Irregular snow crystals: structural features as revealed by low temperature scanning electron microscopy

TitleIrregular snow crystals: structural features as revealed by low temperature scanning electron microscopy
Publication TypeJournal Article
Year of Publication2002
AuthorsWergin W.P., Rango A., Foster J., Erbe E.F., Pooley C.D.
JournalScanning
Volume24
Pagination247-256
Date PublishedSeptember 1, 200
ARIS Log Number133886
Abstract

For nearly 50 years, investigators using light microscopy have vaguely alluded to a unique type of snow crystal known as an irregular snow crystal. However, the limited resolution and depth-of-field of the light microscope has prevented investigators from characterizing these crystals. In this study, a field-emission scanning electron microscope equipped with a cold stage was used to document the structural features, physical associations and atmospheric metamorphosis of irregular snow crystals. The crystals appear as irregular hexagons measuring 69 to 90 um across when viewed from the a-axis. Their length (c-axis) rarely exceeds the diameter. The irregular crystals are occasionally found as secondary particles on other larger forms of snow crystals; however, they most frequently occur in aggregates consisting of more than 100 irregular crystals. In the aggregates, the irregular crystals have their axes oriented parallel to one another and collectively tend to form columnar structures. Occasionally, these columnar structures exhibit rounded faces along one side, suggesting atmospheric metamorphoses during formation and descent. In extreme cases of metamorphoses, the aggregates would be difficult to distinguish from graupel. Frost, consisting of irregular crystals, has also been encountered suggesting atmospheric conditions that favor their growth can also occur terrestrially.

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