May 2024 Gannon Superstorm: Insights from Ground-based Magnetometer Measurements

On May 10–11, 2024, one of the strongest geomagnetic storms in recent years swept across the planet. Several interplanetary coronal mass ejections (ICMEs) originated from the source active region (AR 13664), propelling solar energetic particles toward Earth. Triggered by intense solar eruptions, the storm reached a Kp index of 9 (the highest on the scale), causing a remarkable expansion of auroras visible far beyond their usual high latitudes. The unprecedented strength of the storm highlights the necessity of monitoring geomagnetic disturbances using ground-based instruments to assess the far-reaching impacts of space weather events, especially in regions well beyond the typical auroral zones. In this study, geomagnetic data from several observatories located in mid-latitudes (30°-60°N) in the Northern Hemisphere were therefore utilized to analyze the G5-level super-intense Gannon storm. These observations enable the detection of geomagnetic variations, including sudden storm commencements (SSCs), prolonged negative excursions in the Disturbance Storm-Time (Dst) index, as well as localized magnetic fluctuations indicative of intensified ionospheric currents. Additionally, the auroral electrojet strength and the asymmetric distribution of geomagnetic disturbances provide critical insights into the spatial and temporal evolution of ionospheric and magnetospheric processes during the extreme geomagnetic storm, helping to understand its impacts on mid-latitude regions. The results highlight the spatial variability and temporal synchronicity of the impacts of the storm, demonstrating the crucial role of mid-latitude observatories in capturing ionospheric and magnetospheric responses during extreme geomagnetic events.