Abstract:In this study,using daily data from the NCEP/NCAR reanalysis dataset and precipitation observations recorded at 574 stations,two heavy rainfall processes during the periods of June 7-11 and 18-22,2010 occurring in the middle and lower reaches of the Yangtze River(MLRYR) are compared based on their respective circulations,Rossby wave activity fluxes,and tropical convection activities.The results show that a downstream propagation Rossby wave and double-block high were present in the mid-high latitudes throughout the time when these two processes occurred.During these events,it is shown that the intensity of the western Pacific subtropical high(WPSH) was stronger and the western extension point was more westward than normal in the low latitudes.However,two major differences are observed between the events:1)The source of the Rossby wave was located in northern Europe.Due to a low-pressure trough over the Lake Baikal area,the cold air turned southward to about 36°N.At the same time,the strengthened and westward WPSH were located at about 95°E.Next,the cold and warm air converged,leading to heavy rainfall.2)The source of the Rossby wave was located in northern Europe and central Siberia.The low-pressure trough in East Asia was more prominent than in the first rainfall process,which was conducive to the cold air reaching the MLRYR(about 30°N).In addition,the westward extension of the WPSH was located at about 90°E.The cold and warm air converged in the MLRYR and in its southern area,thereby leading to heavy precipitation in these regions.