More-Persistent weak stratospheric polar vortex states linked to cold extremes
- 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 weakThe 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.…
Author details: | Marlene KretschmerORCiD, Dim CoumouORCiDGND, Laurie Agel, Mathew Barlow, Eli TzipermanORCiD, Judah CohenORCiD |
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DOI: | https://doi.org/10.1175/BAMS-D-16-0259.1 |
ISSN: | 0003-0007 |
ISSN: | 1520-0477 |
Title of parent work (English): | Bulletin of the American Meteorological Society |
Publisher: | American Meteorological Soc. |
Place of publishing: | Boston |
Publication type: | Article |
Language: | English |
Date of first publication: | 2018/01/01 |
Publication year: | 2018 |
Release date: | 2022/03/09 |
Volume: | 99 |
Issue: | 1 |
Number of pages: | 12 |
First page: | 49 |
Last Page: | 60 |
Funding institution: | German Federal Ministry of Education and ResearchFederal Ministry of Education & Research (BMBF) [01LN1304A]; National Science Foundation (NSF)National Science Foundation (NSF) [AGS-1303647, PLR-1504361]; NOAANational Oceanic Atmospheric Admin (NOAA) - USA [NA15OAR4310077]; NSFNational Science Foundation (NSF) [AGS-1303604] |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie |
DDC classification: | 5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik |