Not all auroras slither through the sky like snakes. Some – called diffuse aurora – are more like a good glow dispersed throughout the sky.
Scientists know a good bit about these diffuse auroras, but an old video from 2002 revealing what seems to be an undocumented auroral phenomenon shows we definitely do not know everything.
“We found these events in movie taken the night of March 15, 2002 in Churchill, [Manitoba], Canada,” the researchers write during a summary of their research.
“They appear as a small area of diffuse aurora that rapidly brightens, then disappears and also erases the background aurora. Then, over the course of several tens of seconds, the diffuse aurora recovers to its original brightness.”
The researchers think this is often the primary time this phenomenon has been reported within the scientific literature, and that they haven’t any idea what’s causing them.
“It raises the question: Are these a standard phenomenon that has been overlooked, or are they rare?” says University of Iowa astronomer Allison Jaynes.
“Knowing they exist means there’s a process that’s creating them, and it’s going to be a process that we’ve not began to check out yet because we never knew they were happening until-now .”
Auroras are the dancing glow emitted by ionized particles in Earth’s upper atmosphere. These particles are energized by solar winds, and their shedding of this excess energy creates the ethereal light we see.
Some auroral appear as discrete objects floating within the sky, whilst others are more diffuse – permeating equally over a large area.
Diffuse aurora are linked to 2 specific sorts of atmospheric waves – electron cyclotron harmonic and upper‐band chorus – which may scatter electrons produced within the magnetosphere to make the glow.
Although this is often well understood, scientists aren’t sure what proportion each wave type contributes to the make-up of diffuse aurora, or maybe whether another sort of waves – called whistler mode hiss waves – also are helping the method along.
The team hopes that identifying the diffuse auroral erasers from this old video will help answer a number of these questions.
Although the published research is new, its origins began almost 20 years ago. Back in 2002, David Knudsen, a physicist at the University of Calgary, captured the video footage on a cold-night in Churchill.
While they saw little on the-night, when the video was analyzed later, the phenomenon was noticed by Knudsen, who scribbled in his notebook “pulsating ‘black out’ diffuse glow, which then fills in over several seconds”.
However, the note wasn’t followed up at the time, and it wasn’t until recently that Jaynes handed the video and notebook to a graduate-student to research further.
The graduate-student , astrophysicist Riley Troyer, created a computer-program to research the video, finding that it took on the average 20 sec for the aurora to ‘recover’ its brightness.
“The most precious thing we found is showing the time that it takes for the aurora to travel from an eraser event (when the diffuse aurora is blotted out) to be filled or colored again and the way long it takes to travel from that erased state back to being diffuse aurora,” says Troyer.
“Having a worth thereon will help with future modeling of magnetic fields.”
There’s many research to still do, but the team hopes that now we all know the erasers exist, we’d be ready to find more.
We just hope it won’t take another 20 years to get them.
The research has been published in the Journal of Geophysical Research: Space Physics.