南京梅雨降水同位素组成从事件到年际尺度的变化特征

Temporal variability of the isotope compositions of plum rain in Nanjing from event to interannual time scales

梅雨降水量占季风区全年降水量的40%~50%,为了厘清梅雨降水同位素从事件到年际尺度上的变化特征及其影响因素,本研究分析了2015—2022年南京梅雨期间降水同位素特征,使用具有比湿分析的混合单粒子拉格朗日综合轨迹模型(HYSPLIT)分析了南京梅雨降水同位素的水汽来源和影响因素。结果表明:1)南京大气降水同位素组成夏季贫化、冬季富集,氘盈余(d_(x))夏低冬高,梅雨降水同位素组成较全年平均水平更为贫化;2)梅雨降水δ^(2)H和δ^(18)O与局地气象条件无显著相关关系;但雨量较小的降水事件中d_(x)较低,反映出云下二次蒸发的影响;梅雨降水量较多的年份,梅雨期间平均d_(x)明显较高;3)低纬度南海源区和西太平洋源区为梅雨提供水汽,水汽源地的转换会导致连续降水过程中同位素信号的突变。本研究能为季风区降水同位素研究提供数据支持,并为深入理解梅雨降水机理和研究东亚季风区大气环流季节变化提供参考。

Precipitation in the plum rain period accounts for 40%-50% of annual precipitation in the monsoon region.To clarify the temporal variability of the isotopic composition of precipitation during the plum rain period from event to interannual time scale and identify the influencing factors,we analyzed the isotopic composition of precipitation and its influencing factors in Nanjing from 2015 to 2022.By using the Hybrid Single-particle Lagrangian Integrated Trajectory(HYSPLIT)model with specific humidity analysis,we investigated the water vapor source and influencing factors.The results showed that 1)the isotopic abundance of atmospheric precipitation was depleted in the summer and enriched in winter.d_(x)was lower in summer and higher in winter.The isotopic abundance of precipitation from the plum rain was depleted compared to mean value of the whole-year.2)There was no significant correlation between δ^(2)H and δ^(18)O of the plum rain(precipitation)with local meteorological factors.However,d_(x) was lower in light rain,reflecting the effect of sub-cloud evaporation.The average d_(x) was higher during plum rain period in years with more total plum rain precipitation.3)The low-latitude South China Sea and the western Pacific Ocean source area provided water vapor for the plum rain.The shift of moisture source region led to abrupt changes in precipitation isotopes.Our results could provide data support for studies on precipitation isotopes in the monsoon region,as well as a reference point for further understanding the precipitation mechanism of the plum rain and studying the seasonal variability of atmospheric circulation in the East Asian monsoon region.