Most sudden stratospheric warming (SSW) events initiate with their centers being displaced from the pole. Some retain their displaced form until termination but some split into two vortices during their course. Here, we show that existence of a transition during the course of the SSW life cycle can be attributable to the condition of North Atlantic Oscillation (NAO) preceding before onset: Positive NAO favors SSW of displacement type with no transition while negative NAO favors the displacement–split type. We show that, in positive NAO precondition, vertical flux of wave activity immediately before onset is mostly contributed only by wavenumber 1 component, which contrasts with the relatively stronger contribution of wavenumber 2 in negative NAO precondition. Whole Atmosphere Community Climate Model (WACCM) simulation results are also consistent with the observational findings. Therefore, NAO can be regarded as a useful precursor for determining the type of forthcoming SSW events.

中文翻译：

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平流层突然变暖对先前北大西洋涛动条件的依赖

大多数平流层突然变暖（SSW）事件都是以其中心偏离极点开始的。一些保持其位移形式直到终止，但一些在其运动过程中分裂成两个涡流。在这里，我们证明了南半球振荡生命周期过程中过渡的存在可以归因于发病之前的北大西洋涛动（NAO）：正NAO有利于位移类型的SSW，没有过渡，而负NAO有利于位移–拆分类型。我们发现，在正的NAO前提下，波活动之前的垂直波通量主要仅由波数1的分量贡献，这与负的NAO前提下波数2的相对较强的贡献相反。整个大气社区气候模型（WACCM）的模拟结果也与观测结果一致。因此，NAO可被视为确定即将发生的SSW事件类型的有用先兆。