Processes of cold‐air pool (CAP) erosion in an Alpine valley during south foehn are investigated based on a real‐case large‐eddy simulation (LES). The event occurred during the second Intensive Observation Period (IOP 2) of the PIANO field experiment in the Inn Valley, Austria, near the city of Innsbruck. The goal is to clarify the role of advective versus turbulent heating, the latter often being misrepresented in mesoscale models. It was found that the LES of the first day of IOP 2 outperforms a mesoscale simulation, is not yet perfect, but is able to reproduce the CAP evolution and structure observed on the second day of IOP 2. The CAP exhibits strong heterogeneity in the along‐valley direction. It is weaker in the east than in the west of the city with a local depression above the city. This heterogeneity results from different relative contributions and magnitudes of turbulent and advective heating/cooling, which mostly act against each other. Turbulent heating is important for faster CAP erosion in the east and advective cooling is important for CAP maintenance to the west of Innsbruck. The spatial heterogeneity in turbulent erosion is linked to splitting of the foehn into two branches at the mountain range north of the city, with a stronger eastward deflected branch. Intensification of the western branch at a later stage leads to complete CAP erosion also to the west of Innsbruck. Above the city centre, turbulent heating is strongest, and so is advective cooling by enhanced pre‐foehn westerlies. These local winds are the result of CAP heterogeneity and gravity‐wave asymmetry. This study emphasizes the importance of shear‐flow instability for CAP erosion. It also highlights the large magnitudes of advective and turbulent heating compared to their net effect, which is even more pronounced for individual spatial components.

中文翻译：

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PIANO IOP 2期间Inn山谷中foehn-冷池相互作用的大涡模拟

基于实际大涡模拟（LES），研究了南福恩地区高寒山谷中冷空气池（CAP）的侵蚀过程。该事件发生在奥地利因斯布鲁克市附近的Inn Valley的PIANO野外实验的第二个密集观测期（IOP 2）中。目的是弄清平流与湍流加热的作用，后者在中尺度模型中常常被错误地描述。已发现，IOP 2第一天的LES优于中尺度模拟，尚不理想，但能够重现IOP 2第二天观察到的CAP演变和结构。谷方向。东部地区比西部地区弱，城市上方有局部凹陷。这种异质性是由于湍流和对流加热/冷却的相对相对贡献和大小不同而引起的，它们之间相互影响很大。湍流加热对于东部CAP的快速腐蚀很重要，而对流冷却对于因斯布鲁克西部的CAP维护很重要。湍流侵蚀的空间异质性与城市北部地区的foehn分裂成两个分支有关，并具有更强的向东偏转分支。稍后，西部分支的集约化也会导致因斯布鲁克西部的CAP完全侵蚀。在市中心以上，湍流加热最强，而射流前西风的增强也有利于对流冷却。这些局部风是CAP异质性和重力波不对称的结果。这项研究强调了剪切流不稳定性对CAP侵蚀的重要性。它也突出了与对流和湍流的净效应相比，对流和湍流加热的幅度很大，这对于单个空间分量而言更为明显。