Rare clouds that give off bright, multi-colored light like an aurora were recently
spotted at multiple locations in the Arctic. But what causes them?
© Jónína Guðrún Óskarsdóttir
Bright multi-colored clouds shining in the night sky above Mount Jökultindur in Iceland on Jan. 25.
The dark skies in the
Arctic Circle recently shone with ethereal multi-colored light.
But this jaw-dropping spectacle was not caused by auroras. Instead, the iridescent rainbows were caused by clouds of tiny ice crystals floating higher in the atmosphere than is normally possible.
The clouds, known as polar stratospheric clouds (PSC), only form when the lower stratosphere reaches temperatures below minus 114 degrees Fahrenheit (minus 81 degrees Celsius). Normally, clouds do not form in the stratosphere because it is too dry, but at these extremely low temperatures "widely-spaced water molecules begin to coalesce into tiny ice crystals" that form into clouds,
Spaceweather.com reported. This means PSCs can form much higher up than normal clouds, between 9.3 and 15.5 miles (15 to 25 kilometers) above the ground.
As sunlight shines through these crystal clouds, it gets scattered, creating multiple different wavelengths of light, which has inspired the PSCs nickname, "rainbow clouds." Due to the extreme altitude of the clouds sunlight can hit the crystals and scatter above an observer even if the sun is beyond the horizon, which is when these clouds appear brightest.
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