This week, a magnificent meteorological phenomenon was observed over portions of Virginia: a so-called “rainbow cloud,” which appears as a dazzling prism of color behind fluffy clouds. Several residents in Hamilton, Virginia, emailed WUSA-TV, the CBS affiliate in Washington, D.C., photographs of the event.
While many referred to it as a “rainbow cloud,” it is actually an atmospheric phenomenon known as cloud iridescence. But what is it exactly? “Cloud iridescence occurs when the water droplets or ice crystals in the cloud diffract the light around the outside of the droplet, as opposed to bending the light through it,” a meteorologist from The Weather Channel told CBS News.
“The spectrum’s hues are not as well ordered in iridescence as they are in a rainbow,” she remarked. The iridescence of clouds reminds me of fairy dust or unicorn sprinkles.
According to Carfango, co-host of “America’s Morning Headquarters,” rainbow clouds are relatively uncommon. In the winter, they are frequently sighted around the arctic regions or in mountainous places. The clouds must be close to the sun.
The clouds must be composed of ice crystals or water droplets of consistent size and thickness. Consequently, lenticular or alto-cumulus, cirrus, and cirrocumulus clouds typically exhibit iridescence.
This week in Northern Virginia, a pileus cloud, also known as a ‘cap cloud,’ emerged on top of a late afternoon cumulonimbus cloud, according to Carfagno. This cap cloud is a frequent occurrence atop intense thunderstorms.
A rainbow cloud resembles a rainbow, halo, sundog, and circumhorizontal arc due to the fact that it is created by the diffraction or refraction of light.
Vermont witnessed a similar “fire rainbow” in 2018. Technically known as a circumhorizontal arc, this phenomenon occurs when the sun is above 58 degrees above the horizon and its light is refracted by ice crystals in the atmosphere, according to the National Weather Service (NWS).
This phenomena is only apparent in cirrus clouds, which are composed of ice crystals and have a wispy appearance. According to the NWS, when cirrus clouds are colored, they can be mistaken for iridescence.
Carfagno noted that rainbow clouds and fire rainbows are distinct, and the colors in a fire rainbow are far more vibrant than in a rainbow cloud.
Carfagno stated that the “rainbow cloud” sighted over Virginia has been described by some as having a psychedelic hue, which is an accurate description of the cloud type.
“Cloud iridescence lacks the color uniformity of a typical rainbow, halo, or circumhorizontal arc,” she explained.