Aurora-Associated Ionospheric Disturbances at European Mid-Latitudes During the May 10, 2024, Geomagnetic Storm

The extreme geomagnetic storm on May 10, 2024, caused an unprecedented expansion of auroral activity toward the equator over Europe. This provided a unique opportunity to study ionospheric disturbances associated with auroras at mid-latitudes. In this study, we analyze the ionosphere's response based on observations from a dense network of Global Navigation Satellite System (GNSS) receivers and simultaneous measurements made with an all-sky imaging camera. We analyzed total electron content (TEC), TEC gradients and anomalies, and the rate of TEC index (ROTI), comparing them with the spatial and temporal evolution of auroral emissions.

Our results indicate that increased TEC amplitudes, strong TEC gradients, and elevated ROTI values are closely associated with auroral precipitation and stable red auroral arcs. We observed visible TEC disturbances spreading southward, but their propagation was spatially limited and closely corresponded to the expansion of the auroral boundary. These disturbances did not extend to subauroral regions or mid-latitudes outside the auroral zone.

Combined GNSS and optical observations suggest that auroral particle precipitation and related electrodynamic processes predominated during this event. There was limited evidence of large-scale, freely propagating ionospheric disturbances. This study underscores the importance of multi-instrument observations for correctly interpreting ionospheric disturbances during storms and for assessing the impact of space weather on GNSS-based systems in mid-latitudes.