Fire rainbows are not actually rainbows and have no connection with fires. The true name for this exquisitely beautiful optical effect is “circumhorizontal arc”. The phenomenon can only be viewed under certain precise conditions: the cirrus clouds that act as prisms must be at least 20,000 feet high and the sun must strike them when it is at an elevation of 58 to 68 degrees. Fire rainbows are never seen at locations situated more than 55 degrees north or south.
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 the sun must hit the clouds at 58 degrees. ~Poppet
circumhorizontal arcs - this atmospheric phenomenon, otherwise known as a fire rainbow, is created when light from a sun that is at least 58 degrees above the horizon passes through the hexagonal ice crystals that form cirrus clouds which, because of quick cloud formation, have become horizontally aligned. Photo by Andy Cripe.
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*
The proper name for the phenomena known as a ‘fire rainbow’ is circumhorizontal arc and it’s actually an optical phenomena - a ice-halo formed by plate-shaped ice crystals in high level cirrus clouds. On sunny afternoons, cumulus clouds boil upwards, pushing layers of moist air above them even higher where they cool and condense to form cloud caps or ‘pileus’. When pileus clouds form very quickly, their water droplets tend to be all the same size, the perfect condition for iridescent…