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Identification and Frequency of 23° Parroids

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A marginally known pyramidal halo that can be e.g. referred as “23° parroid” is unexpectedly emerging at least as one of the three most frequent rare halos. It appears that during this century hundreds of high solar elevation 23° parroids have been missidentified as 22° upper tangent arcs. An Antarctic display from year 1950 offers an example where a low solar elevation 23° parroid has been missinterpreted as a Parry arc. In Finland during the April-August period numerous 23° parroids have been sighted annually in weak or mediocre halo displays since 1994 when the error in the identification criteria was first confirmed. Due to unknown reason the visibility of 23° parroids seems to peak in sultry days.

© 1997 Optical Society of America

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