Influence of the Quasi-Biennial Oscillation on tropical convection and its teleconnection to the midlatitudes in boreal winter

Recently, a connection between the quasi-biennial oscillation (QBO) and the Madden-Julian oscillation (MJO) was found in observations. The boreal winter seasonal mean amplitude of the daily MJO is anticorrelated with the QBO winds measured at 50 hPa. We investigate whether this relationship is captured in reforecasts of past winters in a seasonal prediction system, and find the ensemble mean response does not show this association, with essentially zero correlation. By repeated subsampling of the ensemble reforecast data, we also show that the observed correlation is very unlikely to arise merely as the result of sampling in the relatively short observational record. Instead, we conclude that the reforecasts genuinely cannot capture the observed QBO-MJO seasonal relationship. We also consider the boreal winter seasonal mean response of tropical convection to the QBO and its influence on the subtropics. We find that the reforecasts are able to capture the stationary pattern found in the observed outgoing long-wave radiation (OLR) over the tropical west Pacific in response to the QBO. We also find that the associated upper tropospheric divergence in observations interacts with the west Pacific subtropical jet to produce atmospheric Rossby wave patterns that propagate across the midlatitude Pacific Ocean. These extratropical waves have the potential to interfere with the climatological waves in midlatitudes, modifying the strength of the midlatitude annular mode through interactions with the extratropical stratosphere. However, the observed influence on wavenumber 1 is not captured by the reforecasts, suggesting a weak extratropical influence and a partial explanation for the weaker-than-observed QBO teleconnection to the Arctic Oscillation and North Atlantic Oscillation. We investigate whether the observed December-January-February (DJF) seasonal relationship between the quasi-biennial oscillation (QBO) and the Madden-Julian oscillation (MJO) is captured in a seasonal prediction system and find that the reforecasts cannot capture this relationship. We also consider the observed DJF relationship between the QBO and tropical outgoing long-wave radiation (OLR) and find that the stationary OLR patterns are captured in reforecasts. However, the associated atmospheric Rossby waves that propagate across the midlatitude Pacific Ocean differ between observations and reforecasts with implications for teleconnections. The figure shows the winter-mean QBO teleconnections to tropical convection. OLR response to QBO-easterly minus QBO-westerly (QBOE - W) at 50 hPa in boreal winter for (a) European Centre for Medium-Range Weather Forecasts Reanalysis version 5 (ERA5) (winters 1980-2020), and (b) GloSea5 (GS5) hindcasts (winters 1993-2017). Significance at the two-sided 90% level is indicated by stippling. Strong El Nino-Southern Oscillation (ENSO) winters (1982/3, 1997/8, 2015/6) have been excluded from this analysis. image