Rare

A surprising climate phenomenon was noticed over elements of Virginia this week – a so-called “rainbow cloud,” which seems like a vibrant prism of shade behind smooth clouds. A number of folks in Hamilton, Virginia, despatched in photographs of phenomenon to WUSA-TV, a CBS affiliate in Washington, D.C. 

Whereas many had been calling it a “rainbow cloud,” it’s extra precisely an atmospheric optic known as cloud iridescence. However what precisely is that?

“Cloud iridescence varieties when the water droplets or ice crystals within the cloud diffract the sunshine across the outdoors of the droplet, versus bending the sunshine by way of it,” The Climate Channel meteorologist Jen Carfagno advised CBS Information. 

“The colours of the spectrum usually are not as neat and arranged in iridescence as in a rainbow,” she added. “Cloud iridescence jogs my memory of pixie mud or unicorn sprinkles.”

So-called rainbow clouds are pretty uncommon, mentioned Carfango, who co-hosts “America’s Morning Headquarters.” They’re typically noticed close to the polar areas, or in mountain areas within the winter. The clouds should be close to the solar.  

The clouds have to be very skinny and product of ice crystals or water droplets of uniform measurement. So cloud iridescence normally occurs in lenticular or alto-cumulus, cirrus and cirrocumulus clouds.  

“Within the case from this week in Northern Virginia, what occurred was {that a} pileus cloud, AKA a ‘cap cloud,’ fashioned on prime of a late afternoon cumulonimbus cloud,” Carfagno mentioned. “This cover cloud is a standard characteristic on prime of robust thunderstorms.”

A rainbow cloud is an identical rainbow, halo, sundog, circumhorizontal arc, as a result of it varieties as a result of diffraction or refraction of sunshine. 

In 2018, a comparable “fireplace rainbow” was noticed in Vermont. This phenomenon, technically known as a circumhorizontal arc, happens when the solar could be very excessive within the sky – larger than 58 levels above the horizon – and its mild is refracted by ice crystals suspended within the ambiance, in line with Nationwide Climate Service (NWS). 

This phenomenon seems like a really giant halo and is just seen in cirrus clouds, that are made out of ice crystals and look wispy. When the cirrus clouds are lit with shade, they are often mistaken for iridescence, in line with the NWS. 

Rainbow clouds and fireplace rainbows are totally different, and the colours in a fireplace rainbow are far more vivid than in a rainbow cloud, Carfagno defined. 

Carfagno mentioned the “rainbow cloud” noticed over Virginia has been described by some as psychedelic in shade, which is an effective description as a result of it offers a clue in regards to the cloud kind. 

“Cloud iridescence shouldn’t be as uniform in shade as is a daily rainbow or a halo or a circumhorizontal arc,” she mentioned.