Multidecadal investigation of integrated surface Ultra-violet radiation and its coincidence with total column ozone and cloudiness

Document Type : Research Article


Water Engineering Department, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran


The solar radiation that reaches the Earth's surface has a significant impact on human health, agricultural productivity, terrestrial, aquatic ecosystems and air quality. Continuous monitoring of ultraviolet flux and total column ozone in Iran is limited to only two local sites that have been stopped for months and years due to technical difficulties such as calibration and high cost of maintaining. These difficulties motivate the researchers to rely on other database such as satellites and reanalysis radiation data. In the present work, the integrated daily solar ultraviolet-visible radiation (total integral of ultraviolet-visible radiation from 200 to 440 nm) was extracted from the ERA5 reanalysis database during the historical period of 1979-2020. Moreover, total column ozone (TCO), and the percentage of cloudiness (CF) were also obtained from the same database. The study area was divided into 8 clusters by Analytic Hierarchy Process (AHP) method and trend analysis was performed using Mann-Kendall test. Results indicate that mean annual integrated UV-VIS200-440 radiation of north and northwest of the country (clusters 5, 6, 7, and 8) has experienced a positive trend during the last four decades, but no significant trend was detected for other parts of the country. The study of the TCO also showed that in all 8 clusters, the TCO trend during 1979 to 2000 has experienced a significant decreasing trend, but the sign of the TCO trend has been reversed from 2001 onward. The maximum annual correlation (r) was found between UV-VIS200-440 and the cloudiness (0.81). However, the highest r between UV-VIS200-440 and the TCO was 0.25. This result highlights the fact that the variation in cloudiness plays more important role on determination of surface UV radiation than the changes in ozone concentration.


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