长沙地区近地面水汽中氢氧稳定同位素的变化特征

Variations of hydrogen and oxygen isotopes in atmospheric water vapor of near surface in Changsha

基于在长沙地区2014年10月—2015年10月监测的近地面水汽中氢氧稳定同位素组成(δv)及相关气象要素,对水汽中氢氧稳定同位素的变化特征、影响因素及与降水中稳定同位素(δp)的相互关系进行了分析.结果表明:大气水汽中氢氧稳定同位素存在显著的季节变化和日变化,冬、春季值高于夏、秋季值,夜晚值高于白天值.δv^(18)O的季节变化与大尺度水汽输送的季节性变化有关,日变化则与地表蒸散发、大气湍流等局地气象条件有关.通过对δv^(18)O的平衡模拟发现,水汽中和降水中稳定同位素在暖季处于或接近平衡状态,在冷季处于非平衡状态.不同季节的大气水汽线和大气水线具有一定程度的相似性,两者的斜率均为暖季大于冷季;受下垫面新降水蒸发的影响,降水日大气水汽线的斜率和截距相对于无降水日均有增加,暖季分别增加0.11和3.52‰,冷季分别增加0.07和0.14‰.

In this study,variations of hydrogen and oxygen isotopes in water vapor near surface,their related meteorological parameters,and the interrelationship with stable precipitation isotopes were analyzed and compared based on the monitoring data in Changsha,Hunan,from October 2014 to October 2015. The results show that the stable isotopes in atmospheric water vapor have obvious seasonal and diurnal variations with higher δv^2H and δv^18O during winter and spring and in daytime. The seasonal variation of stable vapor isotopes is related to large-scale vapor transport,while their diurnal variation is related to local weather conditions,such as surface evapotranspiration,atmospheric turbulence,etc. By modeling the equilibrium between liquid and vapor phase,vapor isotopes and precipitation isotopes are in or near the equilibrium state in the warm season,but in non-equilibrium state in the cold season. The seasonal variations of the meteoric vapor line（ MVL） and the meteoric water line（ MWL） are similar with higher slopes in warm season. Affected by evaporation from new precipitation on the surface,the slope and intercept of MVL on precipitation days increase by 0.11 and 3.52‰ in warm season and 0.07 and 0.14‰ in cold season,respectively.