Seasonal variation of coastal refractivity gradients in a tropical environment

Abstract

Variation of radio refractivity in the troposphere is an important factor for predicting the behavior of electromagnetic wave propagation as well as performance of terrestrial communication systems. This effect can be quite pronounced in coastal areas especially in the Tropics. This paper presents results of analysis radiosonde data obtained from Lagos (a southern Nigeria city on the Atlantic coast of West Africa) between 1991 and 1993. The effort is to determine the variability of vertical refractivity gradient at various height ranges within the first kilometer above the surface. The result shows that high prevalence of isolated strong ducting events due to severe refactivity gradients occur in clear-air-conditions while more moderate ducting, or even subrefractive, gradients also occur during the wet season. Variability of surface temperature and refractivity gradients are highest in wet season, and the monthly means of surface refractivity and vertical refractivity gradients are generally poorly correlated. Observed propagation conditions and their seasonality have considerable impacts on terrestrial radio applications.