Contrasting Impacts of Developing Phases of Two Types of El Nino on Southern China Rainfall

The potential influence of the developing phases of the two types of El Nino (i.e., EP El Nino and CP El Nino) on rainfall over southern China was investigated using observational data sets from 1979 to 2008. The developing phases of the CP El Nino events are associated with enhanced rainfall over southern China during summer, whereas the influence is not significant in autumn. During the developing phases of the EP El Nino events, rainfall significantly increases over southern China during autumn but no significant increases are observed in summer. These increases in rainfall are a result of the circulation anomalies associated with the two types of El Nino events. The western Pacific subtropical high (WPSH) shifts northeastward during developing phases of the CP El Nino events in summer and is accompanied by enhanced convection and ascending flow. The WPSH shifts westward during the developing phases of the EP El Nino events in autumn and is associated with anomalous southwesterlies over southern China. These circulation anomalies favor more rainfall in southern China. No significant circulation anomalies occur during the developing phases of the CP El Nino events in autumn or the EP El Nino events in summer. These results highlight the importance of considering their developing phases when investigating effects of these two types of El Nino events on climate.