Articles | Volume 17, issue 20
Atmos. Chem. Phys., 17, 12845–12869, 2017
Atmos. Chem. Phys., 17, 12845–12869, 2017

Research article 27 Oct 2017

Research article | 27 Oct 2017

Vertical distribution of microphysical properties of Arctic springtime low-level mixed-phase clouds over the Greenland and Norwegian seas

Guillaume Mioche1,2,4, Olivier Jourdan1,2, Julien Delanoë3, Christophe Gourbeyre1,2, Guy Febvre1,2, Régis Dupuy1,2, Marie Monier1,2, Frédéric Szczap1,2, Alfons Schwarzenboeck1,2, and Jean-François Gayet1,2 Guillaume Mioche et al.
  • 1Université Clermont Auvergne, OPGC, Laboratoire de Météorologie Physique, 63000 Clermont-Ferrand, France
  • 2CNRS, UMR 6016, LaMP/OPGC, BP80026, 63177 Aubière, France
  • 3Laboratoire Atmosphère, Milieux et Observations Spatiales, UVSQ/CNRS/UPMC-IPSL, 78035 Guyancourt, France
  • 4IUT d'Allier, CS 82235, 03101 Montluçon, France

Abstract. This study aims to characterize the microphysical and optical properties of ice crystals and supercooled liquid droplets within low-level Arctic mixed-phase clouds (MPCs). We compiled and analyzed cloud in situ measurements from four airborne spring campaigns (representing 18 flights and 71 vertical profiles in MPCs) over the Greenland and Norwegian seas mainly in the vicinity of the Svalbard archipelago. Cloud phase discrimination and representative vertical profiles of the number, size, mass and shape of ice crystals and liquid droplets are established. The results show that the liquid phase dominates the upper part of the MPCs. High concentrations (120 cm−3 on average) of small droplets (mean values of 15 µm), with an averaged liquid water content (LWC) of 0.2 g m−3 are measured at cloud top. The ice phase dominates the microphysical properties in the lower part of the cloud and beneath it in the precipitation region (mean values of 100 µm, 3 L−1 and 0.025 g m−3 for diameter, particle concentration and ice water content (IWC), respectively). The analysis of the ice crystal morphology shows that the majority of ice particles are irregularly shaped or rimed particles; the prevailing regular habits found are stellars and plates. We hypothesize that riming and diffusional growth processes, including the Wegener–Bergeron–Findeisen (WBF) mechanism, are the main growth mechanisms involved in the observed MPCs. The impact of larger-scale meteorological conditions on the vertical profiles of MPC properties was also investigated. Large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations and air mass origins from the south, which can lead to very low values of ice crystal size and IWC. On the contrary, clean situations with low temperatures exhibit larger values of ice crystal size and IWC. Several parameterizations relevant for remote sensing or modeling studies are also determined, such as IWC (and LWC) – extinction relationship, ice and liquid integrated water paths, ice concentration and liquid water fraction according to temperature.

Short summary
This paper is a study about the mixed-phase clouds frequently occurring in the Arctic region. It is based on airborne measurements and highlights the microphysical properties of these particular clouds composed of liquid droplets at cloud top and ice crystals below precipitating down to the surface. This work may help to improve the representation of the mixed-phase clouds in numerical prediction models as well as the retrieval of their properties from remote sensing observations.
Final-revised paper