Turbulent Flows and Scalar Transport in the Forest-Atmosphere Interface over a Complex Terrain

复杂地形上森林-大气界面的湍流和标量传递

• 批准号: 1419614
• 负责人: Heping Liu
• 金额: $ 44.99万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-11-15 至 2018-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419614&HistoricalAwards=false
• 关键词: Turbulent; Flows; Scalar; Transport; Forest

Complex terrain poses significant problems to eddy covariance measurements above forest canopies. Improving eddy covariance measurements over complex terrain requires a better understanding of how complex terrain influences spatial and temporal variability in turbulent flows above and within forest canopies. This will lead to improvements in measurements of the exchange of momentum, heat, and scalars between the atmosphere and vegetation, so that reliable interpretations/assessments of the surface energy balance, water cycle, and carbon budget over complex terrain can be made over various temporal and spatial scales. Currently, there is no clear understanding of how the simultaneous action of complex terrain, dynamic and thermodynamic conditions of inflows, and plant canopies modulate turbulence structures and thus transport of momentum, heat, water vapor, and carbon dioxide. In this research, turbulence in the forest canopy-atmosphere interface over a complex terrain will be examined by conducting analyses of the data measured in a European EGER experiment (ExchanGE processes in mountainous Regions) integrated with large-eddy simulations (LES). The Washington State University (WSU) research team along with six other international groups participated in the EGER experiment that was conducted in June and July of 2011 at the FLUXNET site in Weidenbrunnen Waldstein (DE-Bay), located in North-Eastern Bavaria, Germany. Each group contributed different instruments and research activities to map, to the fullest extent possible, three-dimensional turbulence structures at the site. In addition to data analysis, a multi-layer canopy module will be incorporated into the Weather Research and Forecasting Model (WRF) - LES (WRF-LES) to explore spatial variations and temporal evolutions of mean/turbulent flows and quantify relative contributions of different mechanisms to momentum/heat/H2O/CO2 transfer. Collectively, this research will examine:1) How does the interaction of 'real' topography-induced pressure perturbations and canopy alter turbulence structures, including coherent structures and high-order turbulent statistics such as velocity variances, turbulent stresses/fluxes, pressure variance, and production/loss of TKE above and within the canopy, as compared with the structures observed over idealized hills?2) How do different atmospheric stability conditions alter spatial and temporal variations in the main features of mean/turbulent flows within and above the canopy, as compared with previous results under neutral atmospheric conditions? The main features of turbulent flows include shear layer, inflexion point, TKE, second-order statistics, skewness and kurtosis of u and w profiles, wake region and wake depth (lee side only), and recirculation (lee side only).3) How do mean/turbulent flows as a result of the simultaneous actions of topography, canopy, and stability, lead to spatial and temporal variations in CO2 fluxes, horizontal and vertical advections, flux divergence, and CO2 sources and sinks? What are the dynamic mechanisms for these spatial and temporal variations in CO2 fluxes and the implications for tower measurements of CO2 fluxes?Intellectual Merit: Overall, the study will provide an improved understanding of mean and turbulent flows and exchange of momentum, heat, and scalars (e.g., CO2) between the canopy and the atmosphere over mountainous regions. Applications include: 1) simulation of carbon cycling in complex terrain, 2) wind energy predictions in complex terrain, and 3) pollutant dispersion in complex environments.Broader Impacts: Results from this work will improve our overall ability to quantify carbon, water, and energy flows in complex terrain and thus improve our understanding of important components of global carbon science. The results will be beneficial to carbon cycle science and the FLUXNET community in helping constrain the carbon budget and upscale CO2 fluxes from tower to landscape scale and even to regional scale over complex terrain. The updated WRF-LES modeling system with a multi-layer canopy module will be beneficial to a variety of research communities in studying canopy flows and PBL flows over complex terrain; wind energy applications in terms of identifying potential locations for wind turbines; forest management in identifying locations of high risks of tree damage in windy conditions; and forest fire behaviors in quantifying fire propagation; The research will contribute directly to the educational research training of Ph.D. students at WSU. The results will be disseminated to a broader audience through the FLUXNET community, conferences, and seminars, and will be used in courses and workshops related to WSU's undergraduate and graduate curriculum as well as the summer REU program which is focused on atmospheric chemistry, air quality, and climate change.

复杂的地形给森林冠层上方的涡流协方差测量带来了重大问题。改进复杂地形上的涡流协方差测量需要更好地了解复杂地形如何影响森林冠层上方和内部湍流的空间和时间变化。这将改进大气和植被之间动量、热量和标量交换的测量，从而可以在不同的时间范围内对复杂地形的地表能量平衡、水循环和碳预算进行可靠的解释/评估。和空间尺度。目前，对于复杂地形、流入的动态和热力学条件以及植物冠层的同时作用如何调节湍流结构并从而调节动量、热量、水蒸气和二氧化碳的传输还没有明确的了解。在这项研究中，将通过对欧洲 EGER 实验（山区交换过程）中测量的数据与大涡模拟 (LES) 相结合来检查复杂地形上森林冠层-大气界面的湍流。华盛顿州立大学 (WSU) 研究团队与其他六个国际小组一起参与了 EGER 实验，该实验于 2011 年 6 月和 7 月在德国巴伐利亚州东北部 Weidenbrunnen Waldstein (DE-Bay) 的 FLUXNET 站点进行。每个小组都贡献了不同的仪器和研究活动，以尽可能地绘制现场的三维湍流结构。除了数据分析之外，多层冠层模块将被纳入天气研究和预报模型（WRF）- LES（WRF-LES）中，以探索平均/湍流的空间变化和时间演变，并量化不同因素的相对贡献动量/热量/H2O/CO2 传递机制。总的来说，这项研究将研究：1）“真实”地形引起的压力扰动和冠层的相互作用如何改变湍流结构，包括相干结构和高阶湍流统计数据，例如速度方差、湍流应力/通量、压力方差、与在理想化山丘上观察到的结构相比，树冠上方和树冠内部 TKE 的产生/损失？2) 不同的大气稳定性条件如何改变树冠主要特征的时空变化与之前在中性大气条件下的结果相比，冠层内部和上方的平均/湍流？湍流的主要特征包括剪切层、拐点、TKE、二阶统计量、u和w剖面的偏度和峰度、尾流区域和尾流深度（仅背风侧）以及再循环（仅背风侧）。3）地形、冠层和稳定性同时作用导致的平均/湍流如何导致二氧化碳通量、水平和垂直平流、通量散度和二氧化碳通量的空间和时间变化二氧化碳源和汇？ CO2 通量的这些空间和时间变化的动态机制是什么，以及对 CO2 通量塔测量的影响是什么？ 智力优点：总体而言，该研究将加深对平均流和湍流以及动量、热量和标量交换的理解（例如，二氧化碳）在山区的树冠和大气之间。应用包括：1) 复杂地形中的碳循环模拟，2) 复杂地形中的风能预测，3) 复杂环境中的污染物扩散。 更广泛的影响：这项工作的结果将提高我们量化碳、水和污染物的整体能力。能量在复杂地形中流动，从而提高我们对全球碳科学重要组成部分的理解。研究结果将有利于碳循环科学和 FLUXNET 社区，帮助限制从塔到景观尺度，甚至复杂地形上的区域尺度的碳预算和高档二氧化碳通量。更新后的带有多层冠层模块的WRF-LES建模系统将有利于各种研究团体研究复杂地形上的冠层流和PBL流；风能应用，确定风力涡轮机的潜在位置；森林管理，以确定大风条件下树木受损高风险的位置；以及森林火灾行为以量化火灾蔓延；该研究将直接有助于博士生的教育研究培训。华盛顿州立大学的学生。研究结果将通过 FLUXNET 社区、会议和研讨会向更广泛的受众传播，并将用于与 WSU 本科生和研究生课程以及重点关注大气化学、空气质量的夏季 REU 课程相关的课程和研讨会和气候变化。