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| Titel |
The origins of ice crystals measured in mixed-phase clouds at the high-alpine site Jungfraujoch |
| VerfasserIn |
G. Lloyd, T. W. Choularton, K. N. Bower, M. W. Gallagher, P. J. Connolly, M. Flynn, R. Farrington, J. Crosier, O. Schlenczek, J. Fugal, J. Henneberger |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 22 ; Nr. 15, no. 22 (2015-11-24), S.12953-12969 |
| Datensatznummer |
250120177
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| Publikation (Nr.) |
 copernicus.org/acp-15-12953-2015.pdf |
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| Zusammenfassung |
| During the winter of 2013 and 2014 measurements of cloud microphysical
properties over a 5-week period at the high-alpine site Jungfraujoch,
Switzerland, were carried out as part of the Cloud Aerosol Characterisation
Experiments (CLACE) and the Ice Nucleation Process Investigation and
Quantification project (INUPIAQ). Measurements of aerosol properties at a
second, lower site, Schilthorn, Switzerland, were used as input for a primary
ice nucleation scheme to predict ice nuclei concentrations at Jungfraujoch.
Frequent, rapid transitions in the ice and liquid properties of the clouds at
Jungfraujoch were identified that led to large fluctuations in ice mass
fractions over temporal scales of seconds to hours. During the measurement
period we observed high concentrations of ice particles that exceeded
1000 L−1 at temperatures around −15 °C, verified by multiple
instruments. These concentrations could not be explained using the usual
primary ice nucleation schemes, which predicted ice nucleus concentrations
several orders of magnitude smaller than the peak ice crystal number
concentrations. Secondary ice production through the Hallett–Mossop process as
a possible explanation was ruled out, as the cloud was rarely within the
active temperature range for this process. It is shown that other mechanisms
of secondary ice particle production cannot explain the highest ice particle
concentrations. We describe four possible mechanisms that could lead to high
cloud ice concentrations generated from the snow-covered surfaces surrounding
the measurement site. Of these we show that hoar frost crystals generated at
the cloud enveloped snow surface could be the most important source of cloud
ice concentrations. Blowing snow was also observed to make significant
contributions at higher wind speeds when ice crystal concentrations were
< 100 L−1. |
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