Sawtooth and dune auroras simultaneously driven by waves around the plasmapause

The dune aurora, at a scale of ~30 kilometers, was reported recently using ground camera. The small-scale dune aurora occurs on the duskside and exhibits a monochromatic oscillation in the auroral emission, implying fundamental energy conversions. However, whether the dune auroras correspond to atmospheric waves or are associated with magnetospheric dynamics should be determined. This paper reports a dune aurora that occurred during a storm; further, we demonstrate that it was the substructure of the sawtooth aurora that was generated by plasmapause surface waves. Conjugate observations in the magnetospheric source region suggest that the exohiss waves, which are periodically modulated by the plasmapause surface wave-excited ultralow frequency wave, might be responsible for the generation of the dune aurora. Most reported dune aurora events have occurred simultaneously with sawtooth auroras, suggesting that both are plasmapause-driven cross-scale auroral structures.