Interplay of source/seed electrons and wave-particle interactions in producing relativistic electron PSD enhancements in the outer Van Allen belt

Abstract

We perform a superposed epoch analysis on two groups of selected geospace disturbance events, emerging from single and isolated interplanetary drivers, and resulting in either the enhancement or the depletion of the average relativistic electron Phase Space Density (PSD). We investigate the occurrence of behavioural/temporal patterns of solar wind and geomagnetic parameters, chorus and ULF Pc5 wave activity, and the source/seed electron PSD in the outer Van Allen radiation belt. Our results indicate that the source electron population of μ = 10 MeV/G exhibits a similar behaviour during both event groups, while the μ = 1 MeV/G population can be considered as negligible for the whole process of wave excitation and electron energisation. Moreover, events that result in relativistic electron enhancement are characterised by statistically stronger and prolonged storm, substorm and wave activity, combined with an abundance of seed electrons of μ = 100 MeV/G, mostly at L* = 4–5, the nominal heart of the outer radiation belt.