Prolonged Intervals of Relativistic Electron Storm-Time Flux Enhancements in the Magnetotail at Lunar Distance

Abstract

We report on prolonged enhancements of electron fluxes at energies at or above 500 keV, observed in the magnetotail by the lunar-orbiting Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) during the recovery phase of a magnetic storm with minimum $D_{st}$ $\approx$ −200 nT during periodic auroral electrojet ($AE$) activations. The enhanced energetic electron fluxes were omnidirectional and observed near the magnetic equator. No solar energetic particle background was detected. Although ARTEMIS detected earthward magnetic flux transport impulses exceeding 2 mV/m, along with associated broadband electrostatic fluctuations, no correlation was evident between these phenomena and the relativistic electron flux enhancements. Spectra obtained during the relativistic electron flux enhancements are fit by the Kappa function, $\kappa$ = 3.75, similar to that of the quiet-time plasma sheet electron population at lunar distance. Multiple reconnection events at large distances are, most likely, responsible for the electron heating.