Synoptic-scale variation of δ18O in summer monsoon rainfall at Lijiang, China

Based on the daily δO data in June―September 2003 at Lijiang and the daily mean NCEP/ NCAR reanalysis data, synoptic-scale variation of δO in summer monsoon rainfall was investigated. The ’precipitation amount effect’ is obvious for the daily δO variation, whereas the ’temperature effect’ is insignificant. Alternate occurrences of active phase and break phase of the southwest monsoon probably influence the synoptic-scale δO variation prominently. Moreover, the isotopic composition in precipitation during the late monsoon months is presumably influenced significantly by recycling of monsoon precipitation. Both the above factors disturb the ’amount effect’ of isotopic variation in the monsoon region. This study also indicates that the synoptic-scale rainfall δO variation at Lijiang in summer is domi-nated by the Indian monsoon depression (low pressure) system at large scale. These results are important for further studying the ’amount effect’ and reconstructing paleoclimate in the monsoon region.