To find out the causes of abnormal summer rainfall in North China and to improve climate prediction technologies, a comprehensive analysis on the relationship between East Asian summer monsoon and summer precipitation in North China is carried out in this paper by defining the index of East Asian summer monsoon with the meridional wind field and based on such data as summer precipitation in North China and general atmospheric circulation reanalyzed by NCEP/NCAR. The results of the analysis indicate that:1) North China has more summer rainfall during strong East Asian summer monsoon years but less summer rainfall during weak East Asian summer monsoon years. An opposite case also exists. The spatial distribution pattern of more (less) rainfall in East Asian strong summer monsoon years is significantly different from that of more (less) rainfall in weak East Asian summer monsoon years. (2) Irrespective of strong or weak East Asian summer monsoon years, the circulation conditions contributing to more summer rainfall in North China are sufficient water vapor sources (strong summer monsoon years:abnormal water vapor carried by southwest wind; weak summer monsoon years:abnormal water vapor carried by southeast wind) and good dynamic conditions (with convergence circulation at 850 hPa in North China, prominent zonal circulation at 500 hPa at middle latitude, and more low-pressure trough transit in North China). (3) The circulation pattern related to less summer rainfall in North China is significantly different:No effective dynamic conditions (with divergence circulation at 850 hPa in North China, prominent meridional circulation at 500 hPa at middle latitude, and less low-pressure trough transit in North China) are created both in strong summer monsoon years with sufficient water vapor sources (abnormal southwest wind) and weak summer monsoon years with insufficient water vapor sources (abnormal northerly wind). (4) Although there are sufficient water vapor sources in strong East Asian summer monsoon years, the summer rainfall differs a lot in different years in North China due to diverse dynamic conditions. If the dynamic conditions are good, North China will have abnormally more summer rainfall; otherwise, it will also have abnormally less summer rainfall. (5) In weak East Asian monsoon years, water vapor carried by southwest wind is reduced significantly, so North China will have abnormally less summer rainfall if there is lack of water vapor supplement from other paths and the dynamic conditions are poor. Although water vapor carried by southwest wind is reduced significantly in weak summer monsoon years, sometimes there are also sufficient water vapor sources in North China if more water vapor is carried by southeast wind. At the same time, if the dynamic conditions are good, North China may also have abnormally more summer rainfall, as the case during 2011 2013. In terms of the prediction of summer rainfall in North China, it cannot be simply considered that North China will have more summer rainfall in case of strong East Asian summer monsoon or will have less summer rainfall in case of weak East Asian summer monsoon, as the intensity change of East Asian summer monsoon only suggests different water vapor conditions. The summer rainfall in North China can only be well predicted after the dynamic conditions are also considered.
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