Intra-seasonal summer precipitation anomaly over eastern China and evolution characteristics of its associated tropical and mid-to-high latitudes atmospheric circulation

Based on CPC (Climate Prediction Center) daily precipitation data, NCEP/NCAR daily reanalysis data and NOAA outgoing longwave radiation data from May to August for the period 1981—2020, the characteristics of main modes of summer intra-seasonal precipitation anomalies in eastern China (named Southern type and Jiang-huai type precipitation anomalies) and the evolution features of associated atmospheric intra-seasonal oscillation (ISO) signals in tropical and mid-to-high latitudes are analyzed using EOF decomposition and lead-lag composite analysis. The causes of intra-seasonal precipitation anomalies are preliminarily discussed as well. The results show that: (1) The Southern type precipitation anomaly events are almost evenly distributed in early, middle and late summer, while the Jiang-huai type precipitation anomaly events mainly occur in middle summer. (2) In early summer, the Southern type precipitation anomalies are mainly presented as precipitation anomalies in the south of the Yangtze River, and in middle and late summer, while the precipitation anomalies in the north of the Yangtze River are also significant. (3) The Southern type precipitation anomaly events are affected by atmospheric ISO signals in the tropical and mid-to-high latitudes. The warm and moist air transport carried by the tropical atmospheric convection and the cold air activity accompanied by the propagation of the Rossby wave train in the mid-to-high latitudes generate water vapor convergence in the southern region, which is conducive to the development and maintenance of precipitation anomalies. In addition, atmospheric ISO signals in the tropical and mid-to-high latitudes are modified by intra-seasonal variations of sea surface temperature, subtropical high and jet stream. From early summer, mid-summer to late summer, the ISO source and propagation path of the tropical atmosphere have changed, and the propagation path and intensity of the Rossby wave train in the upper troposphere at mid-to-high latitudes are also different. (4) Reversed change of the middle and lower reaches of the Yangtze River and South China coast appears during Jiang-huai type precipitation anomaly events, accompanied by the east-west movement of the Western Pacific Subtropical High. The convective anomaly propagating northward and northwestward from the equatorial western Pacific Ocean and the intra-seasonal combined variation of the blocking highs over the Ural Mountains and the Sea of Okhotsk at mid-to-high latitudes are the main reasons for the formation of Jiang-huai type precipitation anomalies.