Impact of the North Atlantic Oscillation on the forecast skill of the Madden-Julian Oscillation

[1] Using the output of the intraseasonal hindcast experiment conducted with the Global Environmental Multiscale (GEM) atmospheric model during 24 extended winters, the association between the forecast skill of the Madden-Julian Oscillation (MJO) and the amplitude of the North Atlantic Oscillation (NAO) in the initial condition is investigated. It is found that with a lead time of about 10 to 25 days, the MJO forecast skill is significantly influenced by the NAO amplitude in the initial condition. A strong NAO leads to a better MJO forecast skill than a weak NAO. The model is able to reproduce the increase (decrease) of westerly wind in the equatorial African and Indian Ocean region that is observed about 10 days after an extreme positive (negative) NAO. This leads to an increased forecast skill of zonal wind in that region when a strong NAO exists in the initial condition. These results confirm that there is a strong Northern extratropical influence on the MJO and its forecast skill.