The Effect of Land Surface Heterogeneity on the Atmospheric Boundary-Layer Structure and Measurements

在LITFASS-2003试验中，收集了非均质陆地表面大气边界层结构的综合实验数据集。这项活动是在德国气候研究计划（DEKLIM）的EVA grip（网格和像素尺度蒸发）项目中实现的。测量包括14个地面通量站的运行，两个位于99米高塔上的涡流协方差系统，三个大孔径闪烁仪（LAS），以及使用直升机携带的湍流探测器Helipod进行35次低空飞行的性能。在EVA grip（于2004年到期）中，对有关蒸发面积平均值的测定的实验数据进行了分析。根据目前的建议，我们的目标是进一步分析LITFASS-2003数据集，以消除我们对非均质陆地表面湍流ABL结构和过程的理解方面的现有缺陷。需要调查的问题如下：1。地形非均质性、非均质土地利用和非均质大气强迫对ABL结构的相对重要性是什么？在非均质陆地表面上，ABL在什么条件下和在什么水平上发生水平混合？不同空间尺度上的异质性效应能否解释非封闭表面能量平衡？不同的时间尺度、标量相似性和热诱导的二次环流如何影响湍流通量的测量，对大气模式中湍流通量的参数化有什么影响？实验数据的分析将通过对已经完成的大涡模拟（LES）运行数据的进一步解释，以及根据我们以前的发现和具体的研究目标专门设置的新LES运行的性能来支持。最后，将推导出测量、数据分析和建模策略的含义，包括在异质景观中对表面层和剖面测量系统的适当设置和选址的建议。实验策略应辅以适当校正局部湍流表面通量的方法，以实现表面能量平衡的封闭。

An comprehensive experimental data set on the structure of the atmospheric boundary layer (ABL) over a heterogeneous land surface has been collected during the LITFASS-2003 experiment. This campaign was realised within the EVA GRIPS (Evaporation at Grid and Pixel Scale) project of the German Climate Research Program (DEKLIM). Measurements included the operation of 14 surface flux stations, two eddy-covariance systems at a 99 m tower, three large-aperture scintillometers (LAS) and the performance of 35 low-level flights using the Helipod, a turbulence probe carried by a Helicopter. Within EVA GRIPS (which expired in 2004), the experimental data have been analysed with respect to the determination of area-averaged values of evaporation.With the present proposal we aim at a further analysis of the LITFASS-2003 data set in order to remove existing deficits concerning our understanding of the turbulent ABL structure and processes over a heterogeneous land surface. The following issues shall be investigated:1. What is the relative importance of terrain heterogeneity, heterogeneous land use and heterogeneous atmospheric forcing on the ABL structure?2. On which conditions and at which levels does horizontal mixing occur in the ABL over a heterogeneous land surface?3. Can heterogeneity effects at different spatial scales explain the non-closed surface energy balance?4. How do different time scales, scalar similarity and thermally-induced secondary circulations influence turbulent flux measurements, and what are the implications for the parameterisation of turbulent fluxes in atmospheric models?Analysis of experimental data will be supported by a further interpretation of data from Large-Eddy Simulation (LES) runs already completed and by the performance of new LES runs set up specifically in light of our previous findings and specific research aims. Finally, implications for measurement, data analysis and modelling strategies shall be derived, including recommendations for a suitable set-up and siting of surface layer and profile measurement systems in a heterogeneous landscape. The experiment strategy shall be supplemented by a methodology to appropriately correct local turbulent surface fluxes in order to achieve closure of the surface energy balance.