Analysis of global and net radiation fluxes in relation to surface albedo at DACCIWA site in Ile-Ife, southwest Nigeria

Abstract

Measurements of global solar and net radiation fluxes were made above a grass-covered surface at DACCIWA site in a tropical location, Ile-Ife, southwest Nigeria for a period of three years (2017 -2019). The radiation data sets were obtained from a four-component net radiometer (model NR01). Observations were made for cases of clear sky and cloudy conditions during the measurement period. The results showed considerable fluctuations of both radiation fluxes occurring during the period of measurements at the location. For clear sky conditions, the magnitudes of global and net radiation fluxes were higher than those observed for cloudy conditions due to attenuation by clouds and aerosols. For the period of observation, the highest radiation flux values occurred in 2018 while the lowest were observed in 2017. The daily surface albedo (𝛼) values ranged from 0.16 to 0.22 at the site. Empirical relationships obtained for global solar and net radiation are 𝑅 𝑁 = 0.754 𝑅 𝐺 -17.4 Wm -2 and 𝑅 𝑁 = 0.657 𝑅 𝐺 -32.7 Wm -2 for wet and dry seasons respectively. Based on the empirical relationships, daily net and global solar radiation can be obtained when measurements like these are not available. Linear relationships between 𝑅 𝑁 and 𝑅 𝐺 show that for all days (cloudy and clear sky conditions), average 𝑅 𝑁 is about 65 % of 𝑅 𝐺 , and about 50 % of 𝑅 𝐺 for clear sky conditions at the location.