资源环境科技发展态势分析平台

Plasmaspheric hiss plays a key role in shaping the radiation belt environment, whose origin remains under active debate. Using the wave and particle data of Van Allen Probes, Geostationary Operational Environmental Satellites, and Time History of Events and Macroscale Interactions during Substorm spacecraft, we here examine the nightside plasmaspheric hiss generation during a substorm. The substorm-electron injection caused the plasmapause to shrink promptly from L-pp = 6.6 to 5.1. Corresponding to the azimuthal drift of the injected electrons, the plasmaspheric hiss was intensified gradually from nightside to dayside. Particularly, in the inner postmidnight plasmasphere free from the substorm injection, the instantaneous peak amplitude of hiss reached 0.9 nT. The enhanced hiss within the locally unchanged plasma must originate from other spatial regions. Our data and modeling demonstrate that the large-amplitude hiss was generated by the substorm-injected electrons drifting into the outer postmidnight plasmasphere, rather than linked to the nightside chorus suffering strong Landau damping or the dayside chorus/hiss propagating azimuthally to the nightside plasmasphere.

Plain Language Summary Plasmaspheric hiss, a naturally occurring electromagnetic emission (0.1-2.0 kHz) in the dense cold plasma surrounding the Earth, can precipitate energetic electrons from the Van Allen radiation belts into the atmosphere. Since its discovery in 1969, the origin of plasmaspheric hiss has remained a puzzle to be solved. We here use the data of seven magnetospheric spacecraft to investigate the nightside plasmaspheric hiss generation during a substorm. Corresponding to the azimuthal drift of substorm-injection front, the plasmaspheric hiss is found to be intensified gradually from nightside to dayside. In the inner nightside plasmasphere free from the substorm injection, the instantaneous peak amplitude of hiss is shown to increase from less than 40 pT to 0.9 nT. Within the locally unchanged plasma, the substorm-enhanced hiss must originate from other spatial regions. Our data and modeling support the previously proposed hypothesis that the nightside hiss is excited by the hot electrons in the outer plasmasphere and then propagates to the inner plasmasphere. This experimental confirmation will allow further developments in modeling and forecasting of the plasmaspheric hiss spatiotemporal distribution and the Earth's radiation belt behavior.