EXTREMELY rare clouds known for their pearly-white appearance, normally limited to the polar regions, appeared over Scotland on Tuesday.
Weather-watchers caught the nacreous clouds, which form at 80,000 to 100,000 feet above the ground, over Edinburgh and Fife.
They require temperatures below -78C to exist, levels of cold which usually only appear in the polar reaches of Canada, Scandinavia and Russia.
Pearl nacreous cloud above Edinburgh tonight. 😍 pic.twitter.com/JI9LS9icHk
— Ross Cunningham (@Ross_in_Orkney) December 19, 2023
Scattering of sunlight around the tiny ice crystals inside the clouds causes their pearly, iridescent appearance.
The clouds also appeared over Staffordshire, Lincolnshire, Merseyside and Cheshire.
Viewers were both amazed and confused by the display, with some questioning if they were the Northern Lights.
Strange clouds/ atmospheric conditions above Edinburgh tonight while walking the dog. Look almost like mini northern lights. pic.twitter.com/uqtM33021t
— Cat (@cat_cutmore) December 19, 2023
Some kind of beautiful rainbow cloud thing over the Western sky of Edinburgh tonight. What is it? I'm thinking northern lights pic.twitter.com/10Bpia6t0l
— Alex Ellis (@ajpellis1) December 19, 2023
Other people took a more humorous tack, with one Twitter/X user suggesting its orange oblong shape was a contrail from Santa's sleigh.
Anyone else see this crazy cloud in Edinburgh last night? Santa sleigh con trail? pic.twitter.com/zM9yxm55qB
— Ian Mackenzie (@IanMack202) December 20, 2023
Meteorologist Jo Farrow explained on Twitter/X why the clouds were so brilliant after sunset, writing: "The usual clouds are dark because the sun has set but the nacreous clouds are so high that they are still receiving the sun's rays, which makes them stand out."
Some great photos yesterday from Princes Street #Edinburgh. The usual clouds are dark because the sun has set but the #Nacreous clouds are so high that they are still receiving the sun's rays, which makes them stand out. https://t.co/tTQuT3NSac
— JoFarrowWx (@jofwx) December 20, 2023
The clouds last appeared over Scotland in January, forming above Aberdeenshire, Moray and the Highlands.
The Met Office describes some of the clouds' unique characteristics on its website, saying: "Nacreous clouds form in the lower stratosphere over polar regions when the sun is just below the horizon.
"The ice particles that form nacreous clouds are much smaller than those that form more common clouds.
"These smaller particles scatter light in a different way, which is what creates the distinctive luminescent appearance."
