Based on analysis of monthly average precipitation data collected at 66 stations of the China Meteorological Administration and reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR),summer rainfall in southern China is classified into Yangtze-River Pattern (YRP) and South China Pattern (SCP) in this study.Atmospheric circulations and differences in earlier period SST and atmospheric circulations corresponding to the two rainfall patterns are analyzed to investigate the formation mechanisms and predictors for the above two rainfall patterns.Results show that the SCP occurrence frequency was higher than that of the YRP before the 1980s,while the YRP occurrence frequency increased after the 1980s.During the YRP years,the western Pacific subtropical high (WPSH) strengthened and shifted southwestward;the East Asian summer monsoon (EASM) weakened,accompanied by a southward shift of the subtropical westerly jet and stronger Ural blocking high (UB) and Okhotsk blocking high (OB).Under such a circulation pattern,the high-latitude Eurasia was under control of meridional circulations;cold and warm airmasses converged over the lower Yangtze River Valley,leading to abundant precipitation in this region.The atmospheric circulation pattern in the SCP years was almost opposite to that in the YRP years.Coupled with more landing typhoons in the SCP years,cold and warm airmasses often converged over South China,causing more precipitation in this region.Among all the influential factors,the location of the WPSH ridge-line and the intensity of the middle-and high-latitude blocking highs are two key factors that determine the YRP and SCP rainfall patterns.In addition,an analysis of sea surface temperature (SST) indicate that the pre-winter SSTs during the YRP years were warmer than normal in the central and eastern equatorial Pacific,which corresponded to the typical Eastern-Pacific type of El Niño,and the pre-winter subtropical South Indian Ocean Dipole (SIOD) was in negative phase.In contrast,the above two phenomena weakened in the spring of the YRP years when a continuous increase in SST could be observed in the Indian Ocean.The earlier period SST anomalies in the SCP years were also nearly opposite to that in the YRP years.Moreover,the correlations between summer rainfall in the middle and lower reaches of the Yangtze River (YRR) or in South China (SCR) with the pre-winter SST anomaly indices of Ninor3.4 and SIOD and with the spring Indian Ocean basin-wide (IOBW),both weakened after the 1980s,which is mainly attributed to the weakening of correlations between SSTs over the three key regions and the EASM and the ridgeline of the WPSH.Comparisons of earlier period atmospheric circulations for the two rainfall patterns show that significant differences in the atmospheric circulation between the YRP and SCP years mainly occurred in the spring.During the YRP years,the WPSH,the South China Sea subtropical high,the Mascarene high and Australian high all were stronger than that in the normal years,while the Euro-Atlantic polar vortex was weaker than that in normal years,and the NPO was in positive phase.For the SCP years,no significant key atmospheric circulations anomalies could be observed in early spring except that the Euro-Atlantic polar vortex was stronger than normal and the NPO was in negative phase.The abnormal signals of these key atmospheric circulation systems can be used as predictors for the two rainfall patterns.