Radial Response of Outer Radiation Belt Relativistic Electrons During Enhancement Events at Geostationary Orbit

Abstract Forecasting relativistic electron fluxes at geostationary Earth orbit (GEO) has been a long‐term goal of the scientific community, and significant advances have been made in the past, but the relation to the interior of the radiation belts, that is, to lower L ‐shells, is still not clear. In this work we have identified 60 relativistic electron enhancement events at GEO to study the radial response of outer belt fluxes and the correlation between the fluxes at GEO and those at lower L ‐shells. The enhancement events occurred between 1 October 2012 and 31 December 2017 and were identified using Geostationary Operational Environmental Satellite (GOES) 15 >2 MeV fluxes at GEO, which we have used to characterize the radial response of the radiation belt, by comparing to fluxes measured by the Van Allen probes Energetic Particle, Composition and Thermal Plasma Suite Relativistic Electron‐Proton Telescope (ECT‐REPT) between 2.5< L <6.0 at E =2.1 MeV. We have found that in general the response of the radiation belts during enhancement events is cohesive for L >5.0 and generally similar for L >4.5. Post‐enhancement maximum fluxes show a remarkable correlation for all L >4.0 although the magnitude of the pre‐existing fluxes on the outer belt plays a significant role and makes the ratio of pre‐enhancement to post‐enhancement fluxes less predictable in the region 4.0< L <4.5. For L <4 the fluxes are poorly correlated with geostationary orbit, but they also tend to be less variable. We have also examined S Y M ‐ H , K p , and A E indices and found that depending on their magnitude, the response of different parts of the outer belt can be better quantified.