Mixed mode oscillations of the El Ni\~no-Southern Oscillation

TL;DR

This paper demonstrates that the sporadic strong El Niño events can be explained as Mixed Mode Oscillations in a simplified climate model, revealing a critical threshold for rapid amplitude growth linked to a saddle-focus equilibrium.

Contribution

It introduces a novel explanation for ENSO bursting behavior as MMOs using a low-dimensional model and mathematical tools for fast-slow systems.

Findings

ENSO bursts can be modeled as MMOs in a simplified climate system.

A critical threshold for rapid ENSO amplitude growth is identified.

Link between MMO dynamics and a saddle-focus equilibrium point is proposed.

Abstract

Very strong El Ni\~no events occur sporadically every 10-20 years. The origin of this bursting behavior still remains elusive. Using a simplified 3-dimensional dynamical model of the tropical Pacific climate system, which captures the El Ni\~no-Southern Oscillation (ENSO) combined with recently developed mathematical tools for fast-slow systems we show that decadal ENSO bursting behavior can be explained as a Mixed Mode Oscillation (MMO), which also predicts a critical threshold for rapid amplitude growth. It is hypothesized that the MMO dynamics of the low-dimensional climate model can be linked to a saddle-focus equilibrium point, which mimics a tropical Pacific Ocean state without ocean circulation.