Nagoya University

Graduate School of Science, The University of Tokyo

Osaka University

The Japan Aerospace Exploration Agency

Summary of Presentations

Professor Lynn Kistler, Professor Yoshizumi Miyoshi, and Designated Associate Professor Tomoaki Hori, Nagoya University, Associate Professor Kazushi Asamura, Professor Iku Shinohara, The Japan Aerospace Exploration Agency (JAXA), Associate Professor Satoshi Kasahara and Assistant Professor Kunihiro Keika, the University of Tokyo, Associate Professor Shoichiro Yokota, Osaka University, and other researchers in the United States discovered in an international joint research project that the main source of space storms is plasma originating from the Earth, rather than plasma originating from the Sun as previously thought.

Through this international collaboration, the research team analyzed data from a total of four scientific satellites including a Japanese satellite "Arase." They succeeded for the first time in separating the composition of solar- and Earth-origin plasma in near-Earth space (i.e., geospace) and discovered that the plasma in the Earth's magnetosphere changes from solar to Earth origin during space storms. They also identified that the Earth-origin hydrogen ions are initially dominant in the development of space storms, and that the Earth-origin oxygen ions later become the main population of space storms.

The results indicate that not only ions of solar origin but also ions of terrestrial origin affect the development of space storms. During space storms, the space environment around the Earth changes drastically, which can cause problems/anomalies to satellites and the power grid on the ground due to strong electric currents. This research highlights the importance of understanding the behavior of both solar- and Earth-origin plasma to comprehend and predict the changes in the space environment caused by space storms. The findings of this research will lead to a significant shift in the understanding of space storms.

The research results were published in Nature Communications on October 30, 2023, at 7:00 p.m. (JST).

Figure: Observations of the solar wind and geospace by the combination of satellites from Japan, the USA and Europe. The results revealed that the plasma in the inner magnetosphere when a space storm develops is mainly composed of plasma originating from the Earth, rather than those from the solar wind.

For more information, please visit the websites of Nagoya University and the Japan Aerospace Exploration Agency.

Journal

Journal name	Nature Communications
Title of paper	The variable source of the plasma sheet during a geomagnetic storm