A New Approach for Classifying Two Types of El Nino Events

In recent decades, the typical El Ni?o events with the warmest SSTs in the tropical eastern Pacific have become less common, and a different of El Ni?o with the warmest SSTs in the central Pacific, which is flanked on the east and west by cooler SSTs, has become more frequent. The more recent type of El Ni?o was referred to as central Pacific El Ni?o, warm pool El Ni?o, or dateline El Ni?o, or the El Ni?o Modoki. Central Pacific El Ni?o links to a different tropical-to-extratropical teleconnection and exerts different impacts on climate, and several classification approaches have been proposed. In this study, a new classification approach is proposed, which is based on the linear combination (sum or difference) of the two leading Empirical Orthogonal Functions (EOFs) of tropical Pacific Ocean sea surface temperature anomaly (SSTA), and the typical El Ni?o index (TENI) and the central El Ni?o index (CENI) are able to be derived by projecting the observed SSTA onto these combinations. This classification not only reflects the characteristics of non-orthogonality between the two types of events but also yields one period peaking at approximate two to seven years. In particular, this classification can distinguish the different impacts of the two types of events on rainfall in the following summer in East China. The typical El Ni?o events tend to induce intensified rainfall in the Yangtze River valley, whereas the central Pacific El Ni?o tends to induce intensified rainfall in the Huaihe River valley. Thus, the present approach may be appropriate for studying the impact of different types of El Ni?o on the East Asian climate.