Scaled-up Analysis of Surface Refractivity across West Africa

The scaled-up analysis of surface refractivity over a period of 22 years (1983 – 2005) for different climatic zones in West Africa was calculated using the results of surface refractivity at 2 m, and 10 m averaged monthly and annually. The annual surface refractivity normalised value is 0.91 for Z2/Z1, 0.97 for Z3/Z1, and 0.94 for Z4/Z1 at 2 m while the normalised value of surface refractivity is 1.00 for Z2/Z1, 0.98 for Z3/Z1, and 0.96 for Z4/Z1 at 10 m. At 10 m, the value is relatively constant. The monthly variation shows that surface refractivity reduced as latitude increases in West Africa except in wet months for climatic zone 3 at 2 m and wet months in climatic zone 2 at 10 m. The wet months had a characteristic of reduction in normalised surface refractivity value with most severe reduction within latitudes 10°N and 15°N. This decrease in refractivity across the latitude translates into an increase in the velocity of terrestrial propagation across the latitude, resulting in excessive bending of electromagnetic waves toward the earth's surface, along curves with radii less than the radius of the earth.