Decadal Variability of the Extratropical Response to the Madden-Julian Oscillation

The Madden-Julian Oscillation (MJO) is the leading mode of sub-seasonal variability in the tropical atmosphere and is a source of predictability for extratropical weather through its teleconnections. MJO teleconnection patterns can be modulated by the El Nino-Southern Oscillation (ENSO) on seasonal to interannual time scales. However, changes over decadal time scales are less well understood. ERA5 reanalysis data are used to show that the boreal winter MJO teleconnection pattern in the Northern Hemisphere has changed in recent decades in line with changes in the Pacific Decadal Oscillation and Atlantic Multidecadal Variability. Changes are seen in the circulation, temperature and precipitation responses. In particular, from 1997, intraseasonal cold anomalies appear over Europe and the eastern United States due to MJO convection over the western Pacific; these were not present 20 years previously. The decadal variability observed is not the product of aliasing of ENSO modulation of the teleconnection. Weather in different regions of the globe can be linked by planetary-scale atmospheric waves, and these links can help forecasters to predict the weather. One such link, or teleconnection pattern, connects changes in rainfall over Indonesia and the tropical Pacific (from a weather system called the Madden-Julian Oscillation or MJO) to changes in the weather in North America and Europe. This study assesses this teleconnection pattern in two separate time periods (roughly the mid-1970s to mid-1990s and mid-1990s to late 2010s) to analyze if and how it has changed. We find that the pattern has changed, and that this is due to large-scale changes in the background state of the atmosphere. These changes in the link between the tropics and extratropics will have implications for weather forecasts on weekly to monthly time scales. The extratropical response to the Madden-Julian Oscillation has changed on decadal time scalesThis decadal variability coincides with changes in low-frequency oceanic modes in both the Pacific and Atlantic basinsChanges on decadal time scales are different to those modulated by the El Nino-Southern Oscillation on interannual scales