A generation mechanism for chorus emission

[摘要] A chorus generation mechanism is discussed,which is based on interrelation of ELF/VLF noise-like and discrete emissionsunder the cyclotron wave-particle interactions. A natural ELF/VLF noiseradiation is excited by the cyclotron instability mechanism in ducts withenhanced cold plasma density or at the plasmapause. This process is accompaniedby a step-like deformation of the energetic electron distribution function inthe velocity space, which is situated at the boundary between resonant andnonresonant particles. The step leads to the strong phase correlation ofinteracting particles and waves and to a new backward wave oscillator (BWO)regime of wave generation, when an absolute cyclotron instability arises at thecentral cross section of the geomagnetic trap, in the form of a succession ofdiscrete signals with growing frequency inside each element. The dynamicalspectrum of a separate element is formed similar to triggered ELF/VLF emission,when the strong wavelet starts from the equatorial plane. The comparison isgiven of the model developed using some satellite and ground-based data. Inparticular, the appearance of separate groups of chorus signals with a duration2-10 s can be connected with the preliminary stage of the step formation. BWOregime gives a succession period smaller than the bounce period of energeticelectrons between the magnetic mirrors and can explain the observed intervalsbetween chorus elements.

Key words. Magnetospheric physics (Energetic particles· trapped). Space plasma physics (wave-particle interactions; waves andinstabilities)

[学科分类] 地球科学(综合)