Collaborative Research: Understanding Interactions between Mesoscale and Microscale Flows in the Stable Boundary Layer over Shallow Terrain

不稳定条件下的大气流动（例如，晴天）比稳定条件下的更容易理解，后者经常发生在夜间。如果地形不完全平坦或表面有植被，流动就变得更加难以理解。这种不确定性意味着夜间天气预报可能缺乏准确性。在美国中部的大部分地区，这在略微倾斜的地形中尤其如此。该项目将回答地球上大部分地区稳定条件下存在的基本物理问题，包括：植物，地形和海拔变化如何影响大气流动？受影响的大气流动如何与来自其他区域的流动相互作用？在缓坡地区存在什么特殊的气流（如下沟冷气流;气流碰撞）？该项目将使用以前收集的实验数据来推断经验关系，定义这些现象可能发生的时间，地点和原因。这一理论框架的完善将进一步加深对夜间污染物传输和转化的理解。改进对化学或生物有害污染物迁移的定量预测，可使公众健康和安全受益。农业界将受益于对控制田间温度的物理过程的更多了解，包括影响作物健康的物理过程和导致霜冻和随后作物损失的物理过程，这是确保全球粮食安全的一项重大挑战。利用在NSF资助的稳定大气变率和运输（SAVANT）活动期间进行的独特观测，这项工作将导致更好地了解浅层复杂地形对稳定边界层的机械和热力学特性的影响，并填补环境和当地流量之间的尺度相互作用的知识空白，特别是关于发生在浅层地形中的流型。SAVANT在2018年秋季的两个密集月份收集了同时进行的原位和遥感观测。通过田间试验，研究了浅沟冷空气排水（下沟）流的成因和影响。用多个激光雷达（光探测和测距）系统跟踪的示踪剂羽流释放提供了在多个空间尺度上检查相互作用流的独特机会。两个关键因素稳定层湍流混合在复杂的地形，风切变和稳定的分层，将被用来分层观测，以描述最活跃的湍流涡使用塔数据内和上方的主要沟壑，增强空间剪切观测激光雷达。将研究湍流涡旋的垂直尺度因子和排水流的影响。导致排水流量不均匀的因素（即，脉冲流、曲折流和会聚流）将被详细描述。塔和三维激光雷达观测的独特组合将允许改进能量和质量交换的参数化，这将提高预测模型的能力。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Atmospheric flows under unstable conditions (e.g., sunny days) are better understood than that under stable conditions which often occur at night. If the terrain is not perfectly flat or the surface is vegetated, flows become even more difficult to understand. This uncertainty means nighttime weather forecasts can lack accuracy. This is particularly true in slightly sloping topography as seen through much of the central US. This project will answer fundamental physics questions that exist for stable conditions over much of the planet including: How do plant, terrain, and elevation changes impact atmospheric flows? How do the impacted atmospheric flows interact with flows from other regions? What special flows (like down gully cold air flow; flows colliding) exist in gently sloped areas? This project will use previously collected experimental data to deduce empirical relationships defining when, where, and why these phenomena are likely to occur. This improvement of current theoretical frameworks will further understanding of nighttime pollutant transport and transformation. Public health and safety can benefit from improved quantitative prediction of transport of chemical or biological hazardous pollution. The agricultural community will benefit from increased knowledge of physical processes controlling field-scale temperature, including those affecting crop health and those leading to patches of frost and subsequent crop loss, a major challenge in ensuring global food security. Using unique observations taken during the NSF funded Stable Atmospheric Variability ANd Transport (SAVANT) campaign, this work will lead to an improved understanding of impacts of shallow complex terrain on mechanical and thermodynamic properties of the stable boundary layer and to fill the knowledge gap in scale interactions between environmental and local flows, specifically with respect to flow patterns that occur in shallow topography. SAVANT collected concurrent in-situ and remote sensing observations during two intensive months in the fall of 2018. The field setup was designed to investigate causes and effects of cold air drainage (down gully) flow in a shallow gully. Tracer plume releases tracked with multiple lidar (Light Detection and Ranging) systems offer the unique opportunity to examine interacting flows at multiple spatial scales. Two critical factors for stable-layer turbulent mixing in complex terrain, wind shear and the stable stratification, will be used to stratify observations to describe the most energetic turbulence eddies using the tower data within and above the main gully, augmented by spatial shear observations from lidars. Vertical scaling factors for turbulent eddies and the influences of drainage flows will be investigated. Factors leading to non-uniform drainage flows (i.e., pulsing, meandering, and converging flows) will be detailed. The unique combination of tower and 3-D lidar observations will allow for improved parameterizations of energy and mass exchanges, which will improve predictive model capabilities.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.