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| Titel |
Predicting the abundance of ice nucleating particles of biological origin in precipitation |
| VerfasserIn |
Emiliano Stopelli, Franz Conen, Cindy Morris, Christine Alewell |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124379
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| Publikation (Nr.) |
 EGU/EGU2016-3803.pdf |
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| Zusammenfassung |
| Ice nucleation is a key step for the formation of precipitation on Earth. Ice nucleating
particles (INPs) of biological origin catalyse the freezing of supercooled cloud droplets at
temperatures warmer than -12 ˚ C. In order to understand the effective role of these INPs in
conditioning precipitation, it is of primary importance to describe and predict their variability
in the atmosphere.
Over the course of two years, 14 sampling campaigns in precipitating clouds were
conducted at the High Altitude Research Station Jungfraujoch, in the Swiss Alps, at 3580 m
a.s.l. A total of 106 freshly fallen snow samples were analysed immediately on site for the
concentration of INPs active at -8 ˚ C (INPs−8) by immersion freezing. Values of INPs−8
ranged from 0.21 to 434⋅ml−1. Environmental parameters (like temperature of the air, wind
speed, the stable oxygen ratio δ18O of snow, the number of particles larger than 0.5 μm) were
used as independent variables to build a set of multiple linear regression models
to describe and predict the observed variations of INPs−8 over time. The model
providing the best results was based on fV (the fraction of remaining vapour in
precipitating clouds, derived from δ18O) and on wind speed. It indicates that a
coincidence of strong atmospheric turbulence and little prior precipitation from a cloud
coincides with large concentrations of INPs−8. These conditions can be frequently
encountered when air masses are suddenly forced to rise, for instance by the passage of a
cold front, where also meteorological conditions are favourable to the onset of
precipitation.
To obtain more information on the presence of INPs−8 of biological origin and their
relative composition, a set of precipitation samples were progressively filtered through
different meshes (5 μm, 1.2 μm, 0.22 μm) followed by heating (40 ˚ C and 80 ˚ C). Almost
all ice nucleating activity is lost after heating at 80 ˚ C, and a significant part of INPs−8 is
sensitive to warming at 40 ˚ C. This indicates that the INPs−8 we measured are
of biological origin and can be readily denatured. Still, each sample presents a
specific distribution of the sizes of INPs−8, suggesting that INPs−8in environmental
samples are a mix of molecules and cells either freely floating in the atmosphere
or clumped or attached to mineral and soil particles. The abundance of bacterial
cells and the presence of culturable Pseudomonas syringae were studied as well.
Just a minor fraction of the INPs−8 is potentially due to bacterial cells or living
P. syringae, indicating that the majority of INPs−8 measured in environmental
samples may be therefore made of molecules released or detached from organisms. |
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