Relationship between Ultraviolet-B Radiation and Broadband Solar Radiation under All Sky Conditions in Kuwait Hot Climate

Abstract

In the present study, continuous measurements of solar global (G) and ultraviolet-B (UVB) radiation are taken in Kuwait for 2014–2019 for all weather conditions. Hourly curves show a sinusoidal behavior for both G and UVB radiation. Statistical analysis indicates that there is a good agreement between hourly G and hourly UVB as the coefficients of determination (R2) for all years are larger than 0.91 and the root-mean-square error (RMSE) and mean bias error (MBE) are very small. The hourly percentage ratio (UVB/G) is found to decrease with G due to cloudy sky conditions. In addition, the ratio (UVB/G) tends to decrease with global clearness index (KT), indicating that a higher ratio of (UVB/G) can be obtained for a cloudier atmosphere. Another interesting finding is that KT and the UVB index (KTUVB) are directly proportional, and a third-order polynomial fit gives an acceptable formula (R2 = 0.859). Daily G and UVB values are very well correlated as R2 is very close to unity for all years. The values of RMSE and MBE obtained from daily analysis are greatly enhanced as the values of RMSE and MBE are almost zero. The maximum G and UVB radiation obtained is 27.94 MJ/m2 and 0.0044 MJ/m2, respectively, with both occurring in June 2015. Finally, there is an excellent linear fit between the monthly G and monthly UVB radiation as R2 is almost equal to unity and RMSE and MBE are negligible. Thus, the predicted daily or monthly empirical formula can be utilized with a very high accuracy to predict both daily and monthly UVB values at locations in Kuwait where G is measured.

Keywords

• global solar radiation
• ultraviolet B radiation (<i>UVB</i>)
• ratio of <i>UVB</i> to broadband <i>G</i>
• zenith angle
• global and <i>UVB</i> clearness indices