A study from University of Iowa researchers reveals that the aurora borealis — the northern lights — appear brighter when electromagnetic waves in space interact with particles inside the aurora.
Connor Feltman, a postdoctoral researcher in the Department of Physics and Astronomy at Iowa, examined data from two rockets that were launched into the aurora from Andøya, Norway, in 2022, an Iowa-led experiment known as the ACES-II mission.
Alfvén waves, a type of wave common in plasma, are created when a magnetic field is “plucked,” similarly to a violin string. These waves then follow in the same direction as the magnetic field lines, where they move through the plasma and can occasionally interact with particles such as electrons or protons. Under certain conditions, particles that interact with the Alfvén wave can gain energy, which is known as Alfvén wave-particle acceleration.
In the study, the researchers found that the Alfvén waves passed through different regions: one inside the aurora and one outside of it. There were accelerated electrons in both regions, but they didn’t look the same; the electrons inside the aurora were more intense, which Feltman says highlights the importance of auroras in boosting the process. The researchers learned the difference was likely not caused by the waves themselves but by the differences in the charged plasma particles the waves interacted with.
Researchers found that auroral electrons are already moving faster because the aurora is generating momentum for the electrons; this makes them more likely to further interact with the waves.
“Understanding this process more deeply through in situ measurements is not only useful for understanding the processes that create the aurora — which we still do not fully understand — but also emphasizes the importance and potential dangers of wave activity,” Feltman says. “For example, if you gauged the radiation safety of your new spacecraft only upon whether you see typical auroral particles or not when flying through these polar regions, you would underestimate the total energy imparted to your payload by large margins since we observed electromagnetic waves that can enhance auroral particle energies many times in strength. This is not healthy for satellites nor people.”
The findings could help scientists better understand how the continuous jet of energy from the sun, called the solar wind, moves through space and slips into Earth’s atmosphere. This is critical for predicting space weather, which can damage satellites and disrupt telecommunications and electricity infrastructure on Earth.
Other study authors were Gregory Howes, Scott Bounds, David Miles, Craig Kletzing (deceased), and Robert Broadfoot, from the University of Iowa; and Kenton Greene, John Bonnell, and Roger Roglans from the University of California, Berkeley.
The NASA-funded study, “Inferential Evidence for Suprathermal Electron Burst Intensification Due to Inverted-V Precipitation via Inertial Alfvén Waves,” was published June 17 in Journal of Geophysical Research: Space Physics.