Impact of the Northern Hemisphere extratropics on the skill in predicting the Madden Julian Oscillation

Using a series of relaxation hindcast experiments, this paper shows that the northern extratropics have a significant impact on the skill of the ECMWF forecast system in predicting the Madden Julian Oscillation (MJO) during boreal winter. The westerly wind burst associated with the March 1997 MJO event is a high‐profile example of an event that was influenced by extratropical circulation anomalies. The propagation speed of MJO events is overall improved when the northern extratropics are relaxed towards analysis fields. Additional experiments in which the relaxation is confined to different areas of the Northern Hemisphere extratropics suggest that it is atmospheric circulation anomalies in the North Pacific region which most strongly affect the skill in predicting the MJO.