Back in 2016, the Alberta Aurora Chasers Facebook group brought a new atmospheric phenomenon – a narrow band of purple and white light – to the attention of scientists. Now, a team from the US and Canada has found that such STEVE events are probably not caused, as auroras are, by charged particles precipitated into the upper atmosphere. Instead a new ionospheric mechanism may be responsible.
“Our main conclusion is that STEVE is not an aurora,” says Bea Gallardo-Lacourt of the University of Calgary, Canada. “So right now, we know very little about it. And that’s the cool thing, because this has been known by photographers for decades. But for the scientists, it’s completely unknown.”
To come up with this finding, the team used All-Sky Imagers based on the ground in eastern Canada and data from a NOAA Polar Orbiting Environmental Satellite (POES) that happened to cross a STEVE event on 28 March 2008 at the centre of the All-Sky Imager field-of-view. The light from this STEVE covered roughly 1000 km from east to west but was only tens of kilometres wide. An aurora had appeared beforehand.
The POES-17 satellite did not detect any charged particles raining down to the ...