Microfronts and Other Nocturnal Submeso Motions over Microtopography

微地形上的微锋和其他夜间亚细观运动

• 批准号: 2309208
• 负责人: Larry Mahrt
• 金额: $ 47.3万
• 依托单位: NorthWest Research Associates, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2309208&HistoricalAwards=false
• 关键词: Microfronts; Other; Nocturnal; Submeso; Motions

This award examines the boundary layer of air adjacent to the ground surface that cools at night. Strongest cooling occurs with clear skies and low wind speeds. This situation is poorly understood compared to other boundary layers with more significant winds or daytime heating. The strong cooling leads to practical issues including freezing street surfaces and frost damage to sensitive crops. The strong surface cooling also reduces vertical mixing and thus increases the probability of high concentrations of pollutants. The weak winds correspond to large variability of wind direction that spreads the pollutants over a variety of wind directions. This process is currently hard to predict. Formation of dense fog is another outcome of the strong cooling and weak vertical mixing. Local spatial variation of the surface cooling is an important feature requiring more attention. This project will increase understanding through analysis of intense measurements from different sites. Each site contains a network of clustered stations. The above analyses will improve the boundary-layer part of forecast computer models. The general analysis of different subclasses of very stable nocturnal boundary layers, and the relation of submeso motions to these subclasses, will be investigated. Very stable nocturnal boundary layers most often occur with strong stability associated with low wind speeds and clear skies. Submeso motions occur on scales just larger than the largest turbulent eddies but smaller than the mesoscale motions. Submeso motions include microfronts, wave motions, meandering motions, and more complex structures. These motions densely populate the very stable boundary layer. The analyses will be based on time series, spatial information across networks, and combined time-space domains from different datasets. The analysis will first concentrate on microfronts. The first stage focusses on increasing horizontal gradients of temperature. The second stage includes horizontal convergence that concentrates horizontal gradients into microfronts. Analysis of other submeso motions will follow with both individual analyses of each type of submeso motion and collective analysis of all submeso motions. Examination of the large wind-direction variability caused by submeso motions will be examined in detail. Additional data sets will be evaluated with possible recommendation of a new tailored field program.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.

该奖项考察了在夜间冷却的地面附近的空气边界层。 最强的冷却发生在晴朗的天空和低风速。 与其他具有更显著风或白天加热的边界层相比，这种情况知之甚少。强烈的冷却导致了实际问题，包括冻结街道表面和霜冻对敏感作物的损害。 强烈的地面冷却也减少了垂直混合，从而增加了污染物高浓度的可能性。弱风对应于风向的大变化，使污染物在各种风向上传播。这个过程目前很难预测。浓雾的形成是强冷却和弱垂直混合的另一个结果。 地面冷却的局部空间变化是需要更多关注的重要特征。 该项目将通过分析不同地点的密集测量增加理解。 每个站点都包含一个群集站点网络。 上述分析将改进预报计算机模式的边界层部分。将研究非常稳定的夜间边界层的不同亚类的一般分析，以及亚中尺度运动与这些亚类的关系。 非常稳定的夜间边界层通常出现在与低风速和晴朗天空相关的强稳定性。 亚中尺度运动的尺度仅大于最大湍流涡旋，但小于中尺度运动。 亚中尺度运动包括微锋、波浪运动、曲流运动和更复杂的结构。 这些运动密集地分布在非常稳定的边界层中。 这些分析将基于时间序列、跨网络的空间信息以及来自不同数据集的组合时空域。 分析将首先集中在微观方面。第一阶段的重点是增加温度的水平梯度。 第二阶段包括将水平梯度集中到微锋中的水平会聚。 对其他亚中运动的分析将遵循对每种类型的亚中运动的单独分析和对所有亚中运动的集体分析。 将详细研究次中尺度运动引起的大风向变化。 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。