The dynamics of the El Niño–Southern Oscillation diversity in the recharge oscillator framework

This study investigates the observed El Niño-Southern Oscillation (ENSO) dynamics for the eastern Pacific (EP) and central Pacific (CP) events in reference to the canonical ENSO (T). We use the recharge oscillator (ReOsc) model concept to describe the ENSO phase space and polar coordinate statistics, based on the interaction of sea surface temperature (T) and thermocline depth (h), for the different types of ENSO events. We further look at some important statistical characteristics, such as power spectrum and cross-correlation as essential parameters for understanding the dynamics of ENSO. The results show that the dynamics of the EP and CP events are very different from each other and from the canonical ENSO events. The canonical ENSO (T) events fit closest to the idealised ReOsc model and has the most clearly oscillating ENSO phase space, suggesting it is the most predictable ENSO index. The EP phase space evolution is similar to the canonical ENSO, but the phase transitions are less clear, suggesting less of an oscillatory nature and that the index is more focussed on extreme El Niño and discharge states. The CP phase space, in turn, does not have a clear propagation through all phases and are strongly skewed towards the La Niña state. The interaction between CP and h are much weaker, making the mode less predictable. Wind forced shallow water model simulations show that the CP winds spatial pattern do not force significant h tendencies, strongly reducing the delayed negative feedback, which is essential for the ENSO cycle.