A large-scale magnetospheric line radiation event in the upper ionosphere recorded by the China-Seismo-Electromagnetic Satellite

This paper reports a large-scale magnetospheric line radiation (MLR) event during a moderate geomagnetic storm on September 11, 2018, which was well recorded by the China-Seismo-Electromagnetic Satellite (CSES) in the upper ionosphere. The event shows a symmetrical propagation feature at the conjugated points, with a large spatial extension between 53°S and 54°N. The parallel structures are clearly visible in the electric and magnetic spectrogram, ranging from the local proton cyclotron frequency (several hundred Hertz) to ~1.6 kHz. The wave intensity of parallel spectral lines was most intensive in high-latitude regions, relatively weaker at mid-low latitudes, and almost absorbed in the equatorial region, exhibiting a distinct V-shaped structure. The frequency spacings between neighboring spectral lines roughly vary from ~80 to 90 Hz in the high latitudes and from ~85 to 120 Hz in the low latitude region, suggesting a slight variation feature with latitude. The parallel spectral structures of MLR also drift between ~0.39-0.57 Hz/s at high latitudes and ~0.18-0.19 Hz/s at low latitudes. The wave vector analysis shows that the MLR waves are right-hand polarized, obliquely propagating toward the Earth with a wave normal angle ranging between 30° and 90°, where the Poynting flux is primarily oriented perpendicular to the total magnetic field. Finally, by analyzing a few other MLR events, we found that they all exhibit similar parallel structures and polarization characteristics, suggesting the universality of such a phenomenon.