Observation Of Solar Ultraviolet Radiation In Tibet

Qinghai-Tibet Plateau is one of the regions with the highest solar UV radiation in the world.The measurements of solar UV radiation in Tibet have scientific significance in various research field,e.g.plateau ecology,agriculture and human health,etc.We observe the solar biologically effective UV radiation,UVA and UVB radiation,UV index(UVI)and the influence factors of UV radiation,e.g.ozone and cloud,in Tibet.The measurements are carried out at five stations,i.e.Lhasa,Nyingchi,Nagchu,Tingri and Xigatse,and implemented through the Norwegian multichannel bandwidth instruments—NILU-UV irradiance meters.The studies of this thesis include: the ground-based solar UV radiation from July 2008 to December 2017 in Lhasa;the study on influence factors of UV radiation based on the ground-based UVI at Lhasa in 2015 and radiation transfer model;the comparison of ground-based UV radiation from January 2015 to December 2017 in Lhasa,Nyingchi,Tingri and Xigatse;the comparison between the ground-based data by NILU-UV instruments and the satellite data by Aura/OMI from 2008 to 2017 at Lhasa and Nagchu.Firstly,the result of ground-based measurements in Lhasa show that the solar UV radiation fluctuate in various degrees during the last ten years,while it don't show a significant long-term variation trend.The ratio of UVB radiation to solar UV radiation is about 6.7% in Lhasa.The total ozone column(TOC)over Lhasa vary slightly,with an average of 259.2 DU during the period,and the highest seasonal mean TOC appears in springs while the lowest in autumns.Based on the study of influence factors,the key factor modifying UV radiation is cloud except for solar zenith angle in Lhasa.The UVI in a cloudy summer day indicate that the broken cloud that partly mask the solar disk increase the surface UVI by 10.2%.Secondly,the thesis presents the comparison of the ground-based solar UV radiation in Lhasa,Nyingchi,Tingri and Xigatse.The result show that the maximum value of UVI in Tingri(Mount Everest region)is 30.8,28.8 in Xigatse,20.8 in Lhasa and 15.2 in Nyingchi,which are all extreme values.Tingri have the highest solar UV radiation among the stations,and the erythemal effective UV dose in Tingri is higher than that of Xigatse,Lhasa and Nyingchi by 5.6%,38.6% and 116.0%,respectively.Lhasa and Nyingchi have the similar latitude,however the UVI in Lhasa is 49.8% higher than that in Nyingchi due to the influence of altitude and cloud.The thesis also presents the comparison of the satellite-derived data and the ground-based observation data under cloud-free conditions.The results show that the UVI derived by the satellite in Lhasa and Nagchu are 15.1% and 12.1% higher than the UVI observed on the ground,respectively.