Correlation Between Ultraviolet Radiation and Global Radiation in Riyadh, Saudi Arabia

The global ultraviolet and global radiation were measured and recorded on an hourly basis in Riyadh, Saudi Arabia (lat. 24.6°N, long. 46.7°) during the period 1984–1989. Global radiation, G, was measured by an Eppley PSP pyranometer (0.285≤λ≤2.8 μm) and an Eppley TUVR radiometer (0.29≤λ≤0.385 μm) was used for the measurement of the ultraviolet radiation, UV. Both instruments were mounted on a horizontal surface. The results showed that the monthly average daily ultraviolet radiation was 197.6 Whm⁻². The ratio of the monthly average daily ultraviolet radiation to the monthly average daily global radiation (K_u) varied between 0.031 to 0.037, with a mean value of 0.034. Comparison with results obtained in Kuwait, Dhahran, and Makkah showed that the data of Riyadh are in good agreement with those of Makkah and Dhahran; however, it underestimates Kuwait data. A regression correlation between K_u and K_T (the ratio of the monthly average daily values of global radiation to extraterrestrial radiation) is developed. Another regression correlation between ultraviolet and global radiation on an hourly basis is also developed.