Preprints
https://doi.org/10.5194/acp-2021-710
https://doi.org/10.5194/acp-2021-710

  12 Oct 2021

12 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

The diurnal and seasonal variability of ice nucleating particles at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland

Cyril Brunner1, Benjamin Tobias Brem2, Martine Collaud Coen3, Franz Conen4, Martin Steinbacher5, Martin Gysel-Beer2, and Zamin Abdulali Kanji1 Cyril Brunner et al.
  • 1Institute for Atmospheric and Climate Science, ETH, Zurich, CH-8092, Switzerland
  • 2Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
  • 3Federal Office of Meteorology and Climatology, MeteoSwiss, CH-1530 Payerne, Switzerland
  • 4Department of Environmental Sciences, University of Basel, CH-4056 Basel, Switzerland
  • 5Laboratory for Air Pollution / Environmental Technology, Empa, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland

Abstract. Cloud radiative properties, cloud lifetime, and precipitation initiation are strongly influenced by the cloud phase. Between ~ 235 and 273 K, ice nucleating particles (INPs) are responsible for the initial phase transition from the liquid to the ice phase in cloud hydrometeors. This study analyzes immersion-mode INP concentrations measured at 243 K at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.) between February 2020 and January 2021, thereby presenting the longest continuous, high-resolution (20 min) data set of online INP measurements to date. The high time resolution and continuity allow to study the seasonal and the diurnal variability of INPs. After exclusion of special events, like Saharan dust events (SDEs), we found a seasonal cycle of INPs, highest in April (median in spring 3.1 INP std L−1), followed by summer (median: 1.6 INP std L−1) and lowest in fall and winter (median: 0.5 INP std L−1 and 0.7 INP std L−1, respectively). Pollen or subpollen particles were deemed unlikely to be responsible for elevated INP concentrations in spring and summer, as periods with high pollen loads from nearby measurement stations do not coincide with the periods of high INP concentrations. Furthermore, for days when the site was purely in the free troposphere (FT), no diurnal cycle in INP concentrations was observed, while days with boundary layer intrusions (BLI) showed a diurnal cycle. The seasonal and diurnal variability of INPs during periods excluding SDEs is with a factor of 7 and 3.3, respectively, significantly lower than the overall variability observed in INP concentration including SDEs of more than three orders of magnitude, when peak values result from SDEs. The median INP concentration over the analyzed 12 months was 1.2 INP std L−1 for FT periods excluding SDEs, and 1.4 INP std L−1 for both FT and BLI, and incl. SDEs, reflecting that despite SDEs showing strong but comparatively brief INP signals, they have a minor impact on the observed annual median INP concentration.

Cyril Brunner et al.

Status: open (until 23 Nov 2021)

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Cyril Brunner et al.

Cyril Brunner et al.

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Short summary
Microscopic particles called ice-nucleating particles (INPs) are essential for ice crystals to form in clouds. INPs are a tiny proportion of atmospheric aerosol and their abundance is poorly constrained. We study how the concentration of INPs changes diurnally and seasonally at a mountain top station in central Europe. Unsurprisingly, a diurnal cycle is only found when considering air masses that have had lower altitude ground contact. The highest INP concentrations occur in spring.
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