Astrophys Space Sci ( 2020) 365:116 https://doi.org/10.1007/s10509-020-03833-2 ORIGINAL ARTICLE Ionospheric electron density characteristics over Africa from FORMOSAT-3/COSMIC radio occultation Mefe Moses 1 · Sampad Kumar Panda 2 · Sunil Kumar Sharma 3 · Joseph D. Dodo 4 · Lazarus M. Ojigi 1 · Kola Lawal 1 Received: 27 May 2020 / Accepted: 5 July 2020 © Springer Nature B.V. 2020 Abstract With the widespread availability of ground and space-based global navigation satellite system (GNSS) ob- servables, continuous and long-term explorations of iono- spheric variations have been made possible worldwide or on regional basis with improved accuracy. The Formosa Satel- lite Mission#3/Constellation Observing System for Meteo- rology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) mission has a huge database of radio occultation (RO) soundings at regional and global scales with a high vertical resolution. Comparative studies between radio occultation, incoherent scatter radar and ionosonde observations indi- cate that COSMIC profiles agree well with ground measure- ments. The present paper investigates the ionospheric pro- files over Africa using COSMIC data for the period from 2006 to 2017, representing almost a solar cycle year of study. The spatiotemporal variation of electron density con- firms a hemispheric asymmetry among the equinoctial sea- sons and the solstice seasons during both low and moder- ate solar activity. Seasonal/winter anomaly manifestation is also clearly noticed in our observations with relatively high electron density during the winter solstice than the sum- mer solstice. Moreover, the electron density over the re- gion show apparent spatial and temporal variations identical to earlier ground-based ionospheric monitoring results over B S.K. Sharma s.sharma@mu.edu.sa 1 Department of Geomatics, Ahmadu Bello University, Zaria, Nigeria 2 Department of ECE, Koneru Lakshmaiah Education Foundation, Guntur, Andhra Pradesh, India 3 College of Computer and Information Sciences, Majmaah University, Majmaah, Saudi Arabia 4 Centre for Geodesy and Geodynamics, NASRDA, Toro, Bauchi State, Nigeria the African region. The outcomes from this study would strengthen the understanding of the ionospheric alterations and modelling activities in Africa, especially the areas with inadequate ground-based measuring instruments, hence, our results may complement the progress in global ionospheric modelling. Keywords Africa · Electron density · FORMOSAT-3/COSMIC · GNSS · Ionosphere · Radio occultation 1 Introduction The primary concept of global navigation satellite system (GNSS) based radio occultation (RO) involves observa- tion of GNSS satellites radio signals by receivers onboard Low-Earth Orbit (LEO) satellites. Generally, radio occul- tation technique relies on radio waves bending owing to the refractive behaviour of a planetary atmosphere (Fyt- terer et al. 2014; Jensen et al. 2003; Pelliccia et al. 2010; Potula et al. 2011; Zhang et al. 2011). A LEO satellite with an onboard GNSS receiver captures the signals transmitted by a setting or ascending GNSS satellite behind the Earth- limb, thereby, proving vertical profiling of the atmosphere along these lines by exploiting the relative motion of GNSS and the LEO satellites. GNSS RO has the potential for observing the highly dy- namic ionosphere (Lackner et al. 2011; Scherllin-Pirscher et al. 2011) owing to its exclusive advantages of being all- weather operational, high spatiotemporal resolution, global coverage and long-term stability of its measurements. Ad- ditionally, the measurements are reasonably accurate and don’t require instrument calibration or drift corrections (Fyt- terer et al. 2014; Gobiet and Kirchengast 2004; Steiner