Clouds have a wide variety of formations that sometimes leave us amazed. Iridescent clouds are commonly referred to as rainbow clouds or irisation clouds. This captivating optical phenomenon is most characteristically seen in the form of a rainbow cap (pileus) that typically appears above certain types of clouds. The appearance of these clouds is different from the rainbows we typically see after rain. So, how does an iridescent cloud occur? Here are some interesting facts!
1. Iridescent Cloud Meaning
Iridescent clouds have several other names, such as fire rainbows and rainbow clouds. So, why are these clouds more commonly known as iridescent clouds? A name like rainbow cloud, for example, would be easier to understand. Originally derived from Greek, the word iridescent is named after a goddess named Iris. In Greek mythology, Iris is described as a goddess tasked with conveying messages through rainbows.
The term iridescence, or irisation, is commonly used to describe the way certain substances display varying colors at different angles, reflecting the way these clouds form. In everyday life, we see this in feathers, soap bubbles, butterfly wings, beetle backs, fish scales, pearls in shells, and even oil spills.
2. Why Are They Called Rainbow Clouds?
An iridescent cloud is often referred to as a rainbow cloud because of its multicolored appearance. The colors resemble a soft rainbow painted directly onto the cloud surface. Unlike full rainbows, however, the colors in an iridescent cloud are usually more pastel, uneven, and constantly shifting as the clouds move.
3. Where to See an Iridescent Cloud
If you are wondering where to see an iridescent cloud, they can appear almost anywhere in the world under the right atmospheric conditions. They are more commonly seen when the sun is partially hidden behind thin clouds during daytime hours. Mountain regions, open landscapes, and areas with changing weather conditions can increase your chances of spotting a rainbow cloud. However, because the phenomenon is unpredictable, sightings are often brief and spontaneous.
4. Rainbow Clouds Appear due to Optical Phenomena
The phenomenon of iridescent clouds occurs due to diffraction of sunlight. This reflection then hits very small, uniformly shaped water droplets or ice crystals within a cloud system, or a cloud system that is still relatively thin or new. The iridescent cloud produces a repeating color pattern, starting with blue, then green, then red, then purple, and finally returning to blue again. This phenomenon generally occurs in pileus clouds such as lenticular or altocumulus, cirrus, and cirrocumulus.
The appearance of pileus clouds is caused by thunderstorms that push air into the upper atmosphere through a layer of water vapor. This results in the appearance of fog-like clouds that appear as a glowing dome above the thunderstorm. The iridescent cloud then rises above these clouds, resembling a hat atop the cloud.