Near-Earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeVelectron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L approximate to 5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50mV/m) over approximate to 40s and a dispersionless injection of electrons up to approximate to 3MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.