Equatorial Electron Acceleration and Transport Towards the Inner Magnetosphere Modeled with Superposed Transient Electric and Magnetic Fields

Abstract:

Particle injections in the magnetotail are signatures of particle energization and transport towards the inner magnetosphere and radiation belts. Recent statistical studies of observations of trans-geosynchronous injections by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission indicate that injections are correlated with fast flows, dipolarization fronts, and impulsive dawn-dusk electric field increases. This correlation extends down the magnetotail as far as 30 R_E, and the associated magnetic and electric fields are azimuthally localized. We therefore model particle transport analytically using the guiding-center equations of motion for electrons under the effects of localized, earthward traveling electric and magnetic fields superposed on background fields. During an injection, THEMIS spacecraft observe increases in particle energy flux. We simulate injections by altering parameters of the electric and magnetic field model to transport particles in agreement with observations, constraining the location, velocity, width, and magnitude of the fields. We explain features of the simulated energy flux spectrograms, and therefore features of the observed spectrograms, by examining particle trajectories prior to and during the injection. Modeling particle injections illuminates how features of fast flows and dipolarization fronts affect the trajectories of energetic particles. Thus, we provide insight into how particle acceleration due to phenomena associated with reconnection in the magnetotail affect the particle populations of the inner magnetosphere, including the populations of the radiation belts.