Classifying El Nino Modoki I and II by Different Impacts on Rainfall in Southern China and Typhoon Tracks

Based on their opposite influences on rainfall in southern China during boreal fall, this paper classifies El Nino Modoki into two groups: El Nino Modoki I and II, which show different origins and patterns of SST anomalies. The warm SST anomalies originate in the equatorial central Pacific and subtropical northeastern Pacific for El Nino Modoki I and II, respectively. Thus, El Nino Modoki I shows a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific, whereas El Nino Modoki II displays an asymmetric distribution with the warm SST anomalies extending from the northeastern Pacific to the equatorial central Pacific. Additionally, the warm SST anomalies in the equatorial central Pacific extend farther westward for El Nino Modoki II than for El Nino Modoki I. Similar to the canonical El Nino, El Nino Modoki I is associated with an anomalous anticyclone in the Philippine Sea that induces southwesterly wind anomalies along the south coast of China and carries the moisture for increasing rainfall in southern China. For El Nino Modoki II, an anomalous cyclone resides east of the Philippines, associated with northerly wind anomalies and a decrease in rainfall in southern China. The canonical El Nino and El Nino Modoki I are associated with a westward extension of the western North Pacific subtropical high (WNPSH), whereas El Nino Modoki II shifts the WNPSH eastward. Differing from canonical El Nino and El Nino Modoki I, El Nino Modoki II corresponds to northwesterly anomalies of the typhoon steering flow, which are unfavorable for typhoons to make landfall in China.