An “Exceptionally Gigantic” Polar Rain Aurora Blanketed the Arctic Sky

Lying roughly 600 miles south of the North Pole, the Norwegian archipelago of Svalbard is the world’s northernmost permanently inhabited place. About 2500 shivering year-round residents live in the capital, Longyearbyen, a former coal-mining colony, where the regular appearances of northern lights brighten the polar night. 

But the scene over Longyearbyen on Christmas Day 2022 baffled scientists for over a year. The ink-black sky was overtaken by an all-encompassing faint green light. Unlike most aurorae, the green mass did not take the form of flickering ribbons or wavy curtains. It was remarkably smooth. It lingered for 28 hours and then was gone. 

A team of Japanese and American astronomers now have an explanation. According to a new study in Science Advances, they think the incident—which they call “exceptionally gigantic”—was one of the largest and most spectacular displays of a phenomenon called “polar rain” ever observed.

Magnetic Magic

As a feature of the sun’s relationship to Earth, solar discharges get caught up in Earth’s invisible magnetic lines, which circle Earth from pole to pole. Typical aurorae, like the northern lights—which have dazzled observers for millennia—result from particles escaping the sun’s magnetosphere, traveling along solar winds, and then tickling Earth’s magnetosphere. 

Another kind of solar discharge that travels along this path is a beam of super-charged electrons emitted directly by the corona, the sun’s outermost layer. When this beam crashes into the Earth’s magnetosphere, it creates “polar rain.”

Through astronomers have studied it using satellites, polar rain is usually diluted by solar winds and rarely visible to the human eye. 

The astronomers who studied the December ’22 phenomenon noted from satellite data that solar wind was very low on that date, allowing for a huge polar “rainfall.” The aurora may have extended for 2485 miles, making it one of the largest displays of the phenomenon on record. In terms of solar weather patterns, it was a really big deal—and a once-in-a-lifetime Christmas present for sky nerds.

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