Data and code from: Propagation of the Madden–Julian oscillation as a deterministic chaotic phenomenon

The Madden–Julian oscillation (MJO), a gigantic weather system marked by eastward travel of cumulus cloud clusters over the Indo-Pacific, often causes severe weather and climate events worldwide. Despite its frequent realization, the physics and predictability characteristics of MJO propagation are not well understood. We here reveal the chaoticity of MJO propagation, using 4,000-member ensemble global cloud-system-resolving simulations of two MJOs. Against previous linearized thinking, multiple regimes supporting MJO propagation emerge under a single atmosphere-ocean background, depending critically on the equatorial asymmetry of climatological sea surface temperature. Selection of the bifurcated regimes results from the stochastic modulation of moisture transport via westward-propagating equatorial waves, fostered or inhibited by tropical-extratropical interplay. Tracking the nonlinear processes we found gives metrics for predicting the timing of MJO propagation.