The Global Teleconnection Signature of the Madden‐Julian Oscillation and Its Modulation by the Quasi‐Biennial Oscillation

Recent research has suggested that the tropical and extratropical character of the Madden‐Julian oscillation (MJO) depends on the state of the stratospheric quasi‐biennial oscillation (QBO). With this in mind, we use both reanalysis and a global climate model (CESM2‐WACCM) to analyze the global character of upper tropospheric‐lower stratospheric geopotential height anomalies connected with the MJO and quantify dependencies of these teleconnections on the state of the QBO. We find that the global teleconnection signature of the MJO depends upon the state of the QBO. Globally, within reanalysis the fraction of 20‐ to 90‐day 250‐hPa geopotential height variance linked to the MJO is largest during boreal winter and summer for easterly QBO phases and smallest during westerly QBO phases of boreal winter. The difference between QBO phases is mostly driven by changes in the tropical signature of the MJO, although during boreal winter the Northern Hemispheric teleconnections are particularly more prominent during easterly QBO phases. Otherwise, the QBO modulation of extratropical MJO teleconnections is mainly realized through changes in the locations of the teleconnections. A QBO‐MJO relationship is also apparent within CESM2‐WACCM but is weaker than that observed. This extratropical modulation implies that the regions that benefit from increased subseasonal predictability due to the MJO may also change as a function of the QBO. In a broader sense, these findings emphasize that knowledge of the tropical stratospheric state, particularly as it relates to the QBO, is important for understanding the connections between the MJO and the extratropics. Key Points The QBO modulates the locations of MJO teleconnections, mainly through the locations in which they occur The modulation is greatest during boreal winter but occurs to some extent during all seasons A modulation also exists within CESM2‐WACCM but is weaker and has a different spatial pattern