Simultaneous Observation of Whistler‐Mode Chorus and Fast Magnetosonic Waves During the Magnetic Peak in the Inner Magnetosphere

• Published in: Geophysical research letters Vol. 50; no. 16
• Main Authors: Huang, Zheng, Yuan, Zhigang, Yu, Xiongdong, Deng, Dan, Xue, Zuxiang
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-08-2023; Wiley
• Subjects: Anisotropy; Charged particles; Distribution; Electron energy; Electrons; Fluxes; Free energy; Growth rate; Jupiter; Magnetic field; Magnetic fields; magnetic peak; Magnetospheres; MS waves; Particle physics; Pitch (inclination); Protons; ring current particles; Ring currents; Structures; Velocity; Wave excitation; Whistlers; whistler‐mode chorus waves
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL104647

Simultaneous observations of whistler‐mode chorus and magnetosonic (MS) waves are reported within a magnetic peak in the inner magnetosphere for the first time. During the magnetic peak, Van Allen Probe A observes flux enhancements of both ring current electrons and relativistic electrons, while medium‐energy proton fluxes are reduced but high‐energy proton fluxes are raised. Those flux variations of ring current particles are almost concentrated in the perpendicular direction of the background magnetic field, leading to enhancements of the electron temperature anisotropy and a positive gradient of proton velocity distributions. The calculated linear growth rates show that unstable electrons with temperature anisotropic instabilities and unstable protons with ring distribution during the magnetic peak structure can provide free energy for the excitation of whistler‐mode chorus and MS waves, respectively. Our findings suggest that injected particles encountering the magnetic peak structure may form more complex unstable electron and ion distributions driving multiple instabilities simultaneously.
Plain Language Summary
Recently, dipolarizing flux bundles have also been observed in the inner magnetosphere. These magnetic field structures are usually accompanied by dispersion of particle energies and pitch angles, resulting in complex and unstable particle distributions during magnetic structures, which may provide free energy for wave excitation. Previous observed waves during magnetic structures belong to single instability (electron type or proton type), rarely taking into account waves driven by both proton and electron instabilities. In this letter, simultaneous observations of chorus and magnetosonic (MS) waves are reported during a magnetic peak in the inner magnetosphere for the first time. Our results show that the complex distribution in the velocity phase space of ring current electrons and protons during the magnetic peak in the inner magnetosphere has the potential to simultaneously trigger chorus and MS waves.
Key Points
Whistler‐mode chorus and fast magnetosonic (MS) waves are simultaneously observed during the magnetic peak in the inner magnetosphere
Enhancements of ring current particle instabilities during the magnetic peak cause the excitation of whistler‐mode chorus and MS waves
Our results contribute to understanding the evolution of injected electrons and protons encountering the magnetic peak