Atmos. Chem. Phys. Discuss., 10, 24763-24780, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment
J.-F. Gayet1, G. Mioche1, V. Shcherbakov1,2, C. Gourbeyre1, R. Busen3, and A. Minikin3
1Laboratoire de Météorologie Physique, UMR 6016 CNRS/Université Blaise Pascal, France
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

Abstract. Preferential horizontally-oriented ice crystals with a prevalent hexagonal-plate shape revealed by the Cloud Particle Imager can explain systematic larger Lidar CALIOP extinctions when compared with extinction derived from co-located in situ measurements. Surprisingly, the Polar Nephelometer does not reveal any signature of 22° (and 46°) halos, showing a rather featureless scattering phase function in this case. In contrast, well pronounced 22° halo peaks are observed with predominant similar-shaped ice crystals in other cirrus situations. This paper discusses the results of a careful examination of CPI images with Polar Nephelometer observations in order to explain occurrence and non occurrence of the 22° halo feature. Observations highlight that halo peaks are evidenced only by the presence of perfect plate ice crystals (or pristine crystals). On the basis of previous data sets 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 are smooth and featureless and best represent cirrus scattering properties.

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. Discuss., 10, 24763-24780, doi:10.5194/acpd-10-24763-2010, 2010.
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