Recharge Oscillator Mechanisms in Two Types of ENSO

El Niño and Southern Oscillation (ENSO) in recent decades tends to behave arguably in two different types. One is the canonical cold-tongue (CT) -type ENSO with major sea surface temperature anomalies (SSTA) positioned over the eastern Pacific. The other is a warm-pool (WP) -type ENSO with SSTA centered in the central Pacific by the WP edge. In this study, we examine the basic features and main feedback processes of these two types of ENSO. It is shown that the interannual variability of upper-ocean heat content exhibits recharge-discharge processes throughout the life cycles of both the CT and WP types of ENSO. Through heat budget analyses focused on the interannual variability, we further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of the both types of ENSO, whereas the zonal advective feedback contributes mainly to their phase transitions. The westward shift of the SSTA center of the WP ENSO and the presence of significant surface easterly wind anomalies over the far eastern equatorial Pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for its eastern-Pacific SSTA. Nevertheless, both the WP and CT ENSO can be understood to a large extent by the recharge oscillator mechanism.