The Dominant Modes of Precipitation Anomalies in Eastern China during the Peak of Pre-rainy Season in South China and Possible Causes

Based on daily observed rainfall data at 316 stations in China and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset for 1958-2011, dominant modes of precipitation anomalies over eastern China (to the east of 105°E) during the peak of pre-rainy season in South China (21 May to 10 June) and accompanying circulation as well as possible causes are investigated using statistical and diagnostic methods. Two dominant modes are revealed by empirical orthogonal function (EOF) analysis. The first EOF mode (EOF1) depicts a seesaw in precipitation anomalies between South China and the middle reaches of the Yellow River basin, while the second EOF mode (EOF2) shows a seesaw in precipitation anomalies between the eastern coastal region of South China and the mid-lower reaches of the Yangtze River valley. The major circulation characteristics corresponding to the two modes are different. EOF1 is attributed to the meridional displacement of the East Asian subtropical westerly jet stream (EAJS) and the zonal displacement of the western North Pacific subtropical high (WNPSH), while EOF2 is attributed to the intensity anomalies of the EAJS and the WNPSH. For EOF1, the 200-hPa Silk Road pattern wave train and the low-level wind anomalies jointly contribute to the corresponding circulation anomalies. For EOF2, the circulation anomalies are first induced by Polar Eurasia pattern and the circumglobal teleconnection. Anomalies in the lower levels are attributed to the dynamic effects of high level anomalies. Differences between the vertical structures of the two modes are also discussed.