An upside down rainbow? No it's not, there's no rain! This optical phenomenon is called a circumzenithal arc. It looks similar to rainbows, but instead of being caused by refraction from raindrops, it's caused by refraction of sunlight through horizontally-oriented ice crystals, usually in cirrus clouds. Also a circumzenithal arc is on the same side as the sun. I spotted this one back in July 2012.
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