Joint Influences of the MJO and the Stratospheric Polar Vortex on the Northern Hemisphere Extratropical Circulation

This study analyzes the combined interactions of the MJO and the stratospheric polar vortex on extended-range predictability of NH winter weather patterns, using the ERA-Interim reanalysis dataset. The analysis takes place through a series of conditional composites involving MJO-only, strong/weak polar vortex-only, and MJO + polar vortex composites. In general, we find that, even when considered collectively, in the Pacific basin, the MJO has a more prominent control over the tropospheric pattern, while the Atlantic tropospheric pattern is seemingly controlled by stratospheric polar vortex. This result suggests that, for example, using only the stratospheric polar vortex for Eastern US and European extended-range forecasts may lead to higher forecast errors than those forecasts also considering the state of the MJO. Wave diagnostics like Eliassen-Palm (EP) flux diagrams are also used to show that wintertime activity of the MJO and polar vortex variability leads to anomalous responses in polar jet speeds and positions, with a potential feedback between the MJO and polar vortex at work. Finally, the investigation into the path and position of the Rossby waves during these periods and subsequent impacts on extreme winter weather are further explored through the use of blocking indices.

This study analyzes the combined interactions of the MJO and the stratospheric polar vortex on extended-range predictability of NH winter weather patterns, using the ERA-Interim reanalysis dataset. The analysis takes place through a series of conditional composites involving MJO-only, strong/weak polar vortex-only, and MJO + polar vortex composites. In general, we find that, even when considered collectively, in the Pacific basin, the MJO has a more prominent control over the tropospheric pattern, while the Atlantic tropospheric pattern is seemingly controlled by stratospheric polar vortex. This result suggests that, for example, using only the stratospheric polar vortex for Eastern US and European extended-range forecasts may lead to higher forecast errors than those forecasts also considering the state of the MJO. Wave diagnostics like Eliassen-Palm (EP) flux diagrams are also used to show that wintertime activity of the MJO and polar vortex variability leads to anomalous responses in polar jet speeds and positions, with a potential feedback between the MJO and polar vortex at work. Finally, the investigation into the path and position of the Rossby waves during these periods and subsequent impacts on extreme winter weather are further explored through the use of blocking indices.