Space storms light up Japan's sky

On special nights, you might catch a faint red glow quietly lighting up Japan’s sky, stretching low along the horizon as a soft crimson haze. But behind this glowing beauty are countless charged particles from space, traveling along Earth’s magnetic field and colliding with oxygen atoms high above our planet. These atoms release their energy as a dim red light, creating the auroras we see from the ground. 

In a new study published in the Journal of Space Weather and Space Climate, researchers from Hokkaido University and the Okinawa Institute of Science and Technology (OIST), along with the help of citizen scientists, observed red auroras over Hokkaido, Japan that stretched to unexpectedly high altitudes, 500 to 800 kilometers above Earth. Their findings not only challenge our understanding of how auroras form, but also how we measure the strength of space storms. 

“We found that red auroras can extend to extremely high altitudes even during those storms that are measured as moderately intense,” says Tomohiro M. Nakayama, lead author of the study. “This suggests that these storms may actually be stronger than conventional measurements indicate.” 

Typically, red auroras, particularly those that appear further south, including in Japan, are linked to strong geomagnetic storms and occur at lower altitudes of around 200 to 400 kilometers. However, red auroras can also occur during storms that only measure as moderately intense, while reaching far higher altitudes. 

The team analyzed several auroral events observed from Hokkaido between June 2024 and March 2025. During these events, bursts of charged particles from the Sun compressed Earth’s magnetosphere — the invisible magnetic shield that surrounds the planet. Although the storms appeared moderate based on standard indices, this compression was unusually strong.

The researchers propose that this intense compression of Earth’s magnetosphere, driven by dense streams of solar wind, would have heated the upper atmosphere and lifted the region where red auroras form to much higher altitudes than usual. At the same time, the outflow of charged particles could have masked the true strength of the storms, making them appear weaker than they actually were. 

As part of their study, the team combined satellite data with photographs taken by citizen scientists from across Japan. By analyzing the angles of the auroras in these images and tracing them along Earth’s magnetic field lines, they reconstructed how high the glowing structures extended into the sky. 

“The contribution from citizen scientists across Japan to identify and capture these rare, auroral events from multiple locations was crucial,” says senior author Dr. Ryuho Kataoka, who leads space physics research at OIST.   

These findings have important implications beyond the beauty of the night sky. When the upper atmosphere heats and expands, it increases atmospheric drag on satellites orbiting the Earth. This can alter their paths and, in some cases, cause them to lose altitude more quickly than expected. 

“As the number of satellites in low Earth orbit continues to grow, understanding these effects is increasingly important,” says Nakayama. “Our results could help improve space weather forecasting and support safer satellite operations.” 

Adapted from original press release by Megha Kalra, Hokkaido University Science Writer, available here.