Accurate prediction of propagation of the Madden-Julian Oscillation (MJO) over the Maritime Continent (MC) is critical for skillful subseasonal-to-seasonal prediction of downstream climate and weather extremes in both tropics and extratropics. Our current understanding and modeling capability of the detailed interactive processes between the MJO and MC, however, remain rather limited.

In this study, with a particular focus over the Sumatra Island, key processes underlying the damping effect of MC islands on the eastward propagating MJO are investigated based on a series of idealized atmospheric-only global climate model (AGCM) simulations with realistic MC topography and land-sea distribution embedded in an aqua-planet environment, which effectively isolates influences due to the variability in the large-scale environment.

By capitalizing on realistic simulations of the observed MC damping effect on the MJO in the control experiment, additional experiments suggest that the topography over the MC only plays a minor role (~25%) for the damping effect on the MJO. Rather, the land-atmosphere coupling through interactions among clouds, radiation, and land surface is found to play a key role in dampening the MJO convection over the MC islands. Among these interactive processes, it is found that including the diurnal cycle of convection in the model can significantly enhance this damping effect (~35%) due to a more active interaction between convection and solar radiation, in agreement with previous hypotheses and modeling studies. While a crucial role of the surface latent heat flux over the MC lands for the weakening of MJO convection has been emphasized in previous studies, our model results suggest that the variability of surface turbulent fluxes over MC land is not essential in leading to the weakening of MJO convection.

Within the context of these above key processes identified in the idealized GCM simulations, representation of interactions between the MJO and MC are further examined in the year-long CESS simulations from the DOE’s Simplified Cloud-Resolving E3SM Atmosphere Model (SCREAM). While significant deficiencies in simulating the eastward propagation of the MJO and thus the MJO-MC interactions are noted in CESS simulations from SCREAM, the underlying physics responsible for these deficiencies is further explored by taking advantage of short-term hindcasts by a regionally-refined SCREAM (RRM-SCREAM) covering the tropical Indian Ocean and MC.

(This work is supported by the DOE RGMA Program under Award DE-SC0024315.)