The Relationship between Contiguous El Niño and La Niña Revealed by Self-Organizing Maps

Abstract

his study introduces a new methodology for identifying El Niño and La Niña events. Sea surface temperature (SST) anomaly patterns for El Niño and La Niña onset, peak, and end phases are classified by self-organizing maps (SOM) analysis. Both onset and end phases for El Niño and La Niña exhibit eastern Pacific (EP) and central Pacific (CP) types. The SST anomaly patterns in peak phase can be classified into EP, EP-like, and CP types for El Niño, and EP, mixed (MIX), and CP types for La Niña.The general type of each El Niño or La Niña event is then defined according to the SST type for each of the three phases. There is no robust connection between the general types of the contiguous El Niño and La Niña except that the MIX La Niña rarely induces a subsequent CP El Niño. However, there are strong relationships between the end-phase type of El Niño and the onset-phase type of the subsequent La Niña. The EP-end-type El Niño favors transition to the CP-onset-type La Niña, while the CP-end-type El Niño favors transition to the EP-onset-type La Niña. On the other hand, the CP-end-type La Niña favors transition to EP-onset-type El Niño. Furthermore, an El Niño that occurs after the decay of La Niña favors initiating as an EP-onset type. These relationships are driven by different atmosphere?ocean dynamics, such as coupled air?sea feedback, thermocline feedback, slow SST mode, and Bjerknes feedbacks.