The role of spatial shifting in El Niño/Southern Oscillation complexity

The El Niño-Southern Oscillation (ENSO) represents the most consequential fluctuation of the global climate system, with dramatic societal and environmental impacts. Here we show that the spatial shifting movements of the Walker circulation control the ENSO space-time complexity in a major way. First, we encapsulate the process in a conventional recharge-discharge oscillator for the ENSO by replacing the regionally fixed sea surface temperatures (SST) index against a warm pool edge index. By doing so, we can model essential ingredients of ENSO diversity and nonlinear behavior without increasing the complexity of the dynamical model. Second, we propose a data-driven method for estimating equatorial Pacific SST variability resulting from spatial shifting. It consists in time-averaging conditions respective to the evolving warm pool edge position, then generating back SST data with reduced dimensionality (one degree of freedom) from the movements of the resulting "shifted-mean" profile. It is shown that the shifted-mean SST generated in this fashion reasonably reconstructs observed interannual SSTs both in terms of amplitude and pattern diversity. We discuss implications of the present paradigm of spatial shifting for understanding ENSO complexity, including tropical basins interactions.