它们的空间和时间变异性的信息。人们对了解跨陆架运输对俄勒冈州陆架和海岸的生物过程和生态的影响很感兴趣。这里开发的数据分析方法和数值模型将直接用于由Levine开设的关于2006-07学年俄勒冈州立大学内部潮流的课程的研究生教育。这门课将由攻读海洋学博士学位的研究生学习。学生们将通过运行模型并亲自分析观测结果来了解内潮。

The goal of this research project is to improve our understanding of the generation, propagation and dissipation of the oceanic internal tide on the continental shelf. The internal tide is an internal wave generated when the stratified ocean is forced over bathymetric relief by the barotropic tide. The internal tide that propagates across the shelf toward the shore can become quite complex and often develops into packets of nonlinear internal waves. The internal tide is a major source of variability on continental shelves around the world and is potentially an important source of energy for generating the turbulence responsible for mixing scalars and momentum. It is important to determine the role the internal tide plays in the energy and momentum budgets to better understand and model coastal ocean circulation. It is also important to know the contribution of the internal tide to processes that lead to cross-shelf transport of mass, which includes nutrients, larvae, and sediment. The specific scientific objectives of this project are to: characterize the amplitude, energy flux, and vertical structure of the internal response near tidal frequencies on the shelf, describe the vertical structure and propagation characteristics of the nonlinear internal tide as it propagates across the shelf, quantify the internal wave background frequency continuum on the shelf, and assess the potential impact of the internal tide on cross-shelf transport of biota and sediment and parameterizations of mixing used in current numerical models of coastal circulation. The approach to accomplish these objectives is to analyze the wealth of observations made off the Oregon coast during three comprehensive experiments in summer 1999, summer 2001 and winter 2003. Previously funded analysis focused on the low-frequency wind-forced circulation. This project focuses on the internal tide and higher frequencies. A two-dimensional primitive equation numerical model of the internal tide will be used as a tool to guide the analysis. The purpose of the model is to help us understand the basic physical balances that are consistent with the observations.Broader Impacts: The internal tide contributes to the dissipation of energy and mixing, however, the tide is typically not explicitly included in circulation models. Research, such as that proposed here, will help determine the potential importance of internal tide, eventually leading to direct inclusion of the tide into models, or modification of the existing parameterization used for mixing. Nonlinear internal wave packets may be important in transporting biota, such as larvae, onshore, and sediment offshore. This study will provide some insight into these processes, including information on their spatial and temporal variability. There is much interest in understanding the impacts of cross-shelf transport on biological processes and the ecology of the Oregon shelf and coast. The data analysis methods and the numerical model developed here will be used directly in the education of graduate students in a class being offered by Levine on the internal tide at Oregon State University during the 2006-07 academic year. This class will be taken by graduate students pursuing PhDs in oceanography. The students will learn about the internal tide by running the model and analyzing observations for themselves.