摘要
在干旱地区,降水中的氢氧稳定同位素组成常受到雨滴云下二次蒸发作用的影响而发生改变。基于全球降水同位素网(GNIP)在我国西北东部站点的数据并结合气象数据,分析雨滴二次蒸发作用发生的条件、季节特征、影响因素以及对降水氢氧稳定同位素组成的影响规律。研究表明:在我国西北东部,当近地表水汽压差(VPD)等于0.52 k Pa时,降水中氢氧稳定同位素组成规律发生显著改变。当VPD>0.52 k Pa时,地区降水线(LMWL)的斜率和截距与全球降水线(GMWL)无显著差别,且氘剩余(d-excess)也与VPD不存在显著相关关系。然而,当VPD>0.52 k Pa时,LMWL的斜率和截距显著地小于GMWL,d-excess与VPD存在显著的负相关关系。表明当VPD<0.52 k Pa时,保留了云层中热力学平衡分馏特征,而当VPD>0.52 k Pa时,降水氢氧稳定同位素经历了动力学非平衡分馏过程——云下雨滴在降落过程中二次蒸发作用。根据Tetens公式,当气温(t)<7.0℃时,空气饱和水汽压不可能超过0.52 k Pa,所以,当t<7.0℃时不可能发生雨滴二次蒸发过程。这样,在温带干旱地区,在t较低的冬半年降水中的δ18O只存在显著的温度效应,而在t较高的夏半年降水中的δ18O同时存在温度和降水效应。
In arid area,stable hydrogen and oxygen in precipitation change considerably after secondary evaporation of raindrop under cloud down to ground. Based on the data of stable hydrogen and oxygen in precipitation downloaded from GNIP and the meteorological data in the east of northwest China,the conditions,seasonal change and effect of secondary evaporation of raindrop and the composition of stable isotopes were analyzed and discussed. The results revealed that,when the low of vapor pressure deficit（VPD） was at 0. 52 k Pa,the composition of stable isotopes changed significantly. When VPD 0. 52 k Pa,there was no significant difference between the slope and intercept of local meteoric water line（LMWL） and the global meteoric water line（GMWL）,and there was no significant correlation between deuterium excess（d-excess） and VPD. However,when VPD 0. 52 k Pa,the slope and intercept of LMWL were significantly smaller than those of GMWL,and d-excess decreased significantly with VPD. It was demonstrated that,when VPD 0. 52 k Pa,the stable hydrogen and oxygen remained the thermodynamic equilibrium fractionation in cloud,whereas when VPD 0. 52 k Pa,they underwent the kinetic disequilibrium fractionation process of raindrop secondary evaporation under cloud down to ground. The results of Tetens formula revealed that,when air temperature（t） below 7. 0 ℃,saturated vapor pressure was not beyond 0. 52 k Pa,and there was no possibility to occur raindrop secondary evaporation when t 7. 0 ℃. Consequently,in temperate arid and semiarid areas,there is a temperature effect of δ18 O only when t is low in winter half year,but there are both temperature and precipitation effects when t is high in summer half year.
出处
《干旱区研究》
CSCD
北大核心
2017年第6期1263-1270,共8页
Arid Zone Research
基金
国家自然科学基金(41371079)
中国科学院前沿科学重点研究项目(QYZDJ-SSW-DQC014)资助
关键词
降水量效应
氘剩余
地区降水线(LMWL)
二次蒸发作用
水汽压饱和差
温度效应
中国西北东部
precipitation effect
deuterium excess （d-excess）
local meteoric water line （LMWL）
secondary evaporation
temperature effect
vapor pressure deficit （VPD）
east of northwest China
