Climatological significance of stable isotopes in precipitation over south-west China

摘要

The variations of stable isotopes including deuterium excess d over south-west China are displayed, and the relationships of the stable isotopes in precipitation with temperature and humidity at different altitudes are also researched. Under the prevailing monsoon system, distinct seasonality for δ~(18)O and d in precipitation are shown and the reverse correlations with vapour pressure and atmospheric precipitable water (PW) are marked clearly for the sampling at the Mengzi, Tengchong and Simao stations. Analyses indicate that the relationship between δ~(18)O and d in precipitation with temperature and humidity in the middle and low troposphere is consistent. Taking into account the relationships of δ~(18)O and d in precipitation with atmospheric humidity comprehensively, it is deduced that the main causation affecting stable isotopic variations in precipitation over south-west China is mainly related to the property of air mass for rainfall, whereas the evaporation-enrichment action in a falling raindrop works in a relatively weaker manner. During the rainy season, vapour generating precipitation with high humidity and low stable isotopic ratios owing to the rainout of vapour on the transport routine, and also the small d in precipitation, comes primarily from low-latitude oceans. In contrast, vapour generating precipitation with low humidity and great stable isotopic ratios and high d in precipitation in dry seasons is assumed to be primarily from the westerlies' transportation and results, with high probability, from the replenishment of re-evaporated vapour inland. On an annual timescale, the precipitation amount weighted mean δ~(18)O values suggest negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa.