Decadal variability of Madden–Julian oscillation teleconnections in a coupled climate model

The Madden–Julian oscillation (MJO) is a key source of predictability for global weather. Through both tropospheric and stratospheric teleconnection pathways, the MJO is able to alter the extratropical circulation and, in turn, causes shifts in other modes of variability, such as the Pacific–North American pattern and North Atlantic oscillation. MJO teleconnections are known to vary on a range of time-scales, but their variability on decadal and multidecadal time-scales is not well understood. Using the UK Earth System Model 1 coupled climate model, we show that both Atlantic multidecadal variability (AMV) and the Pacific decadal oscillation (PDO) alter MJO teleconnection patterns and their impact on extratropical modes of variability. AMV and the PDO modulate the mean state of the atmosphere, in particular the Aleutian low, which controls how the circulation responds to the MJO. When the Aleutian low is deepened (e.g., during the positive phase of the PDO), this provides the conditions necessary for the MJO teleconnection to project onto the climatological low, either constructively or destructively. During the positive phase of the AMV and negative phase of the PDO, which favour a weak Aleutian low, the MJO cannot drive a significant cyclonic response in the region. Changes in the stratospheric polar vortex, preceded by MJO-related anomalies in the Aleutian low, also control extratropical weather. We hypothesise that this stratospheric teleconnection pathway is also modulated by both AMV and the PDO. These results have implications for improving the predictability of extratropical weather patterns over the coming decades. By understanding how MJO teleconnections are altered by internal modes of decadal and multidecadal variability, the impact of anthropogenic climate change can be better identified in future projections. This context will improve both long-range forecasts of MJO-driven variability and short-term forecasts in different sea-surface temperature conditions.