The long-term meteorological data of Era-interim from 1979 to 2014 covering the observation at 00, 06, 12 and 18 have been used to derive vertical refractivity gradient in the lowest 100. Diurnal, seasonal and annual variations of refractivity gradient and its component are analyzed for coastal and plateau areas of Nigeria. The relative frequency of the occurrence of gradient below -100 N-units/km used in clear air propagation study is derived from cumulative distribution of the gradient. Occurrence of anomalous propagation in each region is also estimated. The result will help in the effective wireless link planning and design.
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