Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment 1Laboratoire de Météorologie Physique UMR 6016 CNRS/Université Blaise Pascal, France
17 Mar 2011
2LaMP – Institut Universitaire de Technologie de Montluçon, Avenue A, Briand-BP 2235, 03101 Montluçon Cedex, France
3Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
Received: 22 September 2010 – Published in Atmos. Chem. Phys. Discuss.: 22 October 2010 Abstract. In this paper, we describe in situ observations of mid-latitude
cirrus cloud band carried out on 16 May 2007 during the CIRCLE-2 experiment.
The Polar Nephelometer and the Cloud Particle Imager (CPI) instruments with
PMS FSSP-300 and 2D-C probes were used for the description of the optical
and microphysical cloud properties. Two selected cloud regions are compared
and discussed in detail. Significant differences in optical properties are
evidenced in terms of 22° halo occurrences even though prevalent
planar-plate ice crystals are observed in both cloud regions. Featureless
scattering phase functions are measured in the first cloud region located
near the trailing edge of the cirrus-band at about 11 800 m/−57 °C. In
contrast, well pronounced 22° halo peaks are observed with predominant
similar-shaped ice crystals near the cirrus-band leading edge at 7100 m/−27 °C.
CPI ice crystal images with Polar Nephelometer observations are
carefully analysed and interpreted from a theoretical light scattering model
in order to explain occurrence and non-occurrence of the 22° halo
feature. The results highlight that the halo peaks are inherent only in
perfect plate ice crystals (or pristine crystals). On the basis of previous
datasets in mid-latitude cirrus, it is found that simple pristine crystals
are uncommon whereas particles with imperfect or complex shapes are
prevalent. As a result, phase functions that are smooth and featureless best
represent cirrus scattering properties.
Revised: 07 February 2011 – Accepted: 25 February 2011 – Published: 17 March 2011
Citation: Gayet, J.-F., Mioche, G., Shcherbakov, V., Gourbeyre, C., Busen, R., and Minikin, A.: Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment, Atmos. Chem. Phys., 11, 2537-2544, doi:10.5194/acp-11-2537-2011, 2011.