| Both UV-B and total ozone were measured with Brewer#054 spectrometer over the Qinghai-Xizang Plateau, at Mt. Waliguan for the time period 1991-2001 and Lhasa for the time period June-October in 1998. The observational data are analyzed to illustrate the characteristic of UV-B over the Qinghai-Xizang Plateau. Special attention is paid to the influence of total ozone and cloud on UV-B. The inverse correlation between UV-B irradiance and total ozone are found by obseved at Mt. Waliguan over the whole time period. The surface UV-B irradiance increases significantly while the total ozone decreases year after year. From 1993 to 2001, the UV-B at Mt. Waliguan increases 5.4% in winter. Clouds usually decrease the UV-B irradiance received at the ground, but occasionally it might cause UV-B enhancement. The UV-B radiation over the Qinghai-Xizang Plateau exceeds the corresponding values at those measured in the vicinity of the same latitude over the plain area. The effects of altitude, surface albedo, total ozone, aerosol and cloud on UV-B are studied with a radiative transfer model桾UV. By means of the sensitivity experiment, the proper parameters of surface albedo, aerosol and cloud modification method for Mt. Waliguan are found. Introduced these parameters and method into the model, the UVI and spectral irradiance of UV-B at Mt. Waliguan are simulated, and compared with the observational data. The results of the comparisons of between the measurements with the model outputs show that TUV is very accurate for the clear sky condition. The long time series of UVI at the surface of Mt. Waliguan during the time period 1979-2001 is simulated with TUV implemented with the long time series of total ozone at Mt. Waliguan observed by Brewer, or the TOMS data when no measurement data are available. Model simulations indicate that the surface UVI at Mt. Waliguan will increase 5% from 2000 to 2010, 16% from 2000 to 2030 if the total ozone decreases by 0.34%yr-1.
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