In arid regions,the stable hydrogen and oxygen isotopic composition in raindrops is often modified by sub-cloud secondary evaporation when they descend from cloud base to ground through the unsaturated air.As a result...In arid regions,the stable hydrogen and oxygen isotopic composition in raindrops is often modified by sub-cloud secondary evaporation when they descend from cloud base to ground through the unsaturated air.As a result of kinetic fractionation,the slope and intercept of the δ^(2)H-δ^(18)O correlation equation decrease.The variation of deuterium excess from cloud base to the ground is often used to quantitatively evaluate the influence of secondary evaporation effect on isotopes in precipitation.Based on the event-based precipitation samples collected at Urumqi Glacier No.1,eastern Tianshan during four-year observation,the existence and impact of secondary evaporation effects were analyzed by the methods of isotope-evaporation model.Under high air temperature,small raindrop diameter and precipitation amount,and low relative humidity conditions,the remaining rate of raindrops is small and the change of deuterium excess is large relatively,and the slope and intercept of δ^(2)H-δ^(18)O correlation equation are much lower than those of Global Meteoric Water Line,which mean that the influence secondary evaporation on precipitation enhanced.While on the conditions of low air temperature,high relative humidity,heavy rainfall,and large raindrop diameter,the change of deuterium excess is small relatively and the remaining rate of raindrops is large,and the slope and intercept of δ^(2)H-δ^(18)O correlation equation increase,the secondary evaporation is weakened.The isotope-evaporation model described a good linear correlation between changes of deuterium excess and evaporation proportion with the slope of 0.90‰/%,which indicated that an increase of 1%in evaporation may result in a decrease of deuterium excess about 0.90‰.展开更多
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...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。展开更多
基金funded by The Second Tibetan Plateau Scientific Expedition and Research(No.2019QZKK0201)the Strategic Priority Research Program of Chinese Academy of Sciences(Class A)(Nos.XDA20060201,XDA20020102)+1 种基金the National Natural Science Foundation of China(Nos.41761134093,41471058)The SKLCS founding(No.SKLCS-ZZ-2020)。
文摘In arid regions,the stable hydrogen and oxygen isotopic composition in raindrops is often modified by sub-cloud secondary evaporation when they descend from cloud base to ground through the unsaturated air.As a result of kinetic fractionation,the slope and intercept of the δ^(2)H-δ^(18)O correlation equation decrease.The variation of deuterium excess from cloud base to the ground is often used to quantitatively evaluate the influence of secondary evaporation effect on isotopes in precipitation.Based on the event-based precipitation samples collected at Urumqi Glacier No.1,eastern Tianshan during four-year observation,the existence and impact of secondary evaporation effects were analyzed by the methods of isotope-evaporation model.Under high air temperature,small raindrop diameter and precipitation amount,and low relative humidity conditions,the remaining rate of raindrops is small and the change of deuterium excess is large relatively,and the slope and intercept of δ^(2)H-δ^(18)O correlation equation are much lower than those of Global Meteoric Water Line,which mean that the influence secondary evaporation on precipitation enhanced.While on the conditions of low air temperature,high relative humidity,heavy rainfall,and large raindrop diameter,the change of deuterium excess is small relatively and the remaining rate of raindrops is large,and the slope and intercept of δ^(2)H-δ^(18)O correlation equation increase,the secondary evaporation is weakened.The isotope-evaporation model described a good linear correlation between changes of deuterium excess and evaporation proportion with the slope of 0.90‰/%,which indicated that an increase of 1%in evaporation may result in a decrease of deuterium excess about 0.90‰.
文摘在干旱地区,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。
