Journal Article

In Situ Observations of the Influence of Nonlinear EMIC Waves on Relativistic Electrons in the Outer Radiation Belt

Shinohara, Iku, Teramoto, Mariko, Jun, Chae‐Woo, Takashima, Takeshi, Higashio, Nana, Mitani, Takefumi, Kim, Khan‐Hyuk, Matsuoka, Ayako, Bortnik, Jacob, Lyons, Larry, Yamamoto, Kazuhiro, Miyoshi, Yoshizumi, Hori, Tomoaki

2025

Overview

This study demonstrates the influence of electromagnetic ion cyclotron (EMIC) rising‐tone emissions on relativistic electrons in the inner magnetosphere using data obtained from the Van Allen Probes and Arase satellites. We find that the intense EMIC rising‐tone emissions occur during the increase in the solar wind pressures, creating favorable conditions for triggering nonlinear wave growth. The strong flux drop‐out of relativistic electrons in the parallel directions of the magnetic field, with energies of 0.2–4 MeV, was associated with the wave activity. We calculated the nonlinear triggering conditions and the minimum resonant energy of relativistic electrons interaction with EMIC waves, based on our observations. We conclude that EMIC rising‐tone emissions contribute not only to the rapid loss of MeV electrons through EMIC wave‐particle interactions while extending the resonance energy to a few MeV by broadening bandwidth via nonlinear wave growth but also to interactions with sub‐MeV electrons through the nonresonant effect. Plain Language Summary Electromagnetic ion cyclotron (EMIC) wave‐particle interactions play an important role in controlling the dynamics of the inner magnetosphere, particularly the loss of energetic protons (1–100 keV) and relativistic electrons (several MeV) in the radiation belts. Nonlinear wave growth of EMIC rising‐tone emissions contributes to the rapid loss of relativistic electrons and ring current ions. Remarkably, EMIC rising‐tone emissions meet the nonlinear triggering conditions driven by the compressed dayside magnetosphere. Significant decreases in relativistic electrons in the parallel direction to the magnetic field are associated with the wave activity. The present result provides new insights into the dynamics of the inner magnetosphere, including radiation belts, by EMIC WPI. Key Points Nonlinear EMIC waves observed in the dayside uniform zone, caused by solar wind compression, meet conditions for the nonlinear wave growth The significant flux drop‐out of electrons within energies of 0.6–4 MeV was associated with the intense EMIC rising‐tone emissions Nonlinear EMIC emissions cause a rapid loss of MeV electrons by nonlinear effect and extend scattering to sub‐MeV by nonresonant effect

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Cyclotrons / dayside magnetospheric compression / Electrons / EMIC nonlinear wave growth / EMIC rising‐tone emissions / Emissions / loss of sub‐ and relativistic electrons in the inner magnetosphere / Magnetic field / Magnetic fields / Magnetospheres / Nonlinear waves / Outer radiation belt / Particle interactions / Radiation belts / Relativistic effects / Solar wind / Solar wind pressures / Wind pressure