Recently the Arctic sky glowed with an ethereal, multi-colored light. But it was not an aurora, despite
Clouds known as polar stratosphericClouds form only when the temperature in the lower stratosphere reaches below -81°C. Normally, clouds don't form in the stratosphere because it's too dry, but at these low temperatures, water molecules coalesce into tiny ice crystals and then into clouds. Polar stratospheric clouds form much higher than normal clouds, from 15 to 25 km above the Earth's surface.
It is the extreme freezing conditionsin the stratosphere led to the appearance of rainbow clouds beyond the Arctic Circle - in Iceland, Norway and Finland. Amateur photographer Jónin Guðrún Óskarsdóttir captured a stunning image of the bright clouds above the peak of Mount Jökultinður in Iceland (view here).
There are two types of polar stratospheric clouds:
Type I consists of a mixture of ice crystals and nitric acid, giving less bright colors;
Type II is made from pure ice crystals and has brighter colors. Those that have recently formed above the Arctic Circle are of the second type.
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Cover photo: Matiasm, CC BY-SA 3.0, via Wikimedia Commons