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Journal Article

More-persistent weak stratospheric polar vortex states linked to cold extremes

Authors
/persons/resource/kretschmer

Kretschmer,  Marlene
Potsdam Institute for Climate Impact Research;

/persons/resource/coumou

Coumou,  Dim
Potsdam Institute for Climate Impact Research;

Agel,  L.
External Organizations;

Barlow,  M.
External Organizations;

Tziperman,  E.
External Organizations;

Cohen,  J.
External Organizations;

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(Publisher version), 6MB

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Citation

Kretschmer, M., Coumou, D., Agel, L., Barlow, M., Tziperman, E., Cohen, J. (2018): More-persistent weak stratospheric polar vortex states linked to cold extremes. - Bulletin of the American Meteorological Society, 99, 1, 49-60.
https://doi.org/10.1175/BAMS-D-16-0259.1


Cite as: https://publications.pik-potsdam.de/pubman/item/item_21717
Abstract
The extratropical stratosphere in boreal winter is characterized by a strong circumpolar westerly jet, confining the coldest temperatures at high latitudes. The jet, referred to as the stratospheric polar vortex, is predominantly zonal and centered around the pole; however, it does exhibit large variability in wind speed and location. Previous studies showed that a weak stratospheric polar vortex can lead to cold-air outbreaks in the midlatitudes, but the exact relationships and mechanisms are unclear. Particularly, it is unclear whether stratospheric variability has contributed to the observed anomalous cooling trends in midlatitude Eurasia. Using hierarchical clustering, we show that over the last 37 years, the frequency of weak vortex states in mid- to late winter (January and February) has increased, which was accompanied by subsequent cold extremes in midlatitude Eurasia. For this region, 60% of the observed cooling in the era of Arctic amplification, that is, since 1990, can be explained by the increased frequency of weak stratospheric polar vortex states, a number that increases to almost 80% when El Niño–Southern Oscillation (ENSO) variability is included as well.