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Successful Observation of Space Environment Variations Induced by a Super Geomagnetic Storm

— Discovery of Suppressed Plasma Supply from the Ionosphere to Outer Space —
November 21, 2025

National Institute of Information and Communications Technology

A research team led by the Institute for Space–Earth Environmental Research (ISEE) at Nagoya University, in collaboration with the National Institute of Information and Communications Technology (NICT) and other partner institutions, has successfully observed large-scale variations in the electron density of the plasmasphere and iono-sphere during the super geomagnetic storm that occurred on May 10, 2024. By analyzing observation data from the Global Navigation Satellite System (GNSS) and Japan’s geospace exploration satellite Arase, the team identified that plasma supply from the ionosphere to outer space was significantly suppressed during the event.

Background

The near-Earth space environment is shaped by solar activity and includes regions such as the ionosphere (*1) and plasmasphere (*2). These regions play a crucial role in satellite positioning and communications using GNSS signal (*3). During geomagnetic storms (*4), disturbances in the Earth’s magnetic field lead to fluctuations in ionospheric electron density, phenomena known as ionospheric storms (*5), which can cause communication disruptions and navigation errors. The plasmasphere, located above the ionosphere, shrinks during geomagnetic storms. Although its recovery is believed to be influenced by ionospheric conditions, the detailed relationship between the two regions has not been fully understood.

Details

The super geomagnetic storm of May 10, 2024, the most intense in approximately 21 years (*6), generated low-latitude auroras visible across the globe. JAXA’s Arase satellite and global GNSS receiver networks detected rapid changes in the plasmasphere’s structure and widespread ionospheric disturbances, respectively.

The research team combined ionospheric total electron content (TEC) data (*7) obtained from GNSS receiver networks with electron density data collected by JAXA’s Arase satellite, to analyze how ionospheric disturbances influenced plasmaspheric recovery.

The analysis revealed that the plasmasphere required more than four days to recover after the storm, an exceptionally long duration compared to past events. A statistical study of 77 geomagnetic storms between March 2017 and December 2024 confirmed that the May 2024 event exhibited an unusually prolonged recovery period.

Moreover, TEC observations indicated that ionospheric electron density decreased by 50–90% across the Northern Hemisphere during the storm. These findings demonstrate that the delayed recovery of the plasmasphere was caused by suppressed plasma supply from the ionosphere.

Statistical analysis of plasmaspheric recovery times for 77 geomagnetic storms between March 2017 and December 2024. The horizontal axis represents plasmaspheric recovery time (days), and the vertical axis represents geomagnetic storm intensity (nT).

Importance of the Results

This study is the first in the world to reveal that disturbances in the ionosphere during the May 2024 super geomagnetic storm significantly delayed the recovery of the plasmasphere. The results show that a reduction in ionospheric electron density can strongly influence both the structural evolution and the recovery process of the plasmasphere by limiting plasma supply from the ionosphere.

These findings will contribute to the advancement of space weather forecasting models and are expected to improve the accuracy of satellite communication and navigation predictions in the future.

Glossary of Terms


(*1) Ionosphere:
A region of Earth’s upper atmosphere (altitude 60–1,000 km) containing ionized particles formed by ultraviolet and X-ray radiation. It affects radio wave propagation through absorption, refraction, and reflection.
(*2) Plasmasphere:
A dense region of low-energy plasma originating from the ionosphere, located inside the Earth’s magnetosphere. Plasma density drops sharply at its outer boundary.
(*3) Global Navigation Satellite System (GNSS):
A general term for satellite positioning systems, including the U.S. GPS, Japan’s Quasi-Zenith Satellite System (QZSS), Russia’s GLONASS, and the EU’s Galileo.
(*4) Geomagnetic Storm:
A disturbance in Earth’s magnetic field caused by solar activity.
https://swc.nict.go.jp/knowledge/magnetosphere.html#geomagnetic_storm
(*5) Ionospheric Storm:
A variation in ionospheric electron density associated with geomagnetic disturbances.
https://swc.nict.go.jp/report/topics/202405101630.html
(*7) Total Electron Content (TEC):
The integrated number of electrons along the path between a GNSS satellite and receiver, calculated using frequency differences in the satellite signals.

Paper Information

Journal:
Earth, Planet and Space
Title:
Characteristics of temporal and spatial variation of the electron density in the plasmasphere and ionosphere during the May 2024 super geomagnetic storm
Authors and Affiliations:
Atsuki Shinbori (1), Naritoshi Kitamura (1), Kazuhiro Yamamoto (1), Atsushi Kumamoto (2), Fuminori Tsuchiya (2), Shoya Matsuda (3), Yoshiya Kasahara (3), Mariko Teramoto (4), Ayako Matsuoka (5), Takuya Sori (6), Yuichi Otsuka (1), Michi Nishioka (7), Septi Perwitasari (7), Yoshizumi Miyoshi (1), Iku Shinohara (8)
DOI:
https://doi.org/10.1186/s40623-025-02317-3

(1) Nagoya University, Institute for Space–Earth Environmental Research (ISEE)
(2) Tohoku University, Graduate School of Science
(3) Kanazawa University, College of Science and Engineering
(4) Kyushu Institute of Technology, Graduate School of Engineering
(5) Kyoto University, Graduate School of Science
(6) Kyoto University, Research Institute for Sustainable Humanosphere
(7) National Institute of Information and Communications Technology (NICT), Radio Research Institute
(8) Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Science (ISAS)

Contact

Michi Nishioka
Septi Perwitasari
Space Environment Laboratory
Radio Propagation Research Center
Radio Research Institute

E-mail: nishiokaat signnict.go.jp
E-mail: septi.perwitasariat signnict.go.jp

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