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| Titel |
Repeatability and randomness in heterogeneous freezing nucleation |
| VerfasserIn |
G. Vali |
| 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 ; 8, no. 16 ; Nr. 8, no. 16 (2008-08-29), S.5017-5031 |
| Datensatznummer |
250006348
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| Publikation (Nr.) |
 copernicus.org/acp-8-5017-2008.pdf |
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| Zusammenfassung |
| This study is aimed at clarifying the relative importance of the specific
character of the nuclei and of the duration of supercooling in heterogeneous
freezing nucleation by immersed impurities. Laboratory experiments were
carried out in which sets of water drops underwent multiple cycles of
freezing and melting. The drops contained suspended particles of mixtures of
materials; the resulting freezing temperatures ranged from −6°C to
−24°C. Rank correlation coefficients between observed freezing
temperatures of the drops in successive runs were >0.9 with very high
statistical significance, and thus provide strong support for the modified
singular model of heterogeneous immersion freezing nucleation. For given
drops, changes in freezing temperatures between cycles were relatively small
(<1°C) for the majority of the events. These frequent small
fluctuations in freezing temperatures are interpreted as reflections of the
random nature of embryo growth and are associated with a nucleation rate
that is a function of a temperature difference from the characteristic
temperatures of nuclei. About a sixth of the changes were larger, up to ±5°C,
and exhibited some systematic patterns. These are thought to arise
from alterations of the nuclei, some being permanent and some transitory.
The results are used to suggest ways of describing ice initiation in cloud
models that account for both the temperature and the time dependence of
freezing nucleation. |
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