A research group consisting of the National Institute of Polar Research, the Institute of Statistical Mathematics, and the University of Tokyo called on people across Japan to take aurora photos on X (formerly Twitter) in response to the massive geomagnetic storm that occurred on May 2024, 5. After examining the aurora photos collected in response to the call, two mysterious features were discovered.
First, the aurora was observed from low latitude areas such as Hyogo Prefecture. The research group analyzed 1 aurora photos taken by citizens and attempted to estimate the altitude at which the aurora was shining by determining the location of the photo and the elevation angle of the top of the aurora. As a result, it was estimated that, surprisingly, while a normal aurora shines at an altitude of no more than 179 km, the location where the aurora was shining on this day was likely to have been at an altitude of over 600 km. This is said to be the main reason why the aurora could be observed even in low latitude areas if the view was good.
Another characteristic was that the color of the aurora was magenta, rather than the typical red seen in low-latitude auroras during geomagnetic storms. This was because, in May, even though it was night on the ground, high altitudes were in the solar radiation zone, and the blue color of the scattered nitrogen molecular ions was added by the resonant scattering of sunlight, making the blue scattered light visible at the same time. Normally, nitrogen molecular ions do not exist at altitudes above 1 km, but it is thought that during geomagnetic storms, atmospheric heating and other factors caused large amounts of nitrogen molecular ions, the source of resonant scattering, to fly up in the air.
This research is an example that demonstrates the importance of aurora observation as citizen science. It is expected that citizen science will continue to contribute to further advances in elucidating the realities of aurora observations and geomagnetic storms.
Paper information:[Scientific Reports] Extended magenta aurora as revealed by citizen science
