Collaborative Research: The Role of Coherent Structures in Scalar Transport over Heterogeneous Landscapes

来自或到达陆地表面的标量通量，包括感热、潜热和微量气体（如CO2、甲烷、氨）通量，对天气和气候、空气质量、农业管理和生态系统服务有直接影响。更好地了解低层大气中的湍流是更好地量化和模拟这些标量通量的先决条件。在过去的几十年里，人们对典型湍流边界层和对流系统中相干结构的拓扑结构和输运能力进行了积极的研究。然而，微气象学的实际相关问题并没有从这些研究中获益。本项目旨在通过研究非均匀地形上大气边界层流动中相干结构在标量输运中的作用来填补研究空白。该项目侧重于在点和景观尺度上陆地表面异质性和连贯结构之间的相互作用，以及它们对描述标量通量的莫宁-奥布霍夫相似理论（MOST）崩溃的影响。在点尺度上，MOST的分解来自于传递地表异质性特征的平流项和具有相干结构特征的垂直运输项。在进行空间平均的景观尺度上，色散通量是由地表非均质性和相干结构之间的相互作用产生的。本研究通过通量平衡方程及其空间平均版本，将现场实验和大涡模拟（LES）结合在一个统一的框架下。野外试验将在爱达荷州爱达荷瀑布一个相对平坦但不均匀的地形上进行，有一个62米高的塔和几个短塔，配备涡相关方差系统，一个雷达，一个带RASS的风廓线仪，35个中网站和其他仪器。实地工作将在三维和高分辨率上提供相干结构和标量湍流的独特表征。它将允许同时量化标量通量预算中的水平和垂直项。一系列的LES运行将用于将现场实验提供的见解从点扩展到景观尺度。将采用一种基于时间和空间象限分析的新方法来模拟色散通量。野外试验产生的新数据集将为探索与大气边界层和地表过程有关的其他主题提供机会。除了辅导两名研究生和两名本科生外，该项目还将涉及几个教育和推广组成部分。它将为pi教授的几门关于边界层气象学、应用气象学和流体动力学的研究生和本科生课程的学生生成小型项目。将制作短片和视频，向研究人员和公众展示研究结果的重要性。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。

Scalar fluxes including sensible heat, latent heat, and trace gases such as CO2, methane, ammonia fluxes, from or to land surfaces have direct impacts on weather and climate, air quality, agricultural management, and ecosystem services. A better understanding of turbulence in the lower atmosphere is the prerequisite for better quantification and modeling of these scalar fluxes. Over the past few decades, there has been active research on the topology and transporting capacity of coherent structures in canonical turbulent boundary layers and convective systems. However, problems of practical relevance in micrometeorology have not profited from these studies. This project aims to fill the research gap by investigating the role of coherent structures in scalar transport in atmospheric boundary layer flows over heterogeneous landscapes. The project focuses on the interactions between land surface heterogeneity and coherent structures at the point- and landscape- scales, and their implications for the breakdown of Monin-Obukhov Similarity Theory (MOST) in describing scalar fluxes. At the point-scale, the breakdown of MOST arises from advective terms communicating the signatures of land surface heterogeneity and vertical transport terms bearing the signatures of coherent structures. At the landscape-scale where a spatial averaging is conducted, dispersive fluxes arise from the interactions between land surface heterogeneity and coherent structures. This work combines field experiments and large-eddy simulations (LES) under a unifying framework via flux budget equations and their spatially-averaged version. The field experiment will be conducted over a relatively flat but heterogeneous terrain in Idaho Falls, Idaho, with a 62-m tower and several short towers to be equipped with eddy covariance systems, a sodar, a wind profiler with RASS, 35 mesonet stations, and other instruments. The field work will provide a unique characterization of coherent structures and scalar turbulence in three dimensions and at high resolutions. It will allow quantification of horizontal and vertical terms in the scalar flux budget simultaneously. A series of LES runs will be used to extend the insights afforded by the field experiment from point to landscape scales. A novel approach based on quadrant analysis in time and space will be employed to model dispersive fluxes. The new datasets generated by the field experiment will provide opportunities for exploring other topics related to atmospheric boundary layer and land surface processes. Beyond the tutoring of two graduate students and two undergraduate students, the project will involve several educational and outreach components. It will generate mini-projects for students in several graduate and undergraduate courses taught by the PIs on boundary layer meteorology, applied meteorology, and fluid dynamics. Short films and videos will be created to present the significance of the findings to researchers and the general public.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.