The Observational Study Of Biologically Effective Uv Radiation On The Land Surface Of Tibet

Solar ultraviolet(UV) radiation has a wide range of effects on terrestrial ecosystems, yet, there is currently a paucity of data that records the status of UV radiation of the Tibetan Plateau, related to stratospheric ozone depletion. In this work, continuous measurements on UV radiation in the 280-400 nm spectral range are analyzed for the period between July 2008 and October 2014. These measurements are carried out at five stations in Tibet, i.e. Lhasa, Nyingchi, Nagchu, Tingri and Xigaze.The interannual variability of plant-action-spectra-weighted(CLW) and erythemally weighted(CIE) UV radiation are examined together with variations of ozone and cloud transmission. There is no statistically significant trend found with the CLW UV radiation, corresponding to the change of ozone during the work period. While the total column of ozone appears to be stable, there is a significant drop observed in the year of 2009 and 2010, however, a noticeable growth was detected after the year of 2011 and made the drop up. For the erythemal-weighted UV radiation, extremely high values of UV index(UVI) can be found more and more frequently. During the work period, the number of days when the value of UVI exceeds 20 for Lhasa, Nagchu, Tingri and Xigaze are 16, 59, 90 and 42, respectively. Extremely high values of UVI and corresponding atmospheric conditions are of particular concern. It is shown that these extremely high values are mostly recorded in the presence of clouds. And the highest UVI in Nyingchi is 18.26 measured on 2011.7.28, and the highest one of all stations is 28.48 in Nagchu on 2013.7.3.