CAREER: A New Direction into Atmospheric Near-Surface Transport for Weak-Wind Conditions in Plant Canopies

职业：植物冠层弱风条件下大气近地表传输的新方向

• 批准号: 0955444
• 负责人: Christoph Thomas
• 金额: $ 73.67万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-15 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0955444&HistoricalAwards=false
• 关键词: CAREER; New; Direction; into; Atmospheric

Air exchange between forests and the lower atmosphere plays an important role in the transport of heat, moisture, momentum and trace gases between the ground surface and the atmosphere, thereby directly impacting human life and the environment. Much remains to be learned about the mechanisms of air exchange within the forest canopy layer, and its interaction with the overlying deeper atmospheric boundary layer. The generally weak nature of subcanopy winds and mechanical barrier presented by the network of tree branches forming the canopy render conceptual frameworks for turbulent transfer (such as commonly applied similarity theories) inadequate. The common generation of turbulence by shear on a variety of time scales, poor exchange between the subcanopy and above-canopy air, and short-circuiting of the energy cascade are not included in similarity theory that forms the basis for turbulent fluxes in models. Moreover, ubiquitous background "submesoscale" motions with spatial scales from tens of meters to several kilometers become important and can lead to unpredictable sudden wind direction changes, intermittent mixing, and non-equilibrium turbulence. No current physical concept describes the nature of these motions. Cases of weak airflow in concert with limited vertical mixing can result in high concentrations of contaminants near the surface.Intellectual merit: New field observations will be collected and analyzed at various contrasting sites to generalize findings with the objective to:i) identify forcing mechanisms of submesoscale motions, ii) evaluate the impact of plant canopies of different overstory density on the wind, temperature, and humidity fields, and iii) improve predictors for mixing in plant canopies that incorporate the important physical mechanisms. These investigations are key steps toward the long-term goal to develop a novel improved framework to describe the flow and resulting transport under weak-wind conditions for a range of overstory density and stratification. Observations will be made with a unique combination of new and standard techniques, including optical fiber measurement of temperature structure, acoustic remote sensing, ultrasonic anemometers, and laser-illuminated flow visualizations. The research will be integrated with educational activities in the classroom. A new graduate-level field course will be developed and taught for students from several disciplines. Both classroom and field activities will help spark the students' curiosity and interest to better understand interactions between the lower atmosphere and the land surface. The curricula will be enriched by connecting theoretical concepts with hands-on research experience based on access to state-of-the-art instrumentation.Broader Impacts: The novel framework and new analysis techniques will lead to improved formulations of turbulent fluxes applicable in non-ideal boundary layer conditions. These generalized formulations will be designed for use in regional and large-scale models, as well as dispersion and diffusion models. A set of practical recommendations will be developed for the applied flux community to reduce uncertainties in scalar budgets and predictions of water availability. Two graduate students will be trained in theoretical and observational boundary layer meteorology. This skill set is in high demand and demand likely will grow if/when monitoring of greenhouse gases becomes mandatory. The hands-on field education will foster critical thinking, improve retention of concepts, and help many students to reach technical proficiency. One Oregon K-12 high school teacher will be actively involved in field research and data analysis by partnering with the Oregon Natural Resources Education program at Oregon State University. This teacher's involvement will be leveraged to reach large numbers of K-12 students in addition to the hundreds of students directly connected to the participating teacher. Shared interests in air movement across the forested landscape will stimulate an exchange of information with the Willamette National Forest personnel.

森林与低层大气之间的空气交换在地表与大气之间的热量、水分、动量和微量气体的输送中起着重要作用，从而直接影响人类的生活和环境。关于森林冠层内空气交换的机制及其与上覆较深大气边界层的相互作用，仍有许多有待了解的问题。树冠下风的一般弱性质和树冠树枝网络所呈现的机械屏障使得湍流转移的概念框架（如常用的相似性理论）不充分。在各种时间尺度上由剪切共同产生湍流、冠层下和冠层上空气交换不良以及能量级联短路等都不包括在相似理论中，而相似理论是模型中湍流通量的基础。此外，无处不在的空间尺度从几十米到几公里的背景“亚中尺度”运动变得重要，并可能导致不可预测的突然风向变化，间歇性混合和非平衡湍流。目前还没有物理概念描述这些运动的性质。弱气流加上有限的垂直混合会导致靠近地表的污染物浓度很高。知识价值：将在不同的对比地点收集和分析新的野外观测结果，以概括研究结果，目的是：i)确定亚中尺度运动的强迫机制，ii)评估不同植被密度的植物冠层对风、温度和湿度场的影响，以及iii)改进包含重要物理机制的植物冠层混合预测。这些调查是实现长期目标的关键步骤，该目标是开发一种新的改进框架，以描述在弱风条件下一系列上层密度和分层的流动和由此产生的运输。观测将采用新技术和标准技术的独特组合，包括温度结构的光纤测量、声学遥感、超声波风速计和激光照明流可视化。研究将与课堂教学活动相结合。将为来自多个学科的学生开发和教授新的研究生水平的实地课程。课堂和实地活动将有助于激发学生的好奇心和兴趣，以更好地了解低层大气和地表之间的相互作用。课程将通过将理论概念与基于获得最先进仪器的实践研究经验联系起来而丰富。更广泛的影响：新的框架和新的分析技术将导致适用于非理想边界层条件的湍流通量的改进公式。这些广义公式将被设计用于区域和大尺度模型，以及弥散和扩散模型。将为应用通量界制定一套实用建议，以减少标量预算和水可用性预测中的不确定性。两名研究生将接受边界层气象学理论和观测方面的培训。这一技能需求量很大，如果/当温室气体监测成为强制性规定时，需求量可能会增加。动手实地教育将培养批判性思维，提高概念的保留，并帮助许多学生达到技术熟练程度。一名俄勒冈州K-12高中教师将与俄勒冈州立大学的俄勒冈自然资源教育项目合作，积极参与实地研究和数据分析。这名教师的参与将被利用来接触大量的K-12学生，以及与参与教师直接相关的数百名学生。对穿越森林景观的空中运动的共同兴趣将促进与威拉米特国家森林人员的信息交流。