Electron filling and proton loss in radiation belts and SAA during 2018 storm based on ZH-1 satellite observations

Based on data from the ZH-1 satellites, companied with Van Allen Probes and NOAA observations, we analyze the high energy particle evolutions in radiation belts, slot region and SAA during August 2018 major geomagnetic storm (minimum Dst ≈ −190 nT). 

  1) Relativistic electron enhancements in extremely low L-shell regions (reaching L ∼ 3) were observed during storm. Contrary to what occurs in the outer belt, such an intense and deep electron penetration event is rare and more interesting. Strong whistler-mode (chorus and hiss) waves, with amplitudes 81–126 pT, were also observed in the extremely low L-shell simultaneously (reaching L ∼ 2.5) where the plasmapause was suppressed. The bounce-averaged diffusion coefficient calculations support that the chorus waves can play a significantly important role in diffusing and accelerating the 1–3 MeV electrons even in such low L-shells during storms.

2) A robust evidence is clearly demonstrated that the energetic electron flux with energy 30∼600 keV are increased by 2∼3 times in the inner radiation belt near equator and SAA region on dayside during the major geomagnetic storm. This is the first time that the 100s keV electron flux enhancement is reported to be potentially induced by the interaction with magnetosonic waves in extremely low L-shells (L<2) observed by Van Allen Probes. Proton loss in outer boundary of inner radiation belt takes place in energy of 2~220 MeV extensively during the occurrence of this storm but the loss mechanism is energy dependence which is consistent with some previous studies. It is confirmed that the magnetic field line curvature scattering plays a significant role in the proton loss phenomenon in energy 30-100 MeV during this storm. This work provides a beneficial help to comprehensively understand the charged particles trapping and loss in SAA region and inner radiation belt dynamic physics.