Nocturnal radiation measurements in Nigeria

Experimental work was carried out to determine the net flux of the long-wave radiation from the earth's surface to the atmosphere for clear nights in Nsukka, Nigeria. Values of the effective sky temperature were also obtained. The experimental radiator consisted of a flat mild steel plate coated with high emissivity black enamel paint. Data were obtained for the months of February through May. This seasonal period is free from the harmattan dust haze which characterizes part of the dry season and is free from the rain-bearing clouds of the wet season. A comparison of the measured downward flux of the atmospheric radiation was made with the data generated from the empirical formulas of some investigators using standard surface observations. Generally, the theoretical models yielded values that are lower than the observed results. However, the analytical values derived from Idso and Jackson's empirical model gave the best agreement with the experimental data. Agreement was within 0–5 per cent. The effective sky temperatures obtained are on the average 12.2°C less than the surface air temperatures. This was in close agreement with the result of Exell for the tropical climate of Thailand. The overall results presented are suitable for use in Nigeria and other regions with similar tropical or near-equatorial climate.