Abstract:The main characteristics of the general atmospheric circulation in October 2021 are as follows. The polar vortex presented a unipolar pattern, with location shifting from the North Polar to Siberia. The circulation at 500 hPa showed a five-wave pattern in middle-high latitudes, with negative anomaly of geopotential height over the region from Northeastern Asia to Northeast Pacific, and positive anomaly over the North America to Arctic region. The subtropical high presented a long and narrow strip shape and almost surrounded the Northern Hemisphere. The Northwest Pacific subtropical high was smaller than those in recent years in the same period. The monthly mean precipitation was 52.1 mm, which is 45.4% more than normal, ranking the top 4th since 1961. Moreover, the distribution of the precipitation was unevenly. The monthly mean temperature was 10.7 ℃, 0.4 ℃ higher than normal. Three heavy rainfall processes and two cold air processes occurred in October, while four typhoons and one tropical depress were generated and developed. Among them the first heavy rainfall process was jointly caused by the northeast cold vortex, the low-level jet and the low-layer shear line, and became a long-term, heavy and extreme rainstorm process with a large amount of accumulated precipitation. Another two heavy rainfall processes were produced by Typhoon Lionlock (No.2117) and Kompasu (No.2118), both of which landed on Qionghai City of Hainan Province and brought heavy precipitation to the coastal area of southeastern and southern China.