A Comparative Study on Estimation of the Earth’s Albedo and Its Variation with other Meteorological Parameters between two Tropical Stations in Nigeria

Abstract

Estimation of albedo is paramount in the evaluation of solar energy collectors, atmospheric radiative transfer and studies that relates to atmospheric thermal balance. This study, employed the shortwave solar energy balancing at the edge of the Earth’s
atmosphere to estimate and compare the variation of albedo for two locations, Gusau (Latitude 12.170N, Longitude 6.700E and
altitude 463.9 m above sea level) and Calabar (Latitude 4.970N, Longitude 8.350E and altitude 61.9 m above sea level) situated
across the Sahelian and Coastal climatic zones of Nigeria respectively using measured monthly mean daily meteorological
parameter of global solar radiation obtained from the National Aeronautics and Space Administration (NASA) during the period
of twenty two years (July 1983 – June 2005). The variation of albedo with clearness index, relative humidity and mean temperature were investigated. The variation of emitting Earth’s surface temperature and maximum wavelength for each location were also investigated. The results in this study revealed that the estimated surface albedo depicts a direct opposite relationship with the clearness index, an inverse relationship with the emitting Earth’s surface temperature and a direct relationship with the wavelength for the studied locations. The highest and lowest values of albedo simulated for Gusau was in the months of August and February with 0.4933 and 0.3270 respectively, while for Calabar are in the months of August and January with 0.6949 and 0.4218 respectively; the estimated albedo obtained for Calabar in this study are more than that of Gusau throughout the months for the period under investigation suggesting that as the location’s latitude and global solar radiation increases the albedo or
reflectance decreases. The variation of clearness index with albedo for Gusau suggests the availability of abundant global solar
radiation throughout the months in the region while for Calabar revealed the availability of abundant global solar radiation only in the months of January, February and December. The emitting Earth surface temperature for Gusau ranged between 235.1297 K in August and 252.4133 K in February while for Calabar ranged between 207.1236 K in August and 243.0097 K in January, these
values agrees closely to the standard emitting Earth surface temperature value (255.0000 K). The maximum emitting wavelength values for both locations revealed that the radiation is longwave and are found within the infrared region of the electromagnetic
spectrum. The variation of relative humidity with albedo depicts almost a similar trend for both locations. The results showed that
as albedo increases during the rainy season the mean temperature decreases