兰州市两场典型降水事件稳定同位素特征及其水汽来源  

Characteristics of Stable Isotopes and Moisture Sources of Two Typical Precipitation Events in Lanzhou City

作　　者：韩婷婷 张明军[1] 王圣杰[1] 杜勤勤 马转转 郭蓉[1] 曹晏风 HAN Ting-ting;ZHANG Ming-jun;WANG Sheng-jie;DU Qin-qin;MA Zhuan-zhuan;GUO Rong;CAO Yan-feng(College of Geography and Environmental Science,Northwest Normal University,Lanzhou 730070,C hina)

机构地区：[1]西北师范大学地理与环境科学学院,兰州730070

出　　处：《环境科学》2020年第9期3993-4002,共10页Environmental Science

基　　金：国家自然科学基金项目(41771035)。

摘　　要：为了加深对短时间尺度下降水同位素变化规律的认识,利用兰州市2019年夏季典型的长历时弱降水(6月26~27日)和短时强降水(7月28日)事件短时间尺度(10 min和30 min)的连续样品,结合HYSPLIT模型对降水氢氧稳定同位素的变化特征及其机制进行分析.结果表明,降水初始阶段,二次蒸发效应使事件内连续降水的大气水线(SMWL)斜率偏小.连续样点大都分布在GMWL和LMWL上方,且SMWL的截距都大于局地年平均过量氘(8.13),说明降水一定程度上经历了水汽再循环.6月26~27日连续2 d的降水事件,第1 d的δ18O呈"L"型变化,第2 d呈波动变化,δ18O不遵循降雨量效应.7月28日,δ18O呈平稳下降趋势,变化范围超过9‰.6月26日,500 m高度层水汽输送路径整体较短,27日以局地水汽蒸发为主.7月28日降水的水汽来源变化不明显,气团较单一,同位素值无明显波动.因此,对于短时间尺度下的单次降水事件,水汽来源的异同也是降水期间同位素变化的原因之一.To better understand the isotope variations on a short time scale,this study focused on a long-term rainfall event with light precipitation(June 26-27)and a short-term one with heavy precipitation(July 28)in Lanzhou City in the summer of 2019.Combined with HYSPLIT model,samples collected during a continuous precipitation event every 10 min and 30 min were analyzed to explore the characteristics and mechanism of stable hydrogen and oxygen isotopes in precipitation.The results indicate that the effect of sub-cloud secondary evaporation makes the slope of the sequential meteoric water line(SMWL)smaller at the beginning of the rainfall event.Most of the continuous sampling points are distributed above the global meteoric water line(GMWL)and local meteoric water line(LMWL).Moreover,the deuterium excess is larger than the local average annual deuterium(8.13),indicating that the samples have experienced moisture recycling to a certain extent.During two consecutive days(June 26-27)of rainfall,the variations in oxygen isotopeδ18O did not follow the effect of precipitation amount;the precipitationδ18O of the first day was"L"shaped,and it fluctuated the next day.On July 28,δ18O steadily decreased,and the range ofδ18O exceeded 9‰.On June 26,the moisture transport path was short at the height of 500 m and on June 27 local evaporation was the main pathway.On July 28,with a relatively stable air mass,the moisture source of the entire precipitation event did not change significantly,neither did the isotope value.Therefore,for a single precipitation event on a short time scale,the difference in moisture sources is one of the reasons for isotope variations.

关 键 词：短时间尺度 典型降水 连续采样 氢氧稳定同位素 水汽来源 兰州市 

分 类 号：X142[环境科学与工程—环境科学]