Statistical analysis of the phase space density changes of radiation belt source, seed, and relativistic electrons in response to geomagnetic storms

The radiation belt “source” (a few to tens of keV), “seed” (hundreds of keV), and “relativistic” (>1 MeV) electrons are highly fabricated by geomagnetic storms or substorms. The present study statistically analyzed the phase-space density (PSD) of the radiation belt electrons at the first adiabatic invariant μ = 10¹-10⁴ MeV/G between L^* (the inversion of the third adiabatic invariant) from 2.5 to 5.5 in response to geomagnetic storms. The statistical results indicate that after the storms, more than 25% of the relativistic electron PSD were pumped at L^* > ∼3.5, with a peak at approximately L^* = 4.0, while approximately 25% of them also showed a clear loss at L^* > 3.5. Comparably, the source electrons mainly increased within almost the whole outer radiation belt, and the seed electrons may serve as intermediary populations, in which source and loss processes engage in strong competition. As the dynamic pressure and substorm intensify, the primary “enhancement region” and “loss region” converge near a few 10² MeV/G. Furthermore, analysis that the magnetopause shadowing effect mainly contributed to the observed losses one day after the main phase, while the substorm-injected particles and the seceded acceleration processes likely accounted for the observed increase in the electron PSD three days after the main phase. The present study provides a new and comprehensive insight into the statistical understanding of the change rates of the electron PSD and the competition between source and loss processes in response to geomagnetic storms.