The stratosphere above the Arctic Circle is getting cold … very cold. That’s one way – the only way for space weather scientists – to explain these colorful clouds – polar stratospheric clouds (PSCs) – which require temperatures around -85ºC to form and appeared over Norway and Sweden on Dec. 20th:
This absolutely stunning display of stratospheric clouds appeared high above the ordinary gray rainclouds. It’s very seldom to see PSCs with such vivid colours as today.
As their name implies, these surreal clouds form in the extremely dry stratosphere, high above Earth’s surface. In this second layer of Earth’s atmosphere – starting between 33,000–43,000 ft; 6.2–8.1 mi) and ending at 50 km (160,000 ft; 31 mi) almost no clouds of any type can form.
However, when the the air up there becomes extremely cold, rare water molecules coalesce and form ice crystals. High-altitude sunlight refracting on the ice creates these mind-blowing iridescent colors.
Keep your eyes to the sky, the 2017-18 winter season for polar stratospheric clouds is just starting.