Investigations of ABL dynamics and structure over heterogeneous surfaces with turbulence-resolving simulations (LES)

传统上，大气边界层中的传输是基于湍流理论来量化的，该理论依赖于水平均匀流动的假设。这允许通过垂直方向上的一维通量进行局部描述。虽然这一假设可能适用于地面附近的小尺度湍流，但众所周知，在典型的白天对流条件下，亚中尺度输送过程往往构成边界层中部能量和物质垂直交换的主要部分。然而，实验数据表明，这种区别在现实中并不那么明显。因此，我们的目标是研究在多大程度上可以忽略白天近地面层(SL)的亚中尺度输送，以及如何定量地表征沿向混合层(ML)过渡的亚中尺度输送。大涡模拟(LES)将被用来研究与这些次中尺度次级环流相关的色散通量如何依赖于地面以上高度和其他表征静态稳定性的大气尺度变量，以及这种高度依赖关系如何受到地面非均质性的影响。在WP1中，基于理想的模拟和尺度分析以及边界层气象学中常用的Buckingham-Pi定理，发展了一个弥散通量的参数化。然后，该参数将被用于修正测量到的涡旋协方差通量，以用于其他未封闭的表面能量平衡。然后，在WP2中，将对中心Lafo观测期进行真实的大涡模拟，以便能够利用多普勒、拉曼和拨盘激光雷达的三维大气运动数据进行评估。Palm Les模型将被采用，网格间距小于4米，覆盖至少10 x 10公里的区域。中尺度强迫由WRF模拟提供。然后，在WP3中，将探索深度学习方法的潜力，以模拟地表非均质性对弥散通量产生的影响。在整个项目期间，在这个子项目上工作的博士研究员的技能发展和LAFI研究单位社区内的团队建设将作为WP4的一部分得到促进。

Traditionally, transport in the atmospheric boundary layer is quantified based on a turbulence theory that relies on the assumption of horizontally homogeneous flow. This allows for a local description through one-dimensional fluxes in the vertical direction. While this assumption may hold for small-scale turbulence near the surface, it is well-known that sub-mesoscale transport processes often constitute a majority of the vertical exchange of energy and matter in the middle of the boundary layer under typical daytime convective conditions. However, experimental data indicate that this distinction is not that clear in reality. Hence, we aim to investigate to what extent sub-mesoscale transport can be neglected in the daytime surface layer (SL), and how the sub-mesoscale transport along the transition towards the mixed layer (ML) can be characterized quantitatively. Large-eddy simulations (LES) will be conducted to investigate how the dispersive fluxes associated with these sub-mesoscale secondary circulations depend on the height above the surface and other atmospheric scaling variables characterizing static stability, and how this height-dependence is influenced by surface heterogeneity. In WP1, a parameterization of the dispersive fluxes is developed based on idealized simulations and scaling analysis and the Buckingham-Pi theorem, which is a common method in boundary-layer meteorology. This parameterization will then be used to correct the measured eddy-covariance fluxes for the otherwise unclosed surface energy balance. Then, in WP2, realistic LES will be carried out for the central LAFO observation period in order to allow for an evaluation with data of the three-dimensional atmospheric motion from Doppler-, Raman- and DIAL lidars. The PALM LES model will be employed with a grid-spacing of less than 4 m covering a domain of at least 10 x 10 km. The mesoscale forcing is provided by WRF simulations. Afterwards, in WP3, the potential of deep learning methods will be explored to model the influence of surface heterogeneity on the generation of dispersive fluxes. During the entire project period, skill development of the doctoral researcher working on this sub-project, and team building within the LAFI research unit community will be promoted as part of WP4.