A COMPARATIVE STUDY OF TEC AT LOW AND MIDDLE LATITUDES OF AFRICA DURING DIFFERENT SOLAR ACTIVITY PHASES

English Abstract:

The total electron content (TEC) variability for three levels of solar activities; high solar active period (HSP; year 2000), moderate solar active period (MSP; year 2004) and low solar active period (LSP; year 2008) over middle and low latitudes of Africa were investigated. We have studied the day-to-day, monthly mean, seasonal relative standard deviation (SVR) and yearly mean changes. As expected, for the middle (Sutherland) and low (Libreville) latitudes, TEC variability was observed to be highest during HSP and higher in MSP compared to LSP. Comparing TEC variability between Sutherland and Libreville in each phase, the TEC magnitudes in each phase of the solar levels is always higher in Libreville compared to Sutherland during daytime hours. The range in magnitude of TEC during HSP at Libreville is ~ 50TECU-130 TECU and at Sutherland, it ranges between ~ 20 TECU and ~ 80 TECU. For MSP, the range was between ~ 35 TECU and ~ 80 TECU and between ~ 10 TECU and ~ 40 TECU at Libreville and Sutherland, respectively. In year 2008, the TEC magnitudes variability observed at Libreville is higher (~38 - ~59 TECU) compared to that of Sutherland (~20 - ~1TECU). Although, it is expected that SVR generally decreases when solar activity increases especially at nighttime. Interestingly, our results show that at different phases of solar activities on all seasons and hours, the SVR magnitudes at Sutherland were ~ halved of magnitudes observed at Libreville. Apart from photo-ionization that influences their magnitudes at different levels, their location played significant role regarding additional magnitudes of TEC. We therefore suggest stronger equatorial low latitude anomaly associated with the photo-ionization as the primary mechanism that initiated these higher magnitudes of TEC at Libreville. This is possible, since Libreville is situated along the highly variable equatorial anomaly crests of Africa and Sutherland is found where the anomaly is absent. The yearly mean changes on HSP, MSP and LSP at Libreville and Sutherland are also investigated and possible mechanisms responsible for their variability were discussed.