Researchers led by the University of Iowa have learned more about how Earth’s uppermost atmospheric layer may contribute to aurora, the colorful dance of lights in the skies in the Northern and Southern hemispheres.

An aurora is formed when a jet of energy from the sun traveling at a million miles per hour, called the solar wind, slams into the Earth’s magnetic field. That magnetic field directs the energy from these powerful interactions toward Earth’s polar regions, where it collides with the uppermost part of Earth’s atmosphere, called the ionosphere. 

Some scientists had thought the interaction of the solar wind and the Earth’s magnetic field was the primary instigator in the aurora’s formation, with the ionosphere acting as a bystander. But more recently, computer models simulating the aurora and some direct experiments suggest the ionosphere may play a role after all.

The Iowa-led research team put that theory to the test in November 2022 by launching from Norway a rocket 115 miles skyward into an aurora. The ACES-II sounding rocket measured changes in the ionosphere’s density and electric and magnetic fields on the edges of the aurora. Instruments aboard the ACES-II rocket also observed Alfven waves — which move along magnetic field lines in an energized fluid called plasma — in the ionosphere, a further indication the region was more than a passive environment.

“We observed a correlation between electromagnetic waves and ionospheric plasma density, which suggests that the ionosphere may play a role shaping the glowing ribbons, sheets, and beads that give the northern lights its vibrant character,” says Kenton Greene, the study’s corresponding author, who earned his doctorate from Iowa in 2024. 

“These observations are consistent with a model of the northern lights where the changes in the ionosphere participate in the creation of small-scale features in the aurora. We hope that these measurements will help us to understand how the ionosphere helps to create these features,” adds Greene, who now is a postdoctoral researcher at the University of California-Berkeley.

The study, “In situ evidence of ionospheric feedback instability adjacent to a quiescent auroral arc,” was published online Feb. 3 in the journal Geophysical Research Letters.

Co-authors from Iowa are David Miles, professor in the Department of Physics and Astronomy; Scott Bounds, associate research scientist; and Connor Feltman, a post-doctoral research fellow. Additional co-authors are John Bonnell and Roger Roglans from California-Berkeley; and Anatoly Streltsov, from Embry‐Riddle Aeronautical University.

NASA funded the research.