O‐Mode Instability for Non‐Thermal Continuum Radiation Generated Near the Plasmapause

• Published in: Journal of geophysical research. Space physics 2024-10, Vol.129 (10), p.n/a
• Main Authors: Cheng, Chio Z., Kim, Eun‐Hwa, Boardsen, Scott A., Cairns, Iver H., Johnson, Jay R.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Anisotropy; Continuum radiation; Cyclotron frequency; Electron plasma; Electrons; Energy sources; Harmonics; Instability; Magnetic equator; Magnetic fields; Magnetic resonance; Plasma frequencies; Plasmapause; Relativistic velocity; Resonance
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2024JA032626

Analysis of the ordinary mode (O‐mode) instability is performed to comprehend the nonthermal continuum (NTC) radiation near the plasmapause, taking into account the relativistic wave‐electron resonance effect. The energy source is the anisotropy in the velocity of the minority suprathermal electron population. Numerical solutions demonstrate that the O‐mode can be unstable with multiple narrow frequency bands located close to harmonics of the electron cyclotron frequency above the local electron plasma frequency. These waves have narrow beaming angle bands of nearly 90° $90{}^{\circ}$ relative to the ambient magnetic field. Our findings indicate that NTC radiation generated by this wave‐electron resonance instability near the plasmapause can propagate nearer to the magnetic equator with multiple harmonics, which is in agreement with a recent statistical study using Van Allen Probes. Key Points The ordinary mode electron anisotropy instability is examined to comprehend the non‐thermal continuum radiation near the plasmapause Resonant ordinary modes are unstable over multiple narrow frequency and wavevector ranges NTC radiation generated by the instability near the plasmapause can propagate nearer to the magnetic equator