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| Titel |
Sensitivity estimations for cloud droplet formation in the vicinity of the high-alpine research station Jungfraujoch (3580 m a.s.l.) |
| VerfasserIn |
E. Hammer, N. Bukowiecki, B. P. Luo, U. Lohmann, C. Marcolli, E. Weingärtner, U. Baltensperger, C. R. Hoyle |
| 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. 18 ; Nr. 15, no. 18 (2015-09-18), S.10309-10323 |
| Datensatznummer |
250120038
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| Publikation (Nr.) |
 copernicus.org/acp-15-10309-2015.pdf |
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| Zusammenfassung |
| Aerosol radiative forcing estimates suffer from large uncertainties as a result of insufficient
understanding of aerosol–cloud interactions. The main source of these uncertainties is dynamical
processes such as turbulence and entrainment but also key aerosol parameters such as aerosol
number concentration and size distribution, and to a much lesser extent, the composition. From
June to August 2011 a Cloud and Aerosol Characterization Experiment (CLACE2011) was performed at the
high-alpine research station Jungfraujoch (Switzerland, 3580 m a.s.l.) focusing on the
activation of aerosol to form liquid-phase clouds (in the cloud base temperature range of −8 to
5 °C). With a box model the sensitivity of the effective peak supersaturation
(SSpeak), an important parameter for cloud activation, to key aerosol and
dynamical parameters was investigated. The updraft velocity, which defines the cooling rate of an
air parcel, was found to have the greatest influence on SSpeak. Small-scale
variations in the cooling rate with large amplitudes can
significantly alter CCN activation. Thus, an accurate knowledge of the air parcel history is
required to estimate SSpeak. The results show that the cloud base updraft
velocities estimated from the horizontal wind measurements made at the Jungfraujoch can be divided
by a factor of approximately 4 to get the updraft velocity required for the model to reproduce the
observed SSpeak. The aerosol number concentration and hygroscopic properties were
found to be less important than the aerosol size in determining SSpeak. Furthermore
turbulence is found to have a maximum influence when SSpeak is between approximately
0.2 and 0.4 %. Simulating the small-scale fluctuations with several amplitudes,
frequencies and phases, revealed that independently of the amplitude, the effect of the frequency on
SSpeak shows a maximum at 0.46 Hz (median over all phases) and at higher frequencies, the
maximum SSpeak decreases again. |
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