The diurnal and seasonal variation of surface refractivity over Nigeria was studied using four years in-situ meteorological data from eight location over Nigeria. At all the stations studied, it was observed that the diurnal refractivity variation was caused majorly by the dry term in the rainy season and the wet term is the major cause of refractivity variation in dry season except Sokoto and Jos. In Sokoto the result was found to be opposite and it is attributed to the fact that in dry season the humidity is almost close to zero while in rainy season the pressure seems to be almost constant but the temperature fluctuates rapidly and consequently the humidity. The variation pattern in Jos is as observed because of the altitude (~1000 m above sea level). At this altitude pressure variation seems to be insignificant. The result also show that the surface refractivity generally have higher value during rainy season than dry season at all location studied. The result also show that the value of surface refractivity increases from arid region in the north to the coastal area in south. The result also show that the diurnal refractivity variation is basically a function of local meteorology and while seasonal variation is caused follows the climatic condition.
2. ITU-R, "The radio refractive index: Its formula and refractivity data,", 453-459, 2003.
3. Smith, E. K. and S. Weintraub, "The constants in the equation for atmospheric refractive index at radio frequencies," Proc. Inst. Radio Eng., Vol. 41, 1035-1037, 1953.
4. Bean, B. R., C. A. Cahoon, C. A. Samson, and G. D. Thayer, A World Atlas of Radio Refractivity, Monograph, No. 1, Environmental Sciences Services Administration, U.S. Government Printing Office, Washington D.C..
5. Bean, B. R. and B. A. Cahoon, "Correlation of monthly median transmission loss and refractive index profile characteristics," J. Res. N.B.S., Vol. 65, No. 1, 67-74, 1961.
6. Hall, M. P. M., E®ects of the Troposphere on Radio Communications, 14-46, IEEE Peter Peregrinus Ltd., London and New York, 1979.
7. Lane, J. A. and B. R. Bean, "A radio meteorological study. Part I: Existing radio meteorological parameters; Part II: An analysis of V.H.F. ¯eld strength variations and refractive index profiles; Part III: a new turbulence parameter," J. Res. Natl. Bur. Std., Vol. 67, 589-604, 1963.
8. Misme, P., "Models of the atmospheric radio refractive index," Proc. IRE, Vol. 48, No. 8, 1499-1501, 1960.
9. Flavell, R. G. and J. A. Lane, "The application of potential refractive index in tropospheric wave propagation," J. Atmos. Terr. Phys., Vol. 24, 47-56, 1962.
10. Saxton, J. A., "Proceedings commission II, radio and troposphere," XIVth General Assembly, URSI, 117-126, 1963.
11. Bean, B. R. and G. D. Thayer, "Comparison of observed atmospheric radio refraction effects with values predicted through the use of surface weather observations," J. Res. Natl. Bur. Std., Vol. 67, No. 3, 273-285, 1963.
12. Owolabi, I. E. and V. A. Williams, "Surface radio refractivity patterns in Nigeria and the southern Cameroons," J. West Afr. J. West Afr., Vol. 15, No. 1, 3-17, 1970.
13. Kolawole, L. B., "Climatological variations of surface radio refractivity in Nigeria," Bull. Nig. Inst. Phys. , Vol. 4, 97-117, 1980.
14. Adebanjo, T. I., "A semi-empirical radio refractive index variation over Nigeria," Bull. Nig. Inst. Phys., Vol. 2, No. 2, 69-78, 1977.
15. Oyedum, O. D. and G. K. Gambo, "Surface radio refractivity in northern Nigeria," Nig. J. Phys., Vol. 6, 36-41, 1994.
16. Oyedum, O. D., "Seasonal variability of radio field strength and radio horizon in Nigeria," Book of Readings, 1st Annual S.S.S.E. Conf. F.U.T., Vol. 1, 184-195, 2005.
17. Adeyemi, B., "Surface water vapour density and tropospheric radio refractivity linkage over three stations in Nigeria ," Journal of Atmospheric and Solar-terrestrial Physics, Vol. 68, No. 10, 1105-1115, 2006.
18. Titus, A. A. and M. O. Ajewole, "Vertical profile of radio refractivity gradient in Akure, south-west Nigeria," Progress In Electromagnetics Research C, Vol. 4, 157-168, 2008.
19. Falodun, S. E. and M. O. Ajewole, "Radio refractive index in the lowest 100m layer of the troposphere in Akure," South-western Journal of Atmospheric and Solar-terrestrial Physics, Vol. 68, 236-243, 2006.
20. Samson, C. A., "Refractivity gradients in the northern hemisphere," An Executive Summary of U.S. Department of Commerce , 1975.
21. Dhein, N. R., M. S. Pontes, and M. L. Silva, "Statistical Behaviour of refractivity gradient in the tropics," IEE Conference Publ., No. 370, 340-343, 1993.
doi: --- Either ISSN or Journal title must be supplied.