Alfvénic Dynamics and Fine Structuring of Discrete Auroral Arcs: Swarm and e‐POP Observations

Abstract

AbstractThe electrodynamics associated with dual discrete arc aurora with antiparallel flow along the arcs were observed nearly simultaneously by the enhanced Polar Outflow Probe (e‐POP) and the Swarm A and C spacecraft. Auroral imaging from e‐POP reveals 1–10 km structuring of the arcs, which move and evolve on second timescales and confound the traditional single‐spacecraft field‐aligned current algorithms. High‐cadence magnetic data from e‐POP show 1–10 Hz, inferred Alfvénic, perturbations coincident with and at the same scale size as the observed dynamic auroral fine structures. High‐cadence electric and magnetic field data from Swarm A reveal nonstationary electrodynamics involving reflected and interfering Alfvén waves and modulation consistent with trapping in the ionospheric Alfvén resonator (IAR). These observations suggest a role for Alfvén waves, perhaps also the IAR, in discrete arc dynamics on 0.2–10 s timescales and ~1–10 km spatial scales and reinforce the importance of considering Alfvén waves in magnetosphere‐ionosphere coupling.