Interseasonal Difference in MJO Propagation during the Extended Boreal Winter: Observations and Climate Model Simulations

Abstract This study investigates climatological interseasonal changes in the Madden–Julian oscillation (MJO)’s propagation diversity using observational data and climate model simulations, with a particular focus on the role of the mean state. In observations, the ratio of the relative frequency of the fast-propagating MJO to that of the slow-propagating MJO shows notable changes from winter to early spring, with a significantly higher ratio during March–April (MA) than during November–February (NDJF). Column-integrated moisture budget analysis reveals that moisture recharge and discharge around the Maritime Continent, which drive the MJO’s eastward propagation, are stronger in MA, with zonally broader and stronger positive moisture tendency to the east of enhanced convection. Further analysis shows that stronger zonal moisture advection is responsible for the enhanced moistening in MA, …