Study of Diurnal Transitions in the Atmospheric Boundary Layer

这个项目是对大气边界层的研究，大气边界层是靠近地球表面的一层，湍流的空气运动在大气和地球之间传递热量、水分和动量。过去的大多数研究都认为这一层处于稳定状态，但转变不断发生并影响其结构。边界层经历了一个日循环，从一个稳定的夜间层经过过渡状态到正午对流期，然后再经过过渡状态回到稳定的夜间状态。本研究将集中在过渡时期和中午对流期。使用的主要工具是大涡模拟（LES），这是一种模型技术，其中显式表示大于某一特定尺寸的湍流运动，而以参数化形式表示较小尺寸运动的平均影响。为了补充LES的结果，研究人员还将检查一组记录良好的过去实验的观察结果，这些实验研究了不同位置的边界层。预期的结果将是将边界层结构的知识扩展到过渡时期，并更好地理解短暂湍流影响该层的方式。这项研究和类似的研究的长期好处将是在天气和气候模式中更好地代表边界层。这样的模型必须能反映地球和大气之间真实的热量、水分和动量的流动，但不能解决造成这种流动的精细结构。因此，通量必须以大尺度变量的形式参数化地表示。准确的参数表示的发展将依赖于像这样的详细研究的结果。该项目还将为研究生提供培训，从而有利于这一研究领域的未来工作。

This project is a study of the atmospheric boundary layer, that layer near the surface of the Earth where turbulent air motions transfer heat, moisture, and momentum between the atmosphere and the Earth. Most past studies have treated this layer as being in a steady state, but transitions occur continually and influence its structure. The boundary layer undergoes a diurnal cycle that moves from a stable nighttime layer through transitional states to a midday convective period and then again through transitional states back to stable nighttime condition. This study will focus on the transition periods and the mid-day convective period. The primary tool to be used is large-eddy simulation (LES), a model technique in which turbulent motions larger than some specified size are represented explicitly while the average influence of the motions at smaller sizes is represented in parameterized form. To complement the LES results, the investigators also will examine observations from a set of well-documented past experiments that have studied the boundary layer in different locations. The expected results will be an extension of knowledge of boundary layer structure to periods of transition and a better understanding of the ways in which transitory turbulence affects that layer.A long-range benefit of this and similar studies will be better representation of the boundary layer in weather and climate models. Such models must represent realistic fluxes of heat, moisture, and momentum between the Earth and the atmosphere but cannot resolve the fine-scale structures responsible for such fluxes. As a result, the fluxes must be represented parameterically in terms of large-scale variables. The development of accurate parametric representations will rely on results from detailed studies like this one. The project will also benefit future work in this area of research by providing training for a graduate student.