Solar-geomagnetic activity effect on NmE over Ouagadougou, an equatorial anomaly station in the African sector

Abstract

The variability of the ionospheric E-region peak electron density (NmE) and its response to solar, solar wind, and geomagnetic forcing are investigated at Ouagadougou (12.4° N, 358.5° E; dip latitude +1.45°), an equatorial station in the African sector. Daytime hourly measurements of the E-layer critical frequency (foE) are analysed in conjunction with selected solar, interplanetary, and geomagnetic indices over the period 1976-1997, spanning solar cycles 21 and 22. The results show a pronounced diurnal variation in NmE and a strong dependence on solar activity. Seasonal variability is weak and not consistently observed across years, as represented by high, moderate, and low solar activity (1991, 1993, and 1996). No clear linear long-term relationship is found between NmE and sunspot number. Geomagnetic activity exerts a measurable influence on NmE, particularly during periods of high and low solar activity. Among the parameters examined, the interplanetary magnetic field magnitude exhibits the strongest association with NmE, while the planetary amplitude index, disturbance storm time, solar wind dynamic pressure, and the southward interplanetary magnetic field component show weaker but detectable effects. Solar wind speed and sunspot number contribute only marginally to NmE variability. These results emphasise the coupled roles of solar and magnetospheric processes in controlling the equatorial E-region ionosphere over the African sector.