Amateur Photo Helps Researchers Uncover New Form Of Aurora

Nicknamed “Steve”, this unusual aurora feature is a 15.5-mile-wide (25 km) ribbon of hot gas flowing westward at about 13,300 mph, more than 600 times faster than the surrounding air. The photo was taken last fall. Copyright:

Last fall, Dave Markel, a photographer based in Kamloops, British Columbia was out photographing the northern lights when he saw something really strange. Crossing over his head and running almost perfectly from east to west, a narrow arc of light glowed for almost an hour. Markel took photos of the phenomenon and posted it on social media.

“It looked like a massive contrail moving rapidly across the sky,” said Markel in an e-mail. The arc was pierced with what he described as “green pickets” or short, parallel streaks of aurora. Perhaps you’ve also seen this peculiar form of aurora. It’s not too common, but I’ve viewed it on 5 or 6 occasions and always wondered exactly what it was and how it formed.

Oxygen atoms are primarily responsible for the greens and reds of the aurora; nitrogen gives us red-bottomed arcs and tall purple rays. Credit: WebExhibits

That’s where aurora researcher Eric Donovan of the University of Calgary steps in. Prof. Donovan met with members of the popular Facebook group Alberta Aurora Chasers. Looking at their photos, he came across Markel’s purple streak and additional photos like it taken by other photographers.

You’ll often here the band described as a “proton arc,” but it’s not, according to Jason Ahrns, an aurorologist and physicist at the University of Alaska-Fairbanks. In a recent post on the Aurorasaurus Facebook page, Ahrns describes a true proton arc:

“It’s green, featureless, and very large. Even a good proton aurora is around 75 times dimmer than the bright, active green aurora.” The accompanying photo shows a faint, greenish veil hanging in the southern sky. At the very least, proton arcs are hardly noticeable and don’t resemble the curious curl captured by Markel. Here’s a photo of one.

The familiar reds and greens of northern light come from oxygen and nitrogen atoms that get clobbered at high speed by tiny electrons in the sun’s particle wind. When they relax back to their pre-collision state, they emit red and green light. Proton arcs in contrast are spawned by protons (basically hydrogen atoms without their electrons) that capture an electron. If they’re excited by another collision, they spit a bit of light out but far less than a typical aurora.

The magnetic field is thought to be largely generated by an ocean of superheated, swirling liquid iron that makes up Earth’s the outer core 3000 km under our feet. Acting like the spinning conductor in a bicycle dynamo, it generates electrical currents and thus the continuously changing electromagnetic field. The three Swarm satellites are designed to measure the magnetic signals from Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere that will allow scientists to study the complexities of our protective magnetic field. Credit: ESA/AOES Medialab

Let’s return to the strange arc. Donovan knew it had to be something else, but what? To find out, he and his colleagues looked through data from the European Space Agency’s Swarm magnetic field mission as well as his network of all-sky cameras. Swarm is comprised of three identical satellites that orbit the Earth and measure the magnetic fields arising from Earth’s core, mantle, crust and oceans, as well as from the ionosphere and magnetosphere high overhead.

He not only discovered that the narrow-band-type aurora was much more common than he’d expected but was able to match a ground sighting of the phenomenon to an overpass of one of the three Swarm satellites.

I photographed a similar narrow band of east-west light back on May 18, 1990. It slowly pulsed in brightness over the hour or so it was visible. The Big Dipper is visible to the right of center. The stars trailed because of the length of the time exposure. Credit: Bob King

“As the satellite flew straight though Steve (the nickname given to Markel-type auroras), data from the electric field instrument showed very clear changes,” said Donovan.

“The temperature 186 miles (300 km) above Earth’s surface jumped by 3000°C and the data revealed a 15.5-mile-wide (25 km) ribbon of gas flowing westwards at about 6 km/second compared to a speed of about 10 meters/second either side of the ribbon.”

This is the eastern half of the arc from May 18, 1990. The bright star at upper right is Arcturus. Sure wish I’d had a fisheye lens! Credit: Bob King

Wow — the feature really was something unique! After hearing the description, a work colleague of mine compared it to a fluorescent light without the glass, an apt analogy.

In decades of aurora watching I’ve only seen this form of aurora a handful of times. On most of those occasions, there was either no other aurora visible or minor activity in the northern sky. The narrow arc, which typically lasted for an hour or so, pulsed and flowed with light and occasionally displayed the little pickets described by Markel.

Aurora — magnificent and soul-stirring. Credit: Bob King

Goes to show you that even today dedicated skywatchers and nighttime photography buffs can help answer scientific questions or even crack open ripe new areas for research. Groups like the Great Lakes Aurora Hunters and Aurorasaurus serve as clearinghouses for observers to report auroral displays, and I encourage you to use them to share your own aurora observations and photos. The path to scientific discovery often begins with a deceptively simple question:

“What is that?”

4 Responses

  1. I’ve wondered what causes the quick moving waves sometimes seen within an aurora. This cuttlefish is the best example I can come up with: I’ve seen auroras with waves this quick. My theory is that the sun has a rotating magnetic field so the solar wind ends up like water from a spinning sprinkler. Looking at part of the spray pattern results in quick moving waves. Does this display have a name?

    1. astrobob

      Hi Glen,
      I wish it did have a name but not quite yet. Researchers are working on it. It’s possible some of that sprinkler effect applies to the aurora as you suggested, but much of its motion and speed originates closer to home in the magnetosphere, where solar electrons are accelerated by a voltage effect along Earth’s magnetic field lines at tremendous speeds into the upper atmosphere.

  2. betty karpen

    Hi Bob,
    I have seen that arc, like a jet contrail, very bright, neither thinner nor thicker between top and bottom, at least 3 times. I live in the woods between torte and silver bay, no light pollution.

    1. astrobob

      Hi Betty,

      That’s it alright. Thanks for writing. I’m discovering that more people than I knew have seen this curious feature.

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