Fire Rainbow: A Rare Cloud Phenomenon

Rainbows of fire are neither fire nor rainbows, but are so named because of their brilliant colors and flames when they appear. Technically, they are formed by hexagonal plate-shaped ice crystals in high-level clouds. The halo is so large that the arc appears to be parallel to the horizon, hence the appropriate name.

You can read more about such a phenomenon as a rainbow in a separate article, but it has little to do with this phenomenon. The brightly colored arc occurs mainly during the summer between certain latitudes. When the sun is very high in the sky, the sunlight entering the hexagonal flat ice crystals is split into individual colors just like in a prism. The conditions required to form a «rainbow of fire» are very precise — the sun must be at an angle of 58° or more, there must be high-altitude clouds with ice plate crystals, and sunlight must pass through them at a certain angle. This is why a fiery rainbow is such a rare occurrence.

The position of the observer is also important. Arcs cannot be seen at locations north of 55°N or south of 55°S. Likewise, there are only certain times of the year when they are visible. For example, in London the sun is only high enough for 140 hours between mid-May and late July. While in Los Angeles, the sun is as high as 58 degrees for 670 hours between the end of March and the end of September. You can admire interesting photos in the collection called «The Wonderful World of Clouds», where there is a description of many interesting species.

Fire Rainbow should not be confused with Iridescent Clouds, which can produce a similar effect. In contrast, iridescence often occurs in altocumulus, cirrocumulus, and biconvex clouds. Rainbow arcs can be so huge that they appear to cover the entire sky.

Visit also a selection with a story about unusually shaped clouds, where there is also something to see.