Feb. 14, 2017: Arctic nights are usually colored by the aurora borealis. Last night was different. The colors came from polar stratospheric clouds (PSCs). Lars Lehnert photographed the display from Abisko, Sweden:

“We saw these clouds all day long,” says Lenart, “and they continued into the night. I’ve never seen anything quite like it.”

In Kiruna, Sweden, longtime PSC photographer Mia Stålnacke saw them, too: “This was a first for me!” she says. “The polar stratospheric clouds which lit up the Arctic skies in daylight are still here. Now they are beautifully lit up by the Moon instead!”

This is a remarkable episode of PSCs–the best in many years according to some longtime residents of northern Sweden. Arctic sky watchers should remain alert for more, both day and night, as this unusual winter continues.

Realtime PSC Photo Gallery

Feb. 13, 2017: Around the Arctic Circle, observers are reporting an outbreak of polar stratospheric clouds (PSCs). “Today, Feb. 13th, the sky was filled with their brilliant colors from sunrise to sunset,” says Mia Stålnacke, who sends this picture from Kiruna, Sweden:

These clouds are newsworthy because normally the stratosphere has no clouds at all. Home to the ozone layer, the stratosphere is arid and almost always transparent. Yet, Stålnacke says, “we’ve been seeing stratospheric clouds very often this winter and last.”

According to multiple longtime residents of the area, the Feb 13th display was exceptional. “Everyone I spoke to agrees it was the best they had ever seen,” says Chad Blakley, who operates the Lights over Lapland tour guide service in Abisko, Sweden.

“I’ve been living here all my life (33 years),” says Stålnacke. “I definitely feel that these clouds are appearing more often then they used to. I remember seeing them a few times/year since I was a kid, but these last couple of years we’ve had them much more often–sometimes for almost a week straight. Others seem to feel the same way; I see local groups on Facebook flooded with photos of PSCs and comments on how often they’re appearing now.”

“The clouds were all over Finland, too,” says Matti Helin who took this picture on Feb. 13th:

What’s going on up there?

PSCs are a sign of very cold temperatures in the stratosphere.  The clouds are made of ice. Indeed, that is the source of their remarkable color: High-altitude sunlight shining through tiny ice particles ~10µm across produce a bright iridescent glow.  For ice crystals to form in the very dry stratosphere, temperatures must drop to around -85º C.

Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone. Indeed, an ozone hole formed over the UK in Feb. 2016 following an outbreak of ozone-destroying Type 1 PSCs.

To investigate these clouds further, Spaceweather.com and the students of Earth to Sky Calculus will travel to Abisko Sweden for a week in March 2017.  We plan to launch a series of space weather balloons into the Arctic stratosphere, measuring temperature, air pressure, and ambient radiation.  If PSCs are present, our sensors will pass directly through them, and our cameras can photograph the colorful clouds at point blank range. Stay tuned!

Dec. 9, 2016: The stratosphere above the Arctic Circle is getting cold … very cold.  That’s the only way to explain these colorful clouds that materialized over Kiruna, Sweden, on Dec. 9th:

“Polar stratospheric clouds are back in the subarctic,” reports photographer Mia Stålnacke. “They were brilliantly beautiful today.”

Icy polar stratospheric clouds (PSCs) form in the lower stratosphere when temperatures drop to around -85ºC. That’s how cold it has to be for ice crystals to form in the very dry stratosphere. High-altitude sunlight shining through tiny ice particles ~10µm across produce the characteristic bright iridescent colors.

“Once seen they are never forgotten,” says atmospheric optics expert Les Cowley. “Polar stratospheric clouds have much more vivid colors than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world.”

Once thought to be mere curiosities, some PSCs are now known to be associated with the destruction of ozone. Indeed, an ozone hole formed over the UK in Feb. 2016 following an outbreak of ozone-destroying Type 1 PSCs.

“Last winter we had these clouds almost daily for long periods of time,” says Stålnacke. Arctic sky watchers are encouraged to be alert for more in the days ahead. The best time to look is just before sunrise or after sunset.

Feb. 5, 2016: For the past week, sky watchers in the UK have witnessed a rare apparition of polar stratospheric clouds (PSCs). Normally restricted to the Arctic Circle, the fantastically colorful clouds have appeared over the British Isles almost every day since Jan. 31st. Colin Fraser photographed the display over Edinburgh, Scotland, on Feb. 2nd:

PSCs form in the lower stratosphere when temperatures drop to a staggeringly-cold -85ºC. High-altitude sunlight shining through tiny ice particles ~10µm wide produce bright iridescent colors by diffraction and interference.

But there is more to PSCs than ice. Some polar stratospheric clouds contain very small droplets of naturally occurring nitric and sulphuric acids. These droplets destroy ozone. Indeed, atmospheric optics expert Les Cowley points out that a temporary ozone hole has formed over Ireland and the UK. It is the blue patch in this Feb. 1st ozone map from NASA’s Arctic Ozone Watch:

“The acid droplets destroy the stratospheric ozone layer that protects us from harmful solar ultra-violet rays,” says Cowley. “They catalyse unreactive forms of man-made chlorine into active free radicals (for example ClO, chlorine monoxide). The radicals destroy many ozone molecules in a series of chain reactions..”

This outbreak of PSCs is truly unusual. “Prior to this outbreak I have seen PSCs over the UK only twice in the last 20 years!” says Cowley. “This episode is exceptional at such low latitudes.  If it goes on any longer my camera will be worn out.”

UPDATE: On Feb. 5th, the outbreak of PSCs has subsided, and so has the UK ozone hole. Click here for updates.