Pacific Modulation of the North Atlantic Storm Track Response to Sudden Stratospheric Warming Events.

Sudden stratospheric warming (SSW) events have been suggested to be followed by a surface impact, though this response varies between events. Using reanalysis data, we identify two types of tropospheric responses to SSWs: Two thirds of the SSW events are dominated by a zonally symmetric tropospheric response with an equatorward shift of the jet in the Atlantic, consistent with the canonical SSW response in the form of a negative signature of the North Atlantic Oscillation. For the remaining third of SSW events, a zonally asymmetric response is found, associated with a poleward shift of the jet in the Atlantic. The Pacific is found to contribute to the sign of the North Atlantic response, as synoptic wave propagation from the Eastern Pacific links the Pacific and Atlantic storm tracks for both equatorward and poleward jet responses. Plain Language Summary: The stratosphere, the layer of the atmosphere starting at about 10 km above the Earth's surface, can have a major impact on surface weather in winter, in particular during stratospheric extreme events, known as sudden stratospheric warmings. The tropospheric response is strongest in the North Atlantic and Europe; however, not all events exhibit the same surface response, which remains a major open research question. Here, we analyze the changes in surface weather after 26 sudden stratospheric warming events. We identify two types of responses: For two thirds of the events, the effect of the stratosphere leads to a southward shift of the westerly jet in the Atlantic and an eastward extension in the Pacific. For the remaining one third of events, sudden stratospheric warmings are associated with a northward shift of the jet in both basins. We find that the anomalous weather patterns in the Pacific may contribute to the sign of the Atlantic response by propagation of synoptic storms from the East Pacific toward the Atlantic. The results of this study can potentially improve the understanding of the coupling between the stratosphere and surface weather and help to extend weather prediction timescales. Key Points: On average over all events, SSW events are followed by a reduction in North Atlantic storm track activityOne third of the SSWs does not exhibit the canonical downward response but shows an increase in storm track activity in the North AtlanticThe Pacific is found to contribute to the sign of the North Atlantic response in both cases [ABSTRACT FROM AUTHOR]