Aurora chasers discovered and filmed a new type of aurora that reaches across the sky like fingers. It's called 'the dunes.'

Rami Valonen

Auroral dunes near Ruovesi, Finland, October 7, 2018.

• Amateur northern-lights chasers made a rare discovery: a new type of aurora, which they dubbed "the dunes."
• The new aurora reaches horizontally across the sky in long green fingers, and it could help scientists study a mysterious region of the atmosphere.
• Researchers think the dunes form when electric currents from space create folds and curls in Earth's atmosphere.
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Mysterious fingers of green light reaching across the sky are a new type of aurora, new research has confirmed.

Amateur northern-lights photographers first spotted the unusual patterns in Finland and called them "the dunes." The patterns seem to come from electricity in space that creates waves in Earth's atmosphere.

Unlike regular aurorae, which spread down vertically from main ribbons of light, the dunes' patterns stretch horizontally.

In a study published Tuesday in the journal AGU Advances, scientists at the University of Helsinki offer their analysis of the phenomenon. They think the dunes could be a visible manifestation of atmospheric waves - undulations of air responding to regions of different temperatures or densities in the atmosphere.

These waves occur at an altitude that's notoriously difficult to study: about 50 to 75 miles above sea level, which is too high for balloons or planes and too low for satellites. So watching the dunes could help scientists learn more about the atmosphere at those altitudes.

"For the first time, we can actually observe atmospheric waves through the aurora - this is something that hasn't been done before," Minna Palmroth, a space physicist and lead author of the study, said in a press release.

Aurorae appear when energetic particles from the sun react with molecules in Earth's atmosphere, creating colorful patterns across polar skies.

But new forms of northern lights are rare findings. Last year, a NASA intern stumbled upon one instance of an unusual aurora in three-year-old video footage. Before that, the most recent major finding was the 2016 discovery of an aurora-like phenomenon called Strong Thermal Emissions Velocity Enhancement (STEVE). That pink ribbon (which is not technically an aurora) was also discovered by aurora hunters.

Video and photos reveal that electricity from space could create the dunes

Citizen scientist Kari Saari shot the video above in Savojärvi, Finland; it shows the dunes extending from the main arc of the aurora.

The aurora chasers who first spotted these lights reached out to Palmroth in October 2018. The group told her that they had searched through her aurora-watching guidebook and found no mention of the type of aurora they'd seen.

"They told me I had excluded one auroral form from the book," Palmroth said.

But it turned out that scientists had never seen the aurora the amateurs had found. So Palmroth asked the group to photograph the new aurora from multiple locations on one night: October 7, 2018.

"One of the most memorable moments of our research collaboration was when the phenomenon appeared at that specific time and we were able to examine it in real time," Matti Helin, one of the aurora enthusiasts and a study co-author, said in the release.

AGU Advances/Palmroth et al.

Auroral dunes photographed simultaneously on October 7, 2018 near Laitila, Finland (top) and Ruovesi, Finland (bottom). The dunes, marked by magenta circles and numbers, extend south from the discrete bright arc in the north.

Palmroth and her colleagues used the photos to calculate the dunes' altitude and collected more measurements in order to better theorize about how the atmosphere creates them.

"Different auroral forms are like fingerprints," Palmroth said. "If you see a certain auroral form, you know basically from that form what's happening further out in space."

The scientists think the dunes come from a type of atmospheric wave that ripples through the atmosphere, making horizontal curls and folds in the air that spread across the sky.

They also found that the dunes appear when charged particles from space transfer energy into Earth's upper atmosphere. Palmroth thinks these particles send electrical currents flowing through the air, creating heat that produces the atmospheric waves that cause the dunes.

"This is a totally new topic," Palmroth said. "We are rather excited."

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