![]() ![]() Moreover, cloud venting defines the process between the PBL and free troposphere caused by cumulus formation in combination with strong upslope winds (Kossmann et al. Vice versa, air from the free troposphere can enter the PBL by entrainment, especially upwind of mountain ranges. Mountain venting describes the process by which upslope winds increase the altitude of the PBL height locally, and if strong enough, trigger the vertical exchange of PBL air into the free troposphere. mixing of PBL air masses into the free troposphere by cloud and mountain venting. However, mountain ranges enable exchange processes, also called handover processes (Kossmann et al. The few available studies are based on highly simplified and idealized parametrizations of mountains, undulating areas or valleys (Stull 1988 Whiteman 2000 Wekker et al. 2004 Weigel 2005), knowledge of PBL behaviour over mountainous areas is rather incomplete to date. While several PBL representations and studies have been designed for flat terrain (Garratt 1994 Wekker et al. The planetary boundary layer (PBL) is the lowest part of the troposphere that is directly influenced by the Earth’s surface-the layer next to the Earth’s surface in which the effects of friction and surface heating are felt on a time scale of about 1 h or less (Stull 1988). The continuous aerosol in situ measurements at Jungfraujoch were clearly influenced by the local PBL development but also by long-range transport phenomena such as Saharan dust or pollution from the south. This was confirmed by the in situ aerosol measurements at Jungfraujoch with a significant increase in particle number concentration, particle light absorption and scattering coefficients when PBL-influenced air masses reached the station in the afternoon hours. Air parcels were transported upwards by slope winds towards Jungfraujoch when the PBL was higher than 2,800 m a.s.l. The results were additionally compared with the PBL height estimated by the numerical weather prediction model COSMO-2, which showed a clear underestimation of the PBL height for most of the cases but occasionally also a slight overestimation especially around noon, when the PBL showed its maximum extent. The retrieved values from the ceilometer and wind profiler agreed well during daytime and cloud-free conditions. Data from the ceilometer were analyzed using two different algorithms, while the signal-to-noise ratio of the wind profiler was studied to compare the retrieved PBL heights. A ceilometer and a wind profiler were installed at Kleine Scheidegg, a mountain pass close to Jungfraujoch, located at an altitude of 2,061 m a.s.l. The high-altitude research station at Jungfraujoch (3,580 m a.s.l.) in the Swiss Alps lies for most of the time in the free troposphere except when it is influenced by the PBL reaching the station, especially during the summer season. The development of the planetary boundary layer (PBL) has been studied in a complex terrain using various remote sensing and in situ techniques. ![]()
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