Vapor Origins Revealed by Deuterium Excess in Precipitation in Southwest China

In order to reveal the vapor origins of precipitation over Southwest China,the variations of stable isotopes including deuterium excess d and the relationships of the stable isotopes with temperature and humidity at Mengzi and Tengchong sampling stations are analyzed.Under the monsoon system,d in precipitation has distinct seasonality with lower values in the rainy season and higher values in the dry season.Analyses show that the relationship of d in precipitation with temperature and humidity in the middle and low troposphere has consistency.If taking into account the relationships of d and δD in precipitation with atmospheric humidity comrehensively,it can be deduced that the main causation of stable isotopic variations in precipitation over Southwest China is related to the property of rainfall air mass,whereas the evaporation enrichment action in falling raindrop is relatively light.In the rainy season of Southwest China,the vapor of generating precipitation,with high humidity,low stable isotopic ratios owing to the rainout of vapor on the transport way,and small d-values in precipitation,is primarily from low-latitude oceans;in the dry season,the vapor of generating precipitation,with low humidity,great stable isotopic ratios and high d-values in precipitation,is primarily from the westerly transportation and the replenishment of re-evaporated vapor in inland.