The Role of Equatorial Rossby Waves in Modulating the Eastward Propagation of the Madden–Julian Oscillation across the Maritime Continent

Abstract This study investigates the influence of equatorial Rossby (ER) waves on modulating the eastward propagation of the Madden–Julian oscillation (MJO). Using classification methods, the standing and jumping MJO clusters are identified as those impeded by ER waves. In these clusters, MJO convection splits and shifts poleward, in contrast to the continuously propagating MJO, which moves through the MC without disruption. Column-integrated moist static energy (MSE) budget analysis and time-scale separation were conducted to understand the dynamic mechanisms underlying the different behaviors among the MJO clusters. The results revealed that the positive MSE tendency anomalies east of the MJO convection, which facilitate the eastward propagation of the MJO, are mainly contributed by the horizontal and vertical advection. However, these positive anomalies straddle to the equator in the standing and jumping MJO clusters, leading convection to propagate poleward. The differences in MSE tendency anomalies are primarily contributed by two nonlinearly rectified terms: meridional advection of the low-frequency background MSE by the MJO-scale winds [ ] and the vertical transport of low-frequency background MSE by the MJO-filtered vertical velocity [ ]. These differences arise from the destruction of the front Walker cell and the anomalous poleward flows to the east of MJO convection by the ER waves. The variations in ER wave intensity among the MJO clusters are associated with differences in the background vertical shear of zonal wind. This study provides new insights into the mechanisms driving MJO propagation and the sophisticated interactions between ER waves and the MJO. Significance Statement Understanding the evolution of tropical weather systems is essential for improving global weather and climate forecasts. This study investigates how equatorial Rossby (ER) waves influence the Madden–Julian oscillation (MJO), a critical driver of intraseasonal variability in the tropics. By classifying MJO events based on their propagation characteristics, the research identifies how ER waves disrupt the MJO’s eastward propagation, inhibiting its convection from moving across the Maritime Continent as expected. The study further reveals the mechanisms behind this disruption and the factors influencing ER wave intensity. These findings offer new insights into tropical atmospheric dynamics and provide the potential to enhance MJO simulations and improve intraseasonal predictability in climate models.