#POLAR #STRATOSPHERIC #CLOUDS: Arctic skies are filling with color today--but it's not the aurora borealis. A rare outbreak of polar stratospheric clouds (PSCs) is underway. Jónína Óskarsdóttir photographed the display from Fáskrúðsfjörður, #Iceland:

"We have been seeing these clouds for a couple of days," reports Óskarsdóttir. "In this picture, Mt. Jökultindur is silhouetted by a sky-full of nacreous color."

Polar stratospheric clouds are rare. Earth's stratosphere is very dry and normally it has no clouds at all. PSCs form when the temperature in the Arctic stratosphere drops to a staggeringly-low -85 C. Then, and only then, can widely-spaced water molecules begin to coalesce into tiny ice crystals. High-altitude sunlight shining through the crystals creates intense iridescent colors often likened to auroras.

https://spaceweather.com/