We so often miss interesting visual effects, especially on days of placid weather, because they’re going on almost directly overhead and with little fanfare. I’m glad, therefore, someone ran inside and told me of this as I was leaving work! The “inverted rainbow” feature at the top is the circumzenithal arc, so named because, if it were an exceedingly rare full circle, it would enclose the zenith. These appear through the same mechanism as the 22-degree halos and parhelia (sundogs): six-edged, disc shaped ice crystals high in the troposphere. That’s why they’re often seen together, as was true here. A faint upper tangent arc even shows at the top of the halo, about halfway between the sun and the circumzenithal arc. For the arcs, the crystals bend sunlight entering their broad sides and out their edges like millions of tiny prisms, creating magnificently separated colors even more “pure” than those of a rainbow. Exposing all these foreground and background features so they would appear on rather unforgiving slide film was difficult, but somehow I made it work!
Norman OK (10 Feb 5) Looking WSW
35.2377, -97.462Circumzenithal Arc
We so often miss interesting visual effects, especially on days of placid weather, because they’re going on almost directly overhead and with little fanfare. I’m glad, therefore, someone ran inside and told me of this as I was leaving work! The “inverted rainbow” feature at the top is the circumzenithal arc, so named because, if it were an exceedingly rare full circle, it would enclose the zenith. These appear through the same mechanism as the 22-degree halos and parhelia (sundogs): six-edged, disc shaped ice crystals high in the troposphere. That’s why they’re often seen together, as was true here. A faint upper tangent arc even shows at the top of the halo, about halfway between the sun and the circumzenithal arc. For the arcs, the crystals bend sunlight entering their broad sides and out their edges like millions of tiny prisms, creating magnificently separated colors even more “pure” than those of a rainbow. Exposing all these foreground and background features so they would appear on rather unforgiving slide film was difficult, but somehow I made it work!
Norman OK (10 Feb 5) Looking WSW
35.2377, -97.462