MEMPHIS, TN (WMC) - Have you ever seen a rainbow that looks upside down in the sky?
This is called a circumzenithal arc or a circumzenith arc. It also has been called an upside-down rainbow or the Bravaris arc. It is referred to as a smile in the sky. It is rather close in appearance with a rainbow, but it is formed quite differently. A rainbow is formed when light refracts or bends off a raindrop whereas the circumzenithal is due to refraction of the suns rays through ice crystals mostly in cirrus or cirrostratus clouds.
It can only form when the sun is at an altitude lower than 32.2. The circumzenithal is the brightest when it is at 22.2 above the horizon. In order to get a circumzenithal there must be no turbulence and no strong up and down drafts. It is apart of the halo family. It is not rare but because it is positioned so far overhead it can sometimes be overlooked. When you see sundogs, look out for circumzenithal as the same type of ice crystals cause them.