Red Auroras Over Japan: A High-Altitude Mystery
Researchers from Hokkaido University and the Okinawa Institute of Science and Technology have analyzed red auroras observed over Japan between June 2024 and March 2025.
These unusual auroras occurred at altitudes of 500-800 km, significantly higher than the typical 200-400 km for low-latitude auroras. While the events were associated with moderately intense geomagnetic storms, the researchers discovered a key difference: the solar wind compressed Earth's magnetosphere more strongly than usual.
The Core Hypothesis
The team hypothesizes that this compression heated the upper atmosphere, effectively lifting the aurora formation region to higher altitudes. Furthermore, the outflow of charged particles during these events may have masked the storms' true intensity.
Methodology
The study combined satellite data with citizen science photographs to accurately reconstruct the auroral altitudes.
Implications for Satellites
The authors note a significant practical consequence: such heating and expansion of the upper atmosphere can increase drag on satellites, affecting their orbits.
"The compression of the magnetosphere heated the upper atmosphere, lifting the aurora formation region."