The dominant intraseasonal variability mode of tropical convection in the 2 weeks before a Northern Hemisphere extreme stratospheric polar vortex
The dominant intraseasonal variability mode of tropical convection in the 2 weeks before a Northern Hemisphere extreme stratospheric polar vortex
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DOI：
10.1002/qj.4205
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发表时间：
2021-11
影响因子：
8.9
通讯作者：
Feiyang Wang;Dan Ye
中科院分区：
文献类型：
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作者：
Feiyang Wang;Dan Ye
近年来，MJO第7相被认为是北方半球平流层突然变暖的驱动因子。然而，MJO阶段3和平流层极涡之间的确切关系仍然存在不确定性。在这里，我们重新检查并比较了在本研究中两种类型的北半球极端平流层极涡事件（即强涡（SV）事件和弱涡（WV）事件）之前观测到的MJO演变。我们的分析表明，MJO第3（7）阶段是SV（WV）事件开始前约2周的主要季节内变率模态，这表明这两个阶段与平流层极涡强度的变化密切相关。MJO阶段3（7）导致极涡加强（减弱），这是由于MJO阶段3（7）诱导的负（正）太平洋-北美（PNA）样模式与背景场之间的相消（相长）干涉导致对流层外平流层中的1号波活动受到抑制（增强）。请注意，对流层外平流层中波活动对MJO阶段3和7的峰值响应的时间尺度分别约为2周和1周。因此，在2周内，MJO阶段3（7）可以被视为加强（减弱）极涡的前兆。
The Madden–Julian Oscillation (MJO) phase 7 has been recognized as a driver for Northern Hemisphere (NH) sudden stratospheric warmings (SSWs) in the literature recently. However, uncertainties remain on the exact relationship between MJO phase 3 and the stratospheric polar vortex. Here, we re‐examined and compared the observed evolution of the MJO before the two types of NH extreme stratospheric polar vortex events (i.e. strong vortex (SV) events and weak vortex (WV) events) in this study. Our analysis reveals that MJO phase 3 (7) is the dominant intraseasonal variability mode in about 2 weeks before onset of the SV (WV) events, suggesting these two phases are closely linked to variation in the intensity of the stratospheric polar vortex. MJO phase 3 (7) leads to a strengthened (weakened) polar vortex due to the suppressed (enhanced) wave‐number 1 wave activity in the extratropical stratosphere resulting from destructive (constructive) interference between the negative (positive) Pacific–North American (PNA)‐like pattern induced by MJO phase 3 (7) and the background field. Note that the time‐scales for the peak responses of wave activity in the extratropical stratosphere to MJO phases 3 and 7 are around 2 weeks and 1 week, respectively. Thus, within 2 weeks, MJO phase 3 (7) can be treated as the precursor to the strengthened (weakened) polar vortex.