Solar ultra-violet radiation changes in Bahrain

Long-term changes in solar ultra-violet radiation (UV) of wavelengths 295 to 385 nm were measured in Bahrain. A tendency occurred towards a reduction in UV intensity during the months of June, July, August and September in each year. A calculation was made, and averaged, over several years regarding the ratio of UV intensity for each month to the average global solar radiation for that month, on a horizontal surface. The average annual ratio was found to be 3.87% with a lowest value of 3.3% and a highest value of 4.35%. The measured UV intensity in Bahrain was compared with those measured in countries in the Arabian Gulf, Middle East, Northern Europe and in Alaska. An empirical equation has been developed which estimates the monthly average UV intensity, with a maximum monthly percentage error of not more than 24%. This equation contains only three variables, namely humidity, sunshine fraction and extra-terrestrial solar radiation.