The circumhorizontal arc also known as the "fire rainbow", which is a type of halo. The formation is that the position of the sun relative to the observer must be at least an elevation angle of 58° and high cloud containing a large number of hexagonal plate ice crystals. The ice crystals slab surface is parallel to the ground plane. In this way, when the sun's rays are incident from the 90° angle of the ice crystal can cause about 58° of light refraction and produce band-like dispersion, so the observer can see that the dispersed colors are arranged with warm colors on the top and cool colors on the bottom, rainbow-like banner ribbon colors. In addition, due to the limitation of the elevation angle of the sun, the location of ice crystals, and the conditions of the angle of refraction, this kind of optical phenomena are easier to observe in high-latitude regions, especially near the polar regions during the permanent day. The duration of occurrence and existence can be longer.