It was in 2018 when scientists confirmed that the sky-glow called “STEVE” is actually not an aurora. Now, researchers of a new study describe the mechanisms that cause it.

'Sky-Glow’

A sky-glow caught the attention of many when it appeared like an aurora in a region that’s farther south that where auroras typically appear, and in shades of mauve rather than the typical aurora green. What’s even stranger is that the mauve lights are sometimes joined by a “picket fence” of green vertical lights.

The new sky-glow was dubbed strong thermal emission velocity enhancement (STEVE), and soon scientists confirmed that STEVE is, in fact, not an aurora. This is because auroras are produced when glowing nitrogen and oxygen atoms on the Earth’s upper atmosphere are excited by the charged particles from the planet’s magnetosphere, and by 2018, scientists already knew that it was not the same mechanism that causes STEVE. However, they were still unaware of STEVE’s true cause, which is why they simply dubbed it as a “sky glow."

STEVE

Now, researchers of a new study published in the Geophysical Research Letters analyzed satellite data and ground images of STEVE, and concluded that there are two different mechanisms that are causing STEVE’s mauve light arc and green picket fence.

First, the green “picket fence” is actually caused by the same mechanism that creates auroras, which makes it one, too, but it is still unique in that it emerges in locations where auroras do not typically appear. Further, they also observed that the picket fence look is created when high-frequency waves from the magnetosphere energize electrons and knock them out of the magnetosphere, thereby creating the striped image.

As for the reddish arc, they observed that it occurs much in the same way that incandescent light bulbs work. Evidently, when a “river” of charged particles in the Earth’s ionosphere collide, it creates friction, heating the particles and causing the reddish arc.

“We suggest that the electron precipitation drives the picket fence, and heating drives the mauve as thermal emission,” researchers wrote.

Citizen Scientists

Apart from their significant findings, researchers also note the relevance of data they gathered from citizen scientists from whom many of the data that they analyzed came from. In fact, in 2018, NASA even called citizen scientists for help in spotting STEVE.