Possible effects of the diurnal cycle in land convection on propagation of the Madden–Julian Oscillation over the Indo‐Pacific Maritime Continent (MC) were investigated using satellite observations. Four features distinguishable from their respective climatology are uniquely associated with MJO events that cross the MC: strong precipitation over land as their convection centers approach the MC, subsequent increased soil moisture, reduced diurnal amplitude of land convection, and the dominance of precipitation over water by nondiurnal convection as their convection centers move over the MC. These results provide observational evidence for a proposed MAritime Continent Convective diurnal Cycle mechanism in which the diurnal cycle in land convection acts as an intrinsic barrier effect on MJO propagation over the MC.

The simulated Madden–Julian oscillation (MJO) events in 27 general circulation models (GCMs) are identified using an MJO tracking method. The results suggest that the occurrence frequencies of simulated MJO events can represent a model’s ability to simulate several characteristics of the MJO to a certain extent during boreal winter, such as propagation range, strength, and termination longitude. All tracked MJO events are classified into those that propagate through the Maritime Continent (MC) (MJO-C) and those that do not (MJO-B), and the weakening and blocking effects on MJO propagation by the MC in GCMs were quantified. In general, if a GCM shows a stronger weakening effect on MJO strength over the MC, it tends to produce a stronger blocking effect on MJO propagation over the MC during boreal winter. The barrier effect of the MC on MJO propagation is exaggerated in most GCMs, while it can be underestimated in some GCMs, especially the coupled GCMs. Strong lower-tropospheric premoistening is identified ahead of the MJO convection center when it is over the central MC for MJO-C but not for MJO-B in most GCMs. Such strong premoistening is mainly attributed to the zonal gradient of lower-tropospheric easterly anomalies within the front Walker cell, which could be a precursor leading to the eastward propagation of MJO convection. In contrast to the observation, the role of the background sea surface temperature and land–sea precipitation contrast in the barrier effect on MJO propagation by the MC is not well captured by most GCMs.

This study explores possible mechanisms for the barrier effect of the Indo-Pacific Maritime Continent (MC) on MJO propagation. In particular, this study examines whether similar mechanisms can be found in both observations and CMIP5 simulations. All models simulate individual MJO events but underestimate the percentage of MJO events propagating into the MC. The simulations are grouped into the top and bottom 50% based on their capability of reproducing the MJO spectral signal. When compared with the observations, the bottom 50% of the simulations significantly underestimate the MJO strength and exaggerate the barrier effect intensity, whereas these discrepancies are not significant in the top 50% of the simulations. From the top 50% of the simulations, the MJO strength, moisture processes, and surface evaporation in the MC all play important roles in constituting the barrier effect. No such evidence is found in observations. The discrepancies may come from small observed sample size and/or misrepresentations of key physical processes in the models. A consistent result is found in the observations and simulations: Whether MJO events can cross the MC depends on the degree to which dominant precipitation over land shifts to over water in the MC as MJO convection centers approach the MC and cross it. This result emphasizes the critical role of precipitation over water in carrying convective signals of the MJO through the MC. The results suggest that diagnosing the model alone on mechanisms for the barrier effect could be misleading; further investigations using a combination of observations, global gridded data, and high-resolution models are needed.

The Madden-Julian Oscillation (MJO;Madden & Julian, 1971, 1972, characterized by eastward-propagating large-scale convection-circulation coupled systems at the intraseasonal time-scale, plays an important role in bridging the gap between weather and climate systems (Zhang, 2013). However, reproducing the MJO in general circulation models remains a challenge (