Collaborative Research: Measurement and Modeling of Aerodynamic Interactions between Tree-Sway Motion and Turbulence in and above a Forest Canopy

冠层粗糙度亚层中的湍流是陆地生态系统与大气交换过程的主要驱动力。这些交流是全球碳、水循环和气候变化研究的重要组成部分。以往对短作物的研究表明，植物的气动弹性对CRSL湍流结构有显著影响。然而，在CRSL的大多数湍流模型中，包括最先进的大涡模拟模型(LES)，都没有正式考虑树木的气动弹性。这在很大程度上是因为缺乏实地实验来量化树木的弹性特性及其复杂的减震摇摆行为，这与矮小作物中的不同。为了研究风对陆地森林生态系统的结构和功能的多方面影响及其对未来气候变化的反应和相互作用，改进对森林树冠和CRSL湍流之间的空气动力学相互作用的理解和建模也具有重要意义。智力优势：这个合作项目是一个跨学科的努力，建立在康涅狄格大学、东卡罗来纳大学和路易斯安那州立大学的森林生态学家和微气象学家的实验和数值模拟专业知识基础上。这项研究包括在缅因州豪兰市一个已建立的ameriFlux森林站点进行为期1.5年的新颖但劳动密集型的野外实验活动，以及将树木摇摆运动物理纳入当前LES的计算密集型建模部分。研究人员将开发改进的树木摇摆及其与大涡耦合的数值模式。总体目标是改善对CRSL湍流结构和森林树冠上方树木摇摆运动之间的空气动力学相互作用的潜在机制的理解和建模。现场活动将同时测量大量树木和湍流风场的摇摆运动以及弹性和空气动力学特性。这些测量将被用来量化树木摇摆运动的时间和空间特征，以及它们与森林冠层中连贯阵风的空气动力学相互作用。耦合的LES树摇摆模型将被用来量化树木摇摆运动对一定范围大气条件下森林内和森林上方气流的影响。此外，PIS将利用LES-树-摇摆-耦合模式进行系统研究，以量化大气边界层高度和稳定度、外部水平气压梯度力、树冠形态和树木的弹性性质对树木摇摆运动和CRSL相干结构特征及其相互作用的影响和相对意义。PIS将对现场测量和LES输出进行一套彻底和全面的分析，以创建对树木摇摆运动和树冠尺度相干结构的空间和时间特征的定性和定量描述，包括它们的关系和相互作用。更广泛的影响：这个合作项目将整合多个教育层次的教学和研究。为了培养和培养基层对科学的追求，PI将实施一项专门为小学生设计的教育计划，通过互动说明如何收集、分析和共享基本数据，并演示天气、气候和森林生态系统之间的联系。这一通过家庭公共教育计划进行的外展活动将激发后代对世界的科学理解，并将利用该项目研究部分应用的一些知识、工具和模型。该项目将为研究生提供支助，他们将接受多个研究领域(微型气象学、边界层气象学、森林气象学、森林生态学)的正式培训，学习和实践重要的实地测量和数值模拟及数据分析技术。该项目的研究成果将用于在两所大学开发微气象学、森林气象学和森林生态学的本科生和研究生课程模块，并通过项目网站提供。

Turbulence in the canopy roughness sublayer (CRSL) is the primary driving force of the exchange processes between terrestrial ecosystems and the atmosphere. These exchanges are vital components in global carbon and water cycles and climate change research. Previous studies of short crops have shown that the aeroelasticity of plants has a significant impact on CRSL turbulence structure. The aeroelasticity of trees, however, has not been formally considered in most turbulence models of CRSL, including state of the art large-eddy simulation models (LES). This is largely due to a lack of field experiments to quantify the elastic properties of trees and their complex damped sway behaviors, which differ from those in short crops. Improved understanding and modeling of the aerodynamic interactions between forest canopies and CRSL turbulence are also significant in order to investigate the multifaceted effects of winds on the structure and function of terrestrial forest ecosystems and their responses to and interactions with future climate change. Intellectual merit: This collaborative project is an interdisciplinary effort built upon the experimental and numerical modeling expertise of forest ecologists and micrometeorologists at the University of Connecticut, East Carolina University and Louisiana State University. The research consists of a novel but labor intensive field experiment campaign over a period of 1.5 years at an established AmeriFlux forest site at Howland, Maine, and a computationally intensive modeling component to incorporate tree sway motion physics into a current LES. The investigators will develop improved numerical models of tree-sway and their coupling with the LES. The overall goal is to improve understanding and modeling of the mechanisms underlying the aerodynamic interactions between CRSL turbulence structures and tree sway motions in and above forest canopies. The field campaign will measure the sway motions and the elastic and aerodynamic properties of a large array of trees and turbulence wind fields simultaneously. These measurements will be used to quantify the temporal and spatial characteristics of tree-sway motions and their aerodynamic interactions with coherent gusts in a forest canopy. The coupled LES-tree-sway-model will be used to quantify the influences of tree sway motions on airflow in and above a forest over a range of atmospheric conditions. In addition, the PIs will conduct systematic investigations, using the coupled LES-tree-sway-model, to quantify the effects and the relative significances of atmospheric boundary layer height and stability, external horizontal pressure gradient force, canopy morphology and elastic properties of trees, on the characteristics of tree-sway motions and CRSL coherent structures and their interactions. The PIs will carry out a thorough and comprehensive set of analyses of field measurements and LES outputs to create both qualitative and quantitative descriptions of the spatial and temporal characteristics of the tree-sway motions and canopy-scale coherent structures, including their relations and interactions. Broader impacts: This collaborative project will integrate teaching and research at multiple levels of education. To cultivate and nurture the pursuit of science at the grass roots, the PIs will carry out an education program specifically designed to engage primary school children with interactive instructions on how basic data are collected, analyzed and shared, and demonstrations of the linkages between weather, climate and forested ecosystems. This outreach via family public education program will excite future generations about scientific understanding of the world, and will utilize some of the knowledge, instruments and models applied in the research portion of this project. This project will provide support to graduate students who will receive formal training in multiple research areas (micrometeorology, boundary-layer meteorology, forest meteorology, forest ecology), learn and practice important field measurement and numerical modeling and data analysis techniques. Research results from this project will be used to develop undergraduate and graduate course modules in micrometeorology, forest meteorology and forest ecology at both universities, and made available through a project web site.