Steve's Atmospheric Phenomena
Circumhorizontal and Circumzenithal Arcs
Thin hexagonal ice crystals oriented like falling leaves produce sundogs. But they still have more tricks up their sleeves. Sunlight
can enter a side facet of the crystal and exit the flat crossectional base to produce a circumhorizontal arc which appears below
the 22-deg halo. Or sunlight can enter the base and exit a side facet producing a circumzenithal arc which forms above the upper
tangent arc.
A circumhorizontal arc appears above a B1-B bomber at an airshow in Tucson.
Another circumhorizontal arc appeared on a camping trip into the White Mountains.
Although I've seen 3 circumzenithal arcs, this was the only one that was at all vivid. This one occurred about 3 hours before
a large thunderstorm came rolling through.
A small section of a circumhorizontal arc appears under the 22-deg solar halo: 4-13-06