A Critical Role of Dry Air Intrusion for Propagation of the Madden-Julian Oscillation Based on Multi-model Simulations

Abstract:

The Madden-Julian Oscillation (MJO) exerts pronounced influences on global climate and extreme weather systems. 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 global MJO model inter-comparison project, key processes responsible for realistic MJO simulations are explored based on budget analysis of moist static energy (MSE). Results suggest that 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.