Wave effects in upper ocean turbulence models

风是海洋上层的主要驱动力。海洋表层湍流混合的结构和强度在陡风浪的存在下变化很大，现有的数值模型在预测方面并不总是非常准确。本研究旨在提高上层海洋混合数值模型中表面波效应的代表性，并扩大验证这些模型对混合层湍流测量的经验基础。将分析在上层海洋的良好混合层上下移动的自由漂移仪器的现有数据，以获得关于在各种波浪条件下湍流垂直结构的新信息。将使用在极高分辨率数值模式中模拟的虚拟漂移物来开发新的分析方法，并增强有限的观测数据集。这项研究将有助于通过扩大和完善模型数据比较的指标来比较波湍流相互作用的竞争理论。 对波浪-湍流相互作用的深入了解将导致新的混合参数化，这些参数化可以通过小尺度湍流测量进行验证，并最终提高海洋环流模型的技能。漂流物测量结果和模型代码的传播也将有利于确定波浪影响参数的其他方法。 改进后的闭合模式再现所观察到的混合层湍流的各向异性以及动量和标量分布的均匀性的能力，将在许多物理和海洋地球化学海洋学领域中引起人们的兴趣，从气候模拟到沿海沉积物输运和溢油预测。在广泛使用的建模框架中实施改进，通用海洋湍流模型（GOTM）将促进广泛的海洋建模者使用这些结果。该项目将促进对工程学和地球物理学之间独特联系的研究，并支持一名研究生研究助理从事漂流物数据分析和模型数据比较。该项目将通过公立学校教室和科学展览会为研究人员正在进行的个人外展活动提供新的材料。二阶矩闭合（SMC）模型的发展建立在最近的进展基础上，包括Craik-Leibovich（CL）涡强迫完全在“准平衡”SMC中，采用动量通量闭合，其中一个分量是斯托克斯漂移梯度和非均匀近地表压力-应变闭合。CL强迫雷诺应力项和新的湍流封闭将被应用于修改较大的类的“弱平衡”SMC的朗缪尔湍流。这些将在GOTM框架中实施和评估，包括朗缪尔湍流和表面波破碎的建模相互作用。对现有高质量拉格朗日浮标数据的新分析将提供动能分量、湍流长度尺度、大涡动动能耗散率和近地表拉格朗日统计数据的剖面，这些数据可以区分边界层湍流表面波强迫理论。新的大涡模拟（LES）将包含嵌入式虚拟浮标，并将包括强迫随机波打破浮标和模型分辨尺度。使用这种LES，研究人员将开发新的数据分析方法，并指导SMC修改波浪强迫。CL强迫的新的近地表闭合将与SMC中湍流协方差的浮力产生的类似处理相结合，用于具有非局部梯度闭合的对流。LES结果和浮动数据将用于验证和调整SMC模型。修改后的SMC模型代码和浮动数据测试用例将通过GOTM框架发布以供公众使用。

Wind is the major driving force for the upper ocean. The structure and intensity of turbulent mixing in the surface layer of the ocean vary greatly in the presence of steep wind waves, and existing numerical models are not always very accurate in their predictions. This study seeks to improve the representation of surface wave effects in numerical models of upper-ocean mixing and expand the empirical basis for validating these models against mixed layer turbulence measurements. Existing data from freely drifting instruments that move up and down the well mixed layer of the upper ocean will be analyzed to yield new information about the vertical structure of turbulence under a wide range of wave conditions. Virtual drifters simulated in very high resolution numerical models will be used to develop new analysis methods and to enhance the limited observational data sets. The study will aid comparisons among competing theories on wave-turbulence interaction by expanding and refining the metrics of model-data comparisons. Insights on wave-turbulence interaction will lead to new mixing parameterizations, that can be validated against small-scale turbulence measurements, and ultimately enhance the skill of ocean circulation models. The dissemination of drifter measurements and model code will also benefit other approaches to parameterizing wave effects. The ability of the improved closure models to reproduce the observed anisotropy of mixed layer turbulence, and the homogeneity of momentum and scalar profiles, will be of interest in many physical and biogeochemical oceanographic fields, ranging from climate modeling to coastal sediment transport and oil spill prediction. Implementing the improvements in a widely used modeling framework, the General Ocean Turbulence Model (GOTM) will facilitate usage of these results by a broad range of ocean modelers. This project will promote study at a unique nexus between engineering and geophysics and supports a graduate research associate to work on drifter data analysis and model-data comparisons. The project will contribute new material to the investigators' ongoing individual outreach activities through public school classrooms and science fairs.The second moment closure (SMC) model developments build on recent advances that include Craik-Leibovich (CL) vortex forcing fully in a 'quasi-equilibrium' SMC, adopting a momentum flux closure with a component down the Stokes drift gradient and an inhomogeneous near-surface pressure-strain closure. The CL forcing Reynolds stress terms and new turbulence closures will be applied to modify the larger class of 'weak-equilibrium' SMCs for Langmuir turbulence. These will be implemented and evaluated in the GOTM framework, including the modeled interaction of Langmuir turbulence and surface wave breaking. New analysis of existing high-quality Lagrangian float data will provide profiles of kinetic energy components, turbulent length scales, large-eddy kinetic energy dissipation rates and near-surface Lagrangian statistics that can discriminate between theories for surface -wave forcing of boundary-layer turbulence. New large eddy simulations (LES) will contain embedded virtual floats, and will include forcing by stochastic wave breaking at float- and model-resolved scales. Using this LES, the researchers will develop new data analysis methods and guide SMC modifications for wave forcing. The new near-surface closure for CL forcing will be combined with similar treatments of buoyant production in of turbulent covariance in SMC for convection with nonlocal gradient closures. LES results and float data will be used to verify and tune SMC models. Modified SMC model code and float data test cases will be distributed for public availability via the GOTM framework.