A circumhorizontal arc, or fire rainbow, is one of nature’s rarest phenomena.Fire rainbows only occur when there is a perfect concoction of sunlight and ice crystals in the cirrus clouds in the atmosphere. Because of how tough it can be for nature to create the right conditions, the phenomenon is very rare and widely celebrated.If you have been wondering, the phrase does not mean that the clouds actually catch fire. The term fire rainbow is a misnomer that was given by a journalist decades ago. The name seemed to stick with people over the years since they found a similarity between the term itself and the actual rainbow.Since cirrus clouds are wispy in nature, when bright colors are seen in a circumhorizontal arc, it seems as if there are flames in the sky! Keep reading for more facts about fire rainbows!Fire Rainbow FormationFire rainbows or circumhorizontal arcs are very fascinating. Because of just how rare they are, people often take a moment to quickly take pictures of the wonderous phenomenon whenever an opportunity presents itself.A fire rainbow is formed by the refraction of light and requires the perfect concoction of plate-shaped ice crystals (of hexagonal shapes) and sunlight falling at the correct angle. A fire rainbow forms in cirrus clouds.If you aren’t sure what cirrus clouds are, the easiest way to understand is that there are three levels of the atmosphere where clouds exist, and they are classified on the basis of altitude; cirrus clouds sit at the topmost height and appear wispy, unlike the cauliflower-shaped clouds that we see on the lower levels on a bright and sunny day. Cirrus clouds, since they are at such a great height of over 20,000 ft (6.09 m) from ground level, often have plate-shaped ice crystals in them.When the sun is at the right degree on the horizon, and its rays fall at a specific angle, light enters the crystals, and through an optical phenomenon known as refraction, it bends. When the bent light comes out through the other surface of the crystals, which are parallel with the ground, the white light is split in order to form a rainbow.Circumhorizontal arcs are not a common sight due to the fact that the plate crystals and sunlight being at the correct angle is a rare phenomenon. However, when high-level cirrus clouds are visible, and the correct conditions present themselves, the iridescent clouds assume the appearance of bright flames or brilliant pastel colors and are called rainbow clouds. They should not be confused with fire rainbows.A circumhorizontal arc may last from anywhere between a couple of minutes to a few hours, depending on how long the sun stays higher than 58 degrees on the horizon.Causes Of Fire RainbowsThe ideal and most probable time for the appearance of a fire rainbow ranges from mid-May to late July. However, there is no fixed position in the world where the phenomenon may take place. It is also important to note that fire rainbows cannot be seen north of 55 degrees north latitude and also south of 55 degrees south latitude. This is because, in order for the refraction to occur, the sun has to be at around 58 degrees with the horizon.In nature, evaporation processes cause moisture to be present in the air. This moisture goes to the clouds. While some clouds, such as the cumulus clouds, are cauliflower-like in appearance, cirrus clouds are wispy. Hence, when the rays of the sun or moon refract in order to create a rainbow, the clouds appear to have caught on fire high in the sky.Why is a fire rainbow rare?The circumhorizontal arc is a rare phenomenon. The cirrus cloud formations and sun being at the correct angle and the hexagonal ice crystals being arranged in the perfect way is quite unusual. Nature has no set methods for this, and hence, a circumhorizontal arc may only appear through sheer coincidence.The Difference Between A Rainbow And A Fire RainbowWhen the light from the sun is refracted and passes through the water droplets present in the air, rainbows are formed. For example, when the sun can peek through during rainfall, the chances are that some of the light will pass through the water droplets in a way that bends the light and splits it into its constituent colors.Fire rainbows, however, do not form because of refraction from water droplets. They form when light from the sun is refracted through ice crystals found in cirrus clouds. Like in the case of rainbows, however, even fire rainbows do not have a fixed location. They can have different positions in the atmosphere. The only thing that remains constant is a dependence on angles.
A circumhorizontal arc, or fire rainbow, is one of nature’s rarest phenomena.
