Fire rainbows are the rarest of all naturally occurring atmospheric phenomena. For a fire rainbow to occur, cirrus clouds must be 20,000 feet in the air with the precise amount of ice crystals, and then the Sun must hit the clouds at 58 degrees. *Stardust*
Cirrus Kelvin-Helmholtz cloud formation. The development of a Cirrus Kelvin-Helmholtz cloud. The whole thing developed from a rippled line right through the whole K-H form, and back to dissipation, all in 12 minutes time.