1. ANALYSES OF TOTAL ELECTRON CONTENT VARIATIONS OVER NORTHERN AND SOUTHERN NIGERIA
Ogwala, A1,*., E.O. Somoye1, O.J. Oyedokun2, R.A. Adeniji-Adele1, E.O. Onori1, O.O. Ometan1, A.S. Ogungbe1, C.O. Ogabi1, O.A. Adejo1, K.S. Oluyo1, A.T. Sode1.
*,1 Department of Physics, Lagos State University, Ojo, Lagos.
2 Department of Physics, University of Lagos, Akoka, Lagos.
PRESENTER: Ogwala, A.
LASU Ionospheric and Radio Propagation Research Group (LIRPRG); Department of Physics, LASU.

2. INTRODUCTION
The ionosphere is a very important part of the earth’s atmosphere (above 60km altitude) most of which lies in space.
The variable nature of the ionosphere, especially over the equatorial/ low latitudes poses serious threats to High frequency (HF) communications (Akala et al., 2011).

3. Recently, rockets and satellites measurements have been used to deduce electron density profiles known as total electron content (TEC) (Davies, 1965).
TEC is a parameter of the ionosphere that produces most of the effects on radio signals.

5. TEC obtained from Global Navigation satellite systems (GNSS) are of two types:
(i) slant TEC (sTEC) and
(ii) vertical TEC (vTEC).
vTEC is obtained from the sTEC using the Modified Single-Layer Model Mapping Function (MSLM) given in equation (2).

7. Figure 1: Signal affected at ionospheric region [Abba et al., 2015]
L1 (1575 MHz) and L2 (1228 MHz) which are used for TEC estimation.
Figure 1: Signal affected at ionospheric region [Abba et al., 2015]

9. Thus, Δt measured between the L1 and L2 frequencies is used to evaluate TEC along the ray path.
The availability of TEC from the Nigerian ionosphere has been made possible through Nigerian GNSS Reference NETwork (NIGNET).

10. This has led to studies and intensifying efforts at understanding the Nigerian equatorial ionosphere by scientist in the region.
The aim of this study is to analyse and compare the behaviour of TEC in Northern Nigeria (Zaria) and southern Nigeria (Enugu) located above and below the magnetic equator respectively.

11. DATA AND METHODOOGY
The data used in this research are hourly TEC values in TEC units obtained from the Continuously Operating Reference Stations (CORS) located in North (Zaria) and South (Enugu) of Nigeria, during the ascending phase of solar cycle 24.

12. Figure 2: Locations of stations used in the study

13. Figure 3: Number of days of data availability at (a) ABUZ station and (b) UNEC station

14. Figure 4: Flow chart for TEC calculation
Compressed GPS data in RINEX format
O files extracted using CRX2RNX HATANAKA
STD files extracted using GPS_TEC Ver
App. Software
Hourly vTEC
Figure 4: Flow chart for TEC calculation

16. RESULT AND DISCUSSIONS
The diurnal variations of mean vTEC in the Nigerian ionosphere shows unique features as those of a typical EIA station as shown in Figures 5.

17. Figure 5: Diurnal variation of TEC for different seasons at (a) ABUZ station and (b) UNEC station.

18. Figure 6 shows the variability of TEC for ABUZ (Zaria) and UNEC (Enugu) respectively.
Nighttime variability is higher than daytime variability with not well defined pre-midnight and post-midnight peaks.

19. Figure 6: Variability of TEC for different seasons at (a) ABUZ station and (b) UNEC station.

20. Thermospheric neutral winds, temperature gradients and RTI are the causes of nighttime variability of ionospheric parameters (Ayorinde et al., 2016).
While variability during the day is reported to be due to electric field strength (Somoye et al., 2011) and meridional winds (Suranya et al., 2015).

21. CONCLUSION
There is a steep increase starting from sunrise and reaches its peak in the afternoon and falls to a minimum at sunset.
Ionospheric range delay at midday varies slightly from 8m at ABUZ (Zaria) in the north to 9m at UNEC (Enugu) in the south of the Nigerian equatorial ionosphere (NEI).

22. On the seasonal behaviour, mean TEC of December Solstice and September Equinox were higher than those of March Equinox and June Solstice at both stations.
It is observed that nighttime variability is higher than daytime variability, pre-midnight and post-midnight peaks are not well defined for the four seasons at both stations

23. ACKNOWLEGMENTS
We thank the following:
Office of the Surveyor General of the Federation (OSGoF);
Gopi Krishna of Boston College, USA;
Dr Wusu of Lagos State University.

24. REFERENCES
Abba, I., Abidin, W.A.W.Z., Masri, T., Ping, K.H., Muhammad, M.S., Pai, B.V. (2015). Ionospheric effects on GPS signals in low-latitude region: A case study review of South East Asia and Africa. Nigerian J. of Technology, 34, 3, 523 – 529.
Akala, A.O., Somoye, E.O, Adeloye, A.B., Rabiu, A.B. (2011) “Ionospheric foF2 variability at equatorial and low latitudes during high, moderate and low solar activity” Indian Journal of Radio and Space Physics.Vol. 40, pp 124 – 129

25. Ciraolo, L. , Azpilicueta, F. , Brunini, C. , Meza, A
Ciraolo, L., Azpilicueta, F., Brunini, C., Meza, A., and Radicella, S. M. (2006). Calibration errors on experimental slant total electron content (TEC) determined with GPS. Springer-Verlag.
Davis, K. (1965). Ionospheric Radio Propagation. National Bureau of Standards Monograph, 80.

26. Somoye, E. O. , Akala, A. O. , Adeniji-Adele, R. A. , Iheonu, E. E
Somoye, E.O., Akala, A.O., Adeniji-Adele, R.A., Iheonu, E.E., Onori, E.O., Ogwala, A. (2013a) “Equatorial F2 characteristic variability: A review of recent observations” Advances in Space Research 52. pp 1261–1266.
Somoye, E.O., Akala, A.O., Onori, E.O. (2013b). Comparison of foE and M(3000)F2 variability at Ibadan, Singapore and Slough. Journal of Atmospheric and solar Terrestrial Physics, 92, 18 – 22.

27. Somoye, E. O. , Akala, A. O. , Ogwala, A. , Onori, E. O
Somoye, E.O., Akala, A.O., Ogwala, A., Onori, E.O., Adeniji-Adele, R.A., Iheonu, E.E. (2017). Longitudinal dependence of day-to-day variability of critical frequency of equatorial type sporadic E (foEsq). Space Weather: Longitude and Hemispheric Dependences and Lower Atmosphere Forcing, Geophysical Monograph 220, First Edition. Edited by Timothy Fuller-Rowell, Endawoke Yizengaw, Patricia H. Doherty, and Sunanda Basu. © 2017 American Geophysical Union. Published 2017 by John Wiley & Sons, Inc.

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