People have been taking photographs of the northern lights for as long as camera technology has been available, and yet there are still forms of this majestic effulgence that have the power to surprise us.
In fact, a previously undocumented form of these celestial lights has just been discovered, thanks entirely to the keen eyes of some curious amateur stargazers, reports The Guardian.
The new form is being likened to sand dunes in the way the shimmering neon braids ripple and flow across the sky. Some are calling them "sky dunes," and the way they take shape can tell us more about how our atmosphere is layered. The video above, taken by Timo Oksanen Productions, is a beautiful illustration of these newly identified auroras flagging across the sky.
All auroras (including the southern variety) are formed when charged particles spewed from the sun disturb the Earth's magnetosphere. Those particles, usually electrons, get funneled toward the planet's poles where they interact with our atmosphere, resulting in brilliant glowing bands.
"This is the same as neon lamps," said Minna Palmroth, a professor of computational space physics at the University of Helsinki, to The Guardian. "Basically we can say the auroras are celestial neon lamps."
Most of the forms that auroras take have been well documented and have become common parlance amongst aurora experts — spirals, coronas, and "quiet arcs" are a few examples. But now we can add "dunes" to the aurora dictionary as well.
'What about these stripes?'
Palmroth took notice to these sky dunes after taking part in an educational forum aimed at helping amateur stargazers identify the different forms of auroras. But lots of the citizen scientists kept coming back to particular photographs, puzzled. "Some of them asked me 'what about these stripes, which form are they?'," she recalled.
Palmroth realized she didn't have a good answer. What these citizens were pointing out was something researchers had overlooked.
To confirm the new discovery, Palmroth implored her community to go out and try to capture as many photos of sky dunes as possible, so she might be able to form a working theory about the conditions that cause them to form. The trait that really seemed to make the dunes stand out was the way their ripples were so even.
"To observe something very even, like the dunes, means that there has to be some active mechanism which is making them so even," she said.
She realized that these even ripples didn't just look like sand dunes, but that they probably formed similar to how tidal bores form dunes in rivers. Tidal bores happen when the leading edge of an incoming tide forms waves of water that travel up a river against the direction of the current. Palmroth believes sky dunes are forming due to an analogous process in the atmosphere, whereby waves travel horizontally between two layers in the atmosphere.
This can happen when the temperature of one atmospheric layer is slightly higher than both the layers above and below it.
"When this inversion layer is forming [in] these places where you can also have the aurora, then you can see the dunes," added Palmroth.
Tidal bores occur in relatively few locations worldwide, so these atmospheric bores are probably uncommon as well. That's likely why sky dunes have taken so long to be identified. But now when they do get captured, we'll have an idea of the unique atmospheric processes taking place, in all of their glimmering glory.
The details of this discovery are featured in the journal AGU Advances.