Researchers in Japan have documented red auroras extending to unexpectedly high altitudes, reaching up to 800 kilometers above Earth's surface. This phenomenon, observed during geomagnetic storms previously classified as only moderately intense, suggests these events may be more powerful than standard measurements indicate.
A new study, published in theJournal of Space Weather and Space Climate, detailed observations from Hokkaido University and the Okinawa Institute of Science and Technology. Typically, auroras seen in Japan and other non-polar regions occur at 200 to 400 kilometers in altitude, usually linked to significant geomagnetic activity. These recent findings challenge conventional understanding of storm intensity and their atmospheric effects.
Unusual Auroral Heights Point to Stronger Storms
Tomohiro M. Nakayama, the study's lead author, expressed surprise at the findings. He noted the extreme height of these auroras, even during storms rated as moderate. This suggests that the storms' true strength might be underestimated by existing indices.
The research team analyzed five auroral events recorded in Hokkaido between June 2024 and March 2025. During these periods, bursts of charged particles from the Sun compressed Earth's magnetosphere, the planet's magnetic shield. While standard metrics labeled the storms moderate, the compression itself appeared unusually intense.
Scientists theorize that dense streams of solar wind compressed Earth's magnetic field with such force that the upper atmosphere heated and expanded upward. This expansion could have pushed the region where red auroras form to much higher altitudes. At the same time, the movement of charged particles may have masked the storms' true intensity, making them appear weaker according to traditional space weather measurements.
Implications for Satellite Operations and Space Weather Forecasting
Tomohiro M.
To investigate the phenomenon, researchers combined satellite observations with photographs taken by citizen scientists across Japan. By studying the angles of the auroras in these images and mapping them along Earth's magnetic field lines, the team estimated the glowing structures' height. Observations from multiple locations proved invaluable, allowing for more detailed study of these rare auroral events.
The findings carry implications beyond the visual spectacle. When Earth's upper atmosphere heats and expands, satellites in low Earth orbit experience increased atmospheric drag. This resistance can alter satellite trajectories and cause spacecraft to lose altitude faster than anticipated. Nakayama stated that as the number of satellites in low Earth orbit grows, understanding these effects becomes increasingly important. He added that the results could help improve space weather forecasting and support safer satellite operations.
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