The role of localized inductive electric fields in electron injections around dipolarizing flux bundles

Abstract

AbstractWe study energetic electron injections by using an analytical model that self‐consistently describes electric and magnetic field perturbations of a transient, localized dipolarizing flux bundle (DFB). This simple model reproduces most injection signatures at multiple locations simultaneously, reaffirming earlier findings that an earthward‐traveling DFB can both transport and accelerate electrons to suprathermal energies, and can thus be considered an important driver of short‐lived (~ < 10 min) injections. We find that energetic electron drift paths are greatly influenced by the sharp magnetic field gradients around a localized DFB. Because a DFB is so localized (only a few RE wide across the tail), there are strong duskward magnetic field gradients on the DFB's dawn flank and strong dawnward magnetic field gradients on its dusk flank. Electrons on the DFB's dawnside therefore ∇B drift farther earthward from the reconnection site, whereas electrons on its duskside can potentially evacuate the inner magnetosphere by ∇B drifting tailward. This results in flux decrease at the front's duskside. As a result, the source of electrons observed during injection depends sensitively on the spacecraft location relative to the DFB and on the DFB's properties. We similarly find that the process of electron energization depends on how the electrons interact with the DFB. The initial injection signature is from electrons that interact with the front and gain the majority of their energy from the increasing magnetic field (∂B/∂t), whereas populations that arrive later gain most of their energy from ∇B drifting across the flow channel and against the DFB's electric fields.