Propagation of the Madden-Julian oscillation as a deterministic chaotic phenomenon

TL;DR

This study demonstrates that the Madden-Julian oscillation's propagation is a chaotic process driven by multi-scale nonlinear interactions, with implications for improved prediction models.

Contribution

It reveals the chaotic nature of MJO propagation caused by cross-scale nonlinear interactions, highlighting the role of equatorial asymmetry and tropical-extratropical interplay.

Findings

MJO propagation exhibits multiple regimes with distinct timings.

Chaotic behavior arises from nonlinear interactions across scales.

Probabilistic regime selection depends on sea surface temperature asymmetry.

Abstract

The Madden-Julian oscillation (MJO), a gigantic tropical weather system, is marked by eastward travel of cumulus cloud clusters over the Indo-Pacific region and often causes severe weather and climate events worldwide. The physics and predictability of MJO propagation remain elusive, partly because of little attention to untangling roles of multi-scale processes relevant to the MJO. Here, we reveal the chaotic nature of MJO propagation arising from cross-scale nonlinear interactions, based on 4,000-member ensemble global cloud-system-resolving simulations of two MJO events. Against conventional linearized thinking, multiple regimes with distinct timings of MJO propagation emerge under a single atmosphere-ocean background. The bifurcation emergence depends critically on the equatorial asymmetry of climatological sea surface temperature. Selection of the bifurcated regimes is probabilistic, influenced by whether tropical-extratropical interplay promotes moistening associated with westward-propagating tropical waves over the western Pacific. These aspects help build a comprehensive MJO model and foresee when the MJO propagates.