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  Impact of surface and near-surface processes on ice crystal concentrations measured at mountain-top research stations

Beck, A., Henneberger, J., Schöpfer, S., Fugal, J. P., David, R. O., Lacher, L., et al. (2018). Impact of surface and near-surface processes on ice crystal concentrations measured at mountain-top research stations. Atmospheric Chemistry and Physics, 18(12), 8909-8927. doi:10.5194/acp-18-8909-2018.

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 Creators:
Beck, Alexander, Author
Henneberger, Jan, Author
Schöpfer, Sarah, Author
Fugal, Jacob P.1, Author           
David, Robert O., Author
Lacher, Larissa, Author
Lohmann, Ulrike, Author
Affiliations:
1Particle Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826291              

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 Abstract:

In situ cloud observations at mountain-top research stations regularly measure ice crystal number concentrations (ICNCs) orders of magnitudes higher than expected from measurements of ice nucleating particle (INP) concentrations. Thus, several studies suggest that mountain-top in situ cloud microphysical measurements are influenced by surface processes, e.g., blowing snow, hoar frost or riming on snow-covered trees, rocks and the snow surface. This limits the relevance of such measurements for the study of microphysical properties and processes in free-floating clouds.

This study assesses the impact of surface processes on in situ cloud observations at the Sonnblick Observatory in the Hohen Tauern region, Austria. Vertical profiles of ICNCs above a snow-covered surface were observed up to a height of 10 m. The ICNC decreases at least by a factor of 2 at 10 m if the ICNC at the surface is larger than 100 L−1. This decrease can be up to 1 order of magnitude during in-cloud conditions and reached its maximum of more than 2 orders of magnitudes when the station was not in cloud. For one case study, the ICNC for regular and irregular ice crystals showed a similar relative decrease with height. This suggests that either surface processes produce both irregular and regular ice crystals or other effects modify the ICNCs near the surface. Therefore, two near-surface processes are proposed to enrich ICNCs near the surface. Either sedimenting ice crystals are captured in a turbulent layer above the surface or the ICNC is enhanced in a convergence zone because the cloud is forced over a mountain. These two processes would also have an impact on ICNCs measured at mountain-top stations if the surrounding surface is not snow covered. Conclusively, this study strongly suggests that ICNCs measured at mountain-top stations are not representative of the properties of a cloud further away from the surface.

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Language(s): eng - English
 Dates: 2018
 Publication Status: Issued
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.5194/acp-18-8909-2018
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Title: Atmospheric Chemistry and Physics
  Abbreviation : ACP
Source Genre: Journal
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Publ. Info: Göttingen : Copernicus Publications
Pages: - Volume / Issue: 18 (12) Sequence Number: - Start / End Page: 8909 - 8927 Identifier: ISSN: 1680-7316
CoNE: https://pure.mpg.de/cone/journals/resource/111030403014016