1Paul Scherrer Institute, Laboratory of Atmospheric Chemistry, 5232 Villigen, Switzerland
2Institute for Atmospheric and Climate Science, ETH Zurich, 8092, Zurich, Switzerland
3Institute for Space Sciences, Freie Universität Berlin, 12165 Berlin, Germany
4Federal Office of Meteorology and Climatology, 1530 Payerne, Switzerland
5Department of Geography, University of Bern, 3012 Bern, Switzerland
6Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
*now at: CERFACS, 31057 Toulouse, France
Received: 08 Mar 2012 – Discussion started: 02 May 2012
Abstract. This paper presents results of the extensive field campaign CLACE 2010 (Cloud and Aerosol Characterization Experiment) performed in summer 2010 at the Jungfraujoch (JFJ) and the Kleine Scheidegg (KLS) in the Swiss Alps. The main goal of this campaign was to investigate the vertical variability of aerosol optical properties around the JFJ and to show the consistency of the different employed measurement techniques considering explicitly the effects of relative humidity (RH) on the aerosol light scattering. Various aerosol optical and microphysical parameters were recorded using in-situ and remote sensing techniques. In-situ measurements of aerosol size distribution, light scattering, light absorption and scattering enhancement due to water uptake were performed at the JFJ at 3580 m a.s.l.. A unique set-up allowed remote sensing measurements of aerosol columnar and vertical properties from the KLS located about 1500 m below and within the line of sight to the JFJ (horizontal distance of approx. 4.5 km). In addition, two satellite retrievals from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as back trajectory analyses were added to the comparison to account for a wider geographical context. All in-situ and remote sensing measurements were in clear correspondence. The ambient extinction coefficient measured in situ at the JFJ agreed well with the KLS-based LIDAR (Light Detection and Ranging) retrieval at the altitude-level of the JFJ under plausible assumptions on the LIDAR ratio. However, we can show that the quality of this comparison is affected by orographic effects due to the exposed location of the JFJ on a saddle between two mountains and next to a large glacier. The local RH around the JFJ was often higher than in the optical path of the LIDAR measurement, especially when the wind originated from the south via the glacier, leading to orographic clouds which remained lower than the LIDAR beam. Furthermore, the dominance of long-range transported Saharan dust was observed in all measurements for several days, however only for a shorter time period in the in-situ measurements due to the vertical structure of the dust plume. The optical properties of the aerosol column retrieved from SEVIRI and MODIS showed the same magnitude and a similar temporal evolution as the measurements at the KLS and the JFJ. Remaining differences are attributed to the complex terrain and simplifications in the aerosol retrieval scheme in general.
Revised: 10 Jul 2012 – Accepted: 31 Jul 2012 – Published: 08 Aug 2012
Zieger, P., Kienast-Sjögren, E., Starace, M., von Bismarck, J., Bukowiecki, N., Baltensperger, U., Wienhold, F. G., Peter, T., Ruhtz, T., Collaud Coen, M., Vuilleumier, L., Maier, O., Emili, E., Popp, C., and Weingartner, E.: Spatial variation of aerosol optical properties around the high-alpine site Jungfraujoch (3580 m a.s.l.), Atmos. Chem. Phys., 12, 7231-7249, doi:10.5194/acp-12-7231-2012, 2012.