A New Model for Clear Sky Downward Longwave Radiation Obtained from a Tropical Climate
Abstract
Though some equations are general in nature, some are locality biased and need to be tested before use in another location. In this work some exiting equations of clear sky downward longwave are tested to see if they significantly predict the measured irradiation beside their correlation. At KT ≥ 0.62, only 39 cases were found in a 2-year data of daily irradiation from September, 1992 to August, 1994 measured in the tropics - Ilorin, Nigeria (8o 321N, 4o 341E). Out of 12 equations, only the original Swinbank (1963) and Brunt (1932) models estimations were found to be statistically significant, having R values of 0.608 and 0.939 respectively. They performed even better when their constants were localised. However from KT ≥ 0.60 with over 70 cases, only the Swinbank (1963) model predicted the irradiation significantly but with a low positive correlation; R = 0.386. By least square method via theoretical modelling, a new equation is presented which mimics the Swinbank’s model but in cooperate water vapour term. It predicts significantly with high positive correlation at KT ≥ 0.60, when tested.