Nagoya University

Graduate School of Science, The University of Tokyo

Kyoto University

Tohoku University

Osaka University

Summary of Presentations

Associate Professor Shigetoshi Kitamura, Professor Yuzumi Miyoshi, Project Associate Professor Satoko Nakamura, and Project Assistant Professor Masashi Koji of the Space and Earth Environment Research Institute, Nagoya University, Tokai National University Corporation, have collaborated with Associate Professor Takanobu Amano of the Graduate School of Science, The University of Tokyo, Professor Zenji Omura and Professor Hirotsugu Kojima of the Research Institute for Sustainable Humanosphere, Kyoto University, Project Assistant Professor Masahiro Kitahara of the Graduate School of Science, Tohoku University, and Associate Professor Masahiro Yokota of the Graduate School of Science, Osaka University. Associate Professor Yoshifumi Saito of the Institute of Space and Astronautical Science (JAXA), Associate Professor Katsuichiro Yokota of Graduate School of Science, Osaka University, and other members of an international research group, have jointly developed a low-energy electron measurement device (FPEM) onboard the Magnetospheric Multiscale (MMS) satellite formation of the National Aeronautics and Space Administration (NASA). The FPI-DES (Low Energy Electron Detection System) on NASA's Magnetospheric Multiscale (MMS) satellites and the analysis of electromagnetic field measurement data have captured the site where electrons supply energy to plasma waves called Whistler mode waves in space outside the near-Earth magnetosphere (near (day side) magnetic reconnection, magnetic sheath region), and directly measured the electron-to-wave energy transport rate. The growth rate of the wave was derived from the direct measurement of the energy transport rate from the electron to the wave based on the observation. Furthermore, it was found that the observed results are consistent with efficient wave growth, which is called nonlinear growth.

Whistler mode waves are thought to play an important role in particle acceleration and scattering in space, such as contributing to relativistic energy particle acceleration in the radiation belt in the magnetosphere and scattering electrons to cause particle landing in pulsating auroras. This is the first time that the efficient growth of waves has been directly observed in space, and is expected to advance our understanding of particle acceleration and scattering in space and the process of electromagnetic wave generation.

The results of this research were published in the British scientific journal Nature Communications at 18:00 (JST) on October 28, 2022.

Figure: Images of whistler-mode waves propagating in a spiral of wave magnetic field (light blue) along a background magnetic field (purple) and electrons (red) interacting with them while passing by (C: The University of Tokyo).

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