Evaluating the Joint Influence of the Madden‐Julian Oscillation and the Stratospheric Polar Vortex on Weather Patterns in the Northern Hemisphere

Abstract

AbstractSubseasonal‐to‐seasonal (S2S) forecasts of Northern Hemisphere (NH) extratropical winter weather patterns continue to be a challenging venture. Past studies have considered the individual influence of two modes of climate variability—the Madden‐Julian oscillation (MJO) and the state of the stratospheric polar vortex (SPV)—on the NH polar jet stream and associated weather regimes. This study takes a different approach and quantifies the joint influence of the SPV and the MJO on NH S2S winter weather patterns. Using ERA‐Interim, we illustrate that variability associated with the MJO primarily influences tropospheric patterns across the North Pacific and western North America 10 to 14 days later, while SPV variability has a stronger influence on tropospheric patterns over the North Atlantic and Europe for the same lags. Over the rest of North America and into the Arctic, however, constructive and destructive interference between the MJO and the SPV teleconnections yields unique jet stream and temperature patterns that differ from the single‐mode composites. As such, S2S forecasts of temperature and jet stream patterns across much of North America may improve in accuracy by considering both modes. The study also shows that MJO Phases 2 and 3 events influence the resulting tropospheric circulation via primarily a tropospheric pathway. By contrast, MJO Phases 7 and 8 events modify both the tropospheric and stratospheric circulation with potential feedbacks on the tropospheric circulation at longer lags. Hence, the study suggests another benchmark by which to test S2S dynamical prediction systems, including the importance for modeling stratosphere‐troposphere coupling dynamics correctly.