Preprints
https://doi.org/10.5194/egusphere-2025-5536
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-5536
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
03 Dec 2025
| 03 Dec 2025
Status: this preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
High temporal resolution photos of SAR arc rays lead to a new interpretation of the physical causes: Wave-particle interactions and energetic electron precipitation
Abstract. High spatial and temporal resolution images of red auroras over Germany during the 10–11 May 2024 magnetic storm have added new information concerning stable auroral red (SAR) arc formation. The high-altitude red aurora displayed brightness streaks/rays, which continued to lower altitude green auroral brightness rays, indicating that energetic electron precipitation along the Earth’s magnetic field lines are causing both auroras. Both the red and green auroras are diffuse in nature, indicating that instability of high-energy ring current particles inside the plasmasphere followed by wave-particle interactions is the most likely cause of the precipitating electrons. The 5577Å diffuse green aurora below the SAR arcs is a new scientific finding. This is named Stable Auroral Green (SAG) arcs. The SAR and SAG arc images were taken during the first and second steps of the 2024 superstorm. They occurred during intense substorms.
How to cite. Tsurutani, B. T., Lakhina, G. S., Hajra, R., Horne, R. B., Iizawa, M., Narita, Y., von Borstel, I., Glassmeier, K.-H., Bothmer, V., Reinsch, K., Schulz, P., and Solanki, S.: High temporal resolution photos of SAR arc rays lead to a new interpretation of the physical causes: Wave-particle interactions and energetic electron precipitation, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-5536, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Bruce T. Tsurutani
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
retired
Gurbax S. Lakhina
Indian Institute of Geomagnetism, Navi Mumbai, India
retired
Rajkumar Hajra
CAS Key Laboratory of Geospace Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, People’s Republic of China
Richard B. Horne
British Antarctic Survey, Cambridge, England
Masatomi Iizawa
Institut für Theoretische Physik, Technische Universität Braunschweig, Braunschweig, Germany
Yasuhito Narita
CORRESPONDING AUTHOR
Institut für Theoretische Physik, Technische Universität Braunschweig, Braunschweig, Germany
Ingo von Borstel
Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Braunschweig, Germany
Karl-Heinz Glassmeier
Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Braunschweig, Germany
Volker Bothmer
Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Germany
Klaus Reinsch
Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Germany
Philipp Schulz
Fraunhofer-Institut für Schicht-und Oberflächentechnik IST, Braunschweig, Germany
Sami Solanki
Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
Short summary
During the 10–11 May 2024 geomagnetic storm, the red auroral rays appear at higher altitudes and connect to green rays lower down. The effect is linked to energetic electrons precipitating into the atmosphere during the storm. As the electrons continue downward, they hit oxygen below 200 km altitude and produce green light (5577 Å), named Stable Auroral Green (SAG) arcs. These observations mark the first reported sightings of such detailed, combined features.
During the 10–11 May 2024 geomagnetic storm, the red auroral rays appear at higher altitudes and...
This manuscript utilizes the full-color photographs as obtained from digital cameras, including a smart phone camera of Google Pixel, to discuss that the greenish feature in the sub-auroral region (around 50 MLAT) is a new type of aurora. However, it is difficult for readers to be confident about the conclusion by reading though the manuscript.
First of all, since the clear ray structure appeared in Figures 3, 4, and 5 is one of typical evidence used for distinguishing auroras from SAR, the starting point of the scientific discussion is confusing. Also, for example, well-known quiet arcs before auroral breakup look diffuse and greenish, but there is no discussion about the essential difference between the quiet arcs and the newly discovered auroral type.
More technically, it is unclear how we can understand that the auroral structures in the photographs shown in Figures 3, 4, and 5 are different from pre-existing categories of auroras. Looking like diffuse and greenish is not likely scientifically enough to convince readers. For example, even if those data are from non-scientific cameras, time-lapse movies may help to partly discuss that the targeted structure in the photograph may or may not be like SAR.
YouTube link is also provided to partly solve that issue by checking the relative motion. However, the time-lapse movie is an artistic collection of many beautiful photographs without exact time stamps, and it is still hard to understand how the authors scientifically distinguish the auroral types. We can see from the YouTube movie that many different types of auroras exist and the mixture of them simultaneously appears in the sub-auroral region during the storm-time when the auroral oval widely extended toward mid-latitude areas.
I also noticed that there might be typical SAR-like feature widely appeared to the South at around the 1:20 YouTube-movie time, although it is still very hard to convince readers about SAR by just referencing this particular YouTube movie. It seems that further critical clarifications and examination of photographs are likely necessary before concluding the discovery/hypothesis, and working on many other citizen science photograph contributions may significantly help to improve the analysis.