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Origin of the Parry arc

Westbrook, C. (2011) Origin of the Parry arc. Quarterly Journal of the Royal Meteorological Society, 137 B. pp. 538-543. ISSN 1477-870X

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To link to this article DOI: 10.1002/qj.761


Laboratory experiments to determine the preferred orientation of free-falling hexagonal prisms were performed at Reynolds numbers appropriate to falling ice crystals in the atmosphere. Hexagonal plates orient with their c axis vertical for aspect ratios < 0.9, whilst hexagonal columns fall with their c axis horizontal. A secondary alignment is also observed: regular hexagonal columns fall preferentially with two prism facets aligned vertically and not horizontally – the latter scenario was previously assumed to be responsible for the rare Parry arc. However, if the column is made scalene in its cross-section, it can orient such that a pair of prism facets is horizontal. This finding indicates that the development of scalene crystals may be key to the production of certain ice-crystal optical phenomena

Item Type:Article
Divisions:Faculty of Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:20663
Uncontrolled Keywords:ice crystal; optical effects; particle orientation
Publisher:Royal Meteorological Society

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