Dec. 17, 2023: (Spaceweather.com) A cold wave just swept through the Arctic stratosphere. Really cold. We know because on Dec. 17th these colorful clouds appeared over Sweden:

Above: A “PSC selfie” by Lights over Lapland driver Dimitrios Roukounakis

“It’s that magical time of year again,” says Chad Blakley, owner of the aurora tour guide service Lights over Lapland in Abisko, Sweden. “We just witnessed a spectacular display of polar stratospheric clouds.”

Widely considered to be the most beautiful clouds on Earth, polar stratospheric clouds (PSCs) 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 that can rival auroras.

NASA forecast models of the polar stratosphere show that temperatures have indeed dropped into the very low range required for colorful Type II PSCs:

Above: Note the temperature dip inside the highlighted yellow oval

During a typical Arctic winter, PSCs appear no more than a handful of times, and the first sightings usually come in January. The apparition on Dec. 17th marks an early start, and may herald many more PSCs to come. Stay tuned!

more images: from Pekka Lähteenmäki of Helsinki, Finland; from Alan C. Tough of Elgin, Moray, Scotland