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| Titel |
The accommodation coefficient of water molecules on ice – cirrus cloud studies at the AIDA simulation chamber |
| VerfasserIn |
J. Skrotzki, P. Connolly, M. Schnaiter, H. Saathoff, O. Möhler, R. Wagner, M. Niemand, V. Ebert, T. Leisner |
| 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 ; 13, no. 8 ; Nr. 13, no. 8 (2013-04-29), S.4451-4466 |
| Datensatznummer |
250018619
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| Publikation (Nr.) |
 copernicus.org/acp-13-4451-2013.pdf |
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| Zusammenfassung |
| Cirrus clouds and their impact on the Earth's radiative budget are subjects
of current research. The processes governing the growth of cirrus ice
particles are central to the radiative properties of cirrus clouds. At
temperatures relevant to cirrus clouds, the growth of ice crystals smaller
than a few microns in size is strongly influenced by the accommodation
coefficient of water molecules on ice, αice, making this
parameter relevant for cirrus cloud modeling. However, the experimentally
determined magnitude of αice for cirrus temperatures is
afflicted with uncertainties of almost three orders of magnitude, and values
for αice derived from cirrus cloud data lack significance
so far. This has motivated dedicated experiments at the cloud chamber AIDA
(Aerosol Interactions and Dynamics in the Atmosphere) to determine
αice in the cirrus-relevant temperature interval between
190 K and 235 K under realistic cirrus ice particle growth
conditions. The experimental data sets have been evaluated independently
with two model approaches: the first relying on the newly developed model
SIGMA (Simple Ice Growth Model for determining Alpha), the second one on an
established model, ACPIM (Aerosol-Cloud-Precipitation Interaction Model).
Within both approaches a careful uncertainty analysis of the obtained
αice values has been carried out for each AIDA
experiment. The results show no significant dependence of αice
on temperature between 190 K and 235 K. In
addition, we find no evidence for a dependence of αice on
ice particle size or on water vapor supersaturation for ice particles
smaller than 20 μm and supersaturations of up to 70%. The
temperature-averaged and combined result from both models is
αice = 0.7−0.5+0.3,
which implies that αice
may only exert a minor impact on cirrus clouds and their characteristics
when compared to the assumption of αice =1. Impact on
prior calculations of cirrus cloud properties, e.g., in climate models, with
αice typically chosen in the range 0.2–1 is thus expected
to be negligible. In any case, we provide a well-constrained αice
which future cirrus model studies can rely on. |
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