Upper Ocean Turbulence in Non-Equilibrium Conditions

海洋表面附近的湍流过程通过将海洋与大气耦合，并通过分配营养物质、污染物、浮游生物和气泡，在天气和气候系统中发挥关键作用。风和海浪通常通过复杂的相互作用驱动这种湍流。我们目前对这些动力学的概念和理论框架是基于一个平衡假设，在这个假设中，波浪和湍流与风的强迫处于平衡状态。然而，最近的调查强调，典型的海洋条件很少处于平衡状态，而是以膨胀和在频率和方向上变化的风浪为特征。这项研究将综合最近的观测、理论和计算进展，系统地评估非平衡条件对海洋表面附近湍流以及与大气的动量和热量交换的影响。改善海气相互作用和海洋湍流的表现，将推进天气和气候的海洋-大气耦合模式。预测海洋污染物分布以及季节波动和长期气候变化的能力具有重要的环境、社会和经济影响。在这项研究中发展的知识将被纳入特拉华大学的课程。该项目将独特地促进学生在与海洋学计算和观测专家合作的环境中进行培训。PI将参加公众宣传活动，例如每年的海岸日，这是由特拉华大学地球，海洋和环境学院赞助的公众开放日。这一场合为科学家提供了一个机会，让公众了解影响环境的科学问题，并使所有年龄段的儿童都能接触到科学和工程领域的职业。通过批判性地评估传统的平衡假设，所提出的研究有望推进我们对海洋表面边界层动力学的基本概念理解。具体而言，本研究将验证以下假设：(1)OSBL的演变取决于复杂的非平衡海况，因此对于相同的表面通量，OSBL动力学变化显著。(2)基于波浪平均Navier-Stokes方程的湍流分辨模型准确地捕捉了观测到的随海况变化的湍流OSBL。(3)破碎波和Langmuir环流（LC）效应的相对重要性取决于海况和OSBL条件，如OSBL深度。(4)通过明确地包括波效应来扩展现有的行星边界层理论和概念框架，将为现实的osbl提供更物理的描述。这些假设将与伍兹霍尔海洋研究所合作，通过分析最近在沿海和开放海洋进行的实地实验的观察结果来解决。这些罕见的数据集包括对波浪、表面通量和上层海洋结构的同时测量，包括对LC特征的独特观测。观测结果将与基于波浪平均Navier-Stokes方程的大涡模拟（LES）结果进行比较。LES模型可以解决湍流问题，同时捕获LC波和破碎波。根据与国家大气研究中心合作的考虑海况影响的风波耦合理论的最新进展，模型的破碎波输入将得到加强。研究人员将与莱布尼茨波罗的海研究所合作，评估区域和全球海洋模型中常用的OSBL湍流模型。对OSBL观测和基于过程的LES的综合分析将为开发新颖、准确的基于物理的OSBL模型提供所需的见解。因此，该研究将有助于改进下一代海洋模式，并增强我们对海洋-大气耦合系统的认识。

Turbulent processes near the surface of the ocean play a key role in weather and climate systems by coupling the ocean with the atmosphere and by distributing nutrients, pollutants, plankton, and bubbles. Wind and waves drive this turbulence, often through complex interactions. Our current conceptual and theoretical framework of these dynamics is based on an equilibrium assumption, in which waves and turbulence are in equilibrium with the wind forcing. However, recent investigations highlight that typical ocean conditions are rarely in equilibrium, but rather are characterized by swell and variable wind waves in terms of frequencies and directions. This study will integrate recent observational, theoretical, and computational progress to systematically assess the influence of non-equilibrium conditions on turbulence near the ocean surface and on the exchange of momentum and heat with the atmosphere. Improving the representation of air-sea interaction and ocean turbulence, will advance coupled ocean-atmosphere models of weather and climate. The ability to predict the distribution of ocean pollutants as well as seasonal fluctuations and secular climate change has important environmental, societal, and economical impacts. The knowledge developed in this study will be incorporated into courses at the University of Delaware. The project will uniquely foster training of students in a collaborative environment with computational and observational experts in oceanography. The PI will participate in public outreach events, such as the annual Coast Day, an open house day for the general public sponsored by the University of Delaware's College of Earth, Ocean and Environment. This occasion provides an opportunity for scientists to inform the general public of the scientific issues that influence the environment and to expose children of all ages to careers in the sciences and engineering.By critically evaluating traditional equilibrium assumptions, the proposed research promises to advance our basic conceptual understanding of ocean surface boundary layer (OSBL) dynamics. Specifically, the study will test the following hypotheses: (1) The evolution of the OSBL depends on complex, non-equilibrium sea states, so that for the same surface fluxes OSBL dynamics vary significantly. (2) A turbulence-resolving model based on the wave-averaged Navier-Stokes equations accurately captures the observed sea state dependent evolution of the turbulent OSBL. (3) The relative importance of breaking wave and Langmuir circulation (LC) effects depends on sea state and OSBL conditions, such as OSBL depth. (4) Extending the existing theoretical and conceptual framework of planetary boundary layers by including wave effects explicitly will provide a more physical description of realistic OSBLs. These hypotheses will be addressed by analyzing observations from recent field experiments in the coastal and open ocean in collaboration with the Woods Hole Oceanographic Institution. Those rare data sets include collocated measurements of waves, surface fluxes, and upper ocean structure, including unique observations of LC characteristics. Observations will be compared to large-eddy simulation (LES) results based on the wave-averaged Navier-Stokes equations. The LES model resolves turbulence and captures both LC and breaking waves. The breaking wave input to the model will be enhanced based on recent progress on wind-wave coupling theory that takes sea state effects into account in collaboration with the National Center for Atmospheric Research. In collaboration with the Leibniz Institute for Baltic Sea Research, the researchers will evaluate common OSBL turbulence models employed in regional and global ocean models. The combined analyses of OSBL observations and process-based LES will provide the needed insights for developing novel, accurate physics-based OSBL models. Thus, the research will contribute to improving the next-generation ocean models and to enhancing our understanding of the coupled ocean-atmosphere system.