Abstract

The ionospheric disturbance dynamo (Ddyn) generates storm-time electric fields during the recovery phase of geomagnetic storms through thermosphere-ionosphere coupling, producing disturbances in the horizontal magnetic field (ΔH). Although Ddyn has been extensively investigated in the American and Asian sectors, observational evidence over Africa remains limited. This study investigated the timing, latitudinal evolution, and relationship of Ddyn signatures in ΔH with the interplanetary magnetic field (IMF Bz), solar wind speed (Vx), Dst index, and AE index during the 12–14 October 2016 and 23–25 April 2023 geomagnetic storms. Hourly ΔH data from five African magnetometer stations (TSU, TAM, HBK, KMH, and HER) together with OMNI solar wind parameters and Kyoto Dst and AE indices were analysed. Both storms showed pronounced ΔH disturbances during the recovery phase following the Dst minimum, confirming the occurrence of disturbance dynamo effects. The stronger 2023 storm produced larger ΔH amplitudes than the 2016 event, demonstrating that Ddyn intensity increases with storm strength. The onset of Ddyn occurred earlier at higher latitudes and later toward lower latitudes, indicating an equatorward propagation of storm-induced disturbance effects. These observations provide new evidence of the latitudinal evolution of disturbance dynamo over Africa and demonstrate that African magnetometer observations can improve regional monitoring of geomagnetic storms. The findings contribute to better understanding of ionosphere-thermosphere coupling and provide useful information for improving space weather forecasting and ionospheric modelling across the African sector.

Key words: Disturbance dynamo, ∆H, African sector, IMF Bz, Dst, Geomagnetic storm, Recovery phase