Influences of Coherent Structures on Validity of the Constant Flux Layer Assumptions in the Unstable Atmospheric Surface Layer

不稳定大气表层相干结构对恒定通量层假设有效性的影响

• 批准号: 2325687
• 负责人: Heping Liu
• 金额: $ 44.08万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2325687&HistoricalAwards=false
• 关键词: Influences; Coherent; Structures; Validity; Constant; Influences; Coherent; Structures; Validity; Constant

In many applications such as weather and climate modeling, it is assumed that the transfer rate for scalars (i.e., scalar fluxes), including heat, water vapor, CO2, and other greenhouse gases, is constant with respect to height in the atmospheric surface layer, the lowest layer of the atmosphere. This so-called constant flux layer assumption is also widely used in land-surface flux measurements to quantify scalar fluxes to and from land surfaces. However, the reported failure of this assumption implies that scalar fluxes measured and modeled in the atmospheric surface layer are not equivalent to the fluxes across the surface-atmosphere interface, leading to uncertainty in measured and modeled fluxes in these applications. Despite the abundant studies on the roles of large turbulent eddies (i.e., coherent structures) in contributing to scalar fluxes, it is not well understood as to how large turbulent eddies contribute to changes in fluxes with height in the atmospheric surface layer. The objective of this project is to study what physical mechanisms regulate the attributes of large eddies across height that lead to varying contributions to fluxes with height, contributing to the failure of the constant flux layer assumption across a wide range of atmospheric conditions. By leveraging the existing facilities and as guided by flux budget equations, a field experiment will be conducted over the large water body of Ross Barnett Reservoir in Ridgeland, Mississippi, with a flux tower equipped with five levels of eddy covariance systems and other instruments. The field experiment will provide a unique dataset that minimizes the influence of advective terms and enables more precise examination of the attributes of large turbulent eddies. A combined approach of several analysis methods, such as fast Fourier transform, wavelet transform, and ensemble empirical decomposition mode, will be used to characterize the attributes of large turbulent eddies and their variations with height across instability ranges. Quadrant analysis will be used to quantify asymmetric flux contributions from sweeps and ejections of large turbulent eddies, enabling an analysis of the underlying mechanisms that modulate changes in fluxes with height. Further, such analyses will allow the study of mechanisms that lead to different behaviors of height-varying fluxes for different scalars. The field experiment will generate a unique dataset valuable for studying a wide range of topics in micrometeorology, hydrometeorology, boundary-layer turbulence, lake evaporation, water-atmosphere interactions, carbon emissions from inland waters, water budget for freshwater management, and aquatic ecosystems. An involved Ph.D. student will gain first-hand experience in designing, preparing, and conducting micrometeorological experiments and learn eddy covariance techniques, data analysis theories and tools, and many other research skills. Mini-research projects using the datasets collected in this project will be developed and incorporated into the curriculum of one undergraduate course and two graduate courses being taught by the PI for students’ term projects. Short films and presentations about the field experiment and research findings will be disseminated in scientific conferences and seminars as well as the PI’s department websites for diverse audiences.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.

在许多应用（例如天气和气候建模）中，假定标量（即标量通量）的转移速率，包括热，水蒸气，二氧化碳和其他温室气体，相对于大气表面层的高度，大气层最低层的高度是持续的。这种所谓的恒定升层假设也广泛用于陆地磁通测量中，以量化沿土地表面的标量通量。但是，该假设的报告失败意味着在大气表面层中测量和建模的标量通量不等于跨大气界面的通量，从而导致这些应用中测量和建模的通量的不确定性。尽管对大湍流（即相干结构）在促进标量通量的作用的作用进行了丰富的研究，但对于大湍流涡流有多么大的促进大气表面层的通量变化的变化，尚未充分理解。该项目的目的是研究哪些物理机制调节高度跨高度的大涡流的属性，从而导致对高度的通量有所不同，从而导致恒定通量层假设在各种大气条件下的失败。通过利用现有设施并在通量预算方程式的指导下，将在密西西比州里奇兰德的罗斯·巴内特水库的大型水体上进行实地实验，并配备了五个级别的涡流协会系统和其他仪器。现场实验将提供一个独特的数据集，该数据集可最大程度地减少高级术语的影响，并可以更精确地检查大型湍流涡流的属性。几种分析方法的组合方法，例如快速傅立叶变换，小波变换和集合经验分解模式，将用于表征大湍流涡流的属性及其在不稳定性范围内的高度变化。象限分析将用于量化大型湍流涡流的不对称通量贡献，从而对基础机制进行分析，以调节高度的通量变化。此外，这种分析将允许研究导致不同标量的高度变化通量行为的机制。现场实验将产生独特的数据集价值，用于研究微型气概，氢化学，边界层湍流，湖泊经济，水 - 大气相互作用，内陆水域的碳排放，用于淡水管理的水预算和水生生态系统的广泛主题。涉及博士学位学生将获得设计，准备和进行微气候实验的第一手经验，并学习涡流协方差技术，数据分析理论和工具以及许多其他研究技能。使用该项目收集的数据集的微型研究项目将被开发并纳入一门本科课程的课程中，PI为学生的学期项目教授了两个研究生课程。有关现场实验和研究结果的短片和演讲将在科学会议和下水道以及PI部门的潜水受众群体网站中传播。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响审查标准来通过评估来诚实地认为，通过评估来诚实地支持。