MORE-PERSISTENT WEAK STRATOSPHERIC POLAR VORTEX STATES LINKED TO COLD EXTREMES
MORE-PERSISTENT WEAK STRATOSPHERIC POLAR VORTEX STATES LINKED TO COLD EXTREMES
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DOI：
10.1175/bams-d-16-0259.1
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发表时间：
2018-01-01
影响因子：
8
通讯作者：
Cohen, Judah
中科院分区：
文献类型：
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作者：
Kretschmer, Marlene;Coumou, Dim;Cohen, Judah
在北半球冬季，对流层外平流层的特征是有一股强烈的绕极西风急流，限制了高纬度地区的最低温度。急流被称为平流层极涡，主要是纬向的，以极为中心;然而，它在风速和位置上确实表现出很大的变化。以往的研究表明，平流层极涡的减弱可以导致中纬度地区冷空气的爆发，但具体的关系和机制尚不清楚。特别是，目前还不清楚平流层的变化是否有助于观察到的欧亚大陆中纬度地区的异常冷却趋势。使用层次聚类，我们表明，在过去的37年中，弱涡状态的频率在中到晚冬（1月和2月）增加，这是伴随着随后的极端寒冷的中纬度欧亚大陆。对于这一地区，在北极放大的时代，即自1990年以来，60%的观测到的冷却，可以解释为平流层弱极涡状态的频率增加，当厄尔尼诺-南方涛动（ENSO）变率也包括在内时，这个数字增加到近80%。
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.