长沙大气水汽、降水中稳定同位素季节变化及与水汽输送关系

Seasonal Variations of Stable Isotope in Precipitation and Atmospheric Water Vapor and Their Relationship with Moisture Transportation in Changsha City

基于2010年1月至2012年12月长沙降水事件同位素资料和搭载在Aura卫星上的TES观测仪所反演的2010年3月至2011年12月全球日大气中HDO、H2O资料,对长沙大气水汽、降水中稳定同位素的变化特征以及它们的关系,不同水汽来源及输送强度变化对降水中同位素的影响进行了研究。结果表明:水汽中同位素值随高度增加而贫化,水汽中同位素较降水中同位素大为贫化,降水中同位素为冬春富集、夏秋贫化,水汽中同位素则表现出春夏富集、秋冬贫化,水汽、降水中同位素存在着较大波动。通过对长沙冬、夏季所有降水事件的水汽输送轨迹的分析发现:夏季降水的水汽主要来源于西南季风和东南季风输送的海洋性气团,降水中同位素贫化;冬季降水的水汽主要来源于西风带输送的大陆性气团,降水中同位素富集。另外,长沙2010~2012年夏季的水汽输送通量与降水同位素的关系再次证明环流效应是可信的。

In this study, the variation and relationship of stable water isotope both in precipitation and atmospheric water vapor, the influence of different moisture sources and their strength during transportation on precipitation isotopes are analyzed by using precipitation events isotope that covered a period of Jan. 2010 to Dec.2012 in Changsha and TES retrievals of daily HDO, H2 O data from Mar. 2010 to Dec.2011. The results show that firstly, decreasing atmospheric water vapor isotope values with increasing altitude. Secondly, comparing atmospheric water vapor with precipitation, the former is more depleted in isotope. Thirdly, precipitation isotopes values are high in winter and spring, low in summer and fall, referring to water vapor isotope, it is high in spring and summer, low in fall and winter. Fourthly, isotopes both in water vapor and precipitation have evident fluctuation. Moisture trajectories of precipitation events for summer and winter in Changsha suggest that in summer, the moisture is transported by the southwest and southeast monsoon from low latitude oceans, with high humidity, low stable isotopic ratios owing to the rainout of water vapor along the transport history. Then,in winter, the water vapor is primarily from the westerly transportation, with low humidity, high stable isotopic ratios in precipitation. Further analysis of the relationship between moisture flux and precipitation isotopes in summer Changsha confirmed that the circulation effect is credible.