贡嘎山亚高山降水稳定同位素特征及水汽来源研究

A STUDY ON PRECIPITATION STABLE ISOTOPES CHARACTERISTICS AND VAPOR SOURCES OF THE SUBALPINE GONGGA MOUNTAIN,CHINA

为揭示青藏高原东南缘贡嘎山地区的大气降水稳定同位素特征和水汽来源,利用贡嘎山东坡亚高山地区2012年5月至10月实测的大气降水稳定氢氧同位素和气象资料,分析了贡嘎山地区的降水线特征、降水稳定氢氧同位素时空分异特征及其与气候因子之间的关系和氘盈余特征,并运用HYSPLIT模型探讨了该区的水汽来源特点。结果表明:贡嘎山亚高山地区大气降水线方程为δD=9.401 9×δ18 O+28.530 3(‰)(R2=0.983 3,p<0.001),反映了该区湿润、多雨、气温较低的气候特点;该区大气降水稳定氢氧同位素季节变化明显,雨季先降低后升高;降水中氢氧同位素的高程效应显著且存在季节差异;降水稳定氢氧同位素受温度、降水气象因子影响较大,降水量效应显著并且与温度存在负相关关系;后向轨迹模型模拟结合同位素特征分析表明该地区雨季水汽来源较为复杂,主要有西风输送、东部季风和局地水汽内循环3个来源。研究结果可为区域水汽循环和降水特征提供科学依据。

The stable isotopic composition of precipitation are integrated tracers of atmospheric processes worldwide.It is widely used to determine vapor sources with precipitation stable hydrogen and oxygen isotopes.More than 20 stations in the Tibetan Plateau has been studied the precipitation isotopic composition since the 1990 s.But the precipitation isotope characteristics and water vapor moving patterns in Tibetan Plateau southeast edge of Gongga Mountain remains unclear.Based on the precipitation samples and detailed meteorological data in subalpine area of Gongga Mountain from May 2012 to October 2012,we analyzed the temporal and spatial variation ofδD andδ18 O.Meanwhile,the water vapor sources of Gongga Mountain was tracked by HYSPLIT model with backwards trajectory method and the modeled trajectories was synthesized withδD andδ18 O values.The results shows that the LMWL（Local Meteoric Water Line）of this region isδD = 9.4019 × δ18 O ＋ 28.5303（‰）（R2= 0.9833,p 0.001）.This LWML＇s slope and interception is higher than the GMWL（Global Meteoric Water Line）,which is caused by the rainy and relatively low temperature meteorological characteristics of the subalpine area of Gongga Mountain.BothδD and δ18 O decreases when the mountain elevation rises,which is because both temperature and precipitation amount changes along the elevation.This＂altitude effect＂differs in different months.TheδD andδ18 O of this region are both high when rainy season begins and ends.The highest radiation at august leads to a small peak on hydrogen and oxygen isotope curves.Statistical analysis indicates that the relationships between stable precipitation isotopes and meteorological factors are closely related.When the temperature and precipitation amount rises,both hydrogen and oxygen isotopes decreases.Besides,hydrogen and oxygen isotopes are negatively and positively correlated with water vapor pressure and wind velocity,respectively.Monthly deuterium excess data shows no ＂altitude effect＂and no differences with global average deuterium excess value 10‰.Backwards trajectory analysis associated with the isotope data reveal that the vapor sources of this area are mainly from westerly transport,eastern monsoon and local evaporation.This pattern is similar to Tibetan Plateau and Himalayas.The results can provide a scientific basis for the study of hydrological and atmospheric processes in alpine ecosystem.