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

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.