Jan. 1, 2020: A spectacular display of polar stratospheric clouds (PSCs) that began two days ago is still going strong around the Arctic Circle. This picture, taken on Dec. 31st by Per-Anders Gustavsson in Jukkasjärvi, Sweden, shows why some onlookers mistake them for daytime auroras:

“The colors were amazing,” says Gustavsson, who drives a tour bus for Visit Abisko. “I was driving by the world-famous Ice Hotel when we saw the clouds. We just had to stop for pictures.”

“I’ve seen a lot of beautiful things during my years in the Arctic,” he adds. “This was easily one of the greatest displays I have ever seen.”

Polar stratospheric clouds are newsworthy because normally the stratosphere has no clouds at all. The stratosphere is arid and almost always transparent. Only when the temperature drops to a staggeringly cold -85C can sparse water molecules assemble themselves into icy stratospheric clouds. PSCs are far more rare than auroras.

The clouds are even visible at night, as shown in this Dec. 31st photo taken by Fredrik Broms in Kvaløya, Norway:

“Better than New Year fireworks – by far!” says Broms. “What an amazing way to end 2019.”

“This really is a rare event,” says Chad Blakley, who runs the Lights over Lapland aurora tour service in Abisko, Sweden. “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. At one point I would say that close to 25% of the sky was filled with the clouds. PSCs we have seen in previous winters have been closer to 1% or 2%.”

Polar stratospheric clouds are intensely colorful because they are made of a special type of ice. High-altitude sunlight shining through microscopic crystals only ~10µm across produce a bright iridescent glow unlike the lesser iridescence of ordinary tropospheric clouds.

Stay tuned for updates as the outbreak continues.