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!