[Below is an abridged version of Dr. Tony Phillip's excellent article-the full version of which is available at spaceweatherarchive.com, dated November 22, 2020.]
STEVE (Strong Thermal Velocity Enhancement) is a relatively recent discovery, first spotted and photographed by Canadian citizen scientists around 10 years ago. It looks like an aurora, but it is not. The purple glow is caused by hot (3000 °C) rivers of gas flowing through Earth's magnetosphere faster than 13,000 mph. This distinguishes it from auroras, which are ignited by energetic particles raining down from space.
"Citizen scientists have been photographing these green streaks for years," says Joshua Semeter of Boston University, lead author of the new paper. "Now we're beginning to understand what they are."
There is a dawning realization that STEVE is more than just a purple ribbon, as photographers routinely catch it flowing over a sequence of green vertical pillars known as the "picket fence". These aren't auroras either.
And now, Semeter's team has identified yet another curiosity: "Beneath the picket fence, photographers often catch little horizontal streaks of green light," explains Semeter: "This is what we studied in our paper."