The Effect of Energetic Ion Dispersionless Injections on the Ring Current Dynamics

Abstract

AbstractEnergetic particle injections, usually observed as sudden flux enhancements of charged particles from tens to hundreds of keV, are one of the main mechanisms for ring current enhancement. In this study, we statistically analyzed the influence of dispersionless injections on Earth's ring current based on the measurements of radiation belt storm probes ion composition experiment onboard Van Allen Probes from 2013 to 2019. We identified 813 dispersionless proton injection events, which are mainly in the pre‐midnight sector. With a greater SuperMAG electrojet index (SME), the observed injections extend to lower L shells. Meanwhile, Helium (He+) and oxygen (O+) ions experience almost simultaneous injections with protons. Superposed epoch results show that ion energy densities enhance significantly after injections. As SMEmax increases, the ring current energy densities of all three species are increasing, and the magnitude of the enhancements, defined as the ratio of the energy densities after and before the injection, hardly changes for protons (∼2.0) and He+ ions (∼2.0) but increases for O+ ions (2.6 and 3.0 for SMEmax < 1,000 nT and SMEmax ≥ 1,000 nT, respectively), suggesting the contribution of O+ ions to ring current becomes more significant during super substorms. With proton injections, the dawn‐dusk electric field is enhanced sharply to twice as large as before. Simultaneously, there is a dip followed by gradual dipolarization of the magnetic fields. Moreover, particle anisotropies increase following ion injections, which may generate electromagnetic ion cyclotron waves. These statistical results indicate that ion injections during substorms contribute significantly to the ring current.