Influence of the QBO on MJO prediction skill in the subseasonal-to-seasonal prediction models

Recent studies have shown that the Madden-Julian Oscillation (MJO) is significantly modulated by the stratospheric Quasi-Biennial Oscillation (QBO). In general, boreal winter MJO becomes more active during the easterly phase of the QBO (EQBO) than during the westerly phase (WQBO). Based on this finding, here we examine the possible impacts of the QBO on MJO prediction skill in the operational models that participated in the WCRP/WWRP subseasonal-to-seasonal (S2S) prediction project. All models show a higher MJO prediction skill during EQBO winters than during WQBO winters. For the bivariate anomaly correlation coefficient of 0.5, the MJO prediction skill during EQBO winters is enhanced byup to 10 days. This enhancement is insensitive to the initial MJO amplitude, indicating thatthe improved MJO prediction skill is not simply the result of astronger MJO. Instead, a longer persistence of theMJO during EQBO winters likely induces a higher prediction skill by having a higher prediction limit.