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

传统上，在大气边界层中的传输是根据湍流理论来量化的，该理论依赖于水平均匀流的假设。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，次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大部分。然而，实验数据表明，这种区别在现实中并不那么明显。因此，我们的目标是调查到何种程度的次中尺度输送可以忽略在白天的地面层（SL），以及如何次中尺度输送沿着过渡到混合层（ML）可以定量的特点。将进行大涡模拟（LES），以调查与这些次中尺度二次环流相关的色散通量如何依赖于地面以上的高度和其他大气尺度变量表征静态稳定性，以及这种高度依赖性如何受到地面异质性的影响。在WP 1中，基于理想化模拟和尺度分析以及白金汉-π定理（Buckingham-Pi theorem），这是边界层气象学中的一种常用方法，开发了色散通量的参数化。这个参数化，然后将被用来纠正测量的涡度协方差通量，否则不封闭的表面能量平衡。然后，在WP 2中，将对LAFO中心观测期进行真实的LES，以便利用多普勒、拉曼和DIAL激光雷达的三维大气运动数据进行评估。将采用PALM LES模型，网格间距小于4 m，覆盖至少10 x 10 km的区域。中尺度强迫由WRF模拟提供。之后，在WP 3中，将探索深度学习方法的潜力，以模拟表面异质性对色散通量产生的影响。在整个项目期间，从事该分项目的博士研究员的技能发展以及LAFI研究单位社区内的团队建设将作为WP 4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.