Influence of the Diurnal Insolation Cycle on MJO Propagation Across the Maritime Continent

The Maritime Continent (MC) has long been hypothesized to hinder the eastward propagation of the Madden–Julian Oscillation (MJO) through its strong diurnal cycle of convection. To evaluate this mechanism, a regional model is used to simulate a boreal spring 2013 MJO event that weakened and stalled over the MC. Two experiments are performed: a control with realistic diurnal insolation (CTL) and a no-diurnal-cycle experiment (NO_DC). MJO propagation is objectively identified using a large-scale precipitation tracking (LPT) method, which distinguishes propagating and non-propagating behavior better than the conventional RMM index. In NO_DC, suppressed diurnal heating reduces land precipitation, leading to more continuous eastward propagation. Moist static energy budget analysis shows that MJO maintenance in NO_DC arises from enhanced longwave heating and reduced advection, while persistent propagation is linked to increased advection and reduced longwave and latent heat flux damping. These responses vary regionally across the MC, highlighting the complex role of diurnal processes in modulating MJO propagation.