Relations between oxygen stable isotopic ratios in precipitation and relevant meteorological factors in southwest China

The correlations of isotopic ratios in precipitation with temperature, air pressure and humidity at different altitudes, in southwest China, are analyzed. There appear marked negative correlations for the delta O-18 in precipitation with precipitation amount, vapor pressure and atmospheric precipitable water (PW) at Mengzi, Simao and Tengchong stations on synoptic timescale; the marked negative correlations between the delta O-18 in precipitation and the diurnal mean temperature at 400 hPa, 500 hPa, 700 hPa and 850 hPa are different from the temperature effect in middle-high-latitude inland. Moreover, the notable positive correlation between the delta O-18 in precipitation and the dew-point deficit Delta T-d at different altitudes is found at the three stations. On annual timescale, the annual precipitation amount weighted mean delta O-18 display the negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa. It can be deduced that, in the years with abnormally strong summer monsoon, more warm and wet air from low-latitude oceans is transported northward along the vapor channel located in southwest China and generates abnormally strong rainfall on the way. Meanwhile, the abnormally strong condensation process will release more condensed latent heat into atmosphere, and lead to the rise of atmospheric temperature during rainfall, but decline of the delta O-18 in precipitation. On the contrary, in the years with abnormally weak summer monsoon, the abnormally weak condensation process will release less condensed latent heat into atmosphere, and lead to the decline of atmospheric temperature during rainfall, but increase of the delta O-18 in precipitation.