FAST satellite observations of electric field structures in the auroral zone

TLDR

The study compares inferred parallel potentials of electrostatic shocks with particle energies to demonstrate particle acceleration by parallel electric fields. FAST satellite observations reveal particle acceleration by quasi‑static parallel electric fields in both upward and downward auroral currents, accompanied by nonlinear structures such as large‑amplitude ion cyclotron waves and intense spiky fields that correlate with electron flux modulations, indicating that parallel electric fields are a fundamental acceleration mechanism in astrophysical plasmas.

Abstract

Electric field and energetic particle observations by the Fast Auroral Snapshot (FAST) satellite provide convincing evidence of particle acceleration by quasi‐static, magnetic‐field‐aligned (parallel) electric fields in both the upward and downward current regions of the auroral zone. We demonstrate this by comparing the inferred parallel potentials of electrostatic shocks with particle energies. We also report nonlinear electric field structures which may play a role in supporting parallel electric fields. These structures include large‐amplitude ion cyclotron waves in the upward current region, and intense, spiky electric fields in the downward current region. The observed structures had substantial parallel components and correlative electron flux modulations. Observations of parallel electric fields in two distinct plasmas suggest that parallel electric fields may be a fundamental particle acceleration mechanism in astrophysical plasmas.