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

分层倒置朗缪尔湍流的数值研究和验证

• 批准号: 2124611
• 负责人: Ramsey Harcourt
• 金额: $ 43.67万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2124611&HistoricalAwards=false
• 关键词: Numerical; investigation; validation; stratified; up

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.

该项目将调查在低风速和强（通常是雨引起的）分层条件下海洋上层的风对齐环流特征。在这些条件下，这些特征不符合典型的朗缪尔湍流或风驱动粘性剪切诱导结构的预期。该假设是，在适当的强迫条件下，分层剪切流在一个表面被困射流的底部变得不稳定的收敛和向上位移的存在下，表面加强斯托克斯剪切。这促使速度较慢、密度较大的水向上涌向地表，并进行再循环。数值模拟和现有数据的进一步分析将被用来测试的假设，所观察到的条纹问题产生于这个过程中的“分层倒置朗缪尔湍流”（SUDL-T）。拟议的活动将导致更好的参数化的混合在海洋表面，具有广泛的相关性的海气通量的热量，气体和动量。该项目将支持一名博士研究生，为当地的公共宣传和教育计划做出贡献，并通过在会议上的演讲，在同行评审的期刊上发表文章以及近地表混合的有效数值模拟的公开可用性进行广泛传播。在温和的风和强烈的近表面盐度分层期间，从雨的海面红外图像显示风条纹的间距，这表明他们是由一个不同的机制比经典的朗缪尔环流或风驱动的表面应力。该项目的目标是通过以下方式研究这种可能新观察到的机制：1）表征与风纹相关的二次环流的垂直尺度、运动学和能量学随环境条件的变化;（二）确定在低风速下观测到的高风速长度尺度的机制，以及与向小尺度过渡和朗缪尔湍流有关的强迫平衡中等风;（3）评估低风速时次级环流对近地面垂直混合的影响。为此，该项目将结合理想化和现实的大涡模拟建模，再加上进一步的数据分析和直接的模型数据比较。建模将包括从旋转向上运行的套件，或从低到中等范围增加强迫，和旋转向下，通过类似的强迫水平放松强迫。观测结果的再分析将集中于确定观测期间的地表强迫和地下水文和剪切，以便形成一个更稳定的基础，通过更现实的建模套件和直接的模型数据比较来验证项目假设。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。