The crystal structure of ice under mesospheric conditions

• Published in: Journal of atmospheric and solar-terrestrial physics Vol. 127; pp. 78 - 82
• Main Authors: Murray, Benjamin J., Malkin, Tamsin L., Salzmann, Christoph G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-05-2015
• Subjects: Amorphous ice; Amorphous solid water; Aspect ratio; Crystal structure; Cubic ice; Earth atmosphere; Ice clouds; Latitude; Lidar; Mesopause; Mesospheric clouds; Noctilucent clouds; Stacking; Stacking disordered ice; Noctilucent clouds; Cubic ice; Mesospheric clouds; Amorphous ice; Amorphous solid water; Stacking disordered ice
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2014.12.005

Ice clouds form in the summer high latitude mesopause region, which is the coldest part of the Earth's atmosphere. At these very low temperatures (<150K) ice can exist in metastable forms, but the nature of these ices remains poorly understood. In this paper we show that ice which is grown at mesospherically relevant temperatures does not have a structure corresponding to the well-known hexagonal form or the metastable cubic form. Instead, the ice which forms under mesospheric conditions is a material in which cubic and hexagonal sequences of ice are randomly arranged to produce stacking disordered ice (ice Isd). The structure of this ice is in the trigonal crystal system, rather than the cubic or hexagonal systems, and is expected to produce crystals with aspect ratios consistent with lidar observations.
•Ice was grown under conditions relevant for mesospheric clouds.•Its crystal structure does not correspond to that of hexagonal or cubic ice.•It is instead made up of randomly arranged cubic and hexagonal sequences.•We refer to this ice as stacking disordered ice I (ice Isd).•We suggest that crystalline ice in mesospheric clouds is stacking disordered.