Polar Stratospheric Clouds in Moonlight over Finland

Polar Stratospheric Clouds in Moonlight over Finland

Unusual weather in the stratosphere has set the stage for rare nighttime displays of polar stratospheric clouds (PSCs). Marianne Bergli took this picture on February 11, 2025, in Kilpisjervi, Finland: "The PSCs were even more colorful than auroras," says Bergli. "The full Moon lit them beautifully."

This kind of display is unusual for two reasons. First, Earth's stratosphere usually has no clouds at all. Only when the temperature drops to a staggeringly-low -85 C can widely-spaced water molecules assemble into icy PSCs. Second, on rare occasions PSCs appear, they are usually seen only during the day. This is when bright sunlight causes them to blossom in color. On Feb. 11th the full Moon did the job of the sun.

According to NASA's MERRA2 climate model, the polar stratosphere has been exceptionally cold this winter with temperatures dropping to 45-year lows. What's going on? Researchers are not certain, but the reason might be the stratospheric polar vortex. This winter's vortex has been strong, keeping cold air bottled up over the Arctic Circle.

If you live in the Arctic, keep an eye on this week's bright Moon. It may come with PSCs!

Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, opposite Estonia. Kilpisjervi is located in Finland's northwestern "arm" near the northwesternmost point of the country.

Image Credit: Marianne Bergli
Capture Location: Kilpisjervi, Findland

Caption Credit: Marianne Bergli / SpaceWeather[dot]com
Image Date: Feb. 11, 2025

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