LAUSR

Recent studies have shown arguments about the connection between stratospheric quasi‐biennial oscillation (QBO) and activities of Madden‐Julian oscillation (MJO) during boreal winter on interannual timescale, especially for the question of which aspects of MJO, amplitude or occurrence frequency, can really be modulated by QBO. This study re-examines the interannual variability of the seasonally averaged amplitude and the occurrence of both ‘active’ (amplitude > 1.0) and ‘inactive’ (amplitude < 1.0) MJO days in boreal winter December–January–February (DJF), and their relation to QBO variation. Significant correlations between the QBO index and the indicators of MJO activity reveal that wintertime amplitude of ‘active’ and ‘inactive’ MJO days are typically larger in QBO easterly phase (EQBO) than in QBO westerly phase (WQBO). More importantly, we can also expect more ‘active’ MJO days and simultaneously less ‘inactive’ MJO days in EQBO winter as a consequence of more days in winter shifting from ‘inactive’ to ‘active’ due to larger MJO amplitudes. The significantly positive (negative) correlation between the time series of averaged amplitude and occurrence of ‘active’ (‘inactive’) MJO days can as well be interpreted as evidence that QBO is closely connected to the occurrence of MJO days via modulating MJO amplitudes. These results update our current understanding of the QBO-MJO connection, which is helpful to advance the MJO prediction.