Tropical origins of the recent trends in Northern Hemisphere wintertime jet streams.

Mid-latitude jet streams are fundamental to global weather and influence high-impact meteorological events. Climate models consistently project a poleward shift of the jets under anthropogenic warming and evidence for such a shift recently emerged in reanalysis data. Here we show that trends in Northern Hemisphere winter jet streams over the past 45 years are closely linked to the increased number of intense mid-latitude precipitation events over a large area in the western North Pacific, themselves favored by tropical precipitation anomalies associated with the more recurrent La-Niña-like conditions but also during recent El-Nino seasons when the Madden Julian Oscillation is under phases 4 to 6. During these events, the North Pacific jet is accelerated on its poleward flank followed by an acceleration of the North Atlantic jet. The findings reveal that tropical Pacific precipitation trends, through their modulation of quasi-stationary and synoptic eddy activity, play a pivotal role in shaping recent mid-latitude jet stream trends in the Northern Hemisphere. This provides an avenue of research to evaluate climate models and their ability to reproduce historical and future trends.