Analytical Study of Electromagnetic Wave Propagation Characteristics in the Ionosphere Over Equatorial Nigeria

The equatorial ionosphere over Nigeria is subject to unique plasma physics phenomena including equatorial electrojet enhancement, sporadic E-layer formation, and equatorial plasma bubbles that significantly affect high-frequency radio wave propagation and navigation satellite signal quality. This study analytically characterizes electromagnetic wave propagation parameters in the ionospheric plasma over the equatorial and low-latitude regions of Nigeria using ground-based ionosonde data from the Ilorin ionosonde station supplemented by GPS total electron content measurements from a network of International GNSS Service receivers. Ionospheric electron density profiles were reconstructed by Tikhonov inversion of ionosonde virtual height-frequency traces for a three-year dataset. The critical frequency, peak electron density, half-thickness parameter, and slab thickness were derived from inverted profiles as functions of local time, season, and solar flux. Magneto-ionic ray tracing calculations using MATLAB-based code were performed to characterize HF radio ray path deviation, skip distance, and maximum usable frequency for oblique incidence propagation paths representing typical Nigerian domestic communication links. The study quantifies the seasonal and diurnal patterns of equatorial ionospheric irregularities affecting L-band GPS signal scintillation indices and develops empirical correction coefficients for positioning error estimation. Results confirm pronounced nighttime plasma bubble activity during September equinox months that degrades GPS positioning accuracy by up to 8 meters in the equatorial electrojet belt region encompassing Kogi and Kwara States. Keywords: ionosphere, electromagnetic propagation, equatorial plasma, GPS scintillation, Nigeria