Abstract Despite evidence for interactions between the El Niño‐Southern Oscillation (ENSO) and the Quasi‐Biennial Oscillation (QBO), the correlation between their indices is elusive and unstable over the observational record. We show that in ERA5, DJF composites of La Niña sea‐surface temperatures (SSTs) are positively correlated with SST composites of the QBO's easterly phase (QBOE), and DJF El Niño SST anomalies are correlated with those of the QBO's westerly phase (QBOW). These correlations change coherently with season; the La Niña/QBOE correlation turns strongly negative in May. QBO and ENSO composites of the surface fluxes of latent heat, the surface absorbed short wave radiation, and the outgoing longwave radiation, are also highly correlated, again with a coherent annual cycle. These findings strengthen the evidence for interactions between ENSO and the QBO, highlighting the role of the seasonal cycle, and may be relevant to the interactions of the QBO and the Madden‐Julian Oscillation.
Randall et al. (Tue,) studied this question.