This spectacular event occurred due to unusual cooling in the upper layers of the atmosphere. Experts say more of these colorful clouds may appear in the next few months.

More about the show

Colorful clouds known as polar stratospheric clouds (PSCs) have been seen in the sky over parts of Norway, Sweden, Finland and Alaska, and even as far south as Scotland. They began to appear on December 18th and remained clearly visible until December 20th. The next day, they became less obvious; Scientists at SpaceWeather say they appear to have long since disappeared.

Ramune Shapailaite took striking photographs of a rare phenomenon on Gran in southern Norway. His photographs show the iridescent hues and opalescent sheen of PSCs.

The colors are magnificent. Clouds were visible in the sky all afternoon, but the colors really popped before sunset.
Shapailaite said this in an interview with Spaceweather.com.

The reason for the appearance of such rare clouds was the presence of unusually low temperatures in the sky for a long time. PSCs arise from tiny ice crystals that refract and scatter sunlight. This separates the light into separate wavelengths, or colors, creating the rainbow effect we see from the ground.

Rainbow clouds / Photo: Ramune Shapailaite

There are two types of PSC:

• Type I consists of a mixture of ice crystals and nitric acid, which gives less striking colors and is associated with the formation of ozone holes.
• Type II, which consists of pure ice crystals and gives brighter colors. The clouds that formed recently over the North Pole belonged to type II.

The glowing structures form only in the lower stratosphere, between 15 and 25 kilometers above the Earth’s surface. Normally clouds do not form this high because the atmosphere is very dry. But at extremely low temperatures (below minus 85 degrees Celsius), widely dispersed water molecules begin to coalesce into small ice crystals, which then form clouds.

Stratospheric temperatures in the Arctic rarely fall below the threshold required for PSC formation, so they are usually observed only a few times a year during the winter months.