Fluxes in Advective and Transition Boundary Layers

这些研究人员将利用科罗拉多州北部公园最近一个项目中由仪表式飞机和地面塔进行的测量，研究陆地表面的变化如何影响该表面上的大气边界层中的热量、水分和动量的传输。大多数对边界层的研究都考察了白天的条件，当地面加热导致良好的湍流和可预测的输送时，大多数研究都是在均匀的地形上进行的。这项研究将把重点放在从夜间稳定条件向白天对流条件的转变上，并将使用从散布的草地和灌木丛导致地表显着不均匀的区域进行的测量。像这样的非均匀表面条件是非常常见的，因此这项研究将提供关于现实边界层的有价值的新信息。研究人员指出，非均质性对地表通量和边界层发展的影响，并不是简单地从均匀地形或甚至具有不连续过渡的地形上的边界层特性得出的。提出了一些具体的假设来指导对这一数据集的分析，包括在稳定条件下，当涡旋尺度最小时，地表非均质性的影响最大，以及瞬变模式，如脉动排水流或风场中的中尺度特征，经常改变地表通量模式和净时间平均通量。这项研究将为改进非均匀地形上边界层中输送过程的表示奠定基础，因此应该会影响未来的天气和气候模型。调查人员计划了几个步骤，以促进他们的结果的使用。将利用一个网站提供查阅数据和成果的途径，并将举办一次讲习班，以帮助向潜在用户提供信息，包括水管理和林业局人员。该项目还将通过对一名研究生的支持和教育，帮助培养今后进行类似研究的能力。这些步骤应该有助于在建模人员和其他潜在用户中宣传他们的研究结果。

These investigators will use measurements that were made by an instrumented aircraft and by surface towers in a recent project at North Park, Colorado to study the ways in which variability in the land surface affects transport of heat, moisture, and momentum in the atmospheric boundary layer overlying that surface. Most studies of the boundary layer have examined daytime conditions when surface heating leads to well-developed turbulence and predictable transport, and most studies have been conducted over uniform terrain. This study will instead focus on the transition from nighttime stable conditions to daytime convective conditions and will use measurements from a region where there is significant surface heterogeneity resulting from interspersed patches of grass and brush. Heterogeneous surface conditions such as these are very common, so the study will provide valuable new information on realistic boundary layers. The investigators note that heterogeneity influences the surface fluxes and the development of the boundary layer in ways that are not simply deduced from the properties of boundary layers over uniform terrain or even terrain with discontinuous transitions. Some specific hypotheses are offered to guide the analyses of this data set, including that the impact of surface heterogeneity is expected to be greatest under stable conditions when the eddy size is smallest and that transient modes such as pulsating drainage flows or mesoscale features in the wind field frequently alter the surface flux patterns and net time-average flux. The research will establish a basis for improved representation of transport processes in boundary layers over inhomogeneous terrain and so should influence future models of weather and climate. The investigators plan several steps that will facilitate use of their results. A web site will be used to provide access to data and results, and a workshop will be held to help inform potential users including water management and Forest Service personnel. The project will also help develop capabilities for similar studies in the future through the support and education of a graduate student. These steps should help publicize the results from their research among modelers and other potential users.