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.

该项目将在低风和强（通常是雨引起的）分层的情况下研究海洋上层的风循环特征。在这些条件下，此类特征不符合典型的Langmuir湍流或风向粘性诱导结构的期望。假设是，在适当的强迫条件下，在表面强化的Stokes剪切的存在下，表面捕获射流底部的分层剪切流对收敛和向上的位移变得不稳定。这驱动了较慢，更密集的水向表面上升，然后再循环。数值建模和对现有数据的进一步分析将用于检验以下假设：观察到的条纹是由“分层倒置Langmuir湍流”（SUDL-T）产生的。所提出的活动将导致在海面混合的更好参数，与热，气体和动量的空气通量相关。该项目将支持博士学位的研究生，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，同行评审期刊的出版物以及对近场混合的经过验证的数值模拟进行广泛传播。在适度的风和强烈的近表面盐度分层期间，海面的红外图像在间距处的风条纹表明它们是由与经典的Langmuir循环或风驱动的表面应力不同的机制产生的。项目目标是通过以下方式研究这种潜在的新观察到的机制：1）表征与风条条纹相关的二次循环的垂直尺度，运动学和能量与环境条件相关的函数； 2）确定负责在低风速下观察到的越野长度尺度的机制，以及与过渡到较小的尺度和中等风中的Langmuir湍流相关的强迫平衡； 3）评估低风中二次循环对近表面垂直混合的影响。为此，该项目将使用理想化且逼真的大型涡模型建模的组合，并结合进一步的数据分析和直接模型数据比较。建模将包括从旋转的套件或从低范围增加到中等范围的强迫，以及向下旋转，通过相似的强迫水平的强迫放松。 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 precious of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.