Citizen scientists identify new kind of northern lights

Citizen scientists in Finland have helped astronomers identify a new kind of aurora, a pattern northern lights enthusiasts dubbed "dunes."

While working on a guide book intended for northern lights hobbyists, Minna Palmroth, professor of computational space physics at the University of Helsinki, recruited citizen scientists to pool and organize photographs of auroras.

Auroras take on different forms based on the shifting dynamics of the collision between solar winds and Earth's ionized upper atmosphere, the ionosphere. While organizing northern lights images, the team of citizen scientists assisting Palmroth identified an aurora pattern that defied classification.

The pattern featured a dunes-like wave of neon green light.

Not long after Palmroth's book was published, the novel aurora pattern appeared in the night sky. Several northern lights hobbyists were watching.

"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," amateur astronomer Matti Helin said in a news release.

After analyzing several photographs captured by citizen scientists, Palmroth and her colleagues were able to pinpoint the altitude and extent of the aurora. Maxime Grandin, a postdoctoral researcher working with Palmroth, determined that the pattern appears at relatively low altitudes, in the upper parts of the mesosphere.

"Due to the difficulties in measuring the atmospheric phenomena occurring between 80 and 120 kilometers in altitude, we sometimes call this area 'the ignorosphere,'" Palmroth said.

To identify the source of the unique aurora pattern, researchers relied on a combination of space science and atmospheric science.

"The differences in brightness within the dune waves could be due to either waves in the precipitating particles coming from space, or in the underlying atmospheric oxygen atoms," said Palmroth. "We ended up proposing that the dunes are a result of increased oxygen atom density."

But scientists still needed to develop a theory for why the green glow takes on such a well formed wave guide. Typically, there are so many gravity waves traveling in various directions within the mesosphere that a large and recognizable wave pattern can't persist for very long.

Occasionally, a form of the tidal bore pattern can take form in the mesosphere. The tidal bore phenomenon is most commonly observed in rivers, when the tide travels up a river channel. In the mesophere, the phenomenon occurs when an inversion layer forms low in the atmosphere and pushes a gravity wave up, trapping it in the upper mesophere and allowing it to persist across long distances.

The newly named dunes aurora occurs when large flows of charged particles penetrate the upper atmosphere and collide with these unusual tidal bore waves.

The study describing the dunes aurora -- published this week in the journal AGU Advances -- marks the first time scientists have documented auroral emissions produced by mesospheric bores.

"The auroral zone as a whole is usually discounted in studies focused on the bore, as auroral emissions impair the technique used to identify mesospheric bores," said Palmroth.

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