A circumzenithal arc is an optical phenomenon similar in appearance to a rainbow, but belonging to the family of halos produced by the refraction of sunlight through ice crystals in the atmosphere rather than through raindrops. It forms when light enters the flat top face of horizontally oriented hexagonal ice crystals and exits through a side face, producing a brightly colored arc roughly forty six degrees above the Sun. The arc requires specific conditions to appear, including a Sun altitude below about thirty two degrees and a layer of ice crystals with a common horizontal orientation undisturbed by turbulence. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/
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Source Circumzenithal arc (Wikipedia)
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Circumzenithal arc (Wikipedia)
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The circumzenithal arc, also called the circumzenith arc (CZA), the upside-down rainbow, and the Bravais arc, is an optical phenomenon similar in appearance to a rainbow, but belonging to the family of halos arising from refraction of sunlight through ice crystals, generally in cirrus or cirrostratus clouds, rather than from raindrops.
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