The 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.
Bibliographical noteFunding Information:
This work was supported by the Canadian Space Agency under grant CARISMA-MIC. D. M. Miles was sup ported by an NSERC PGSD graduate scholarship, funding from the Canadian Space Agency, and faculty startup funding from the University of Iowa. I. R. Mann is supported by a Discovery Grant from NSERC. I. P. Pakhotin was supported by the ESA STSE Swarm + Innovation grant 4000114090/15/NL/MP. A.W. Yau is supported by a Discovery Grant and a Discovery Accelerator Award from NSERC. This study makes use of data from the e-POP spacecraft mission, which is funded by the Canadian Space Agency. e-POP data can be accessed online at http://epop.phys.ucalgary.ca/ data.html. J. K. Burchill was supported by a grant from the Canadian Space Agency. This study makes use of data from the Swarm spacecraft mission, which is funded and managed by the European Space Agency. Swarm data can be accessed online at http://earth. esa.int/swarm. The auroral imaging movie provided as supporting informa tion MS1 was produced using the FAITools library version 2.2 available at http://epop.phys.ucalgary.ca/data.html. The International Reference Ionosphere model was instantiated using the online tool available at http://wdc.kugi.kyoto-u.ac.jp/ionocond/sigcal/index.html.
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- Alfvén wave
- field-aligned current
- ionospheric Alfvén resonator