Impact of the QBO on Prediction and Predictability of the MJO Convection

The impact of the QBO on the prediction of MJO convection is examined with the WMO Subseasonal to Seasonal (S2S) forecast database using the real-time OLR based MJO (OMI) index. It is shown that the OMI prediction skills measured by anomaly correlation coefficient is higher by 5 to 10 days in the boreal winter in the QBO easterly phase than its westerly phase. The MJO predictability measured as signal to noise ratio also shows notably consistent difference in the 2 QBO phases. This is also confirmed by linear regression fitting with a statistical model, which suggest that the MJO skill difference may be due to the initial conditions rather than the predicted QBO state. Observational analysis of the OMI index indicates that the MJO is more coherent and stronger in the QBO easterly phase.

In contrast to robust QBO-MJO connection in boreal winter, the MJO prediction skill by the S2S models in boreal summer is better in QBO westerly phases than its easterly phase during the 1999 to 2010 periods. This is consistent with observation that MJO OLR anomalies are stronger in the QBO westerly phase in the same period. However, observation further indicates that the impact of QBO on boreal summer MJO change in recent decades, and the relation reverses before that period (1979-2000).