Prediction Skill of Madden-Julian Oscillation in the Subseasonal-to-Seasonal (S2S) Prediction Models and its Modulation by the Stratospheric Quasi-Biennial Oscillation

The recent studies have shown that Madden-Julian Oscillation (MJO) is significantly modulated by the stratospheric Quasi-Biennial Oscillation (QBO) during boreal winter. In general, boreal-winter MJO is stronger than normal during the easterly phase of QBO (EQBO). Opposite is also true during the westerly phase (WQBO). In the present study, these findings are applied to the latest operational models for better understanding MJO and its prediction skill. Long-term re-forecasts from the eight models, which participated in the WCRP/WWRP subseasonal-to-seasonal (S2S) project, are examined in the context of QBO-MJO link. These models show a range of MJO prediction skills from 10 to 30 days. Although intermodal spread is substantially large, all the models, without exception, robustly show a higher MJO prediction skill during EQBO than WQBO winter. This modulation of MJO prediction skill by the QBO largely results from a stronger and more persistent MJO during EQBO winter, but is also caused by a better organization of MJO during EQBO winter especially when MJO convections are located over the Indian Ocean and Maritime continent. This result suggests that stratospheric data assimilation is important for S2S prediction not only in the Northern Hemisphere extratropics but also in the tropics.