A spectacular outbreak of rare polar stratospheric clouds (PDCs) was reported around the Arctic Circle, starting December 30, 2019. The display lasted nearly an hour and was commonly regarded as the brightest display that any of the locals have ever seen.
The stratosphere is arid and almost always transparent, so to have clouds there, the temperature must drop to -85 °C (-121 °F) to have water molecules assemble into icy stratospheric clouds.
"This is a once in a lifetime event," Chad Blakey of Lights over Lapland aurora tour service in Sweden said. "They were so intense that lots of the tourists on the ground thought they were looking at daytime auroras. I had to explain that they were actually clouds in the stratosphere."
"No question, this is the best that any of us have ever seen," said tour guide Paige Ellis, who took this video on December 29:
"Local villagers in both Abisko and Kiruna who are more than 70 years old confirmed they have never seen anything of the size, scale, or intensity," Blakley told Dr. Tony Phillips of the SpaceWeather.com. "At one point I would say that close to 25% of the sky was filled with the clouds. PSCs in previous winters have been closer to 1% or 2%."
PSCs are intensely colorful because they are made of a special type of ice, Phillips said. High-altitude sunlight shining through microscopic crystals only ~10µm across produce a bright iridescent glow unlike the lesser iridescence of ordinary tropospheric clouds.
Featured image credit: Lights over Lapland
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