Along-shelf Transport and Cross-shelf Exchange Driven by Surface Waves on the Inner Continental Shelf

内部大陆架之间的交换影响着营养物、有害藻华、污染物、幼虫和沉积物的分布。目前还不完全清楚表面波是如何影响这种交换的。波浪-流相互作用的数值模拟近年来取得了一些进展，但到目前为止，这些模拟研究主要集中在冲浪区。本研究将通过在实验室和实地观测的背景下测试模型结果，将这些建模能力扩展到内大陆架。这项研究将推动波流耦合建模系统的进一步发展，该系统可免费提供给科学界。在这次调查中获得的对波流相互作用过程的洞察将改善实际泥沙输运应用中使用的现实模型的发展。大多数关于大陆架内部环流的研究都集中在风应力的作用上。直到最近，人们才认识到表面波是内大陆架上的一个重要强迫机制。目前对波浪驱动的大陆架内部环流的理解是基于具有限制性假设的分析模型，例如整个水柱的恒定湍流混合，以及大陆架之间没有空间变化。本研究中的模型实验将考虑到湍流混合的更真实的表现，并将包括分层、倾斜的底部和来自冲浪区的动量平流的影响，在那里，破碎波产生强大的沿大陆架流。以前的研究很少量化动量平流对内大陆架的重要性，但它在靠近冲浪带边界的地方具有潜在的重要性，也将在观测中进行评估。在模型实验的基础上，将对不同环境条件下假设机制的相对重要性进行衡量，使结果可以在许多地点普遍应用。本研究的目的是确定由位于破碎海浪近海的内大陆架表面波驱动的观测到的环流空间结构的关键过程。先前的观测已经确定了与内大陆架上的表面波有关的表面强化的近海流动。在与海岸平行的方向上，新的观测分析表明，波浪强迫的复杂响应随水深的变化而变化。为了解释这些观测结果，人们提出了两种不同的假设：一种假设认为地球自转是必要的，另一种假设认为强烈的湍流混合和来自冲浪带的动量传输。在不同的强迫和环境条件下，将进行复杂物理但理想几何的数值模拟实验，以确定这两种机制对观测到的波浪驱动环流的相对贡献。本文将根据现场和实验室观测结果，对一种新的关于海底附近“波流”临界过程的参数化方法进行检验。模式实验，结合对现有观测的新分析，将确定在风和波的联合强迫下，在冲浪区和内大陆架之间产生交换的过程。

Exchange across the inner shelf influences the distribution of nutrients, harmful algal blooms, pollutants, larvae and sediment. It is not yet fully understood how surface waves influence this exchange. Recent advances have been made in the numerical modeling of wave-current interactions, but so far these modeling studies have focused on the surf zone. This study will extend these modeling capabilities to the inner shelf by testing model results in the context of laboratory and field observations. This research will drive further development of wave-current coupling in a modeling system that is freely available to the scientific community. The insight into wave-current interaction processes gained during this investigation will improve the development of realistic models used in practical sediment transport applications. Most studies of inner-shelf circulation have focused on the role of wind stress. Surface waves have only recently been recognized as an important forcing mechanism over the inner shelf. Present understanding of the wave-driven inner-shelf circulation is based on analytical models with restrictive assumptions, such as constant turbulent mixing throughout the water column, and no spatial variations across the shelf. The model experiments in this study will allow for more realistic representations of turbulent mixing, and will include the effects of stratification, a sloping bottom and advection of momentum from the surf zone, where breaking waves generate strong along-shelf currents. Few previous studies have quantified the importance of momentum advection on the inner shelf, but it is potentially important near the boundary of the surf zone and will also be assessed in observations. Based on the model experiments, the relative importance of the hypothesized mechanisms under different environmental conditions will be scaled so that results can be applied generally at many locations. The goal of this study is to identify the key processes that determine the observed spatial structure of the circulation driven by surface waves on the inner shelf, which is located offshore of the breaking surf. Previous observations have identified a surface-intensified offshore flow associated with surface waves over the inner shelf. In the direction parallel to shore, new observational analysis shows a complex response to wave forcing that varies with water depth. Two alternative hypotheses are formulated to account for these observations: one in which the Earth's rotation is necessary, and another that involves strong turbulent mixing and transport of momentum from the surf zone. Numerical modeling experiments, with complex physics but idealized geometry, will be carried out to determine the relative contribution of these two mechanisms to the observed wave-driven circulation during different forcing and environmental conditions. A new parameterization for the critical process of "wave streaming" near the bottom will be tested against field and laboratory observations. Model experiments, in combination with new analysis of existing observations, will identify processes that generate exchange between the surf zone and inner shelf during combined wind and wave forcing.