Magnetospheric Chorus, Exohiss, and Magnetosonic Emissions Simultaneously Modulated by Fundamental Toroidal Standing Alfvén Waves Following Solar Wind Dynamic Pressure Fluctuations

Abstract

Abstract Magnetospheric quasiperiodic whistler‐mode emissions have long been considered a consequence of the relaxation oscillation or the compressional ultralow‐frequency wave modulation. Here we experimentally demonstrate that the whistler‐mode chorus, exohiss, and magnetosonic emissions can be effectively modulated by the toroidal ultralow‐frequency waves. On 04 August 2017, the solar wind dynamic pressure fluctuations excited the fundamental toroidal standing Alfvén waves in the dayside magnetosphere. These regular toroidal pulsations displayed the approximately same periods as the power variations of the whistler‐mode emissions from 50 Hz to 5 kHz. Along with the decay of the toroidal pulsations, the quasiperiodic feature of these whistler‐mode emissions gradually became indistinct. However, no modulation signatures of background parameters and resonant particles for the whistler‐mode emissions were observable near the equator, and the exact cause for this phenomenon remains to be elucidated.

Keywords

• radiation belt
• wave‐particle interaction
• plasma instability
• quasi‐periodic VLF/ELF waves
• ULF pulsations
• solar wind dynamic pressure fluctuations