Articles | Volume 9, issue 18
Atmos. Chem. Phys., 9, 6881–6897, 2009
Atmos. Chem. Phys., 9, 6881–6897, 2009

  21 Sep 2009

21 Sep 2009

Physical properties of High Arctic tropospheric particles during winter

L. Bourdages1, T. J. Duck1, G. Lesins1, J. R. Drummond1, and E. W. Eloranta2 L. Bourdages et al.
  • 1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada
  • 2Space Science and Engineering Center, University of Wisconsin, Madison, USA

Abstract. A climatology of particle scattering properties in the wintertime High Arctic troposphere, including vertical distributions and effective radii, is presented. The measurements were obtained using a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: boundary-layer ice crystals, ice clouds, mixed-phase clouds, and aerosols. Two-dimensional histograms of occurrence probabilities against depolarization, radar/lidar colour ratio and height are given. Colour ratios are related to particle minimum dimensions (i.e., widths rather than lengths) using a Mie scattering model. Ice cloud crystals have effective radii spanning 25–220 µm, with larger particles observed at lower altitudes. Topographic blowing snow residuals in the boundary layer have the smallest crystals at 15–70 µm. Mixed-phase clouds have water droplets and ice crystal precipitation in the 5–40 µm and 40–220 µm ranges, respectively. Ice cloud crystals have depolarization decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere (0.5–3.5 km altitude). Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.

Final-revised paper