Sudden Stratospheric Warming Events Control on Midlatitude Storm Tracks from Intraseasonal to Decadal Time Scales

Impact of stratospheric dynamics onto troposphere represents an important driver of climate variability near the surface with implications for extreme weather and climate events. Sudden Stratospheric Warming (SSW) events represent one of the most critical impacts on the troposphere when the reversed Polar Vortex results in the equatorward shift of the North Atlantic tropospheric storm track. While this concept was generally outlined in the earlier studies, its implication for the positioning of the North Atlantic storm track, Atlantic-to-Europe mid-latitude heat and moisture transport and European precipitation was not explicitly covered. Here we use mid-latitude cyclone trajectories numerically derived form all modern reanalyses (ERA Interim, NCEP CFSR, JRA-55, ERA 5 (if available in late 2018)) and several CMIP5 models and provide for the first time robust quantitative estimates of the southward storm track shifts in response to SSW events. These shifts are closely coordinated with the changes in the major pathways of the moisture transport from the North Atlantic to Europe and in the patterns of European precipitation, including extreme rainfalls. As the SSW events can be precisely detected, our results imply that in many cases European precipitation and associated hydroclimate extremes can be predictable on time scales of several weeks, going far beyond the range of mid-latitude weather forecasts.

We also analyse climatological trends of SSWs frequency in Northern Hemisphere and associate them with long term trends in characteristics of midlatitute storm track (position, cyclone lifecycle characteristics), providing a hint on the driving mechanism of the observed polarward shift of the storm track in Northern Hemisphere.