Association of relativistic electron enhancements with VLF/ULF wave
activity and seed electrons
Abstract
Local acceleration driven by whistler mode chorus waves is fundamentally
important for the acceleration of seed electrons in the outer radiation
belt to relativistic energies. This mechanism depends strongly on
substorm activity and on the source and seed electron populations
injected by substorms into the inner magnetosphere. In this work, a
selection of geospace disturbance events, emerging from single and
isolated interplanetary drivers, is divided into two groups, one
resulting in enhancement and one in depletion of the average
relativistic electron Phase Space Density (PSD). Because substorm
activity does not always coincide with or depend on magnetic storm
occurrence, we have not limited our study to storms, but have included
also non-storm events that are able to cause enhancements and depletions
of the relativistic electrons in the outer radiation belt. We
investigate solar wind and geomagnetic parameters, wave activity and the
seed electron PSD in the outer Van Allen radiation belt, looking for the
occurrence of characteristic patterns, by performing a Superposed Epoch
Analysis (SEA). Our study indicates the importance of
substorm-associated enhancements of seed electrons, along with
prolonged, intense ULF and VLF wave activity and an earthward displaced
plasmapause, as conditions leading to substantial enhancements of
relativistic electrons in the outer Van Allen belt. This work has
received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No 870437 for the SafeSpace
project.