Spatial variation of aerosol optical properties around the high-alpine site Jungfraujoch (3580 m a.s.l.)

Abstract

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 KLSbased 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.

Investigation of the Planetary Boundary Layer in the Swiss Alps Using Remote Sensing and In Situ Measurements

“…and the average minimum-to-maximum increase was about 500 m during fair weather days. Several exceptions are caused by long-range transported Saharan dust (see Zieger et al 2012). Saharan dust might lead to a wrong estimate of the PBL height, e.g.…”

“…During CLACE 2010, remote sensing instruments were installed at the KLS site including a wind profiler, a ceilometer, a sun photometer and a lidar. Zieger et al (2012) discuss the vertical distribution of aerosol optical properties during this campaign.…”

“…From June to August 2010, the Cloud and Aerosol Characterization Experiment (CLACE 2010) campaign took place at the JFJ and KLS sites (see Zieger et al (2012) for an overview). During CLACE 2010, remote sensing instruments were installed at the KLS site including a wind profiler, a ceilometer, a sun photometer and a lidar.…”

Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

“…This commercial Lidar emits laser pulses with a wavelength of 355 nm, a repetition rate of 20 Hz, and an average pulse energy of 16 mJ. It detects attenuated backscatter, both in parallel and perpendicular polarization, enabling a determination of the sphericity and thus the physical state of the scattering particles (Schotland et al, 1971;Kovalev and Eichinger, 2004;Zieger et al, 2012).…”

Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100)

“…Several intensive cloud characterization experiments have been conducted there for many years at different times of the year (e.g. Mertes et al, 2007;Verheggen et al, 2007;Cozic et al, 2008;Targino et al, 2009;Kamphus et al, 2010;Zieger et al, 2012). The aerosol measurements performed at the JFJ are part of the Global Atmosphere Watch (GAW) program of the World Meteorological Organization since 1995 (Collaud Coen et al, 2007).…”