Have You Ever Seen "Fire Rainbow"?
What does "Fire Rainbow" mean?
The circumhorizontal arcs, which are neither a type of rainbow nor flame, are referred to as a "fire rainbow". In particular with cirrostratus or cirrus clouds, this phenomenon occurs because of the light being refracted when it passes from the moon or the sun, when it is higher than 58° above the horizon, across the hexagonal plate ice crystals within the atmosphere. Next, the ice crystals behave as a prism when they are perfectly aligned. Finally, an evocative of rainbow, called "Fire Rainbow", is formed. It is represented by a band of spectrum colours, with Red as the outermost color. Other names for "Fire rainbow" is the lower symmetric 45° plate arc or the circumhorizon arc.
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What Causes "Fire Rainbow" to Form?
As already being mentioned, the vertical flow of sunlight through the ice crystals in the cloud causes the formation of the fire rainbow. The ice crystals are in the horizontal orientation with the hexagonal flat face. Although the ice's thickness has no bearing on how they formed, in some instances or rare occurrences, the formation of the fire rainbow is also influenced by the skewed oriented way of the ice crystals. The exit faces and ray entrance must be inclined at angle of 90° to each other to create an ideal organization of the ice crystals that can separate the spectrum colors. The rays from the sun pass through the ice crystals in angular tilt is a common occurrence that typically will not create a complete separation of the spectral colors.
How Many Times Does This "Phenomenon" Occur?
One of the important factors that affect the frequency of Fire Rainbow's formation is region and latitudinal location. For instances, fire rainbows are much more frequently seen during the summer months in the United States, 10-20 times more often, rather than in Europe. As already mentioned earlier, this phenomenon will occur when the sun is higher than 58° above the horizon, that hardly ever observed in the regions farther than 55° North and South, called High Latitude Regions, because there will be an inhibition in forming circumhorizontal arc. In England (High Latitude Regions), the sun with the elevation more than 58° above the horizon only take place for 140 hours between mid-May and late July, whereas in Los Angeles (Tropic Regions), it will take place for 670 hours between late March and late September. So, there is almost no ideal condition provided by the rays to the formation of Fire Rainbow on High Latitude Regions.
Is There Any Possibilities for High Latitude Regions to See the "Fire Rainbow"?
Although there is a slim likelihood to make the "Fire Rainbow" happen on those regions, the water glass experiment can be done for creating the Artificial Fire Rainbow. In this experiment, water replaces ice crystals as "prism" or splitter of light into the various circumhorizontal arc lights. The first step, set up the glass right next to the wall. As the light directed through an extremely steep angle into a cylindrical glass full of water, it will be refracted into the water. Next, the light will be refracted for the second time and forming a hyperbola projected on the wall. As a result, an artificial phenomenon, called "Fire Rainbow", is formed as it resembles the natural one in appearance.
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Conclusion
To sum up, "fire rainbow" is a phenomenon when the light being refracted as it passes the moon or the sun. It only occurs when the sun is higher than 58° above the horizon. The frequencies of this phenomenon to occur depends on the region, with Tropic Regions more often than High Latitude Region.
References
Victor, Rotich K. (2018). What Is A Fire Rainbow?. Accessed on 22nd April, 2019, from https://www.worldatlas.com/articles/what-is-a-fire-rainbow.html.
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