Solar radiation variability in Nigeria based on multiyear RegCM3 simulations

This study evaluates the seasonal and interannual variability of global solar irradiance over Nigeria as simulated by the International Centre for Theoretical Physics' (ICTP) Regional Climate Model version 3 (RegCM3) over the period 1997 to 2007 using ECHAM5 General Circulation Model as the lateral boundary conditions. The ability of RegCM3 in representing the climatology is also evaluated. The model was validated with two observed datasets viz: gridded weather observations by the Nigerian Meteorological Agency (NIMET) and the National Aeronautic and Space Administration (NASA). RegCM3 was found to replicates the essential features of global solar irradiance and mean air temperature climate for Nigeria and adequately simulates their seasonal variations over the selected climatic zones. The model over-estimates the NIMET observations across the whole zones whereas with NASA dataset RegCM3 gave a slight over-estimation during the rainy season in the south zone and a perfect fit with no under/over-estimation across the whole middle-belt and north climatic regions. The best simulations for seasonal cycle of global solar irradiance were obtained over North zone whereas the worst is over the South region for both the NIMET and NASA observations. The spatial structure of RegCM3 model climatology was found to reproduce the observed global solar irradiance climatologies, though in some months, RegCM3 slightly underestimates the observations. RegCM3 was also found to indicate a poor performance of the interannual variability of solar irradiance and mean air temperature over the different subregions.