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Description
This study provides a comprehensive investigation into the ionospheric response over the African sector during the extreme (G5 scale) geomagnetic superstorm of 10 May 2024. The storm was characterized by a dramatic depression in the SymH index to nearly
$-518\,nT$, highlighting its extraordinary intensity. To examine the ionosphere's behavior under such extreme conditions, we utilized observations from six GNSS (Global Navigation Satellite System) receivers distributed across different African regions, covering the period 08 - 12 May 2024 to capture the pre-storm, main storm, and recovery phases. In addition to ground-based GNSS derived Total Electron Content (TEC) data, satellite measurements from missions such as Swarm and GUVI, were incorporated to provide a multi-instrument perspective. Results reveal that during the main and early recovery phases of the storm, the African ionosphere experienced a substantial depletion of TEC, with values dropping by nearly 50 - 85\% relative to quiet-time baselines. This dramatic reduction was accompanied by the suppression of the Equatorial Ionization Anomaly (EIA) and large-scale perturbations in plasma drifts. As the storm progressed into the late recovery phase, a notable rebound of TEC was observed, with values not only returning to pre-storm levels but exceeding them. This over-recovery coincided with elevated thermospheric $[O]/[N_2]$ ratios and compositional changes, which favored increased ionization rates and plasma production. Supporting evidence from Swarm-B satellite observations further revealed an unusual post-storm depletion in electron density. These findings demonstrate that the ionospheric and thermospheric system over Africa underwent highly dynamic, multi-phase adjustments under the influence of this unprecedented geomagnetic storm. The results underscore the intricate coupling between ionospheric electrodynamics, neutral atmospheric composition and geomagnetic forcing. Thus, the study emphasizes the necessity of continuous and robust space weather monitoring in the African sector, given its vulnerability and the growing societal reliance on GNSS-based navigation and communication services.
