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.

复杂地形对森林冠层上空涡度相关测量带来了很大的困难。改进复杂地形的涡度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。这将导致改进大气和植被之间动量、热量和标量交换的测量，从而可以在各种时间和空间尺度上对复杂地形的地表能量平衡、水循环和碳收支进行可靠的解释/评估。目前，还没有清楚的了解如何同时行动的复杂地形，动力学和热力学条件的流入，植物冠层调节湍流结构，从而运输的动量，热量，水蒸气和二氧化碳。在这项研究中，湍流在森林冠层-大气界面在复杂的地形将进行欧洲埃格实验（山区交换过程）与大涡模拟（LES）集成的测量数据的分析进行检查。华盛顿州立大学（WSU）研究小组沿着其他六个国际小组参加了2011年6月和7月在位于德国巴伐利亚东北部Weidenbrunnen Waldstein（DE-Bay）的FLUXNET站点进行的埃格实验。每个小组都提供了不同的仪器和研究活动，以尽可能全面地绘制该地点的三维湍流结构。除数据分析外，天气研究及预报模式-大涡模拟（WRF-LES）亦会加入一个多层林冠模式，以探讨平均/湍流的空间变化及时间演变，并量化不同机制对动量/热量/H2O/CO2输送的相对贡献。总的来说，这项研究将研究：1）如何相互作用的“真实的”地形引起的压力扰动和冠层改变湍流结构，包括相干结构和高阶湍流统计，如速度方差，湍流应力/通量，压力方差，和生产/损失的TKE以上和冠层内，与理想化的山丘上观察到的结构相比？2)不同的大气稳定度条件如何改变冠层内和冠层上方的平均/湍流的主要特征的空间和时间变化，与以前的结果相比，在中性大气条件下？湍流流动的主要特征包括剪切层、湍流点、TKE、二阶统计量、u和w剖面的偏度和峰度、尾迹区和尾迹深度（仅背风侧）和再循环（仅背风面）。3）地形、冠层和稳定性同时作用的平均/湍流如何导致CO2通量的时空变化，水平和垂直平流，通量散度，CO2源和汇？这些空间和时间变化的CO2通量的动力学机制是什么，以及对CO2通量的塔测量的影响？智力优势：总的来说，这项研究将提供一个更好的理解平均和湍流和交换的动量，热量和标量（例如，二氧化碳）之间的冠层和大气在山区。应用包括：1）复杂地形中碳循环的模拟，2）复杂地形中风能的预测，3）复杂环境中污染物的扩散。更广泛的影响：这项工作的结果将提高我们量化复杂地形中碳、水和能量流动的整体能力，从而提高我们对全球碳科学重要组成部分的理解。研究结果将有助于碳循环科学和FLUXNET社区在复杂地形上限制碳预算和从塔到景观尺度甚至区域尺度的高档CO2通量。更新后的WRF-LES模拟系统具有多层林冠模块，将有利于各种研究团体研究复杂地形上的林冠流和边界层流;确定风力涡轮机潜在位置方面的风能应用;确定大风条件下树木受损高风险位置方面的森林管理;以及量化火灾蔓延方面的森林火灾行为;本研究将对博士生教育研究型人才的培养起到直接的促进作用。WSU的学生。结果将通过FLUXNET社区，会议和研讨会传播给更广泛的受众，并将用于与WSU的本科和研究生课程以及夏季REU计划相关的课程和研讨会，该计划侧重于大气化学，空气质量和气候变化。