Tropospheric radio refractivity over three radiosonde stations in Nigeria

Abstract

The annual variations of radio refractivity parameter within the first 10 km of the troposphere are presented for three radiosonde stations in Nigeria, viz: Oshodi, a coastal area in the southwest, Minna, a middle belt Savannah region and Kano, a sub-Sahelian region to the north. Results have shown that the variations in each zone and at the different atmospheric levels are influenced by the north-south movement of the Inter-Tropical Discontinuity (ITD). Correlation coefficients between the combination of surface radio refractivity, N_s, and any of lower level refractivity (N_L), the upper level refractivity (N_U), and the total refractivity for the entire column (N_T), have been found to be more than 0.70.

Using an analysis of variance (ANOVA) technique on the upper air climatological data spanning over a decade, an empirical relationship of the form N = α(NS)^β (α, β constants) has been established between refractivity aloft and its surface value, N_S , over the three stations in Nigeria. For instance, values of α and β for the refractivity parameters at Oshodi are 0.9308 and 0.9963 for N_L, 37.812 and 0.3547 for N_U, 3.1955 and 0.7820 for N_T respectively. Comparison made between the model and the actual values using the Kolmogorov Smirnov test have shown that the models for the three stations performed well during the dry season.

Key Words: Radio refractivity, troposphere, radiosonde stations, inter-tropical discontinuity, Savannah.

Ife Journal of Science Vol.6(2) 2004: 167-176