Influence of solar, solar wind, and geomagnetic activity on the ionospheric propagation factor M(3000)F2 over Ouagadougou in the African equatorial sector

Abstract. This study examines how solar, solar wind, and geomagnetic activity influence the ionospheric propagation factor M(3000)F2 over Ouagadougou (12.4° N, 358.5° E; dip latitude +1.45°), an equatorial station in the African sector. Hourly ionosonde observations from 1976 to 1997, spanning Solar Cycles 21 and 22, were analysed to investigate diurnal, seasonal, solar cycle, and storm-time variability of M(3000)F2. Representative years of high (1991), moderate (1993), and low (1995) solar activity were selected for climatological analyses, while seven geomagnetic storm events were examined to assess storm-time responses. Relationships between annual mean M(3000)F2 and selected solar, solar wind, and geomagnetic parameters were evaluated using correlation and linear regression analyses. M(3000)F2 exhibits pronounced diurnal and seasonal variability, characterised by higher nighttime and early-morning values, lower daytime values, and distinct equinoctial and solstitial differences associated with equatorial electrodynamics and thermospheric dynamics. An inverse dependence on solar activity is observed, with the highest M(3000)F2 values occurring during solar minimum. The strongest correlation is with the solar radio flux F10.7 (R = -0.810, R² = 0.657, p < 0.001), followed by the interplanetary magnetic field magnitude (B) (R = -0.689, R² = 0.475, p < 0.001) and the disturbance storm time (Dst) index (R = 0.527, R² = 0.277, p = 0.0117). Relationships with the planetary (Ap) index, the southward component of the interplanetary magnetic field (Bz), solar wind dynamic pressure (Psw), and solar-wind speed (Vsw) are weak and not statistically significant. During geomagnetic storms, M(3000)F2 generally decreases during the daytime main phase and recovers within one to two days, depending on storm intensity and background ionospheric conditions. The results indicate that long-term variability of M(3000)F2 over the African equatorial sector is primarily controlled by solar activity, with geomagnetic disturbances providing secondary modulation during storm periods. These findings contribute to a better understanding of equatorial ionospheric variability and provide useful information for HF radio wave propagation, empirical ionospheric modelling, and space weather applications.