High-latitude observations of ULF wave driven ion upflow

Abstract. We present a comprehensive study of the first observations of ionospheric ion upflow generated by ultra-low frequency (ULF) wave driven auroral arcs (UAAs). Ground- and space-based instrumentation, together with inversion models, allow us to study the event at different length scales. This shows the complex dynamics of UAAs and their role in the ionosphere-magnetosphere coupling via ion upflow, field-aligned currents (FACs), and energy dissipation. The UAA event was observed as a series of six poleward moving arcs, primarily in the 630.0 nm emission line. At the northern extent of the arcs incoherent scatter radar (ISR) data indicated that the UAAs have driven type 2 ion upflow with low to medium fluxes of around 3.3×1013 particles m−2 s−1. Data from the ISR, spacecraft, and models, result in FAC magnitudes up to 6 µA m−2, total energy fluxes up to 12 mW m−2, and Joule heating rates up to 11 mW m−2 associated with the arcs. These values mostly correspond to localized measurements, while at large-scale the values are up to 50 % smaller. In addition, ground-based magnetometers suggested that the UAA event is driven by small-scale ULF waves, while energy dissipation rates and FAC magnitudes are significant and comparable to previously reported large-scale wave events, indicating the importance of using a multi-instrument approach when investigating energy dissipation associated with ULF waves. This event thus shows that even small-scale ULF waves can drive ion upflow in the ionosphere.