Winter mean lower tropospheric moisture over the Maritime Continent as a climate model diagnostic metric for the propagation of the Madden-Julian oscillation

Despite its widespread influences on the atmosphere, the Madden-Julian oscillation (MJO) remains poorly represented in state-of-the-art general circulation models (GCMs). Motivated by recent findings that the horizontal advection of the mean low-tropospheric moist static energy or moisture by the MJO winds plays a crucial role in the eastward propagation of the MJO, we investigate the relationship between lower tropospheric moisture patterns over the Indo-Pacific and MJO eastward propagation in a suite of 23 GCM simulations. Model capability of reproducing the observed November-April mean lower tropospheric moisture pattern over the Indo-Pacific, especially near the Maritime Continent (MC), is highly correlated with model skill in simulating MJO eastward propagation. In GCMs with difficulty capturing realistic MJO propagation, the amplitude of the mean low-level moisture over the MC is greatly underestimated, leading to weak horizontal moisture gradients and thus discrepancies in moisture advection, significantly affecting MJO propagation. This study suggests that the mean lower tropospheric moisture pattern over the MC can serve as an important diagnostic metric for MJO propagation in climate models.