Multipoint Observations of Nightside Plasmaspheric Hiss Generated by Substorm‐Injected Electrons

Abstract

Abstract 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.