The Lack of QBO-MJO Connection in CMIP6 Models

Observational analysis has indicated a strong connection between the stratospheric quasi-biennial oscillation (QBO) and tropospheric Madden-Julian oscillation (MJO), with MJO activity being stronger during the easterly phase than the westerly phase of the QBO. We assess the representation of this QBO-MJO connection in 30 models participating in the Coupled Model Intercomparison Project 6. While some models reasonably simulate the QBO during boreal winter, none of them capture a difference in MJO activity between easterly and westerly QBO that is larger than that which would be expected from the random sampling of internal variability. The weak signal of the simulated QBO-MJO connection may be due to the weaker amplitude of the QBO than observed, especially between 100 to 50 hPa. This weaker amplitude in the models is seen both in the QBO-related zonal wind and temperature, the latter of which is thought to be critical for destabilizing tropical convection.