Numerical investigation and validation of stratified up-side down Langmuir turbulence

该项目将研究在低风和强（通常是降雨引起的）分层条件下海洋上层的风向环流特征。在这些条件下，这些特征不符合典型朗缪尔湍流或风力驱动的粘性纯粹结构的预期。假设在适当的强迫条件下，在表面增强的Stokes剪切存在下，表面捕获射流底部的分层剪切流变得不稳定，向辐合和向上位移。这促使较慢、密度较大的水向地表上涌，并进行再循环。数值模拟和对现有数据的进一步分析将用于验证这样一个假设，即观察到的条纹是由“分层倒置朗缪尔湍流”（SUDL-T）过程产生的。拟议的活动将导致更好的海洋表面混合的参数化，与热、气体和动量的海气通量广泛相关。该项目将资助一名博士研究生，为当地的公共宣传和教育项目做出贡献，并通过在会议上的演讲、在同行评议的期刊上发表文章以及向公众提供经过验证的近地表混合数值模拟进行广泛传播。在温和的风和强的近地表盐度分层期间的海面红外图像显示，间隔处的风纹表明它们是由不同的机制产生的，而不是由经典的朗缪尔环流或风力驱动的表面应力。该项目的目标是通过以下方式来研究这种潜在的新观察机制：1)表征与风纹相关的二次环流的垂直尺度、运动学和能量学，并将其作为环境条件的函数；(2)确定低风速下侧风长度尺度升高的机制，以及与向小尺度过渡和中等风条件下Langmuir湍流相关的强迫平衡；3)评价低风次环流对近地面垂直混合的影响。为此，该项目将使用理想化和现实大涡模拟建模相结合的方法，并结合进一步的数据分析和直接的模型数据比较。建模将包括一系列自旋向上运行，或从低到中等范围增加强迫，以及自旋向下运行，通过类似的强迫水平放松强迫。对观测资料的再分析将侧重于确定观测期间的地表强迫和地下水文和剪切，以便通过更现实的建模套件和直接的模式数据比较，为验证项目假设提供更稳定的基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will investigate wind-aligned circulation features in the ocean upper layer during conditions of low winds and strong (typically rain-induced) stratification. Under these conditions, such features do not conform to expectations for either typical Langmuir turbulence or wind-driven viscous sheer induced structures. The hypothesis is that under appropriate forcing conditions, stratified shear flow at the base of a surface-trapped jet becomes unstable to convergence and upward displacement in the presence of surface-intensified Stokes shear. This drives upwelling of slower, denser water towards the surface, and recirculation. Numerical modeling and further analysis of existing data will be used to test the hypothesis that the observed streaks in question arise from this process of ‘stratified upside-down Langmuir turbulence’ (SUDL-T). The proposed activity will lead to better parameterizations of mixing at the ocean surface, with broad relevance for air-sea fluxes of heat, gas, and momentum. The project will support a PhD graduate student, contribute to local public outreach and educational programs, and have broad dissemination through presentations at conferences, publication in peer-reviewed journals, and public availability of validated numerical simulations of near-surface mixing. Infrared imagery of the sea surface during periods of modest winds and strong near-surface salinity stratification from rain shows wind streaks at spacings that suggest they are generated by a different mechanism than classic Langmuir circulations or wind-driven surface stress. The project objectives are to investigate this potentially newly observed mechanism by: 1) characterizing the vertical scale, kinematics, and energetics of the secondary circulation associated with the wind streaks as a function of environmental conditions; 2) determining the mechanism responsible for the observed elevated crosswind length scales at low wind speeds and the balance of forcing associated with transition to smaller scales and Langmuir turbulence in moderate wind; and 3) evaluating the impact of the secondary circulation at low winds on near-surface vertical mixing. To do this the project will use a combination idealized and realistic Large Eddy Simulation modeling, coupled to further data analysis and direct model-data comparison. Modeling will include suites of runs from spin-up, or increasing forcing from low to moderate ranges, and spin-down, the relaxation of forcing through similar forcing levels. Reanalysis of the observations will focus on determining the surface forcing and subsurface hydrography and shear during the observations, in order to form a more stable basis for validating the project hypothesis with a more realistic modeling suite and direct model-data comparison.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.