In Situ Evidence of Ionospheric Feedback Instability Adjacent to a Quiescent Auroral Arc

Abstract

The ACES-II Low sounding rocket, which launched from Andøya Space Center in Andenes, Norway, on 20 November 2022, made low altitude observations consistent with characteristics of the Ionosphere Feedback Instability (IFI) as it traversed a quiet, discrete auroral arc. Small scale Alfvénic signatures are observed in regions of depleted ionospheric plasma density, large perpendicular ionospheric electric fields, and matched Pedersen and Alfvén conductivities—all observational preconditions required for the formation of the IFI. These signatures are consistent with those of standing Alfvén wave modes in the ionospheric resonant cavity driven by the IFI. The observed Alfvénic structures are correlated with small scale perturbations in the background plasma density. The observed features are similar to the predictions of recent numerical simulations of resonant Alfvén waves generated by the IFI. These observations suggest that the IFI mechanism plays a role in the formation and structuring of this discrete auroral arc.