High-resolution numerical studies on the effect of turbulence on the structure of nocturnal radiation fogs

雾作为一种气象现象，会降低大气边界层中的能见度，对经济和人身安全产生重大影响。雾对航空、海洋和陆地运输造成的总经济损失与冬季风暴相当。尽管事实上，有大量的文献雾的研究，我们的知识，导致雾的形成及其微观结构的物理过程仍然是部分。这是由于许多复杂的过程，如辐射冷却，湍流混合和雾的微观物理相互作用的非线性。此外，地表植被和土壤特性的异质性使雾的可预测性进一步复杂化。因此，数值预报模式对雾的预报能力还很差。本计画将利用高解析度大涡模拟（LES）来探讨湍流对夜间辐射雾的影响。LES模式PALM将以1米量级的非常高的分辨率使用，同时采用欧拉体云物理方案和嵌入式拉格朗日粒子模型，该模型允许明确地分辨气溶胶和雾滴。这种创新的方法允许研究雾滴湍流相互作用的第一次LES。本文研究夜间雾层对早晨转捩和白天边界层的影响。此外，本文还利用LES方法研究了地面非均匀性对夜间辐射雾的影响。模拟数据将通过Cabauw（荷兰）和Lindenberg（德国）超级站点的观测数据进行强制和验证。

Fog as a meteorological phenomenon can have a strong impact on the economy but al-so on personal safety by reducing the visibility in the atmospheric boundary layer. Totaleconomic losses associated with fog on aviation, marine and land transportation are comparable to those of winter storms. Despite the fact that there is abundant literature on fog research, our knowledge about the physical processes that lead to fog formation and its microstructure remains partial. This is due to the fact that many complex processes like radiative cooling, turbulent mixing and the microphysics of fog interact non-linearly with each other. Moreover, surface heterogeneity regarding vegetation and soil characteristics further complicate the predictability of fog. Consequently, the fog forecasting capability of numerical weather prediction models is still poor. In this project, high-resolution large-eddy simulations (LES) will be used to investigate the effect of turbulence on nocturnal radiation fogs. The LES model PALM will be used at very high resolution in the order of 1 m with both an Eulerian bulk cloud physics scheme and an embedded Lagrangian particle model that allows for explicitly resolving aerosols and fog droplets will be employed. This innovative approach allows for studying fog droplet turbulence interactions for the first time with LES. The aim of this study is to study the effect of a nocturnal fog layer on the morning transition and the daytime boundarylayer. Moreover, the effect of surface heterogeneity on nocturnal radiation fog will beinvestigated by means of LES with prescribed idealized regular and observed irregular surface heterogeneities. The simulation data will be forced and validated with observational data from the super-sites at Cabauw (The Netherlands) and Lindenberg (Germany).