Rapid Acceleration Bursts in the Van Allen Radiation Belt

The fast Van Allen radiation belt electron dynamics during geomagnetic storms have not yet been fully explained, in part due to limitations of standard satellite missions in both orbit and the number of spacecraft. Here we overcome these limitations using measurements from the Global Positioning System (GPS) constellation during an acceleration event on 26 August 2018. We show that the acceleration of relativistic electrons occurs in two distinct bursts, each dominated by a different acceleration mechanism. The first burst enhances the radiation belt electrons by four orders of magnitude in 2 hr and is consistent with ULF-wave radial diffusion. The second burst is likely caused by the local acceleration and delivers an order-of-magnitude increase in 20 min. This work demonstrates how distributed, operational measurements can be used to resolve phenomena not observable with previous capabilities, and that rapid energization of the radiation belt can occur much faster than previously reported. In this paper, we present a detailed analysis of terrestrially-trapped electron space radiation during the August 2018 geomagnetic storm. This event is characterized by a very fast enhancement in the trapped electron population that increases particle counts by more than a factor of a thousand over only 6 hr. Such fast dynamics cannot be resolved by typical survey missions due to their long orbital periods. We instead use measurements from 20 satellites in the Global Positioning System (GPS) constellation, which allows us to perform an analysis of the space radiation dynamics on much shorter timescales. These GPS data reveal that the fast enhancement during the August 2018 storm occurred in two distinct bursts. By introducing a novel technique for GPS particle data analysis, we also determine that each of the bursts is governed by different physical processes that act on different timescales. The revealed fast dynamics of near-Earth trapped radiation point toward a need to reevaluate the classic paradigm that the changes in the radiation levels are slow and can be revealed by surveys with a low number of spacecraft. Indeed, we foresee a critical role for constellation measurements, such as from GPS, in the future of radiation belt science. Constellation measurements of the Van Allen radiation belt electrons can be used to reveal fast nonadiabatic changes at sub-orbit timescales Electron acceleration during the August 2018 storm consists of two distinct acceleration bursts governed by different physical processes ULF-wave radial diffusion and local acceleration can significantly alter radiation belt electron content on timescales of minutes to hours