Response of the Ionospheric Vertical Total Electron Content (VTEC) over the African Regions during the geomagnetic storms of February, March and April 2023

The ionosphere is a dynamic environment supporting a host of plasma instability processes and is a dispersive medium that substantially influences space radio communication, satellite tracking, navigation and the operation of global positioning satellite (GPS) systems. Geomagnetic storms are one of the factors that can cause this instability of the ionosphere. The aim of this study is to investigate the ionospheric VTEC response over the equatorial African region during the three recent intense and severe geomagnetic storms of February, March and April 2023. We have used the ground-based GPS measurements of VTEC in the stations: MBAR (geographic coordinates: 0.60^o N, 30.74^o E; geomagnetic coordinates: 10.22^o S, 102.36^o E) and YKRO (geographic coordinates: 6.87^o N, 5.24^o W; geomagnetic coordinates: 2.84 ^o S, 67.41^o E). The February 27 has a Dst minimum value of -132 nT and occurred at 12:00 UT; the March 24 has a Dst minimum of -163 nT at 02:00 UT; and the severe geomagnetic storm of April 24 has a Dst minimum value of -212 nT and occurred at 05:00 UT. The results showed that on both stations, the three geomagnetic storms that caused positive and negative VTEC disturbances were observed during the initial, main and recovery phases. In most hours of the storm days on both stations, the two intense geomagnetic storms of February 27 and March 24, 2023, had positive effects on the ionospheric enhancement, while the severe geomagnetic storm of April 24, 2023, had negative effects on the ionospheric variability. The post day of the storm day has higher values of VTEC during the intense geomagnetic storms of February 27 and March 24, 2023, but this is not the case for the severe geomagnetic storm of April 24, 2023. This enhancement of the electron density observed during the recovery day is most likely due to proton density, plasma temperature and neutral composition changes. Generally, during different phases of the three geomagnetic storms, there are positive and negative responses to the values of the VTEC deviations from their quiet-time states, ranging from -400% to 45%.