The fire rainbow appears in the sky with vibrant colors, but it can only be observed in certain areas.
What is a Fire Rainbow?
Steve Ackerman, a professor of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison, calculates that several variables must align for this spectacular phenomenon to occur. A fire rainbow is one of the few types of halos formed by the refraction of light through ice crystals mixed in the atmosphere, typically appearing in cirrus clouds.
A fire rainbow (Circumhorizontal arc) is a multicolored halo that appears horizontally in the sky, also known as a circumhorizontal arc. When seen in the sky, this colorful halo resembles a rainbow. However, it only occurs in cirrus clouds and at specific latitudes.
Fire Rainbow.
According to Mother Nature Network, this optical phenomenon forms from the refraction of sunlight, sometimes from the moon, through ice crystals suspended in the air. The sun must be positioned very high, at about 58 degrees or higher above the horizon.
On Earth, fire rainbows cannot occur north of 55 degrees latitude or south of 55 degrees south latitude. For those living near the poles, witnessing this phenomenon is impossible.
Conditions for Fire Rainbows to Occur
Fire rainbows only appear when there are sufficient 4 special conditions: Light must pass through cirrus clouds at a specific angle. The sun must be at least 58 degrees high above the horizon. The ice crystals through which the light is separated into colors must be hexagonal in shape, with their faces parallel to the ground.
As light passes through the surfaces of these ice crystals, it will refract. This bending of light is akin to the bending of light through a prism. If the crystals are aligned, the cirrus clouds will act like a prism, resulting in a shape resembling a rainbow. Additionally, the cirrus clouds are thin and reminiscent of flames, which is why this phenomenon is commonly referred to as a fire rainbow.
Distinguishing Between Iridescent Clouds and Fire Rainbows
Iridescent clouds are often confused with fire rainbows due to their similar colors and shapes. However, the phenomenon of iridescent clouds originates from the diffraction of light rather than refraction. Diffraction is the bending of light when it encounters an obstacle and is obstructed.
Iridescent clouds with non-sequential color bands can be seen at any cloud level.
With the naked eye, the two phenomena can also be distinguished: fire rainbows only occur at a fixed position in relation to the sun or moon, while iridescent clouds can appear in different locations in the sky. Furthermore, the color bands in a fire rainbow always run horizontally, with red from the VIBGYOR color spectrum on top and violet below. The colors of iridescent clouds do not always display this fixed color sequence; that is, their color order is random.
A fire rainbow with colors in sequence from red to violet, running horizontally, only visible in high-level clouds (cirrus clouds).
Due to the stringent conditions outlined above, fire rainbows are quite rare. Additionally, in places where they are commonly detected, the frequency and duration of their appearance can vary significantly.
For instance, in London, the sun is only high enough for a mere 140 hours from May to July. In Los Angeles, the sun is high enough for 670 hours from March to September. Moreover, European weather is often cloudy, and fire rainbows—phenomena of high-level clouds—can be obscured by low and mid-level clouds, making the detection of fire rainbows in Europe even more elusive.
Fire rainbows are among the most beautiful phenomena in nature. People in Europe and America should consider themselves lucky to witness this rare phenomenon much more frequently than many in other parts of the world!
