Photograph by Owen Humphreys, PA Wire, Associated Press
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A nacreous cloud was seen near Whitley Bay, Northumberland in northern England on February 2, 2016, delighting observers.

Photograph by Owen Humphreys, PA Wire, Associated Press

Rare Shimmering Rainbow Clouds Appear Over the U.K.

Called nacreous or polar stratospheric clouds, the rare phenomena adorned the British sky in the wake of Storm Henry.

"After a hurricane comes a rainbow," Katy Perry sings in her hit Firework. The song could almost describe the scene over Scotland and northern England Tuesday night.

While not quite a hurricane, Storm Henry battered the northern U.K. with winds up to 60 miles per hour (97 kilometers per hour), causing flooding and disrupting power for thousands. The cold air the storm blew in also led to the formation of beautiful nacreous clouds. (Pronounced ney-kree-uh s, the name refers to a resemblance to nacre, or mother-of-pearl.)

The shimmery phenomena above were photographed near Whitley Bay, Northumberland, in northern England. That's an unusual place to spot them, as they usually appear along polar regions.

Also called polar stratospheric clouds (or less precisely, rainbow clouds), nacreous clouds normally only form in high latitudes and at extremely cold temperatures. They're visible when fading light at sunset passes through tiny ice crystals blown along by a strong jet of stratospheric air. (See another photo.)

"These clouds are more than just a curiosity," Andrew Klekociuk, an atmospheric scientist with the Australian Antarctic Division, previously told National Geographic. "They reveal extreme conditions in the atmosphere and promote chemical changes that lead to destruction of vital stratospheric ozone."

Specifically, the clouds form surfaces where chemical reactions can take place that produce ozone-destroying molecules, and can contribute to the formation of polar ozone holes.  

Still, the clouds are hardly the biggest threat to the ozone layer. That would come in the form of manmade chemicals like CFCs, HCFS, freon, and halons, most of which have been dramatically reduced thanks to international agreement. As a result, risk to the ozone hole has decreased over the past few decades and the layer is thought to be on the mend.

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