عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Different factors such as the total ozone, cloudiness and aerosol particles influence the surface UV-B from solar radiation. UV-B is particularly dangerous to life on the surface of the earth. In this paper, the effects of total ozone on UV-B radiation, obtained by the spectrophotometer Brewer (type MK IV) system and measurements of cloud cover over the Esfahan area using meteorological records for July 2003 to June 2004, have been considered. The results show that daily integrated UV-B radiation for this period varied between 0 to 6000 J/m2, its maximum occurred during June and July, and its minimum occurred during December and January. The maximum day-to-day variations of UV-B occurred in May and April. Also, the annual mean of integrated UV-B was approximately 3212 J.m-2.d-1 (Joules per square meter per day).
The results also show that UV radiation can reach critical levels for Esfahan, sufficient to have negative health consequences on humans, especially in June and July. It may be necessary, therefore, for the national weather bureau to issue warnings in this time of the year.
The correlations between UV-B and total ozone and cloudiness also show that substantial cloud cover (generally present between December and April) is more important in harmful levels of UV-B radiation than is total ozone. When cloud cover is insignificant, ozone is more effective in reducing UV-B radiation.
The cloud factor(C) is found to be about 0.25 in this area. High cloud cover (e. g. (7-8) Octas) can reduce UV-B by 70%. Maximum cloudiness occurs during January and the secondary peak occurs in April (mid-spring). The minimum of cloudiness occurs in the period including July, August and September. Additionally, the results show that clear sky conditions usually have a cloud factor of less than 0.3, while the high cloud cover condition measures between 0.6 and 1.0. These values are in agreement with the values of other research results.
Thick cloud cover ((7-8) Octas) can substantially reduce UV-B radiation. Usually, there are negative correlations between cloud cover or total ozone and UV-B radiation. The best defined correlations during cloudy months and clear sky periods were extracted from the analyses and are as follows:
Ln (UV-B) = -1.0294 C + 7.8910
Ln (UV-B) = -2.4156 Ln (O3) + 22.235
All correlation coefficients of linear regressions for the cloud factor versus UV-B is within the 99% confidence level, and for the total ozone and UV-B it is within 95% confidence level. These relationships can be used to determine UV-B radiation in this area, for technical use. The relationship between the logarithm of daily integrated UV-B radiation and the logarithm of total daily ozone for clear sky conditions shows that a (the Radiation Amplification Factor, RAF) has a value of about 2.4.