Temporal Variations of the Spring Persistent Rains and South China Sea Sub-high and Their Correlations to the Circulation and Precipitation of the East Asian Summer Monsoon

National Meteorological Information Center (NMIC) rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains (SPR) and the decay-pentad time index of the South China Sea (SCS) sub-high.These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon (EASM).Results show that,the summer rainfall over southeastern China decreases when SPR onset is late.For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau (TP) strengthens,which makes abnormal anti-cyclonic circulation (cyclonic convergent circulation weakens) appear over southeastern China.When the decay of SCS sub-high delays,abnormal flood prevails over the middle and lower reaches of the Yangtze River (MLYR) and to the south.That is mainly caused by EASM weakening while SCS sub-high strengthening,then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley.The two indexes have high correlations with multivariate ENSO index (MEI) in March, indicating that the climate abnormity in East Asia is related to global climate abnormity tightly.The two time indexes are independent of each other,which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM.From this point of view,we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.