Transport in Stable Boundary Layers and Thin Drainage Flows

稳定边界层和薄排水流中的传输

• 批准号: 0107617
• 负责人: Larry Mahrt
• 金额: $ 61.72万
• 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: 2001
• 资助国家: 美国
• 起止时间: 2001-10-01 至 2007-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0107617&HistoricalAwards=false
• 关键词: Transport; Stable; Boundary; Layers; Thin

The purpose of this project is to improve our understanding of the exchange of heat, moisture, momentum, and contaminants between the earth's surface and the lower atmosphere when the atmospheric layer near the ground is extremely stable. In these conditions, the variation of the wind with height and time and the vertical transport of heat and other material by the atmosphere do not conform to the theories appropriate for ordinary daytime conditions. During the day, surface heating causes the air next to the ground to become unstable, leading to convection, well-developed turbulence, predictable profiles of temperature, wind velocity, and humidity, and therefore predictable vertical fluxes of heat and water vapor. But at night, the surface is cold, the air stable, and the turbulence often intermittent and caused by vertical wind shear associated with terrain-induced drainage flows. The recent CASES-99 field program (Kansas, October 1999) showed that drainage winds often form over ground that is only gently sloping, and may be confined to only the lowest few meters of the atmosphere. The vertical flux of heat and other properties is determined by the shear and turbulence in the drainage flow, but these characteristics are not well known because measurements are ordinarily too widely separated in the vertical to give a good representation of the true structure. Two approaches are pursued in this project. One is to analyze existing data from past field programs (especially CASES-99). The analysis focuses on understanding the intermittent bursts of turbulence that account for much of the eddy transport of heat and momentum in stable conditions. The CASES data make it possible to distinguish between the turbulence generated locally by shear at the top of the drainage flow and that which is created elsewhere and advected over the observing site. The second approach is to conduct a small field program focussed on thin drainage flows employing new instruments to enable measurements with high resolution in space and time. These instruments include hot-film anemometers, sonic anemometers with short path lengths and miniaturized transducers, and laser-Doppler anemometry. The result of the research will be an improved formulation of transport processes in the very stable boundary layer for use in large-scale numerical models for weather forecasting and climate prediction.

该项目的目的是提高我们对地球表面和下部大气之间热，水分，动量和污染物的交换的理解，当时地面附近的大气层非常稳定。 在这些条件下，风与高度和时间的变化以及大气中的热和其他材料的垂直运输不符合适合普通白天条件的理论。 白天，表面加热会导致地面旁边的空气变得不稳定，导致对流，发达的湍流，可预测的温度，风速和湿度的可预测曲线，因此可预测的热和水蒸气垂直通量。 但是到了晚上，表面很冷，空气稳定，湍流通常是间歇性的，并且是由与地形引起的排水流有关的垂直风剪。 最近的99案例野外计划（堪萨斯州，1999年10月）表明，排水风通常在地面上形成，而地面仅倾斜，并且可能仅限于大气中最低的几米。 热量和其他特性的垂直通量取决于排水流中的剪切和湍流，但是这些特征并不众所周知，因为通常在垂直方面的测量值太广泛地分离，无法很好地表示真实的结构。 该项目采用了两种方法。 一种是分析过去现场程序（尤其是案例99）的现有数据。 该分析的重点是理解在稳定条件下热量和动量的大部分涡流运输的间歇性爆发。 案例数据使得可以区分排水流顶部的剪切物以及在其他地方创建并在观测部位上延伸的湍流。 第二种方法是进行小型野外计划，该计划专注于使用新仪器的薄引流流，以实现高分子和时间分辨率的测量。 这些仪器包括热膜启示仪，具有短路径长度和微型换能器的声音动态计和激光多普勒动态计。 该研究的结果将是在非常稳定的边界层中改进​​的运输过程的表述，用于用于天气预报和气候预测的大规模数值模型。