Weingartner, Ernest

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Ernest
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Weingartner, Ernest

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2011 - 20122
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Autor:in: Bukowiecki, Nicolas × Thema: 500 - Naturwissenschaften und Mathematik ×

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  • Vorschaubild
    Publikation
    Spatial variation of aerosol optical properties around the high-alpine site Jungfraujoch (3580 m a.s.l.)
    (Copernicus, 08.08.2012) Zieger, Paul; Kienast-Sjögren, Erika; Starace, Michela; von Bismarck, Jonas; Bukowiecki, Nicolas; Baltensperger, Urs; Wienhold, Frank Gunther; Peter, Thomas; Ruhtz, Thomas; Collaud Coen, Martine; Vuilleumier, Laurent; Maier, Olaf; Emili, Emanuele; Popp, Christian; Weingartner, Ernest [in: Atmospheric Chemistry and Physics]
    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 easurements 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.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    A 17 month climatology of the cloud condensation nuclei number concentration at the high alpine site Jungfraujoch
    (Wiley, 24.05.2011) Jurányi, Zsófia; Gysel, Martin; Weingartner, Ernest; Bukowiecki, Nicolas; Kammermann, Lorenz; Baltensperger, Urs [in: Journal of Geophysical Research: Atmospheres]
    Between May 2008 and September 2009 the cloud condensation nuclei (CCN) number concentration, NCCN, was measured at the high alpine site Jungfraujoch, which is located in the free troposphere most of the time. Measurements at 10 different supersaturations (0.12%–1.18%) were made using a CCN counter (CCNC). The monthly median NCCN values show a distinct seasonal variability with ∼5–12 times higher values in summer than in winter. The major part of this variation can be explained by the seasonal amplitude of total aerosol number concentration (∼4.5 times higher values in summer), but it is further amplified (factor of ∼1.1–2.6) by a shift of the particle number size distribution toward slightly larger sizes in summer. In contrast to the extensive properties, the monthly median of the critical dry diameter, above which the aerosols activate as CCN, does not show a seasonal cycle (relative standard deviations of the monthly median critical dry diameters at the different supersaturations are 4–9%) or substantial variability (relative standard deviations of individual data points at the different supersaturations are less than 18–37%). The mean CCN-derived hygroscopicity of the aerosol corresponds to a value of the hygroscopicity parameter κ of 0.20 (assuming a surface tension of pure water) with moderate supersaturation dependence. NCCN can be reliably predicted throughout the measurement period with knowledge of the above-mentioned averaged κ value and highly time-resolved (∼5 min) particle number size distribution data. The predicted NCCN was within 0.74 to 1.29 times the measured value during 80% of the time (94,499 data points in total at 10 different supersaturations).
    01A - Beitrag in wissenschaftlicher Zeitschrift