A STUDY OF SOLAR ULTRAVIOLET-RADIATION AT MAKKAH SOLAR STATION

Analysis of solar ultraviolet radiation (295-385 nm) and total global radiation (290-3000 nm), continuously recorded at a station in Makkah (21.5-degrees-N, 39.8-degrees-E) for 17 months in 1987-1988, has shown that the monthly average daily UV was 200 Wh m-2. The ratio of UV to total global radiation varied from a maximum of 0.043 to a minimum of 0.028. A drop of 25% below the average 0.036, detected in the summer months, is attributed to scattering and absorption by dust and low tropospheric ozone. Comparison with Dhahran and Kuwait has shown that the effect was localised. A study of diurnal variation and clear, midday hourly radiation and the ratio of UV to global radiation, Iv/Ig, also revealed an overall depletion in the summer months, despite the relative decrease in attenuation of Iv during cloudy days and at low solar altitudes. Multiple regressions of Hv and Iv on relevant variables with coefficients of determination exceeding 90% have been performed. Frequency distribution of daily UV is briefly discussed.