Abstract

A simple conceptual model suggests that the complex behaviour of the El Nino/Southern Oscillation can be explained by zonal shifts in the Walker circulation. The El Nino/Southern Oscillation (ENSO) represents the most consequential fluctuation of the global climate system, with dramatic societal and environmental impacts. Its general dynamics are reasonably well understood in terms of ocean-atmosphere interactions that modify the Walker circulation in the equatorial Pacific. However, some of its space-time features remain stubbornly elusive, such as its event-to-event diversity and asymmetry. Here we show that zonal shifts in the Walker circulation control ENSO space-time complexity in a low-dimensional theoretical framework. We encapsulate these movements in a conventional recharge-discharge oscillator for ENSO by replacing the regionally fixed sea surface temperature index with a warm-pool edge index that displaces the Walker circulation structures. By doing so, we can model essential ingredients of ENSO diversity and nonlinear behaviour without increasing the complexity of the dynamical model. The simple framework is able to reproduce the continuum of ENSO flavours and the asymmetry in the amplitude of warm and cold events. The spatial shifting concept paves the way for a more unified understanding of ENSO and its associated climate teleconnections.