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大气水汽的稳定同位素组成与水汽来源、雨出过程密切相关。因此，研究水汽中稳定同位素变化，将有助于认识地表蒸发机制、水汽输送过程、以及古环境记录的气候意义。目前在青藏高原，甚至在中国有关大气水汽同位素研究极为有限，本论文选择了代表青藏高原季风区(高原南部)的拉萨和聂拉木作为水汽收集点进行大气水汽氧稳定同位素研究。基于水汽稳定同位素数据，结合相关的气象资料和同步降水同位素δ18O监测结果，本研究工作分析了青藏高原南部季风区大气水汽δ18O的变化特征，讨论了水汽δ18O与不同气象要素、同步降水δ18O的关系，揭示了不同的水汽输送模式对大气水汽稳定同位素变化的影响。结果表明：（1）青藏高原南部地区大气水汽稳定同位素波动很大，尤其在雨季因降水事件的影响，水汽δ18O在一个星期内波动幅度能超过20‰。在冬春季，在高原南部的大气水汽稳定同位素变化与大气比湿变化相关，呈显著的正相关关系；气温是影响拉萨旱季大气水汽δ18O变化的次级因素。雨季期间拉萨大气水汽δ18O与比湿呈现显著的负相关。（2）拉萨降水主要集中在5-9月，期间大气水汽和降水δ18O月均值呈现平行的变化趋势。水汽δ18O与同步降水δ18O的差值Δδ18O平均值为11.4‰，两者日变化趋势基本一致。拉萨降水中与水汽在降水事件发生时基本接近于同位素平衡状态。在冬春季喜马拉雅山南坡地区降水（基本是降雪）水汽来源主要是高空自由大气，呈现出异常的水汽-降水δ18O模式，地表水汽δ18O比同步降水平均高3.0‰。自由大气下沉侵入还会造成地表大气水汽δ18O极低值。（3）大气水汽稳定同位素变化与不同的水汽来源和输送过程模式密切相关。水汽来源受西风环流和局地环流控制时，水汽δ18O表现为相对高值；受季风水汽控制时，总体则表现为相对低值，有时受到降雨事件强对流对水汽同位素的淋洗作用，水汽δ18O表现为极低值。冬春季聂拉木地表水汽主要来源于喜马拉雅南部低海拔潮湿的水汽主导，δ18O较高，而来自北部青藏高原内陆的冷干水汽的δ18O则表现为低值。

The stable isotope composition of atmospheric vapor is intimately related to its region, rainout histories. The isotope ratios of atmospheric vapor provide critical information about the mechanisms of evaporation at the land surface moisture transport processes and the paleosedimentary records. Currently only a few studies have considered isotopes in atmospheric water vapor on the Tibetan Plateau even in China. The present thesis focused on a study of stable isotope compositions in the atmospheric vapor samples which are collected at Nyalam and Lhasa site in southern Tibetan Plateau. Combined with the meteorological data and isotope ratio of concurrent precipitation collected at Nyalam and Lhasa, this thesis comprehensively analyzed the temporal variations in the atmospheric vapor isotope ratio observed near the ground, the relationship between the isotope ratio in water vapor and concurrent precipitation, and the relationship between different meteorological variables and the vapor isotope composition. The main transport circulations of atmospheric moisture and its impacts on the vapor isotope ratio are also examined in the thesis. The followings are main results of the study: The temporal variation of isotopic composition in atmospheric vapor shows considerable fluctuations, sometimes exceeding 20 per mil over just one week in rainy season caused by the precipitation events. It's shown that the vapor ratio is a linear function of specific humidity, which has a dominant impact on the variation of the water vapor δ18O. Compared with specific humidity, temperature is the second order factor that affects the atmospheric vapor δ18O at Lhasa during dry season. However, the daily variation of the δ18O is highly correlated with specific humidity in rainy season. The precipitation in Lhasa mainly lasts from May to September. During rainy season, the monthly water vapor isotope ratio changes in parallel with concurrent precipitation. The vapor δ18O is 11.4 per mil lower in δ18O than that in precipitation in average. However both show a similar tendency in daily variation. In precipitation events, the vapor in the surface layer is in general brought to state of equilibrium with falling raindrops. While during winter and spring precipitation events in Nyalam, the vapor that formed snowflakes is from high level of the troposphere, and the average δ18O in surface vapor is higher than that in the concurrent precipitation by 3.0 per mil. The oxygen isotopic composition of vapor near the ground often exhibits the most extreme values caused by the incursion of the free atmosphere moisture. The water vapor is relatively rich in heavy oxygen isotope when water vapor brought by the westerlies and the local circulations. This is in contrast to the water vapor transported through monsoons when the vapor is more depleted in heavy oxygen isotope. And the extreme low value of the water vapor δ18O in the ground level thought to be reflecting the wash-out of the heavy isotope during the strong convection weather occurs in monsoon region. At Nyalam the water vapor near the ground is dominated by northward moist vapor with high δ18O which originated from low altitude area to the southern slope of the Himalayas, while the cold dry vapor from inland of high plateau is characterized with low δ18O.