Parry arcs

Parry arcs

[′par·ē ‚ärks]
(optics)
A class of halos appearing as faintly colored arcs above and below the sun; these refraction phenomena are produced by ice crystals which exhibit a preferred orientation, and are correspondingly more unusual than those associated with randomly oriented crystals.
References in periodicals archive ?
In the past, it has been suggested that tabular ice crystals (hexagonal columns with two opposite prismatic faces much longer than the others) might give rise to Parry arcs and other associated halos.
We conclude that the presence of trigonal crystals in the atmosphere is consistent with rare Parry arc halos and also show that they have distinct radiative properties compared with hexagonal ice.
Examples include Parry arcs, arcs of Lowitz, and Bottlinger's rings.