Sunday, April 17, 2022

'Fire rainbows' enthrall residents in North Carolina on Good Friday

 It wasn't a rainbow, but it was a brilliant atmospheric display that had residents doing a double take when they saw it in the sky.

Western North Carolina residents were treated to a colorful atmospheric phenomenon on the afternoon of Apr. 15, Good Friday. Photos shared on social media showed what is known colloquially as a "fire rainbow" or, as people posting on Twitter referred to them, "rainbow clouds."

The pre-Easter optical phenomenon is known technically a "circumhorizontal arc" and is created by sunlight reflecting off of ice crystals. To see this ice halo, the sun needs to be more than 58 degrees high in the sky, and high cirrus clouds or jet contrails must be present to bring this spectacular display to life.

A visible satellite image over North Carolina on the afternoon of Apr. 15, 2022, shows high clouds and jet contrails that allowed the circumhorizontal arcs to be visible.

NOAA

A very delicate balance in the atmosphere is required for this effect to be achieved.

The hexagonal, plate-shaped ice crystals inside the cirrus clouds also need to be aligned horizontally, so that the light entering through the vertical side of the crystals refracts, bends, and exits through the horizontal bottom. This disperses the light into the seven colors of the spectrum, similar to what we see in a rainbow. 

An optical phenomenon known as a 'circumhorizontal arc' treated people in North Carolina to an unusual sight in the skies on Friday, April 15, 2022. (Brandon Carter)

Brandon Carter

Brandon Carter, who captured the image above, told AccuWeather, "I took the photo in Concord," a suburb of Charlotte that's just northeast of the city. He was driving when he spotted the dazzling spectacle in the sky.

"When I saw it my first thought was to pull over and make sure my daughter could see what became known for the day as 'rainbow clouds,'" Carter, 41, who works in sales and said his true passion is astrophotography, recalled. "It was a great opportunity for my wife and I to talk to her about the science behind rainbows and a really cool moment."

Circumhorizontal arcs are not entirely rare in the skies over the United States but are more common in the tropics. However, they can not be seen in Arctic areas because the sun never appears high enough in the sky to allow for this delicate balance of ingredients to take place.

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