The mysterious little skyglow called STEVE was unopened last year. Physicists turned out that STEVE was not a new form of Aurora – it is actually no kind of Aurora at all. But there was still a big question: What is it?
Now we have the answer. Unlike the charged particles of solar energy, it enters the ionosphere and spans the atoms therein to produce auras, STEVE is created by a flood of charged particles flowing through the ionosphere of the earth.
The phenomenon has been known by photographers and aurora chasers for decades, which first gave it the nickname "stone". but it was only known to scientists in 2016. They officially called the strong thermal exhaust rate increase (STEVE), and originally stated it was a kind of aurora.
It looks like long glowing bands of purple flowing over the sky, sometimes accompanied by a strip of striped green light, referred to as "the picket fence".
Now, space physicists, using satellite data and basic photographs of the phenomenon, have located STEVE's source area in space and identified the mechanisms behind both STEVE and the picket fence.
The picket fence is caused by a similar mechanism to what causes auroras, although far closer to the equator than auroras is usually seen.
However, for STEVE, the flow of charged particles in the ionosphere creates friction; This again produces heat, which is emitted as a beautiful purple glow. It seems much higher in the atmosphere.
"Aurora is defined by particle precipitation, electrons and protons actually fall into our atmosphere, while STEVE atmospheric glow comes from heating without particle precipitation," said physicist Bea Gallardo-Lacourt of the University of Calgary.
"The precipitating electrons that cause the green fence are thus aurora, even though this happens outside the auroral zone, so it is completely unique."
Stakkegn is actually pretty amazing. The team found that it is caused by energetic electrons flowing into the Earth's atmosphere from thousands of kilometers away – a large enough distance to occur in both northern and southern hemispheres simultaneously. According to satellite data, the high frequency waves from the magnetosphere are moved to the ionosphere to activate electrons and knock them out of the magnetosphere, creating STEVE's stripey accoutrement.
We still don't know much about STEVE. We know that skyglow was not seen between October 2016 and February 2017, and then October 2017 and February 2018, suggesting that there may be a seasonal component.
Moreover, it only appears in the presence of aurora (although auroras may occur without STEVE, so he is pretty clingy).
We also know that STEVE appears in both hemispheres and is adjusted east-west. These can all be traces that help scientists find out why the charged particle river pops up in the sky.
This, in turn, can help us understand how charged particles flow into the magnetosphere and ionosphere – not least because they can affect satellite communication.
But that knowledge will also probably be very welcome in the community of Aurora Chasers and photographers – Seekers of our planet's beauty – around the world.
The research has been published in Geophysical Research Letters ].