Classifying el niño modoki I and II by different impacts on rainfall in southern China and typhoon tracks

Abstract

Based on their opposite influences on rainfall in southern China during boreal fall, this paper classifies El Niño Modoki into two groups: El Niñ o 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 Niño Modoki I and II, respectively. Thus, El Niñ o Modoki I shows a symmetric SST anomaly distribution about the equator with the maximum warming in the equatorial central Pacific, whereas El Niñ o 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 Niño Modoki II than for El Niño Modoki I. Similar to the canonical El Niñ o, El Niño 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 NiñoModoki 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 Niñ o and El Niñ o Modoki I are associated with a westward extension of the western North Pacific subtropical high (WNPSH), whereas El Niño Modoki II shifts the WNPSH eastward. Differing from canonical El Niño and El Niñ o Modoki I, El Niño Modoki II corresponds to northwesterly anomalies of the typhoon steering flow, which are unfavorable for typhoons to make landfall in China. © 2013 American Meteorological Society.