Fluxes in Advective and Transition Boundary Layers

这些研究人员将利用最近在科罗拉多北公园的一个项目中由仪表飞机和地面塔进行的测量来研究陆地表面的变化如何影响覆盖在该表面上的大气边界层中的热量、水分和动量的传输。大多数边界层的研究都是在白天的条件下进行的，当时地面加热导致了充分发展的湍流和可预测的输送，而且大多数研究都是在均匀的地形上进行的。这项研究将侧重于从夜间稳定条件到白天对流条件的过渡，并将使用来自一个地区的测量结果，该地区存在显着的表面异质性，这些异质性是由散布的草地和灌木丛造成的。像这样的非均匀表面条件是非常常见的，因此这项研究将为实际边界层提供有价值的新信息。研究人员注意到，非均匀性影响表面通量和边界层的发展，其方式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推导出来的。提供了一些具体的假设来指导这一数据集的分析，包括表面异质性的影响预计将是最大的稳定条件下，当涡的大小是最小的和瞬态模式，如脉动排水流或风场中的中尺度功能经常改变表面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边界层中传输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式。研究人员计划了几个步骤，以促进其结果的使用。将利用一个网站提供数据和结果，并将举办一个讲习班，帮助向包括水管理人员和森林服务人员在内的潜在用户提供信息。该项目还将通过对一名研究生的支持和教育，帮助发展今后进行类似研究的能力。这些步骤应有助于向建模者和其他潜在用户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.