How 'Black Auroras' are Created and Work

Have you ever heard of a black aurora? Scientists have long focused on how the aurora's shimmering curtains of colors are formed, but have struggled to explain the dark patches between the bright beams. Now, scientists have found what happens at the heart of these so-called "black aurora."

About 10 years ago, researchers began to notice something strange in the data being sent down from the ESA Cluster project's four satellites, which collect data on electric and magnetic fields and particle density.

"I noticed a weird combination of electric and magnetic field measurements that were different from normal, and I wanted to understand the physics behind the data," said Tomas Karlsson, one of the researchers, in a news release. "On each occasion, the Cluster spacecraft were flying over the night-time auroral region."

The researchers teamed up in order to better understand the mystery. In the end, they opened up a whole new understanding of how dark recesses are formed insight Earth's aurora borealis.

"For the first time we are able to reproduce the phenomenon of the black aurora and in particular what happens at its heart, where strong electric fields are present," said Karlsson. "We hope that this will lead to a better understanding of the interaction between the upper atmosphere and the space environment."

Inside the colorful displays, other processes happen that create the black region. The black ones are associated with electrons being sucked out from the atmospheres into space. This leaves deep cavities in the upper, electrically conducting-atmosphere, known as the ionosphere. If the downward current intensifies, then it can cause a large number of electrons to move upward into the magnetosphere, thus depleting the ionosphere and creating a density cavity.

The findings are published in the Journal of Geophysical Research: Space Physics.

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