Amateur photographers discover new type of aurora called ‘the dunes’

In October 2018, amateur photographers and aurora enthusiasts spotted beautiful auroras over Finland, lighting up the sky in thin ribbons of green. Typically, auroras are seen vertically, hanging like curtains, but these auroras were oriented horizontally, reaching across the horizon. The photographers documented these auroras and showed their images to researchers at the University of Helsinki, who realized that they had observed an entirely new type of aurora.

The citizen scientists named the new auroral form “the dunes,” after the undulating dunes of sand seen in the desert. And since they were first spotted, scientists have been working to figure out what exactly they are.

Auroral dunes photographed on Oct 7, 2018 near Laitila, Finland.
Auroral dunes photographed on Oct 7, 2018, near Laitila, Finland. Pirjo Koski

Now the researchers have published a paper theorizing that the dunes are “visible manifestations of undulations of air called atmospheric waves.” Atmospheric waves are generated by hot air being obstructed by large objects like mountains, and they can affect both local and regional temperatures and weather. And because they are found high in Earth’s atmosphere, at between 50 to 75 miles above the surface, they can affect satellites and spacecraft re-entering the atmosphere as well.

“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 at the University of Helsinki and lead author of the new study, said in a statement.

The dunes observed by the citizen scientists are believed to have formed in a thin layer at 60 miles above the surface, and from this altitude data the scientists could work out more information about how they formed. “Different auroral forms are like fingerprints,” Palmroth explained. “If you see a certain auroral form, you know basically from that form what’s happening further out in space.”

The particular atmospheric waves shown by the dunes are a type called mesospheric bores, which are spread horizontally across the sky like ripples on a pond. They are a useful target for observation as the area of the atmosphere where they occur is hard to study, being too high for balloons and too low for satellites. Palmroth thinks that the bores could be creating heat via the flow of electrical currents, which is, “a totally new topic,” she said. “We are rather excited.”

The findings are published in the journal AGU Advances.

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