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 radiation (RG) and net radiation (RN) fluxes were made above the grass-covered surface at DACCIWA site, Ile-Ife, southwest Nigeria, from 2017 to 2019. The datasets were obtained from a four-component net radiometer (model NR01, Hukseflux Thermal Sensors B.V., the Netherlands). Observations were made and separated for cases of clear sky and cloudy conditions during the measurement period. The results showed considerable fluctuations for both radiation fluxes. For clear sky conditions, the magnitudes of RG and RN were higher than those observed for cloudy conditions due to attenuation. For the period of observation, LWup fluxes were higher in the dry season than in the wet season due to dry and hotter surface conditions while LWd dominated the wet season at the site. The highest radiation values occurred in 2018, while the lowest were observed in 2017. Daily surface albedo (α) ranged from 0.16 to 0.22. Empirical relationships obtained for RG and RN are RN = 0.754 RG – 17.4 Wm−2 and RN = 0.657 RG – 32.7 Wm−2 for wet and dry seasons, respectively. Based on the empirical relationships, daily RN and RG can be obtained when measurements like these are not available. Linear relationships between RN and RG show that for all days (cloudy and clear sky conditions), daily average RN is about 0.75 RG, and about 0.60 RG for clear sky conditions at the location. However, the results reflect the characteristics of the site and can be applied for gap-filling or careful extension of the measurement period.