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

来自或流向陆地表面的标量通量，包括感热、潜热和微量气体，如二氧化碳、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前提。在过去的几十年里，人们对正则湍流边界层和对流系统中相干结构的拓扑结构和输送能力进行了活跃的研究。然而，微气象学中具有实际意义的问题并没有从这些研究中受益。该项目旨在通过研究在非均匀地貌上的大气边界层流动中相干结构在标量输送中的作用来填补这一研究空白。该项目的重点是在点和景观尺度上陆地表面非均质性和相干结构之间的相互作用，以及它们对描述标量通量的Monin-Obukhov相似性理论(MOST)的崩溃的影响。在点尺度上，MOST的分解是由传递陆地表面非均质性特征的平流项和具有相干结构特征的垂直输送项引起的。在进行空间平均的景观尺度上，陆面非均质性和相干结构之间的相互作用产生了弥散通量。这项工作通过通量平衡方程及其空间平均形式，在统一的框架下结合了野外实验和大涡模拟(LES)。现场实验将在爱达荷州爱达荷州福尔斯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，它们将配备涡流协方差系统、声雷达、带有RASS的风廓线仪、35个中卫站和其他仪器。现场工作将提供三维和高分辨率的相干结构和标量湍流的独特特征。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洞察力从点扩展到景观尺度。一种新的基于时空象限分析的方法将被用来模拟弥散通量。实地试验产生的新数据集将为探索与大气边界层和陆地表面过程有关的其他专题提供机会。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外联部分。它将为PIS教授的几个研究生和本科课程的学生生成微型项目，这些课程涉及边界层气象学、应用气象学和流体动力学。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。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.