The relationship between the Madden–Julian Oscillation and the North Atlantic Oscillation

In this study, the relationship between the Madden–Julian Oscillation (MJO) and the North Atlantic Oscillation (NAO) is investigated by analysing NAO events both when the MJO is active and inactive. The European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim) dataset is used, for the years 1979–2006 and the months December–February. When the MJO is active, negative (positive) NAO events are preceded by enhanced MJO convection over the tropical western and central Pacific Ocean (tropical Indian Ocean and Maritime Continent). The accompanying sea-level pressure (SLP) anomaly fields reveal patterns that closely resemble the northern annular mode (NAM). The MJO-related negative NAO events are preceded by an increase in the vertical propagation of planetary-scale wave activity into the stratosphere, followed by a marked weakening of the zonally symmetric component of the lower stratospheric zonal wind. The opposite behaviour is found for the MJO-related positive NAO events. The MJO-related NAO events are also long-lived, persisting for approximately 30 days. In contrast, when the MJO is inactive, there is little change to the zonally symmetric component of the lower stratospheric zonal wind, these events are relatively short-lived, lasting for about 10 days, and the NAO corresponds to a dipole that is confined to the North Atlantic.