Image Credit: David Knudsen University of Iowa/YouTube
Physicists have found a previously undiscovered phenomenon called ‘diffuse auroral erasers’ while analyzing a video of auroras recorded in 2002.
Earth’s auroras are spectacular light shows that have enthralled human beings for almost our entire existence. From stunning cave paintings created in around 30,000 B.C to drawings of candles in the sky created in China in the 16th Century, this phenomenon has inspired our folklore, art, culture, and more recently, our quest for scientific understanding.
In more modern times, we know the causes of these beautiful displays of nature to be the effect of charged particles from the Sun striking Earth’s magnetic field. Some of these particles slip through this field and fall to Earth, and interact with gases in our atmosphere. These collisions generate the glow that is associated with auroras.
Yet, despite our knowledge of auroras and their causes, that doesn’t mean that we know everything about these events. In fact, there may be things that we have missed in our previous attempts to document and record this phenomenon.
Physicists describe new type of aurora
A team of physicists, led by researchers from the University of Iowa, have discovered evidence of a previously unknown behavior of auroras in historical documentation. The team did not have to delve back to the Cro-Magnon painting ‘macaronis’ — the earliest documented depiction of an aurora — to find this new aspect of these events, however.
The team discovered what is described as ‘diffuse auroral erasers’ in video footage recorded on March 15, 2002, by David Knudsen, a physicist at the University of Calgary, in Churchill, a town along Hudson Bay in Canada.
The biggest thing about these erasers that we didn’t know before but know now is that they exist. It raises the question: Are these a common phenomenon that has been overlooked, or are they rare?
Allison Jaynes, Assistant Professor, Department of Physics and Astronomy, The University of Iowa
Along with Knudsen, who has studied aurora for more than 35 years, Jaynes is the co-author of a paper published in the Journal of Geophysical Research: Space Physics¹ that attempts to answer this question.
A New Phenomena Hidden in Diffuse Auroras and Archive Video
For Knudsen, this new discovery undoes a disappointment that dates back 19 years. His group were initially disappointed with the results of their March 15th video.
The weather forecast for the vicinity of Churchill had predicted the ideal conditions for the observation of auroras, namely clear, dark skies. Yet despite this, it seemed that the auroras had failed to appear in dazzling form for their recording.
Fortunately, Knudsen’s crew were using a camera-equipped to observe even low-intensity light, much in the same way night vision goggles work. That means that while the team saw only darkness, the camera was witness to much more.
This included the important moment in which the aurora appeared to disappear before then reappearing. Knudsen, observing the video as it recorded, remarked in his notebook at the time, “pulsating ‘black out’ diffuse glow, which then fills in over several seconds.”
What surprised me, and what made me write it in the notebook, is when a patch brightened and turned off, the background diffuse aurora was erased. It went away. There was a hole in the diffuse aurora. And then that hole would fill back in after a half-minute or so. I had never seen something like that before.
David Knudsen, Physicist, The University of Calgary
Knudsen’s note was soon filed away and the video went unobserved. That was until Jaynes became aware of it at a conference in 2010, she even referenced Knudsen’s note in her doctoral thesis. Now an assistant professor at Iowa, she tasked Riley Troyer, an Iowa graduate, with the responsibility of investigating it further.
“I knew there was something there. I knew it was different and unique,” says Jaynes. “I had some ideas how it could be analyzed, but I hadn’t done that yet. I handed it to Riley, and he went much further with it by figuring out his own way to analyze the data and produce some significant conclusions.”
Troyer, now in the third year of his doctoral studies and co-author on the paper, was happy to accept the investigation as auroras were very much a part of growing up for the graduate student. He devised software that could hone in on frames of the video in which the erasers were visible.
The program highlighted 22 such events in this two-hour recording.
“The most valuable thing we found is showing the time that it takes for the aurora to go from an eraser event (when the diffuse aurora is blotted out) to be filled or colored again,” says Troyer, who is the paper’s corresponding author, “and how long it takes to go from that erased state back to being diffuse aurora. Having a value on that will help with future modeling of magnetic fields.”
The team will now look for the processes that could drive this phenomenon.
“Knowing they exist means there is a process that is creating them,” Jaynes continues, “and it may be a process that we haven’t started to look at yet because we never knew they were happening until now.”
Implications for Earth and Beyond
Jaynes points out that auroras could have been influencing much more than our art, culture, and science, and that studying these phenomena is for our planet is akin to studying our DNA in order to understand the human body.
Not only could the team’s findings result in a better understanding of auroral effects here on Earth, but they could also have implications for auroras lighting up the skies of other worlds.
“The most valuable thing we found is showing the time that it takes for the aurora to go from an eraser event (when the diffuse aurora is blotted out) to be filled or colored again,” says Troyer, who is the paper’s corresponding author, “and how long it takes to go from that erased state back to being diffuse aurora. Having a value on that will help with future modeling of magnetic fields.”
“Particles that fall into our atmosphere from space can affect our atmospheric layers and our climate,” Jaynes concludes. “While particles with diffuse aurora may not be the main cause, they are smaller building blocks that can help us understand the aurora system as a whole, and may broaden our understanding of how auroras happen on other planets in our solar system.”
References
Troyer. R. N., Jaynes. A. N., Jones. S. L., et al, [2021], ‘The Diffuse Auroral Eraser,’ Journal of Geophysical Research: Space Physics, [https://doi.org/10.1029/2020JA028805]
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