Auroral Signatures of Solar Cycle 25 at Mid-Latitudes: A Comparative Analysis of the November 2023, May 2024, and October 2024 Geomagnetic Storms

Solar Cycle 25 has exceeded initial intensity predictions, characterized by a series of severe geomagnetic disturbances that have expanded the auroral oval well into mid-latitudes. This study presents a comparative analysis of the magnetospheric and ionospheric responses to three distinct events observed over the European sector, including regions such as Türkiye: the geomagnetic storms of November 2023, May 2024, and October 2024. By integrating Global Navigation Satellite System (GNSS)–derived Total Electron Content (TEC) data with ground-based magnetometer observations, the spatiotemporal evolution of these disturbances is characterized. All three events were driven by Coronal Mass Ejections (CMEs), yet their impacts on the mid-latitude ionosphere differed substantially. The May 2024 extreme storm was marked by prolonged negative ionospheric phases and severe TEC depletions over Europe, including Türkiye, primarily linked to compositional changes and disturbance dynamo electric fields (DDEFs). In contrast, the November 2023 storm exhibited coherent magnetic field depressions and rapid recovery phases, indicating a dominant role of prompt penetration electric fields (PPEFs). This comparative framework is extended to the October 2024 storm. Moreover, analysis of the vertical (Z) and horizontal (H) geomagnetic field components recorded at European observatories provides insight into the penetration of high-latitude current systems into lower latitudes during intense space weather events. The results demonstrate that mid-latitude regions experience complex electrodynamic coupling during the solar cycle maximum, governed by multiple mechanisms ranging from prompt electric field penetration to thermospheric heating across the Eastern Mediterranean sector.