A source of superfast electron rain discovered

The downpours can affect satellites and space travel.


Earth’s outer radiation belt, called the Van Allen belt, is filled with energetic electrons. The precipitation of these energetic electrons heats the upper atmosphere and alters its chemical properties. Under certain conditions, whistler waves are generated within the radiation belts, accelerating and powering up the electrons. This effectively stretches out the electrons’ travel path so that they fall out of the belts and precipitate into the atmosphere, creating electron rain.

By using the data from ELFIN mission, UCLA scientists recently detected unexpected, rapid “electron precipitation” from low-Earth orbit. This phenomenon causes the colorful aurora borealis but simultaneously hazards satellites, spacecraft, and astronauts.

When scientists determined the source of these energetic electrons raining, they found that the whistler waves caused the sudden downpour. The study suggests that whistler waves are responsible for far more electron rain than current theories and space weather models predict.

For this study, scientists combined the ELFIN data with more distant observations from NASA’s THEMIS spacecraft. They then created a sophisticated computer modeling that allowed them to understand in detail the process by which the waves cause superfast electron rain.

Electron rain, which can cause the aurora borealis and impact satellites
Electron rain, which can cause the aurora borealis and impact orbiting satellites and atmospheric chemistry. Credit: NASA, Emmanuel Masongsong/UCLA

Xiaojia Zhang, lead author and a researcher in UCLA’s Department of Earth, planetary and space sciences, said, “ELFIN is the first satellite to measure these superfast electrons. The mission yields new insights due to its unique vantage point in the chain of events that produces them.”

Vassilis Angelopoulos, a UCLA professor of space physics and ELFIN’s principal investigator, said, “One can imagine the Van Allen belts as a large reservoir filled with water — or, in this case, electrons. As the reservoir fills, water periodically spirals down into a relief drain to keep the basin from overflowing. But when large waves occur in the reservoir, the sloshing water spills over the edge faster and in greater volume than the relief drainage. ELFIN, which is downstream of both flows, can properly measure the contributions from each.”

Scientists further demonstrate that this superfast electron rain can increase significantly during geomagnetic storms. It, therefore, contributes to enhanced solar activity that can affect near-Earth space and Earth’s magnetic environment.

Colin Wilkins, a co-author of the current research who is the instrument lead on ELFIN, said“It’s so rewarding to have increased our knowledge of space science using data from the hardware we built ourselves.”

Journal Reference:

  1. Zhang, XJ., Artemyev, A., Angelopoulos, V., et al. Superfast precipitation of energetic electrons in the radiation belts of the Earth. DOI: 10.1038/s41467-022-29291-8
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