洞庭湖流域降水同位素与ENSO关系研究

基于洞庭湖流域内长沙市2010年1月至2012年12月降水事件、GNIP(Global Network for Isotopes in Precipitation)长沙站1988~1992年月降水同位素资料及ENSO（厄尔尼诺/拉尼娜和南方涛动）的2个常用指标（南方涛动指数SOI和Nino3区海面温度SST）,分析了流域降水同位素与ENSO关系。结果表明：洞庭湖流域降水中δ¹⁸O与降水量、气温在日、月尺度上均呈负相关且只有月度上与降水量的负相关不显著。洞庭湖流域降水中δ¹⁸O与ENSO的SST指标则呈显著正相关。ENSO对洞庭湖流域降水同位素的影响机制可能如下：春季,La Nina年源自西太平洋的东南风强盛,其转向为西南风的区域达到印度洋,而El Nino年,东南风转向为西南风的发生区域位于印度洋以东,前者有利于挟带印度洋远源水汽向中国东部区域输送,进而造成降水同位素的贫化;夏季,La Nina年印度洋水汽输送在中国南海转为经向继而向北延伸,而El Nino年,源自印度洋的水汽沿纬向穿过南海,在东海转向往北延伸,后者有利于挟带西太平洋的近源水汽输送到中国东部季风区,进而引起降水同位素的富集。

Relationship of Stable Water Isotopes in Precipitation with ENSO in Dongting Lake Basin

In this study, the relationship between stable water isotopes in precipitation and ENSO is analyzed by using isotopic composition of water samples taken from individual precipitation events that covered a period of Jan. 2010 to Dec. 2012 and International Atomic Energy Agency Global Network for Isotopes in Precipitation(GNIP) data set in Changsha, which located in Dongting Lake Basin. The results show that monthly precipitation δ¹⁸O have significant negative correlation with precipitation amount and temperature both at daily and monthly scales, except with precipitation amount atmonthly timescale. The linear regression coefficient is significant and positive between monthly precipitation δ¹⁸O and Nino3’s SST (one of ENSO’s important index).The mechanism for ENSO’s influence on stable water isotopes of precipitation in the study area may be as follows: during the spring season, the region where southeast monsoon turns to southwest monsoon reaches the Indian Ocean in El Nino condition, while the turning takes place in east of the Indian Ocean in La Nina condition, the former picks up long distance moisture and transports to the study area and produces more depleted precipitation isotopes than the latter. During the summer season, long-distance water vapor from the Indian Ocean which drived by the southwest monsoon have northly tranported to the eastern China over the South China Sea in the La Nina condition, while in the El Nino condition, the southwest monsoon passes the South China Sea till the East China Sea and takes more moistue from the West Pacific Ocean to the eastern China, then the latter leads to higher precipitation isotopes in the study area than the former.