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| Titel |
Biological ice nuclei are rapidly lost from precipitating clouds |
| VerfasserIn |
Emiliano Stopelli, Franz Conen, Christine Alewell, Cindy Morris |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102288
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| Publikation (Nr.) |
 EGU/EGU2015-1598.pdf |
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| Zusammenfassung |
| Ice nucleation is a key step for the formation of precipitation in cold clouds. Particularly
interesting is the nucleating behaviour of aerosols of biological origin, showing activity at
temperatures up to -2Ë C. Yet, the effective impact of biological ice nuclei (IN) on the
development of precipitation on global and local scales compared to more abundant IN active
at colder temperatures is still ambiguous.
The results coming from a year of observations at the High Altitude Research Station of
Jungfraujoch, in the Swiss Alps, 3580 m a.s.l. will be presented. Freshly fallen snow was
collected (91 samples in total) from precipitating tropospheric clouds and analysed
immediately on site for the concentration of IN active at temperatures warmer than -12Ë C by
immersion freezing. The stable oxygen ratio (δ18O) of each sample was measured as well;
this value was used to estimate the fraction of water vapour lost from a precipitating cloud
(1-fv) prior to its arrival at Jungfraujoch.
IN and the fraction of water vapour lost showed a very similar pattern of variation both on
a time scale of hours and over the whole year. Our analysis of the data suggests that the
abundance of IN in snowfall is rapidly halved, with every 10% of water vapour lost through
precipitation and that IN tend to be preferentially activated and lost compared to other
particles of similar size. This provides a substantial constraint for the role of such IN in
conditioning precipitation in time and space. Up to 75% of the observed variability in
IN concentrations at Jungfraujoch was explained by the factors 1-fv and wind
speed, suggesting that wind may play a role in keeping activated IN suspended in the
air.
Unresolved issues like the role of other parameters (seasonality, source region) in
describing IN abundances and a deeper characterisation of biological IN active material
collected at Jungfraujoch will be discussed. |
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