Mystery aurora spied over Canada stirs space weather debate
Meteorologist/Science Writer
Wednesday, April 26, 2017, 3:16 PM - There's a strange and mysterious aurora that's been in the headlines lately - perhaps you've heard of 'Steve' - and thanks to the efforts of scientists, citizen scientists and social media, we are getting closer to figuring out exactly what it is!
This story has been updated.
The Aurora Borealis, or Northern Lights, is known for putting on a different light show pretty much every time it shows up in the night sky. It's one of the amazing features of this spectacular phenomenon.
Sometimes, though, something really different shows up, and it takes the combined efforts of citizen scientists over social media, and scientists with access to specialized satellites in orbit, to figure it out.
This is what happened with a special kind of aurora feature, which some have been calling 'Steve'.
Here is 'Steve', shown in the image below, as the purple stream stretching across the sky, captured by photographer Dave Markel in 2016.
'Steve' shines brightly in the autumn B.C. sky. Credit: Dave Markel Photography
Scenes such as this have been recorded for some time, with images of these thin glowing ribbons showing up on social media and space weather websites for years, and they are often labeled as a proton arc.
"We have been photographing these arcs for the past 4 years," says aurora photographer Darlene Tanner. She and her partner, Theresa, captured one such arc back in February 2016.
The typical auroras that are seen in the night sky are caused when energetic particles from the Sun collide with air molecules in the upper atmosphere, and transfer some of their energy to those molecules. The excited air molecules then dump that excess energy in the form of light. Most auroras - the ribbons, swirls and pillars of reds, blues, greens, and pinks - are due to solar electrons doing the colliding.
A proton aurora (as the name implies) occurs when solar protons impart their energy to the air molecules. These are mostly invisible to the naked eye, as the strongest forms of light they emit are in the ultraviolet, beyond what can be perceived by the human eye. They have been recorded, though, showing up in long-exposure photography as wide, hazy swaths of dim green light.
According to space meteorologist Tamitha Skov, proton arcs are different from proton aurora, but earned their name due to sharing certain characteristics with proton aurora, such as the timing of when they occur, and where they show up in relation to the more common electron auroras. It wasn't known exactly what these arcs were, but the name stuck. Since they occur 300 km up, in the ionosphere, she explained, they are definitely a type of aurora, composed of ionized plasma and emitting light in the same way as other auroras.
Recently, when members of the Alberta Aurora Chasers met with Eric Donovan, from the University of Calgary's Auroral Imaging Group, at an annual science conference in Banff, Donovan got a look at these images of long, thin, purple arcs. As other scientists had done, in the past, he concluded that these were not proton auroras.
Not knowing what this was, the Alberta Aurora Chasers decided to name it 'Steve'. Why?
According to the Aurorasaurus blog:
Why Steve? Well, this is a reference to the popular children’s movie Over the Hedge where one of the characters isn’t sure what he is looking at and randomly names it Steve.
With an interest in delving further into this phenomenon, Donovan called upon some special help from space. By examining the timing of the European Space Agency's Swarm satellites, which orbit the planet to read Earth's electric and magnetic fields, he found one instance where one of the trio of satellites had flown right through a 'Steve'.
"As the satellite flew straight though Steve, data from the electric field instrument showed very clear changes," Donovan told the ESA. "The temperature 300 km above Earth’s surface jumped by 3,000oC and the data revealed a 25 km-wide ribbon of gas flowing westwards at about 6 km/s compared to a speed of about 10 m/s either side of the ribbon."
According to the Aurorasaurus blog, this phenomenon can show up as an east-west arc, stretching for hundreds to thousands of kilometres, and far enough south that it has been seen by residents of the southern Prairies or northern US states, and over the United Kingdom. In the southern hemisphere, it has been seen as far north as New Zealand. It can last for up to 20 minutes long, and although it's quite faint to the naked eye, long-exposure images pick it up quite brightly.
Now, is 'Steve' rare? This may be the first time one of these features was probed via satellite, but it's not rare at all.
"It turns out that Steve is actually remarkably common, but we hadn’t noticed it before," Donovan explained. "It's thanks to ground-based observations, satellites, today’s explosion of access to data and an army of citizen scientists joining forces to document it."
As far as the name goes, while the community has known for some time that these arcs are likely not caused by protons - at least not in the same way that proton auroras are - the name 'proton arc' has been in use for years, simply based the similarities mentioned by Tamitha Skov. On the other hand, proponents of using 'Steve' say that calling them 'proton arcs' implies a relationship between them and protons, and a name change would remove that implication.
Will the name be changed to 'Steve', officially? It has been suggested by members of the Aurorasaurus site that Steve could stand for "Strong Thermal Emission Velocity Enhancement", however the name still remains up in the air. One reason for this is that it's still not known exactly what causes one of these ribbons to appear. The community, along with aurora scientists, will likely decide. So, they could still be called proton arcs, or perhaps 'Steve', or they could take on a completely different moniker when their true nature is revealed.
Still, it's fascinating to see a phenomenon that has been documented for so long getting a renewed level of attention and scrutiny, to determine what it truly is.
"Perhaps the most interesting lesson for both the science community and the space weather enthusiasts," Dr. Skov said, "is that in this instance, the citizen-scientists were years ahead of the space-scientists!"
Sources: ESA | Aurorasaurus | Alberta Aurora Chasers | Dave Markel Photography
Editor's note: As the facts behind this story developed throughout the day, the article has been updated to reflect these changes.
