We quantify the QBO-dependence of the global atmospheric response to the MJO using 300-mb geopotential anomalies, which have been shown to be a robust proxy for the tropical and extratropical character of the MJO. The spatial patterns of covariability between the MJO and 300-mb geopotential are presented from the framework of cross-spectral analysis. The magnitude-squared coherence between the Outgoing Longwave Radiation MJO Index (OMI) and time-series of 300-mb geopotential from ERA-Interim reanalysis is calculated for the 1980 through 2016 period for all locations across the globe. We use coherence since it considers both the magnitude and phase between two periodic signals, thereby accounting for more information than simple linear correlation. The analysis is separated into the QBO-ignorant, westerly QBO, and easterly QBO states.
We find that the global signature of the MJO strongly depends upon the state of the QBO. Globally, the fraction of 300-mb geopotential variability linked to the MJO is largest during easterly QBO states, consistent with the more prominent MJO during these periods. Furthermore, the spatial distribution of both tropical and extratropical upper-tropospheric anomalies associated with the MJO strongly depend upon the state of the QBO. These findings emphasize the general importance of the MJO-QBO connection within the overall climate system, and highlight the importance of considering the state of the QBO in any analysis related to the MJO, no matter the specific region of interest.