TY  - JOUR
A1  - Kretschmer, Marlene
A1  - Coumou, Dim
A1  - Agel, Laurie
A1  - Barlow, Mathew
A1  - Tziperman, Eli
A1  - Cohen, Judah
T1  - More-Persistent weak stratospheric polar vortex states linked to cold extremes
T2  - Bulletin of the American Meteorological Society
N2  - 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 Nino-Southern Oscillation (ENSO) variability is included as well.
Y1  - 2018
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/54235
SN  - 0003-0007
SN  - 1520-0477
VL  - 99
IS  - 1
SP  - 49
EP  - 60
PB  - American Meteorological Soc.
CY  - Boston
ER  -