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| Titel |
The Accommodation Coefficient of Water Molecules on Ice and its Role for Cirrus Clouds |
| VerfasserIn |
Julian Skrotzki, Paul Connolly, Monika Niemand, Harald Saathoff, Ottmar Möhler, Volker Ebert, Thomas Leisner |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049285
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| Zusammenfassung |
| One of the parameters governing the growth of ice crystals in cirrus clouds is the
accommodation coefficient of water molecules on ice. However, its magnitude is still unclear,
since experimental results vary from below 0.01 up to unity depending on the design of the
experiment and the examined ice growth process [1]. Values below 0.01 could be an
explanation for the observation of unexpectedly high ice number concentrations and
persisting supersaturations within cirrus clouds [2].
For the ice crystal growth in cirrus clouds, no previous experimental studies regarding the
accommodation coefficient exist. Therefore, dedicated experiments were carried out at the
cloud simulation chamber AIDA [3], examining the ice crystal growth for deposition
nucleation in the temperature range from -75Â Ë C to -40Â Ë C. These experiments were
evaluated with two different models, the Simple Ice Growth Model for determining Alpha
(SIGMA) and the more advanced and extended Aerosol-Cloud-Precipitation Interaction
Model (ACPIM) [4].
The outcome of these two models is compared to absolute in-situ humidity data measured
within AIDA using extractive as well as open path diode laser hygrometers (TDLAS)
[5]. For each experiment, best-fit values for the accommodation coefficient are
obtained and the respective overall uncertainties are estimated by a Monte Carlo
analysis.
First results indicate that the accommodation coefficient is larger than 0.1 in the examined
temperature range. According to previous model studies [6], this suggests that the
accommodation coefficient has no significant influence on ice crystal growth and ice number
concentrations in cirrus clouds.
[1] D. R. Heynes, N. J. Tro, and S. M. George, J. Phys. Chem. 1992, 96, 8502-8509
(1992)
[2] U. Lohmann et al., Environ. Res. Lett. 3, 045022 (2008)
[3] O. Möhler et al., Atmos. Chem. Phys. 3, 211-223 (2003)
[4] P. J. Connolly et al., Atmos. Chem. Phys. 9, 2805-2824 (2009)
[5] D. W. Fahey et al., AquaVIT White Paper, available at
https://aquavit.icg.kfa-juelich.de/AquaVit/AquaVitWiki
[6] K. M. Gierens et al., J. Geophys. Res., 108, D2, 4069 (2003) |
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