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低层大气之间的热量，水分，动量和污染物交换的理解，当近地面的大气层非常稳定时。 在这些条件下，风随高度和时间的变化以及大气对热量和其他物质的垂直输送与适用于普通白天条件的理论不一致。 在白天，表面加热导致靠近地面的空气变得不稳定，导致对流，发展良好的湍流，可预测的温度，风速和湿度分布，因此可预测的热量和水蒸气的垂直通量。 但在夜间，地面寒冷，空气稳定，湍流经常是间歇性的，由与地形诱导的排水流相关的垂直风切变引起。 最近的CASES-99实地项目（堪萨斯，1999年10月）表明，排水风经常形成于坡度不大的地面上，并且可能仅限于大气层最低的几米处。 热的垂直通量和其他性质是由排水流中的剪切和湍流决定的，但这些特征并不为人所知，因为测量通常在垂直方向上相隔太远，无法很好地代表真实的结构。 本项目采取两种办法。 一个是分析过去实地项目（特别是CASES-99）的现有数据。 分析的重点是理解湍流的间歇性爆发，这是稳定条件下热量和动量的涡流传输的主要原因。 CASES数据可以区分由排水流顶部剪切产生的湍流和在其他地方产生并平流到观测点的湍流。 第二种方法是进行一个小型的实地项目，重点是采用新仪器对稀薄的排水流进行测量，以便在空间和时间上进行高分辨率的测量。 这些仪器包括热膜风速计、具有短路径长度和小型化传感器的声波风速计以及激光多普勒风速计。 这项研究的结果将改进非常稳定的边界层中的输送过程公式，用于天气预报和气候预测的大规模数值模式。