Modulation of the MJO‐Related Teleconnections by the QBO

Previous studies have provided observational evidence for a correlation between certain phases of the Madden‐Julian Oscillation (MJO) and the North Atlantic Oscillation (NAO), at a lag of about 10 days. Such a relation implies that the tropical convection of the MJO may provide sources of skill for subseasonal predictions in the extratropical regions. In this study, we show that the MJO‐NAO connection is influenced by the phase of the quasi‐biennial oscillation (QBO). During the westerly phase of QBO (WQBO), a stronger and longer lasting MJO‐NAO teleconnection is observed. About 10 days after the MJO phase 3 (7), which corresponds to enhanced (suppressed) diabatic heating anomaly in the tropical Indian Ocean and reduced (enhanced) convection in the western Pacific, a positive (negative) NAO tends to occur. On the other hand, under the easterly phase of QBO (EQBO), the MJO‐NAO teleconnection is also observed, but weaker and with less statistical significance. The QBO possibly influences the MJO‐related teleconnection by modulating the extratropical basic state. During WQBO years, there is subtropical anomalous westerly wind in the North Pacific, and as a result, the enhanced subtropical westerly jet provides a favorable environment for the MJO‐induced extratropical Rossby wave to propagate. The anomalous high‐latitude North Atlantic westerly is also favorable for troposphere‐stratosphere coupling and for the NAO to develop. Key Points The MJO‐NAO connection is found to be stronger when the QBO is in the westerly than the easterly phase An SVD analysis of tropical OLR and the two‐pentad lagged 500‐hPa geopotential height reveals different dominant patterns under EQBO and WQBO The QBO modulation of the MJO‐NAO connection can likely be explained by differences in the extratropical mean flow