A New Atmospheric Phenomenon Called Steve

For the past three years, members of a Facebook group called the Alberta Aurora Chasers, consisting of photographers who exchange tips and images of the famed northern lights, have been capturing images of a gorgeous arc of light across the sky. The arc can be seen streaking across the northern sky typically in mid-latitude location like Calgary or Edmonton. It has a distinctive purplish or greenish color, and sometimes looks braided like a helix.

The group initially mistook the glowing ribbon of purple and green light as an airplane contrail. It was only when experimenting with their camera settings, like slow shutter speeds, and photo editing software to improve the color saturation, did they realize that the arc of light was self illuminated, unlike condensation trails from airplanes that are lit from light sources on the ground.

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Meet Steve, a stream of hot, fast-moving gas, glowing over Porteau Cove Provincial Park in British Columbia, Canada, in May 2016. Photo credit: Vanexus Photography

For a while, the Alberta Aurora Chasers assumed it was a proton aurora, a rare kind of aurora caused by energized protons, as opposed to electrons, tearing through the earth’s magnetosphere. Then last year, some of the group members went to the University of Calgary to meet astronomy professor Eric Donovan, and showed him the images. Eric Donovan instantly recognized that what he was looking wasn’t a proton arc, but he couldn’t tell what it was.

After they met up with Eric, Chris Ratzlaff, a photographer and weather enthusiast and the Facebook group’s admin, posted a message on the Facebook group suggesting they call it “Steve”. The name comes from a scene in the animation movie “Over the Hedge” where all the animals stare at a frighteningly huge hedge not knowing what it was and begins to feel concerned until one of the animals, a squirrel, says "Let’s call it Steve," and everyone feels better.

Meanwhile, Eric Donovan and his colleagues turned to the European Space Agency and their group of Swarm satellites, that studies the Earth's magnetic field, to learn more about this new phenomenon. By coordinating with ground sightings of the arc and matching it to Swarm's movements, they was able to measure an instance of Steve.

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Photo credit: Dave Markel

We now know that a Steve is a fast moving ribbon of hot gases, about 25 to 30 kilometer wide, aligns east-west, and extends for hundreds, possibly thousands, of miles. The temperature inside a Steve was measured at 3000°C and the ribbon of gas was flowing westwards at about 6 km/s compared to a speed of about 10 m/s either side of the ribbon. A Steve can last for as long as an hour or more, and it appears to be seasonal, disappearing from October to February.

A surprising aspect of Steve is that it’s remarkably common, but it hadn’t been noticed until now.

“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,” Donovan added.

For now, the mysterious atmospheric phenomenon will continue to be known as Steve, until Eric Donovan and his colleagues come up with a better name, along with an explanation, which they are working on.

“I don't think this story would have had the legs it has if we'd given it a more scientific name,” confesses Chris Ratzlaff.

And who knows, the name might even stick. Elizabeth MacDonald from NASA proposed that it be called a “Sudden Thermal Emission from Velocity Enhancement,” or STEVE, in short.

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