Modulation of the MJO-Related Teleconnections by the QBO

摘要

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.