Effect of East Asian Summer Monsoon on Summer Precipitation in Shanxi Province

By using NCEP daily reanalysis data for 1948-2007,monthly precipitation data at 600 observation stations in China for 1960-2007,and monthly and daily precipitation data at 65 observation stations in Shanxi Province for 1960-2007,the date for summer monsoon onset in Shanxi Province was confirmed by verifying the date on which both isolines of pentadly mean potential pseudo-equivalent temperature θse=340 K and pentadly mean meridional south wind speed ≥2.5 m·s-1 overpass 35°N synchronously along 112.5°E on 850 hPa. The summer monsoon index I was constructed by standardizing the ratio of persisting pentads of θse≥340 K to its normal mean pentads. It was verified that I can represent not only the intensity and spatial pattern of East Asian summer monsoon quite well,but also those of summer precipitation in Shanxi Province. The interdecadal variability and linear trend of I showed that the influence of East Asian summer monsoon on precipitation in Shanxi Province has weakened obviously since the 1970s,and the abrupt change was around 1967. Analysis on the dates of summer monsoon onset and retreat in Shanxi Province indicated that the persisting time of the summer monsoon is shorter in recent 48 years. Finally,the characteristics of the general circulations for strong and weak summer monsoon indcies were analyzed,respectively. The authors mainly focused on the study of the influence of the East Asian summer monsoon on the summer precipitation in Shanxi Province. The result is valuable for both of the research and operation.