Estimating Storm‐Time Maximum Fluxes of Outer Radiation Belt Electrons: Combining Van Allen Probes and GPS Satellite Observations

The Earth's outer radiation belt contains highly energetic electrons, also known as “killer electrons”, which can pose a damage to the Earth-orbiting satellites. It is of great importance to understand the maximum fluxes of these electrons and underlying driving factors. By combining 6-year Van Allen Probes data and 19-year GPS satellite NS41 observations, we comprehensively investigated the statistical distributions of the storm-time outer belt electron maximum fluxes and their critical controlling geomagnetic and solar wind conditions. This combined data set covers the maximum and declining phases of Solar Cycles 23 and 24, offering a unique opportunity to examine the maximum fluxes during various extreme space weather events. Our study confirms the crucial role of continuous and strong substorms as measured by the time-integrated AL index (Int(AL)) in controlling the maximum fluxes that can be reached by outer belt electrons. We find that low solar wind pressure and long-lasting and strong solar wind electric field (resulting in continuous substorms) are favorable predictors for electrons to reach their maximum flux levels. Our results are important for future forecasting of extreme cases of radiation belt electrons.