Mystery of massive aurora in Arctic skies in December 2022 solved by astronomers

A small group of astronomers affiliated with a number of establishments in Japan, working with a pair of colleagues within the U.S., has solved the thriller of the unusually easy aurora that appeared within the Arctic sky in December of 2022.

Of their paper printed in Science Advances, the group describes how they pored over each ground-based knowledge and satellite observations recorded through the occasion and what they realized by doing so.

In December of 2020, a ground-based digicam in Norway recorded what was described on the time as a exceptional auroral occasion within the night time sky—one which spanned 4,000 kilometers throughout the polar cap. It was deemed as unusually easy and coated far more of the night time sky than is regular.

For 2 years its supply remained a thriller. On this new examine, the analysis group has lastly decided the circumstances that led to the weird occasion.

The group studied digicam photographs of the occasion after which in contrast them with satellite imagery from 75 magnetic latitudes. In so doing, they discovered a supra-thermal electron stream that got here from the sun’s corona, in emission patterns that appeared remarkably like photographs which have been captured of polar rain aurorae—the place electrons touring from the sun’s corona journey by the Earth’s environment above one of many polar regions.

Satisfied that they have been on to one thing, they did some extra analysis—this time trying into why the aurora was in a position to final so lengthy. They discovered that the distinctive occasion had occurred throughout an unusually calm interval of solar wind.

Because the polar rain aurorae crammed up the night time sky that December, the solar wind density dropped to as little as 0.5 cm^-3—one thing that nearly by no means occurs. The analysis group notes that polar rain aurorae are usually invisible to the bare eye. The rationale the one which occurred in 2022 may very well be seen by a daily digicam was as a result of lack of solar wind.

The examine of auroras, it has been famous, has been vastly assisted by citizen scientists—they have been, for instance, instrumental in fixing the source of purple lights that appeared over the Canadian sky in 2016.

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