| 西藏当雄地基紫外线指数观测研究 |
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| 引用本文： | 陈树,郑向东,林伟立,张勇,扎西达瓦,祁栋林.西藏当雄地基紫外线指数观测研究[J].应用气象学报,2015,26(4):482-491. |
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| 作者姓名： | 陈树 郑向东 林伟立 张勇 扎西达瓦 祁栋林 |
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| 作者单位： | 1.中国气象科学研究院大气成分研究所 中国气象局大气化学重点开放实验室，北京 100081 |
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| 基金项目： | 国家自然科学基金项目(40830102,21177157），中国气象科学研究院基本科研业务经费重点项目（2011Z003,2013Z005） |
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| 摘 要： | 基于西藏当雄2009年9月—2011年8月地基紫外线指数 (UVI) 观测，结合TUV辐射传输模式分析, 该文检验太阳天顶角、云、臭氧、积雪和气溶胶对UVI的影响。结果显示，影响地面UVI主要因素是太阳天顶角和云。晴天地面UVI可简单用太阳天顶角拟合函数表征；地面UVI的云调制因子总体上随云量增加呈下降趋势，但间隙性、未遮蔽日面的云可增强太阳散射辐射，使云调制因子值平均增加约3%~6%，个别情形达40%。臭氧低谷使当雄UVI比同纬度平原地区增加约12%；冬季短期、浅层积雪使UVI增加16%或更低，也低于模式模拟值 (23%)；气溶胶 (光学厚度为0.02~0.1) 对UVI衰减低于3%。因臭氧低谷导致青藏高原臭氧南北分布的差异，相同太阳天顶角下拉萨 (海拔为3650 m) UVI较瓦里关 (海拔为3810 m) 偏高7%~10%。与卫星产品比较表明:OMI卫星UVI产品在当雄、沱沱河、瓦里关和拉萨较地基测值总体偏高65%以上，而晴天则平均分别偏高8.6%，13%，9%和50%。云、地基与卫星像元地理位置差异应是卫星UVI产品偏高的原因。当雄地基UVI测值大于14时，卫星UVI产品反而低3%应与间隙性云有效增强了地面辐射有关。
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| 关 键 词： | UVI 西藏当雄 青藏高原 地基观测 卫星比对 |
| 收稿时间： | 2014-12-10 |
Observational Study on the Ground based UVI at Dangxiong of Tibet |
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| Chen Shu,Zheng Xiangdong,Lin Weili,Zhang Yong,Zaxi Dawa and Qi Donglin.Observational Study on the Ground based UVI at Dangxiong of Tibet[J].Quarterly Journal of Applied Meteorology,2015,26(4):482-491. |
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| Authors: | Chen Shu Zheng Xiangdong Lin Weili Zhang Yong Zaxi Dawa and Qi Donglin |
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| Affiliation: | 1.Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing 1000812.Meteorological Observation Center of CMA, Beijing 1000813.Meteorological Bureau of Tibet Autonomous Region, Lhasa 8500004.Dangxiong Meteorological Bureau of Xizang, Dangxiong 8515005.Qinghai Institute of Meteorological Sciences, Xining 810000 |
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| Abstract: | Factors of solar zenith angle (SZA), cloud, ozone and snow cover modifying the surface ultraviolet index (UVI) in the Tibetan Plateau are presented by the TUV model simulations and the two-year continuous ground-based measurements at Dangxiong (30.48°N, 91.10°E, 4200 m a.s.l) from September 2009 to August 2011. Results show that the key factors affecting the UVI over the Tibetan region are SZA and cloud. Variations of cloud-free surface UVI can be characterized exactly as a simple empirical SZA function. The UVI cloud modification factor (CMF) generally reduces by 46% as the cloud amount increases from 0 to 100%. CMF might increase by 3%-6%, or even by 40% in individual cases if the solar disk is partly masked with broken clouds. The ozone valley enhances 12% summer surface UVI compared to plain regions of the similar latitudes. The winter short-term thin snow coverage could enhance 16% or less surface UVI, and this enhancement is lower than that from the simulations (23%). UVI attenuation caused by aerosols with optical depth of 0.02-0.1 is no more than 3%. As compared with UVI measured at Lhasa (29.67°N, 91.13°E, 3650 m a.s.l), Tuotuohe (34.22°N, 92.43°E, 4500 m a.s.l) and Waliguan (36.29°N, 100.90°E, 3810 m a.s.l), the difference of site-altitude is a key factor influencing the UVI. Under the same SZA conditions, the summer UVI at Lhasa is 7%-10% higher than that at Waliguan due to the southern thinner ozone layer, the ozone valley. Comparison with satellite-derived product shows that, averagely, the OMI-UVI is 80% higher than the ground-based values at Dangxiong but only 8.6% higher under cloud-free circumstances. The OMI-UVIs are all above 65% higher than those ground-based measurements at the other 3 sites but their cloud-free values are only 13%, 9% and 50% higher at Tuotuohe, Waliguan and Lhasa, respectively. Clouds and geographical mismatches between the satellite pixel and fixed ground-based observation site are supposed to be the main factors of higher space-based UVI values, particularly over Lhasa. As the ground-based UVI is more than 14, the coincident space-based UVI is generally 3% lower at Dangxiong owning to the broken clouds strengthening the in-situ radiation. |
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| Keywords: | UVI Dangxiong of the Tibet the Tibet Plateau ground based observation satellite comparison |
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