Microfronts and Other Nocturnal Submeso Motions over Microtopography

这个奖项研究的是在夜间冷却的与地面相邻的空气边界层。最强烈的冷却发生在晴朗的天空和低风速。与其他有更明显的风或白天加热的边界层相比，这种情况知之甚少。强烈的冷却导致了一些实际问题，包括街道表面结冰和对敏感作物的霜冻损害。强烈的地表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异性，将污染物传播到各种风向上。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。地表冷却的局部空间变化是一个值得关注的重要特征。该项目将通过分析来自不同地点的强烈测量来增加理解。每个站点包含一个集群站点网络。上述分析将改进预报计算机模式的边界层部分。本文将研究非常稳定的夜间边界层不同亚类的一般分析，以及亚中观运动与这些亚类的关系。非常稳定的夜间边界层通常与低风速和晴朗的天空有关。亚中尺度运动发生的尺度比最大的湍流涡旋大，但比中尺度运动小。亚中观运动包括微锋、波动运动、蜿蜒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。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前沿。第一阶段的重点是增加温度的水平梯度。第二阶段包括水平辐合，将水平梯度集中到微锋面。对其他亚中观运动的分析随后将对每一种亚中观运动进行单独分析，并对所有亚中观运动进行集体分析。对由亚中观运动引起的大的风向变率的检查将被详细地检查。将对其他数据集进行评估，并可能建议制定新的量身定制的实地计划。该奖项反映了美国国家科学基金会的法定使命，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。

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.