A relationship between timing of El Niño onset and subsequent evolution

Abstract

A relationship between the timing of El Niño onset and the subsequent evolution is examined, using 130‐year long time series of Niño‐3.4 index from 1871 to 2000. It is found that El Niño events can be classified into two major types: one is the onset of which is from April to June (spring type) and the other is from July to October (summer‐fall type). Here, the duration of El Niño is defined as the period when the 5‐month running mean anomaly of Niño‐3.4 index is exceeding 0.5°C. As a result, 24 El Niño events are identified, and classified into 10 spring type events and 14 summer‐fall type events. In general, spring type events grow greater in magnitude, and take the mature phase around a boreal winter and the evolution is relatively regular. On the contrary, summer‐fall type events are relatively weaker in magnitude, and have rather irregular aspects.