Abstract
Abstract. Atmospheric composition measurements at Jungfraujoch are affected intermittently by boundary-layer air which is brought to the station by processes including thermally driven (anabatic) mountain winds. Using observations of radon-222, and a new objective analysis method, we quantify the land-surface influence at Jungfraujoch hour by hour and detect the presence of anabatic winds on a daily basis. During 2010–2011, anabatic winds occurred on 40% of days, but only from April to September. Anabatic wind days were associated with warmer air temperatures over a large fraction of Europe and with a shift in air-mass properties, even when comparing days with a similar mean radon concentration. Excluding days with anabatic winds, however, did not lead to a better definition of the unperturbed aerosol background than a definition based on radon alone. This implies that a radon threshold reliably excludes local influences from both anabatic and non-anabatic vertical-transport processes.
Highlights
High-altitude mountain sites have long been recognised as suitable places for characterising the chemical composition of the lower troposphere
The task of understanding vertical transport becomes complicated in mountainous terrain (Rotach and Zardi, 2007; Weissmann et al, 2005), which affects vertical exchange processes in site-specific ways that are not as well understood as processes occurring over flat terrain (Zardi and Whiteman, 2013)
We examine the implications of anabatic winds, showing that their detection can be linked to meteorological observations (Sect. 3.2), and that anabatic winds influence air-mass properties (Sect. 3.3)
Summary
High-altitude mountain sites have long been recognised as suitable places for characterising the chemical composition of the lower troposphere. The task of understanding vertical transport becomes complicated in mountainous terrain (Rotach and Zardi, 2007; Weissmann et al, 2005), which affects vertical exchange processes in site-specific ways that are not as well understood as processes occurring over flat terrain (Zardi and Whiteman, 2013). Because of this complexity, Stohl et al (2009) found that Alpine sites were less useful than flat sites for constraining regional estimates of greenhouse gas emissions
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