Stratospheric polar vortex splits and displacements in the high‐top CMIP5 climate models
Stratospheric polar vortex splits and displacements in the high‐top CMIP5 climate models
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DOI：
10.1002/2015jd024178
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发表时间：
2016-02
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影响因子：
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通讯作者：
W. Seviour;L. Gray;D. Mitchell
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文献类型：
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作者：
W. Seviour;L. Gray;D. Mitchell
平流层突然变暖(SSW)事件可以作为平流层极地涡旋的分裂或位移而发生。最近的观测研究对这两种类型的SSW对地表气候的相对影响得出了不同的结论。更清楚地了解它们对对流层的影响将有助于中期天气预报，并可增进对平流层-对流层耦合的物理机制的理解。在这里，我们进行了平流层极涡分裂和位移的第一次多模式比较，分析了来自第五次耦合模式对比计划(CMIP5)集合的13个平流层分辨率模式。我们发现模型之间在涡旋的平均状态以及涡旋分裂和位移的频率上都存在广泛的偏差，尽管这些偏差是密切相关的。与观测结果一致的是，几乎所有的模式都显示涡旋分裂在整个平流层深处都是正压的，而涡旋的位移更倾向于斜压。涡旋分裂显示，在爆发后的一个月，北大西洋表面信号略强。然而，地面响应中最显著的区别是，西伯利亚上空的涡旋位移表现出更强的负压异常。这一区域与对流层顶高度的差异是并置的，这表明对低平流层位涡异常的局部响应。
Sudden stratospheric warming (SSW) events can occur as either a split or a displacement of the stratospheric polar vortex. Recent observational studies have come to different conclusions about the relative impacts of these two types of SSW upon surface climate. A clearer understanding of their tropospheric impact would be beneficial for medium‐range weather forecasts and could improve understanding of the physical mechanism for stratosphere‐troposphere coupling. Here we perform the first multimodel comparison of stratospheric polar vortex splits and displacements, analyzing 13 stratosphere‐resolving models from the fifth Coupled Model Intercomparison Project (CMIP5) ensemble. We find a wide range of biases among models in both the mean state of the vortex and the frequency of vortex splits and displacements, although these biases are closely related. Consistent with observational results, almost all models show vortex splits to occur barotropically throughout the depth of the stratosphere, while vortex displacements are more baroclinic. Vortex splits show a slightly stronger North Atlantic surface signal in the month following onset. However, the most significant difference in the surface response is that vortex displacements show stronger negative pressure anomalies over Siberia. This region is shown to be colocated with differences in tropopause height, suggestive of a localized response to lower stratospheric potential vorticity anomalies.