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| Titel |
Deposition and immersion-mode nucleation of ice by three distinct samples of volcanic ash |
| VerfasserIn |
G. P. Schill, K. Genareau, M. A. Tolbert |
| 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. 13 ; Nr. 15, no. 13 (2015-07-10), S.7523-7536 |
| Datensatznummer |
250119885
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| Publikation (Nr.) |
 copernicus.org/acp-15-7523-2015.pdf |
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| Zusammenfassung |
| Ice nucleation of volcanic ash controls both ash aggregation and cloud
glaciation, which affect atmospheric transport and global climate.
Previously, it has been suggested that there is one characteristic ice
nucleation efficiency for all volcanic ash, regardless of its composition,
when accounting for surface area; however, this claim is derived from data
from only two volcanic eruptions. In this work, we have studied the
depositional and immersion freezing efficiency of three distinct samples of
volcanic ash using Raman microscopy coupled to an environmental cell. Ash
from the Fuego (basaltic ash, Guatemala), Soufrière Hills (andesitic
ash, Montserrat), and Taupo (Oruanui eruption, rhyolitic ash, New Zealand)
volcanoes were chosen to represent different geographical locations and
silica content. All ash samples were quantitatively analyzed for both
percent crystallinity and mineralogy using X-ray diffraction. In the present
study, we find that all three samples of volcanic ash are excellent
depositional ice nuclei, nucleating ice from 225 to 235 K at ice saturation
ratios of 1.05 ± 0.01, comparable to the mineral dust proxy kaolinite.
Since depositional ice nucleation will be more important at colder
temperatures, fine volcanic ash may represent a global source of cold-cloud
ice nuclei. For immersion freezing relevant to mixed-phase clouds, however,
only the Oruanui ash exhibited appreciable heterogeneous ice nucleation activity.
Similar to recent studies on mineral dust, we suggest that the mineralogy of
volcanic ash may dictate its ice nucleation activity in the immersion mode. |
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