Speaker
Description
Energetic particle precipitation is common in the South Atlantic Magnetic Anomaly (SAMA), where the weakened geomagnetic field allows particles from the inner radiation belt to reach the atmosphere. During geomagnetic disturbances, this precipitation can be enhanced and may produce ionospheric signatures typically observed in auroral regions. However, the mechanisms controlling the storm-time enhancement and spatial extent of precipitation over the SAMA remain poorly understood. This study investigates the storm-time dynamics of energetic electrons and their precipitation over the SAMA during a geomagnetic storm on 22 June 2015 following interplanetary coronal mass ejections (ICMEs). We combine energetic particle and plasma wave observations from the Van Allen Probes with particle flux measurements from PROBA-V/EPT over the Brazilian sector. Ionosonde observations investigate the response of the lower ionosphere to enhanced particle precipitation. The analysis focuses on electrons with energies of 10s of keV to 800 keV. During the storm, particles were transported inward from the outer magnetosphere, filling the slot region and populating lower-L-shells. Concurrently, the plasmapause was compressed and enhanced hiss-wave activity was observed in the plasmasphere. The enhanced particle fluxes in the inner radiation belt were accompanied by an increase in fluxes over the SAMA and an expansion of the precipitation region beyond the nominal SAMA footprint, extending toward both lower latitudes and auroral-ward latitudes. Ionosonde observations from Cachoeira Paulista revealed the formation of an intense auroral-like sporadic-E layer in the E region during the storm recovery phase on June 24, providing an independent indication of enhanced energetic particle input into the atmosphere. These observations suggest that enhanced precipitation over the SAMA and the delayed response of ionosphere may be associated with the storm-time inward transport and subsequent scattering of energetic electrons into the atmosphere. We use simulations from the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model to reconstruct storm-time evolution of the inner radiation belt and quantify the relative roles of radial transport and pitch-angle scattering in producing the enhanced precipitation.