DATE2026.06.27 #Press Releases

The Key to the Development of Giant Magnetic Storms Lies in the Overwhelming Proportion of Earth-Origin Heavy Ions

Disclaimer: machine translated by DeepL which may contain errors.

—Arase Satellite Directly Observes the Primary Source of Magnetic Field Fluctuations—

Summary

An international research group led by Seiju Kitamura, Project Assistant Professor at the Institute of Space and Earth Environmental Research, Nagoya University; Satoshi Kasahara, Associate Professor at the Graduate School of Science, The University of Tokyo; and Assistant Professor Kunihiro Keika, and Professor Kanako Seki, among others, analyzed observation data from the geospace exploration satellite “Arase” in near-Earth space, along with simultaneous solar wind observation data, anddemonstrated that the majority of the ions driving the ring current during the massive geomagnetic storm that occurred in May 2024 were heavy ions of terrestrial origin, and successfully identified the temporal variations in their distribution and their spatial structure.

It is known that the ring current during magnetic storms is primarily carried by high-energy ions, and understanding the characteristics of these ions—such as their composition and energy—is crucial for understanding the development of magnetic storms. It was previously known that the ions in the ring current are a mixture of solar wind-origin and Earth-origin ions.The solar wind driving this massive geomagnetic storm was high-density, and it was anticipated that solar wind-origin ions might contribute to some extent. However, the observed ions were overwhelmingly of terrestrial origin—particularly heavy ions—and the contribution of solar wind-origin ions was extremely small.This indicates that the supply of ions from the Earth’s atmosphere and the acceleration process are overwhelmingly important for the development of massive magnetic storms. Furthermore, in the high-pressure region of the ring current, the magnetic field strength decreased by as much as 40%, and it is expected that this significant deformation of the background magnetic field will have a major impact on the loss of high-energy electrons.By identifying key underlying processes, the results of this study provide valuable insights that contribute to the understanding and prediction of variations in the space environment around Earth during rare giant magnetic storms.

These findings were published in the U.S. multidisciplinary international academic journal *Science Advances* at 3:00 a.m. on June 27, 2026.

An image of the geospace exploration satellite “Arase” observing the ring current during a magnetic storm.
(Credit: ERG Science Team)

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