“Fire Rainbows” are neither fire, nor rainbows, but are so called because of their brilliant pastel colors and flame like appearance. Technically they are known as circumhorizontal arc - an ice halo formed by hexagonal, plate-shaped ice crystals in high level cirrus clouds. The halo is so large that the arc appears parallel to the horizon, hence the name.
The position of the observer is also important. Circumhorizontal arcs cannot be seen in locations north of 55°N or south of 55°S. Likewise there are certain times of the year when they are visible. For example, in London, England the sun is only high enough for 140 hours between mid-May and late July. While in Los Angeles, the sun is higher than 58 degrees for 670 hours between late March and late September.
Circumhorizon arcs are so large that sometimes we see only parts of them where they happen to 'light' fragments of cirru
Circumhorizon arcs are so huge that their colours sometimes appear to be those of the sky itself rather than an ice crys
This circumhorizon display was photographed through a polarized lens above Dublin, Ohio, in May 2009.
Cirrus fragments lit by a circumhorizon arc, Halifax, Nova Scotia, on 3rd July 2001 with the sun 66° high.
This peculiar 'braided' circumhorizon arc was possibly formed by plate crystals in high cirrus fibratus cloud.