Foehn Dynamics - Lagrangian Analysis and Large-Eddy Simulation

该项目考虑了Foehn研究的一些关键问题：Foehn空气的起源和变暖机制，Foehn下降到北部山谷和冷空气池的移动，不同Foehn味道的机制的变异性，以及NWP模式中Foehn流动的准确性。更具体地说，目标是：(1)对Foehn空气变暖和气团扰动的详细拉格朗日分析将扩展到几种(不同类型的)Foehn气流，从而评估微物理过程对变暖和扰动的影响；此外，沿Foehn轨迹的气团的热量收支将包括湍流和辐射产生的加热；(2)通过在NWP模式中标记和输送被动示踪物，将评估山谷中Foehn空气的来源；特别是，高山南侧的气团的初始高度将用作示踪物。这种分析将扩展现有的关于福恩空气在越过阿尔卑斯山峰顶之前的垂直演化的研究。作为一个额外的好处，标记阿尔卑斯山峰顶以上的气团，然后确定它们在福恩山谷的相对贡献，可以量化向下混合的程度；(3)将对选定的福恩山谷进行热量、水汽和动量收支的欧拉分析和大涡模拟(LES)，从而更好地理解福恩空气和地面之间的陆地-大气耦合，更清楚地了解这些过程如何影响初始冷池的位移(侵蚀)，并更好地理解当前和最近在使用的NWP模式中这些过程的参数化的弱点和强度；(4)为选定的案例研究计划的分析将延长(可能)10年的气候学时间尺度，但细节程度较低。为此，分析工具将与数值预报模拟和分析中的一种新方法(Sinegia项目crCLIM)相结合，其中数值预报模拟和分析工具并行运行，并通过数据虚拟化层相互通信。该项目将广泛使用Cosmo数值预报模式对Foehn案例的后播模拟。高分辨率的轨迹将根据这些后播进行计算。此外，大涡模拟将解决复杂的表面附近的流动演变。观测数据集将用于评估数值模拟。欧拉预算分析和拉格朗日分析将相辅相成，因此可以对福恩流进行全面分析。该项目将收获最新的方法进展，以揭示Foehn研究中的几个长期存在的问题，并有助于在NWP模式中更好地代表Foehn，从而带头改进对阿尔卑斯山地区一种关键的高影响天气现象的预报。

This project considers some of the key problems of Foehn research: the origin and warming mechanisms of the Foehn air, the descent of Foehn into the northern valleys and displacement of the cold air pool, the variability of the mechanisms for different Foehn flavors, and the accuracy of Foehn flows in NWP models. More specifically, the aims are: (i) The detailed Lagrangian analysis of Foehn air warming and of the scrambling of air masses will be extended to several (distinct flavors of) Foehn flows, hence assessing the impact of microphysical processes on warming and scrambling; additionally, the heat budget of the air parcels along the Foehn trajectories will include heating due to turbulence and radiation; (ii) The origin of the Foehn air in the valleys will be assessed by labeling and then transporting a passive tracer in the NWP model; in particular, the initial altitude of the air parcels on the Alpine south side will be used as a tracer. This kind of analysis will extend existing studies on the vertical evolution of Foehn air before it passes over the Alpine crest. As an additional benefit, labeling air masses above the Alpine crest and later determining their relative contribution in the Foehn valleys allows the degree of downward mixing to be quantified; (iii) Eulerian analysis of heat, moisture and momentum budgets and large-eddy simulations (LES) will be performed for selected Foehn valleys, resulting in a better understanding of the land-atmosphere coupling between Foehn air and the surface, in a clearer picture on how these processes influence the displacement (erosion) of the initial cold pools, and in a better understanding of the weaknesses and strengths of current and recently developed parameterizations of these processes in the NWP model used; (iv) The analyses planned for the selected case studies will, with a reduced degree of detail, be extended over a climatological time scale of (potentially) 10 years. To this aim, the analysis tools will be coupled to a novel approach in NWP simulations and analysis (Sinergia project crCLIM), where the NWP simulation and analysis tools run in parallel and communicate with each other by means of a data virtualization layer. The project will extensively use hindcast simulations of Foehn cases by the COSMO NWP model. The high- resolution trajectories will be calculated based on these hindcasts. Further, the LES simulations will address the complex flow evolution near the surface. Observational datasets will be used to evaluate the numerical simulations. The Eulerian budget analysis and Lagrangian analysis will complement each other and hence allow for a comprehensive analysis of the Foehn flow. The project will harvest recent methodological advances to shed new light on several long- standing problems in Foehn research and contribute to a better representation of Foehn in NWP models and hence lead the way for improved forecasts of a key high-impact weather phenomenon in Alpine regions.