Electron Energy Dispersion as seen by the ePOP Suprathermal Electron Imager

English Abstract:

A candidate mechanism for accelerating auroral electrons is acceleration by Alfven waves. These waves can accelerate electrons to velocities of the order of the Alfven speed. Wave acceleration has been linked to energy dispersion, a distinct signature that can be seen in particle detectors. This signature is a burst of electrons where the higher energy ones appear first, followed by decreasing energies. Using data from the Suprathermal Electron Imager (SEI) onboard the enhanced Polar Outflow Probe (ePOP), we document instances of low energy electron dispersion. These events are supported by VLF electric field data, also from ePOP. We also report inverse electron dispersion events, where energy increases with time. This phenomenon has not been recorded in the literature. These observations are not consistent with transient Alfven wave acceleration alone. We explore an alternative explanation involving a slowly drifting source, and present results of a simple simulation of this.