Characteristics of Extreme Precipitation and Associated Anomalous Circulations over Eastern China during Boreal Summer

Anomalous circulations associated with various extreme precipitation events in summer are investigated from the perspective of atmosphere dynamics using daily precipitation data collected at 438 stations from 1961 to 2014 in eastern China and the NCEP/NCAR reanalysis data. The results demonstrate that in the middle and lower reaches of the Yangtze River, increases in the frequency of extreme precipitation always correspond to weaker than normal East Asian summer monsoon, which is reflected in abnormal 850-hPa wind field and water vapor flux that are favorable for more water vapor transport to the middle and lower reaches of Yangtze River. At 500 hPa, a blocking high persists over the Okhotsk Sea, which is conductive to the cold air moving southward. The East Asian subtropical westerly jet anomalously moves southward at 200 hPa, while the westerly wind anomalies to the south of 30°N promotes divergence development, and the wave activity fluxes are favorable for generating and maintaining wave perturbations in this region. In North China, corresponding to increases in the frequency of extreme precipitation, anomalies of 850-hPa wind field and water vapor flux indicate that the East Asian summer monsoon is stronger than normal, which strengths the water vapor transport to North China. The positive anomaly is located over the Sea of Japan and the negative anomalies are located over Mongolia, Baikal and their vicinity at 500 hPa. East Asian subtropical westerly jet abnormally shifts northward at 200 hPa, while the wave activity fluxes are also favorable for generating and maintaining wave perturbations in this region. All the above results suggest that the occurrence of extreme summer precipitation in East China is closely associated with atmospheric dynamics and energy transmission.