Fluxes in Advective and Transition Boundary Layers

这些研究人员将利用最近在科罗拉多州北公园的一个项目中由仪器飞机和地面塔进行的测量，研究地表变化如何影响地表上大气边界层的热量、水分和动量的输送。大多数对边界层的研究都考察了白天的条件，当地面加热导致充分发展的湍流和可预测的运输时，大多数研究都是在均匀地形上进行的。相反，这项研究将侧重于从夜间稳定条件到白天对流条件的转变，并将使用来自一个地区的测量数据，该地区由于散布着草地和灌木丛而存在显著的表面异质性。诸如此类的非均匀表面条件非常常见，因此该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，非均质性影响地表通量和边界层的发展，其方式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性质推断出来的。提出了一些具体的假设来指导该数据集的分析，包括在稳定条件下，当涡旋大小最小时，地表非均质性的影响预计最大，以及脉动排水或风场中尺度特征等瞬态模式经常改变地表通量型和净时间平均通量。这项研究将为改进非均匀地形上边界层中运输过程的表示奠定基础，因此将影响未来的天气和气候模式。研究人员计划了几个步骤来促进他们的结果的使用。将利用一个网站提供获取数据和结果的途径，并将举办一个讲习班，帮助向包括水管理和林务局人员在内的潜在用户提供信息。该项目还将通过研究生的支持和教育，帮助培养将来进行类似研究的能力。这些步骤应该有助于在建模者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.