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Investigation of the effective peak supersaturation for liquid-phase clouds at the high-alpine site Jungfraujoch, Switzerland (3580 m a.s.l.)

Hammer, E. and Bukowiecki, N. and Gysel, M. and Jurányi, Z. and Hoyle, C. R. and Vogt, R. and Baltensperger, U. and Weingartner, E.. (2014) Investigation of the effective peak supersaturation for liquid-phase clouds at the high-alpine site Jungfraujoch, Switzerland (3580 m a.s.l.). Atmospheric chemistry and physics, 14 (2). pp. 1123-1139.

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Abstract

Aerosols influence the Earth's radiation budget directly through absorption and scattering of solar radiation in the atmosphere but also indirectly by modifying the properties of clouds. However, climate models still suffer from large uncertainties as a result of insufficient understanding of aerosol-cloud interactions. At the high altitude research station Jungfraujoch (JFJ; 3580 m a.s.l., Switzerland) cloud condensation nuclei (CCN) number concentrations at eight different supersaturations (SS) from 0.24% to 1.18% were measured using a CCN counter during Summer 2011. Simultaneously, in-situ aerosol activation properties of the prevailing ambient clouds were investigated by measuring the total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems. Combining all experimental data, a new method was developed to retrieve the so-called effective peak supersaturation SSpeak, as a measure of the SS at which ambient clouds are formed. A 17-month CCN climatology was then used to retrieve the SSpeak values also for four earlier summer campaigns (2000, 2002, 2004 and 2010) where no direct CCN data were available. The SSpeak values varied between 0.01% and 2.0% during all campaigns. An overall median SSpeak of 0.35% and dry activation diameter of 87 nm was observed. It was found that the difference in topography between northwest and southeast plays an important role for the effective peak supersaturation in clouds formed in the vicinity of the JFJ, while differences in the number concentration of potential CCN only play a minor role. Results show that air masses coming from the southeast (with the slowly rising terrain of the Aletsch Glacier) generally experience lower SSpeak values than air masses coming from the northwest (steep slope). The observed overall median values were 0.41% and 0.22% for northwest and southeast wind conditions, respectively, corresponding to literature values for cumulus clouds and shallow-layer clouds. These cloud types are consistent with weather observations routinely performed at the JFJ.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Meteorologie, Klimatologie und Fernerkundung > Meteorologie (Parlow)
UniBasel Contributors:Vogt, Roland
Item Type:Article, refereed
Article Subtype:Research Article
Bibsysno:Link to catalogue
Publisher:Copernicus Publ.
ISSN:1680-7316
Note:Publication type according to Uni Basel Research Database: Journal article
Language:English
Identification Number:
Last Modified:31 Dec 2015 10:56
Deposited On:05 Dec 2014 09:45

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