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Spatial heterogeneity of the Inn Valley Cold Air Pool during south foehn: Observations from an array of temperature loggers during PIANO
Meteorologische Zeitschrift ( IF 1.2 ) Pub Date : 2021-04-22 , DOI: 10.1127/metz/2020/1043
Thomas Muschinski , Alexander Gohm , Maren Haid , Lukas Umek , Helen C. Ward

Interactions between foehn and mountain-valley cold air pools (CAPs) strongly influence severe weather and air quality at the valley bottom, but have seen limited research compared to the fully established foehn phase. The Penetration and Interruption of Alpine Foehn (PIANO) campaign was conducted in the Inn Valley near Innsbruck (Austria) during fall and early winter 2017 to investigate these interactions. The focus of this paper is evaluating spatial heterogeneity of the Inn Valley CAP near Innsbruck during south foehn using observations from the six PIANO Intensive Observation Periods (IOPs). In particular, the analysis is concentrated on an array of 50 temperature loggers deployed throughout the greater Innsbruck area. A selection of these loggers were used for slope profiles above the valley floor at four different locations (north, south, east and west of the city center). To obtain a single quantitative measure combining information of both CAP strength and depth, temperature observations from the slope stations were used to approximate mean potential temperatures for each profile. It was found that foehn can lead to strong CAP heterogeneity in both south-north and west-east directions. Stronger and/or thicker CAPs in the west can partially explain the well known pre-foehn westerlies in Innsbruck by enhancing the along-valley pressure gradient at the valley bottom. Typically observed initial foehn breakthroughs east of the city mirrored the spatial heterogeneity within the pre-foehn CAP. West-east differences in profile-mean potential temperatures were compared to west-east valley bottom pressure differences to investigate the cause of the enhanced pressure gradient forcing pre-foehn westerlies. For IOPs 2, 4 and 6, the relationship was approximately linear. The exception was the strongest foehn event IOP 7. The interpretation is that for weaker foehn cases, valley bottom pressure differences are closely related to spatial differences in CAP depth or strength, whereas during stronger foehn, valley-bottom pressure differences mainly result from gravity wave asymmetry within the foehn flow. Differences in profile-mean potential temperatures between north and south were less in magnitude than between east and west. They were found to have a relationship with Froude numbers calculated from the observed upstream foehn wind speed and column integrated buoyancy within the CAP.

中文翻译:

南福恩省Inn Valley冷空气池的空间异质性:来自PIANO期间一系列温度记录仪的观测

福恩河与山谷冷气池(CAPs)之间的相互作用强烈影响着谷底的恶劣天气和空气质量,但与完全建立的福恩河相相比,研究有限。2017年秋季和初冬期间,在因斯布鲁克(奥地利)附近的因河谷(Inn Valley)开展了对阿尔卑斯山的穿透和破坏(PIANO)活动,以调查这些相互作用。本文的重点是使用六个PIANO密集观测期(IOP)的观测值,评估南福恩省因斯布鲁克附近的因斯布鲁克CAP的空间异质性。尤其是,分析集中在遍布整个因斯布鲁克地区的50个温度记录仪组成的阵列上。这些记录器中的一部分用于在四个不同位置(北,南,市中心的东部和西部)。为了获得结合CAP强度和深度的信息的单一定量测量方法,使用斜坡站的温度观测值来近似估算每个剖面的平均潜在温度。发现foehn可以导致南北和西向强烈的CAP异质性。西部的更强和/或更厚的CAP可以通过增强山谷底部的沿谷压力梯度来部分解释因斯布鲁克的著名的前西风。通常观察到的在城市以东的初始foehn突破反映了泡沫前CAP内的空间异质性。将剖面平均潜在温度的西-东差异与西-东谷底压力差异进行了比较,以研究造成压力梯度增加前缘西风的原因。对于IOP 2、4和6,该关系近似线性。例外是最强的foehn事件IOP7。解释是,对于较弱的foehn事件,谷底压力差与CAP深度或强度的空间差异密切相关,而在更强的foehn情况下,谷底压力差主要由重力波引起foehn流内的不对称性。北部和南部之间的剖面平均潜在温度差异在幅度上要小于东部和西部之间。
更新日期:2021-04-20
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