Earth and Planetary Science

Storm‑Time Variability of GNSS‑Derived Ionospheric VTEC over East Africa during Four Major Geomagnetic Storms of Solar Cycle 24

Wilberforce Muniafu

Department of Physics, Masinde Muliro University of Science & Technology, Kakamega 50100, Kenya

Edward Uluma

Department of Physics, Masinde Muliro University of Science & Technology, Kakamega 50100, Kenya
Department of Science Technology and Engineering, Kibabii University, Bungoma 50200, Kenya

Solomon Otoo Lomotey

Department of Physical and Mathematical Sciences, University of Environment and Sustainable Development, PMB, Somanya, Ghana

Atirsaw Muluye Tilahun

Department of Physics, College of Natural and Computational Science, Wachemo University, Hosaena 667, Ethiopia

Moses Mefe

Department of Geomatics, Ahmadu Bello University, Zaria 810221, Nigeria

Joseph Kagotho Muriithi

Department of Space Science and Astronomy, Kenya Space Agency, Nairobi 00100, Kenya
Department of Physics, University of Nairobi, Nairobi 00200, Kenya

George Omondi

Department of Physics and Materials Science, Maseno University, Maseno 40105, Kenya

Boniface Ndinya

Department of Physics, Masinde Muliro University of Science & Technology, Kakamega 50100, Kenya

DOI: https://doi.org/10.36956/eps.v5i1.3205

Received: 17 January 2026 | Revised: 23 March 2026 | Accepted: 25 March 2026 | Published Online: 10 April 2026

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Abstract

This study investigates the ionospheric response to four major geomagnetic storms during solar cycle 24 (18–19 February, 2014, Dst minimum −119 nT; 17–18 March, 2015, Dst minimum −223 nT; 22–23 June, 2015, Dst minimum −204 nT; and 8 September, 2017, Dst minimum −142 nT) using Vertical Total Electron Content (VTEC) data derived from Global Navigation Satellite System (GNSS) observations over the East African region. Our results revealed substantial storm-time VTEC variability characterized by both positive and negative ionospheric phases. The main phases of the storms had significant VTEC enhancements, especially near the Equatorial Ionization Anomaly (EIA) crest. This was attributed to the intensified equatorial fountain process which was primarily driven by Prompt Penetration Electric Fields (PPEF). In contrast, reductions in VTEC were observed during quiet periods. This was attributed to the effect of Disturbance Dynamo Electric Fields (DDEF), compositional changes in the upper atmosphere and storm-induced thermospheric winds. Clear spatial differences in VTEC responses across the GNSS stations were noted, indicating a strong influence of the equatorial electrodynamics on ionospheric variability. The results underscore the critical role of GNSS observations in monitoring space weather impacts and enhancing the understanding of storm-time ionospheric dynamics over the equatorial East African region, which has historically remained underexplored.

Keywords: Geomagnetic Storm; Total Electron Content; Equatorial Ionization Anomaly; Disturbance Dynamo Electric Field; Equatorial Ionosphere

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