POLAR STRATOSPHERIC CLOUDS: Best Ever ?
Around the Arctic Circle, observers are reporting an outbreak of polar stratospheric clouds (PSCs). "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.
"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.
See Space News Page for the Latest Sun Spot Situation/Count