河西走廊中部大气降水δ^(18)O变化特征及水汽输送

Characteristics of δ^(18)O in precipitation and moisture transports in the central Hexi Corridor

河西走廊中部地区气候条件特殊,小循环过程独特复杂,因而应用降水等各种水体中的氢氧稳定同位素信息来明晰水循环特征,成为近年较为常用的方法.利用GNIP张掖站点大气降水稳定同位素资料和NCEP/NCAR再分析资料,通过研究张掖站11年大气降水的氢氧稳定同位素组成,建立了张掖局地大气降水线方程,结合西水、莺落峡、平川、正义峡4个辅助站点资料,分析了河西走廊中部地区氢氧稳定同位素的时间变化规律,并建立水汽输送模式.结果表明,除西水外,其余站点区域大气降水线方程的斜率与截距均低于全球和中国大气水线,说明河西走廊中部地区降水主要来源于大尺度水汽循环,局地蒸发较为强烈且降水过程中张掖站点的蒸发作用强于其他站点.河西走廊中部地区大气降水中δ18O与温度、水汽压之间呈现较为显著的正相关关系;在全年尺度下,降水量效应不明显;由于干旱区降水主要集中在气温较高的月份,在暖季,温度效应掩盖了降水量效应,使得降水量效应无法体现.对过量氘和水汽输送的研究表明,西风带的水汽输送为河西走廊中部地区提供了基本的水汽来源,西风带季节变化对其水汽输送通量散度和d值季节变化有直接的作用.从d值的变化来看,河西走廊中部具有明显的季节变化特征,暖季d值明显小于冷季,且呈现一种先降后升的变化趋势;从数值来看,暖季d值小于10‰的次数多于d值大于10‰的次数,冷季d值大于10‰的次数多于d值小于10‰的次数,说明冷季水汽在运行过程中受到地表水汽补给的作用明显.

Stable hydrogen and oxygen isotopes become a diagnostic tool in geosciences and environmental studies to investigate the circulation mechanism in rivers, lakes and groundwater. Based on the data provided by the Global Network of Isotopes in Precipitation （GNIP） and the national environmental protection agency/national center for atmospheric research （NCEP/NCAR）together with observed stable isotopic composition in Zhangye Region, we analyzed temporal variation of the isotopes and developed local meteoric water line equation and water vapor transportation model. The results show that theslope and intercept of local atmospheric precipitation line equations at all sites except Xishui are lower than those in the national and global atmospheric precipitation line equations. This is because precipitation in the central Hexi corridor region mainly comes from large scale water circulation and Zhangye site has a stronger local rainfall evaporation than other stations. The stable isotope δ18O in precipitation has a significantly positive correlation with temperature and vapor pressure. In the whole year, there is no obvious precipitation effect. As precipitation in arid areas is mainly concentrated in the summer months, temperature effect dominates over precipitation effect. The deuterium and water vapor transportation show that westerly water vapor transport provides the basic water vapor sources in central Hexi corridor and the seasonal variation of westerlies affects the seasonal change of the water vapor transport flux divergence and d value. The range of d value in the warm season is much smaller than the cold season, showing that water sources in the warm season have high relative humidity. The occurrence of d value under 10‰ is higher than above 10‰ in the warm season and vice versa, which indicates that the surface moisture replenishment has an obvious effect during the running process of atmospheric water vapor in the cold season.