The last few weeks have been really good for halos. The first tangent arc I’ve seen, a clear circumscribed halo, the more common sundogs and 22° halos, and now a circumzenith arc, looking like an upside-down rainbow high above the sun, wrapping around the top of the sky.
I think this is the second I’ve seen, but the first was only a fragment.
Like all sun halos, they’re formed by light reflecting through ice crystals. And since those crystals can be in the upper atmosphere, you can see them even in warmer places like Los Angeles.
Taken with my phone through polarized sunglasses. Color and contrast enhanced.