Influence of the QBO on the MJO During Coupled Model Multiweek Forecasts

Abstract Seasonal activity of the Madden‐Julian Oscillation (MJO) is observed to be greater during austral summer when the lower stratospheric winds are in the easterly phase of the quasi‐biennial oscillation (QBO). Using initialized predictions from two coupled model seasonal prediction systems, we show a systematic impact of the QBO on the amplitude of the MJO during the first few days of the forecast before model biases become too large. In both models as for the observed, the difference in MJO amplitude between easterly phases and westerly phases of the QBO increases with lead time, despite having similar initial amplitudes. Enhanced destabilization of the tropopause is argued to be the key mechanism that promotes stronger MJO convection during easterly phase of QBO. Caveats for the inability of the models to reproduce the observed strength of the MJO‐QBO relationship are discussed.