Turbulent fluxes and thermal convection in a valley

该项目是一个正在进行的项目的第三年延伸，该项目利用COPS实验的表面能量交换测量结合大涡模拟(LES)来研究Kinzig山谷(黑森林中心)边界层对流的发展。初步建立了地面湍流通量测量的质控数据库，检查了各通量点的能量平衡闭合情况。在Kinzig河谷，选择了与地面附近开始自由对流情况有关的日子，作为进一步开展大涡模拟研究的基础。将大涡模拟模式应用于Kinzig河谷的非均匀地形，进行了地形复杂、下界热通量强迫不均匀的理想化模式运行。在前期工作的基础上，第三年的延期将使我们能够集中精力模拟一些选定的自由对流情况，测试它们对地表不均匀和地形细节的敏感性，并研究它们对边界层热力学结构的影响。此外，还将用OGO、谱和小波分析方法研究对流事件的空间和时间尺度。考虑二次环流在非均匀地形上发展的通量贡献，尝试在模式区域内借助“虚拟塔”关闭表面能量平衡方程。这将导致根据二次环流的通量贡献对通量测量进行修正。

The proposed project is the 3rd year extension of a running project, which investigates the development of boundary layer convection in the Kinzig valley (center Black Forest) with the help of surface energy exchange measurements of the COPS experiment combined with large-eddy simulations (LES). Preliminary work was done setting up a quality controlled data base of surface turbulent flux measurements and checking the energy balance closure of all flux sites. In the Kinzig valley, relevant days with situations of free convection initiated near the ground were selected, which serve as a base for further LES studies. A LES model was adapted to the heterogeneous landscape of the Kinzig valley and idealized model runs with complex topography and heterogeneous forcing by heat fluxes at the lower boundary were carried out. Based on this preliminary work, the 3rd year extension will allow us to concentrate on the simulation of some selected free convection situations and test their sensitivity to surface inhomogeneities and orographic details and investigate their impact on the thermodynamic structure of the boundary layer. Moreover, the spatial and temporal scales of the convective events will be studied with ogive, spectral and wavelet analysis methods. An attempt to close the surface energy balance equation with the help of “virtual towers“ within the model domain will be made by considering flux contributions of secondary circulations, which develop over heterogeneous terrain and are not captured by stationary fixed-point turbulence measurements. This will lead to a correction of the flux measurements dependent on the flux contributions of the secondary circulations.