Determination of daily total ultraviolet-B in a subtropical region (Upper Egypt): An empirical approach

Abstract

Given the fundamental role played by ultraviolet-B (UVB) and due to the lack of long-term measurements of its magnitude, the present work has established an empirical approach to estimate daily total UVB in all sky conditions (UVBd). Data from eight years (2000–2007) of UVBd and daily total global solar radiation (Gd) have been used. For both variables, the dataset used was examined, and a relationship between these two quantities was developed. In addition, the variation of daily clearness indices of UVB and global solar radiation, G (KtUVB and Kt respectively) was determined. Kt was introduced to determine UVBd. This variable can be considered as an atmospheric modulator of the maximum values of UVBd (under clear-sky conditions, UVB0d). The relationship between UVBd and the product of UVB0d and Kt (UVB0d*Kt) was parameterized. The significance and performance of this empirical approach have been evaluated with the aid of several statistical analysis procedures. The results show that the modeling index (d) and the coefficient of modeling efficiency (ME) were 0.99 and 1 respectively. In addition, the root mean square error (RMSE), the mean bias error (MBE), and the mean absolute error (MAE) were 8%, −0.3%, and 6%, respectively. Datasets for a new time period from Qena and another location (Aswan) were used to validate the proposed approach. The results of this empirical approach were satisfactory, with a correlation coefficient of 0.98 between measured and estimated values of UVBd for both sites.