摘要
文章通过实地测量拉萨和定日两点紫外线强度,介绍了云层对地面紫外线(红斑紫外线、紫外线-A和紫外线-B)强度的影响情况。研究表明,云层一般减弱地面紫外线的强度,最大减弱量达90%。在积状云情况下,局部地面(太阳光照射地)紫外线强度得到增强,增强量达30%。西藏高原紫外线很强,加上云层反射的额外紫外线,使多云天气比晴天更加危险。测量表明,拉萨夏季晴天地面紫外线-B剂量率可达6.0W/m2,是同纬度海平面的两倍以上。夏季部分云天紫外线-B剂量率频繁超过6.0W/m2,甚至可接近8.0W/m2。
The current paper presents cloud impacts on ultraviolet(UV) radiation(erythemal UV,UV-A and UV-B) through field measurements at two points,Tingri and Lhasa.The study shows that clouds,in general,can weaken the intensity of ground UV radiation,the biggest decline amounted to 90%.However,in the case of cumulonimbus,the intensity of ground UV radiation could be enhanced;the enhancement could reach up to 30%.The Tibetan Plateau has strong UV radiation;additional UV radiation reflected from clouds makes cloudy skies even more dangerous than clear skies.The measurements show that the summer clear sky UV-B dose rate on the ground in Lhasa could reach up to 6.0 W/m2,which is more than double value of that at sea level at the same latitude.Partially the cloudy sky UV-B dose rates frequently exceed 6.0 W/m2 during the summer,or even close to the value of 8.0 W/m2.
基金
2007年西藏自治区科技厅项目“西藏两点太阳紫外线的观测和研究”
挪威西藏合作网(Network for UniversityCo-operation Tibet-Norway)项目‘Environmental physics in Tibet’阶段性成果
