Ionospheric Phase Scintillation during Solar Cycle 24 over West Africa: Analysis from GPS Stations at Koudougou and Ouagadougou (BF01)

Ionospheric scintillation is a phenomenon of rapid and irregular fluctuations in the intensity of radiofrequency signals passing through the ionosphere. It generally arises from interactions between GNSS signals and irregularities in the ionospheric plasma. These interactions can lead to rapid variations in the amplitude and/or phase of the signals passing through the ionosphere, giving rise to what is called amplitude and/or phase scintillation. Phase scintillation was the subject of this study. Based on the RINEX data available at the GPS stations of Koudougou and BF01 of Ouagadougou, we calculated for solar cycle 24 (2008-2018), the daily and monthly hourly values ​​of the rate of total electron content change index (ROTI) which is a good indicator of phase scintillation. The study of the ROTI in these two equatorial stations, shows an ionospheric phase scintillation after sunset from 2000 LT to 2300 LT during periods of quiet geomagnetic activity. At this moment of night, maximum ROTI values ​​of approximately 1 tecu/min are recorded. The phenomenon often continues at a low intensity (approximately 0.5 tecu/min) during the night between 0000LT and 0200LT. The nocturnal scintillation phenomenon is explained by the formation of plasma bubbles caused by the Rayleigh-Taylor instability after sunset. Phase scintillation is strongly influenced by solar activity. The ROTI is indeed higher at solar maximum with a peak value exceeding 1.5 tecu/min. Seasonal effects are also noted in the disturbance of GNSS signals. ROTI values ​​are indeed higher at the equinoxes than at the solstices. During geomagnetic storms, phase scintillation is inhibited when the main phase occurs in the morning. When the main phase occurs after sunset, scintillation occurs in the same evening during the main phase or in the overlap phase. After sunset, the increase in the intensity of the ring current in the main phase causes the formation of ionospheric irregularities responsible for scintillation. It is very important to understand ionospheric irregularities in order to better optimize the reliability of GNSS system.