Key Physics of the Madden-Julian Oscillation Based on Multi-model Simulations

The Madden-Julian Oscillation (MJO) exerts pronounced influences on global climate and extreme weather events. Our current general circulation models (GCMs), however, exhibit rather limited capability in representing this prominent tropical variability mode. Meanwhile, fundamental physics of the MJO are still elusive. In this presentation, by analyzing 27 climate models that participated in the WCRP-WWRP/THORPEX YOTC MJO Task Force and GEWEX GASS MJO global model evaluation project, key processes responsible for realistic MJO simulations, including its amplitude and propagation, are explored based on budget analysis of moist static energy (MSE). Results suggest that the convective time scale in a model, namely, the adjustment time for convection in responding to a moisture perturbation, tends to be highly correlated to amplitude of the model MJO. On the other hand, horizontal advection of MSE, particularly the dry air intrusion from the west of the MJO convection, plays a crucial role for realistic eastward propagation of the MJO in GCM simulations. Due to model deficiencies in simulating both the MJO circulation and spatial distribution of background MSE, the horizontal advection of MSE is greatly underestimated in the poor MJO models, and largely offset by effects from radiative and surface fluxes, leading to rather weak eastward or even westward propagation of MJO convection in those models.