Quasi‐biennial oscillation impacts on Madden–Julian oscillation‐associated tropical–extratropical interactions and Kelvin waves

Abstract Several recent works have demonstrated that the Madden–Julian oscillation (MJO) shows more variance in tropical convection and wind during the easterly phase of stratospheric wind in the quasi‐biennial oscillation (QBO). Some of these works have shown that reduced variance during the westerly QBO is associated with fewer repeating cycles of events. This article applies a modulation linear regression algorithm to assess changes in the global atmospheric circulation structure for December–February MJO signals tested when time‐smoothed 50 hPa winds are easterly or westerly at 10 m·s−1. Results show pronounced differences in the associated extratropical upper tropospheric Rossby wave response between the two QBO states, along with a comparatively lower fraction of total eastward wave energy being consistent with Kelvin waves approaching the Indian basin from the west during the westerly QBO. Instead, westerly QBO appears to favour stronger equatorward‐moving extratropical wave precursors across the Western Hemisphere and Eurasia. The results suggest the hypothesis that more dependence on extratropical waves during the westerly QBO may reduce the reliability of the MJO to form sequential trains during the westerly QBO.