A novel insight into MJO predictability: initial errors can trigger a prediction barrier over the maritime continent

Forecasting the eastward propagation of the Madden–Julian Oscillation (MJO) across the Maritime Continent (MC) remains a significant challenge, often characterized by a rapid decline in prediction skill—a phenomenon known as the Maritime Continent prediction barrier (MC-PB). While conventional perspectives have predominantly attributed the MC-PB to model deficiencies, this study demonstrates that initial errors can also trigger a pronounced MC-PB. Furthermore, the results reveal that initial moisture errors are the dominant factor driving the growth of MJO forecast errors. By employing the Conditional Nonlinear Optimal Perturbation (CNOP) method, we identify two distinct types of initial moisture errors that are particularly prone to inducing the MC-PB for different MJO events. These initial errors exhibit distinct spatial patterns and, by modulating westward-propagating equatorial Rossby (ER) waves, disrupt MJO propagation across the MC via two physical pathways. Specifically, one type significantly decelerates MJO propagation, while the other weakens MJO intensity, both ultimately leading to the MC-PB. All these results suggest that optimizing initialization schemes provides a novel pathway for effectively alleviating the MC-PB effect and greatly improving MJO prediction level.