Long-term changes in solar ultra-violet radiation (UV) of wavelengths
295 to 385nm were measured in Bahrain. A tendency occurred towards a r
eduction in UV intensity during the months of June, July, August and S
eptember in each year. A calculation was made, and averaged, over seve
ral years regarding the ratio of UV intensity for each month to the av
erage 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 Bahrai
n was compared with those measured in countries in the Arabian Gulf, M
iddle East, Northern Europe and in Alaska. An empirical equation has b
een 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. (C) 1997 Elsevier Science Ltd.