The Signature of the Deep Solar Cycle 25 on the Equatorial Ionospheric F2 Layer Parameters

Authors

Keywords:

Equatorial Ionosphere, F2-Layer, Deep Solar Minimum, Equatorial Ionisation Anomaly (EIA)

Abstract

This study examines the morphology and variability of the ionospheric F2-layer over two equatorial stations: Ilorin, Nigeria (8.50°N, 4.67°E, -2.96 dip) in the African sector, and Jicamarca, Peru (11.95°S, 76.87°W, 0.74 dip) in the Southern American sector, during the deep solar minimum of 2020 during the unset of the  Solar Cycle 25. Hourly measurements of the critical frequency (foF2), peak height of ionisation (hmF2), and parameters B0 and B1 were extracted from ground-based Digisonde ionosondes and processed to generate diurnal and seasonal averages. Seasonal groupings included the March and September Equinox, June and December Solstice. Variability was quantified using the standard deviation and coefficient of variation, while Pearson correlation analysis assessed internal (foF2-hmF2) and longitudinal (Ilorin-Jicamarca) coupling, with significance tested at 95% confidence. Results indicate that foF2 exhibits pronounced daytime peaks, with maxima of 7.94 MHz at Ilorin and 9.49 MHz at Jicamarca, while hmF2 rises more sharply at Ilorin (399 km) than Jicamarca (324 km), reflecting stronger vertical plasma drifts in the African sector. Seasonal modulation is greater in foF2 (CV 19.97-31.38%) and B0 (up to 61.84%) than in hmF2 (CV < 14%). Longitudinal coupling is stronger during the March Equinox (r  > 0.73), whereas solstices exhibit inverse correlations in hmF2, highlighting hemispheric phase reversals driven by thermospheric winds. Overall, Ilorin consistently shows higher in the observed value of the heights and thicker B0 and B1 parameters than Jicamarca. These findings provide a comprehensive characterisation of equatorial F2-layer dynamics under minimal solar epoch and offer critical observational constraints for refining empirical ionospheric models.

Dimensions

REFERENCES

Adebesin, B. O., Adeniyi, J. O., Adimula, I. A. and Reinisch, B. W. (2014). Ionospheric foF2 morphology and response of F2-layer height over Jicamarca during different solar epochs and comparison with the IRI-2012 model. Journal of Atmospheric and Solar-Terrestrial Physics, 119: 168–181.

Oyekola, O. S. (2011). Comparisons of foF2 with IRI model and equatorial vertical drifts. Advances in Space Research, 48(8): 1318–1326.

Bolaji, O. S., Adeniyi, J. O., Radicella, S. M. and Doherty, P. H. (2012). Variability of total electron content over an equatorial West African station during low solar activity. Radio Science, 47(1): RS1001.

Ameen, M. A., Khursheed, H., Jabbar, M. A., Ali, M. S., Murtaza, G., Atiq, M., Bouya, Z. and Yu, X. (2021). Variation of bottom-side profile parameters (B0, B1) over Multan and their comparisons with IRI-2016 during deep solar minimum of solar cycles 23/24. Advances in Space Research, 68(5): 2059–2073.

Ayokunnu, O. D., Adeniyi, J. O., Dare, O. D. and Adekunle, A. I. (2021). The Quiet Equatorial Ionospheric F2 Layer at Fixed Height During a Low Solar Activity. American Journal of Geophysics, Geochemistry and Geosystems, 7(2): 58–67.

Ayokunnu, O. D., Adeniyi, J. O., Ogunsola, O. E. and Dare, O. D. (2020). Morphology of the Quiet Equatorial Ionospheric F2 Layer During a Low Solar Activity. American Journal of Geophysics, Geochemistry and Geosystems, 6(4): 132-137.

Ayokunnu, O. D., Ogunsola, O. E., Adeniyi, J. O. and Animasaun, I. A. (2023). The latitudinal effect on true height of the electron density profile in the bottom side of the F2 layer of an equatorial region. EGUsphere [Preprint].

Balan, N. and Bailey, G. J. (1995). Equatorial plasma fountain and its effects: Possibility of an additional layer. Journal of Geophysical Research: Space Physics, 100(A11): 21421–21432.

Basu, S., Basu, S., Groves, K. M., MacKenzie, E. and Costa, E. (2010). Dynamics of equatorial F-region irregularities as observed by diverse techniques during a solar minimum. Journal of Atmospheric and Solar-Terrestrial Physics, 72(16): 1199–1207.

Bilitza, D. (2001). International Reference Ionosphere 2000. Radio Science, 36(2): 261–275.

Bilitza, D., Altadill, D., Zhang, Y., Mertens, C., Truhlik, V., Richards, P., Coïsson, P. and Reinisch, B. W. (2014). The International Reference Ionosphere 2012 – A model of international standard. Advances in Space Research, 54(4): 415–432.

Bilitza, D., Pezzopane, M., Truhlik, V., Altadill, D., Reinisch, B. W. and Pignalberi, A. (2022). The International Reference Ionosphere model: A review and description of an ionospheric benchmark. Reviews of Geophysics, 60(4): e2022RG000792.

Bilitza, D. and Reinisch, B. W. (2013). International Reference Ionosphere 2012: A model of international collaboration. Advances in Space Research, 51(4): 570–581.

Daniel, A., Adimula, I. A. and Agboola, O. S. (2016). Response of equatorial ionosphere over Ilorin to space weather conditions during Solar Cycle 24. Nigerian Journal of Space Research, 10: 45–58.

Davies, K. (1990). Ionospheric Radio. Peter Peregrinus Ltd., London.

Derghazarian, S., Hysell, D. L. and Varney, R. H. (2021). Topside measurements at Jicamarca during the 2019–2020 deep solar minimum. Journal of Geophysical Research: Space Physics, 126(8): e2021JA029695.

Ehinlafa, O. O., Adimula, I. A., Oladipo, O. A. and Adeniyi, J. O. (2024). Ionospheric foF2 morphology and F2-region height variations over Ilorin during the recent solar minimum. Nigerian Journal of Physics, 33: 89–102.

Fejer, B. G., de Paula, E. R., González, S. A. and Woodman, R. F. (1991). Average vertical and zonal F-region plasma drifts over Jicamarca. Journal of Geophysical Research: Space Physics, 96(A8): 13901–13906.

Heelis, R. A., Stoneback, R. A., Earle, G. D., Haaser, R. A., Abdu, M. A., McCready, M. A. and Woodman, R. F. (2009). Behavior of the equatorial ionosphere during the 2008–2009 deep solar minimum. Journal of Geophysical Research: Space Physics, 114(A10): A10305.

Huang, X. and Reinisch, B. W. (1996). Vertical electron density profiles from the Digisonde network. Advances in Space Research, 18(6): 121–129.

Kintner, P. M., Ledvina, B. M. and de Paula, E. R. (2007). GPS and ionospheric scintillations. Space Weather, 5(9): S09003.

Lee, C. C. and Reinisch, B. W. (2006). Quiet-time variations of hmF2 at the magnetic equator: Observations and modeling. Journal of Atmospheric and Solar-Terrestrial Physics, 68(13): 1497–1505.

Liu, L., Wan, W., Chen, Y. and Le, H. (2011). Solar activity effects on the ionosphere during the ultra-long solar minimum between cycles 23 and 24. Journal of Geophysical Research: Space Physics, 116(A7): A07311.

Reinisch, B. W., Galkin, I. A., Khmyrov, G. M., Kozlov, A. V., Bibl, K., Lisysyan, I. A., Cheney, G. P., Huang, X., Kitrosser, D. F., Paznukhov, V. V., Luo, Y., Jones, W. and Stelmash, S. (2009). New Digisonde for research and monitoring applications. Radio Science, 44(1): RS0A24.

Rishbeth, H. and Mendillo, M. (2001). Patterns of F2-layer variability. Journal of Atmospheric and Solar-Terrestrial Physics, 63(16): 1661–1680.

Published

2026-09-16

How to Cite

Olomah, C., Ogunsola, O. E., Ayokunnu, O. D., & Ikubanni, S. O. (2026). The Signature of the Deep Solar Cycle 25 on the Equatorial Ionospheric F2 Layer Parameters. Nigerian Journal of Physics, 35(S), 303-309. https://doi.org/10.62292/njp.v35(s).2026.700

Issue

Vol. 35 No. S (2026): Nigerian Journal of Physics - Vol. 35(S)

Section

Articles
Copyright & Licensing

Copyright (c) 2026 Chibuzor Olomah, Oluseyi Enitan Ogunsola, Olalekan David Ayokunnu, Stephen Oluwole Ikubanni

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

How to Cite

Olomah, C., Ogunsola, O. E., Ayokunnu, O. D., & Ikubanni, S. O. (2026). The Signature of the Deep Solar Cycle 25 on the Equatorial Ionospheric F2 Layer Parameters. Nigerian Journal of Physics, 35(S), 303-309. https://doi.org/10.62292/njp.v35(s).2026.700