The Lack of QBO‐MJO Connection in CMIP6 Models
The Madden-Julian Oscillation (MJO) is a dominant mode of variability on the intraseasonal timescale in the tropical troposphere. There is a robust relationship between the stratospheric quasi-biennial oscillation (QBO) and the MJO, with the MJO activity being stronger during the easterly phase than the westerly QBO phase. This relationship is robust in observations and well outside of the range that could be expected to arise due to sampling issues. We investigate here how well CMIP6 models capture the QBO-MJO relationship.
The MJO is an eastward-moving tropical disturbance that alters clouds, rainfall, and precipitation in the tropics, and via teleconnections impacts the mid-latitudes. The MJO contributes to extreme weather events in the United States. Representing the observed variability of the MJO in Earth system models is important to realistically represent the variability and related extreme events in the tropics as well as the extratropics.
We show that not a single CMIP6 model shows the observed QBO-MJO relationship. Differences in MJO related OLR anomalies in QBO West and QBO East years are not distinguishable from sampling natural variability. The lack of simulated QBO-MJO connection in CMIP6 models could be due to the deficiency in QBO amplitude in the lowermost stratosphere that occurs in most CMIP6 models.