Refractivity Gradient Variations and Intertropical Discontinuities Across Nigeria

Abstract

The complexity of the troposphere has a significant impact on radio signal transmission. This has led to the computation of refractivity gradients, which is an important parameter for the estimation of path clearance and propagation effects such as super-refraction, sub-refraction and ducting. This research focuses on the interrelationships that exist between Refractivity Gradient and Intertropical Discontinuity (ITD). The ITD is a major phenomenon that determines weather in West Africa. Refractivity gradient was calculated using hourly data of temperature and relative humidity for the years 2017and 2018 taken at two levels (surface and 1000hpa) collected from the archives of the European Centre for Medium-Range Forecasts (ECMWF) for twenty meteorological stations in Nigeria. The refractivity gradient values obtained were used to characterize the atmospheric conditions of the stations diurnally and seasonally. Results showed that during the dry season, the atmosphere is sub-refractive at the coastal and derived savannah regions while during the rainy season super-refractive conditions prevails. At the guinea and sub-Sahelian regions the atmosphere is mostly sub-refractive. Diurnal variations show that the coastal and derived savannah regions have atmosphere that are super refractive throughout the day, the guinea savannah regions are characterized by atmosphere that is super-refractive in the early morning hours and sub-refractive between late morning and afternoon periods. These occurrences are found to be greatly influenced by the north-south trajectory of the Intertropical Discontinuity.