Spatial and Temporal Distribution of Modified Radio Refractivity Gradient at 875 hPa and 700 hPa over Nigeria

The meteorological effects on radio wave signals propagating through the troposphere are of great concerns in the design and performance of radio communication systems. Often, the effect can lead to anomalous propagation conditions such as ducting, super refraction and sub refraction. In this paper, the spatial-temporal distribution of modified radio refractivity gradient and the effects on radio waves propagating at 875 hPa and 700 hPa pressure levels over sixteen selected locations aloft the four climatic regions of Nigeria are investigated. Five (5) years (2013-2017) meteorological parameters namely: air temperature, relative humidity and atmospheric pressure at ground level and 1 km above ground level were obtained from the European Center for Medium-Range Weather Forecast (ECMWF) at four synopses hours of the day. Modified radio refractivity and its gradient at the two pressure levels were computed using ITU- model. Results on a daily and seasonal basis shows similar trends at both 875 hPa and 700 hPa pressure levels, with higher values of modified radio refractivity gradient recorded at 700 hPa heights at the morning and night hours of the day. Results on seasonal basis shows that during the rainy season, modified radio refractivity gradients were high. On location basis, Port Harcourt (coastal region) recorded the highest value of modified radio refractivity gradient of about 115.5 M-units/km in the night time (00:00 hr. LT). The value depicts the occurrence of normal refraction in this location. The overall results will be useful for microwave links budgeting and design in Nigeria.