Abstract: Based on the monthly precipitation data in 100 weather stations during June to August from 1961 to 2012 in Inner Mongolia, years with abundant and scarce rainfall at a single station and in the study area were classified according to the precipitation anomaly percentage and their characteristics were analyzed. Aiming at the years with abnormally abundant or scarce rainfall, the distribution characteristics of the atmospheric circulation over the northern hemisphere in the corresponding period were discussed. The results show that rainfall is in a decreasing trend in August, while it is periodically abundant (scarce) in June and July and years with scarce rainfall are great than that with abundant rainfall. For the years with abundant rainfall, the circulation distribution in the middle and upper latitude is radial at 100 hPa height field over the Euope-Asia area, and the polar vortex is weak. The circulation situation is two troughs and one ridge in June and Inner Mongolia is located in the front of high ridge, while it is two ridges and one trough in July and August and Inner Mongolia is located in the back of high ridge. The deformation frontogenesis at 500 hPa in Asia is the main circulation causing the abnormally abundant rainfall in June. Meanwhile, the circulation situation in the middle and upper latitude is two ridges and one trough and Inner Mongolia is located in the wide low trough between two ridges in June, while that is high in the east and low in the west and Inner Mongolia is located in the low trough in July and August. It is controlled by cyclonic shear zone or wind convergence zone over Inner Mongolia at 850 hPa contour chart. On the other hand, for years with scarce rainfall, the circulation distribution in the middle and upper latitude is latitudinal, and the polar vortex is strong at 100 hPa and 500 hPa. Inner Mongolia is located in the positive anomaly area of north high pressure in south Asia. Wind field at 850 hPa chart is weak without obvious water vapor transport.

Key words: font-family: "Times New Roman", mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, Abnormal precipitation')">mso-fareast-font-family: 宋体">Abnormal precipitation, Abundant rainfall year, Scarce rainfall year, Atmospheric circulation