Inferential Evidence for Surprathermal Electron Burst Intensification Due To Inverted-V Precipitation via Inertial Alfvén Waves

Abstract

The auroral current and electrodynamic structures II sounding rocket mission launched two payloads from Andøya Rocket Range into a post-dusk discrete auroral arc and observed field-aligned electron dispersions near inverted-V precipitation. Five repetitive suprathermal electron bursts (STEBs) associated with low frequency (8 Hz) magnetic perturbations are observed on the High Flyer at 400 km altitude. Similar fluctuations on the nearby Low Flyer at 180 km are shown to be Earth-ward traveling Alfvén waves, suggesting the High Flyer also observed Alfvénic activity. The electron bursts occur both coincident and outside inverted-V electrons, with those coincident displaying the highest peak energy and average differential flux values. We interpret the events as wave-particle acceleration via inertial Alfvén waves along near-Earth field lines and employ time-of-flight methods to gauge source altitudes. A Levenberg–Marquardt fitting routine is applied to inverted-V structures near the dispersions to characterize the expected STEB source distributions. We show the differences in STEB behavior are better explained by changes in the resonant source population and not from significant variation in Alfvén wave parameters.