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Abstract The magnetospheres of the Earth and other magnetized planets are replete with high‐frequency fluctuations, which are sometimes accompanied by multiple‐harmonic electron cyclotron waves, and lower frequency waves of the whistler‐mode type. Such waves are presumed to be excited by energetic electrons trapped in the dipolar magnetic field, the so‐called loss‐cone electrons, the electron ring distribution being a highly idealized example. The present paper investigates the stability of electron ring distribution with respect to the excitation of quasi‐electrostatic upper‐hybrid wave instability as well as the quasi‐electromagnetic whistler mode instability that operates near electron cyclotron frequency. By employing a two‐dimensional particle‐in‐cell numerical simulation, it is demonstrated that the relatively early dynamics is dominated by the upper‐hybrid wave instability, but over a longer time period it is the whistler mode instability that ultimately determines the final relaxed state. The simulation results are interpreted with the quasilinear theoretical framework.
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O‐Mode Instability for Non‐Thermal Continuum Radiation Generated Near the Plasmapause
Abstract 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 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.
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- Award ID(s):
- 2131013
- PAR ID:
- 10547045
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 129
- Issue:
- 10
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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