POLAR STRATOSPHERIC CLOUDS: Arctic skies are filling with color, but it is not the aurora borealis. A rare outbreak of polar stratospheric clouds (PSCs) is underway around the north pole, caused by extremely cold temperatures in the stratosphere. Full story @ Spaceweather.com
"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.
NASA models of the polar stratosphere show that temperatures have indeed dropped into the very low range required for Type II PSCs:
However, the forecast (yellow) calls for warming as January comes to an end, so now is the time to look. During a typical Arctic winter, PSCs appear no more than two or three times. If you see one, it's definitely worth taking a picture.
more images: from Fredrik Broms of Kvaløya, Norway; from Jónína Óskarsdóttir of Fáskrúðsfjörður, Iceland; from Francois Guilhaume-Bohl of Nellim, Finland
https://spaceweather.com/
