'Like dunes on a sandy beach': Scientists and stargazers ID new form of northern lights

Transcript

Minna Palmroth thought she had seen every kind of aurora borealis — until someone asked her about the ones with the stripes.

Palmroth, a computational space physicist at the University of Helsinki, has identified a previously undocumented form of the northern lights with the help of amateur stargazers in a Finnish Facebook group. 

"They are like dunes on a sandy beach," Palmroth told As It Happens host Carol Off. "This kind of an aurora has not been reported in scientific literature before."

The discovery has been reported in the journal AGU Advances.

Kind of like birdwatching

There's an active community online of people called aurora chasers who track and photograph the northern lights purely out of passion. 

Palmroth says she first became involved with that community about five years ago when she got a "very polite email from the chasers in Finland."

They invited her to join their Facebook group and answer some of the enthusiasts' questions about the images they were sharing. 

"And I did that, and over the years I found that I'm always explaining the same things because, you know, the group grew," she said. "Then I decided that, OK, I'll make a book. I'll write the book so that I don't have to answer all the time."

The book, she says, is essentially a guide for aurora chasers, describing in detail the known forms of northern lights so amateurs can identify them.

She challenged the chasers to track down photos of each form. They delivered, and then some.

"When the book was already done, one of the chasers said to me, 'Oh, well, you didn't say where these stripes belong to,'" she said.

When she looked at the images, she didn't know what to make of them.

"I actually kind of had the shivers," she said. "I hadn't seen anything like that before and I was thinking immediately that this must be something new."

The community set about capturing more images and videos for her, including two different sets of the same phenomenon on the same night in Finland from different perspectives. 

"It was like piecing together a puzzle or conducting detective work," astronomy hobbyist Matti Helin said in a University of Helsinki press release. "Every day we found new images and came up with new ideas"

Palmroth cross-referenced the images with existing scientific literature about the northern lights and discovered that it was, indeed, a previously undocumented form.

"Normally, when we see an aurora, we see a curtain or arc, and now we see this wave form," she said. "It is rather distinctive."

The phenomenon, she said, is barely visible to the naked eye. 

"I actually think ... one of the reasons ... this was found now is the improving of the digital cameras," she said.

How does it work?

Auroras happen when charged particles released by the sun interact with the gasses of Earth's atmosphere, like oxygen and nitrogen, increasing their energy or "exciting" them. That extra energy is then released as light.

What the northern lights look like depends on what exactly is happening in the atmosphere. For example, excited oxygen produces that iconic bright green you so often see on postcards and in photographs.  

In the case of the dunes, the study's authors theorize it's caused by something called a "mesospheric bore," in which gravity waves rise and get filtered and bent between two different layers in the atmosphere. That causes the density of the excited oxygen atoms to vary, producing what looks like peaks and valleys in the light. 

And you don't have to be in Finland to see them.

"Now that this paper is out, I've been already receiving a lot of observations from all around the world, and also from the Canadians," Palmroth said. "Beautiful pictures of the dunes, people have put into Twitter and so on."

Written by Sheena Goodyear. Interview with Minna Palmroth produced by Sarah Jackson.