Troyer, and five co-authors, reported in late 2020 that the source of diffuse aurora has been widely studied and linked to electron cyclotron harmonic and upper-band chorus waves. It is known that these waves scatter 100s of eV to 10s of keV electrons from the plasma sheet, but the relative contribution of each wave type is still an open question. In this study, the authors reported that an interesting and unusual auroral feature observed on March 15, 2002. They proposed that these observations could help further our understanding of waves associated with diffuse aurora. This diffuse auroral feature is characterized by four phases:
1) the initial phase exhibiting regular diffuse aurora;
2) the brightening phase, where an east-west auroral stripe rapidly brightens;
3) the eraser phase, where the stripe dims to below its initial state; and
4) the recovery phase, where the diffuse aurora returns to its original brightness.
Using a superposed epoch analysis of 22 events, the authors calculated the average recovery phase time to be 20 seconds, although this varies widely between events. The hypothesized that the process responsible for these auroral eraser events could be the result of chorus waves modulating diffuse
aurora.
They concluded that aurora are caused by electrons from within the magnetic bubble that surrounds Earth, called the magnetosphere. Sometimes these electrons are deposited into our upper atmosphere, producing light. This process can also transfer large amounts of energy from the magnetosphere to the atmosphere, thus potentially affecting the climate. Pictures of the aurora usually depict discrete green curtains, but this is not the only type of aurora. Diffuse aurora is another, which look like a faint glow over large portions of the sky. Diffuse aurora is extremely common, but not well understood.
The authors determined that there is an unusual process within diffuse aurora that could improve our understanding. We call it a diffuse auroral eraser. They found these events in a video taken the night of March 15, 2002 in Churchill, MB, Canada. The phenomenon appeared as a section 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 authors calculated the average recovery time by overlaying plots of brightness from each of the 22 events that we found. This average time was 20 seconds, although it varied widely between individual events.
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