Estimating the Frequency of Sudden Stratospheric Warming Events From Surface Observations of the North Atlantic Oscillation
Estimating the Frequency of Sudden Stratospheric Warming Events From Surface Observations of the North Atlantic Oscillation
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DOI：
10.1029/2018jd030077
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发表时间：
2019-03-27
影响因子：
4.4
通讯作者：
Domeisen, Daniela I. V.
中科院分区：
文献类型：
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作者：
Domeisen, Daniela I. V.
突然的平流层变暖（SSW）事件可以表现出长期的表面影响，有望改善中期到季节性的可预测性。它们对地面的影响主要是北大西洋涛动的负位相。因此，出现的问题，如果平流层的变化，特别是频率的SSW事件，反过来可以估计从地面NAO条件。这在频繁的高空观测变得可用之前的时期尤其相关，而NAO的每日地面观测可以追溯到1850年。这里的表面的影响是量化的NAO的特点，通常观察到SSW事件后：从一个积极的负NAO和负NAO的持久性，称为NAO事件的开关。发现三分之二的SSW事件之后是持续或切换NAO事件，四分之一的SSW事件之后是两者。另一方面，不到25%的冬季地面NAO事件之前的SSW事件。基于这些研究结果，一个指数纯粹基于地面NAO观测得出估计SSW频率的卫星时代，并将其延伸到1850年，表明十年平流层的变化存在于整个时间序列，没有显着的趋势。20世纪90年代SSW发生频率最低的时间与1850年以来NAO事件最长的消失时间相吻合，这表明20世纪90年代早期可能是150年记录中最长的SSW事件消失时间。简明语言摘要平流层极端事件，即所谓的平流层突然变暖（SSW）事件，对北大西洋的天气有长期的影响，其特点是北大西洋涛动（NAO）的变化。虽然NAO的日常观测可以追溯到1850年，但SSW事件频率的估计只能追溯到20世纪50年代。本研究探讨在何种程度上的频率的SSW事件可以估计从表面NAO的变化作为重建SSW频率在20世纪50年代之前的第一步。据发现，典型地发生在SSW事件后的表面NAO的特征效应仅与SSW事件在所有情况下的四分之一左右。然而，可以完全根据地面信息生成一个指数，该指数可以在很大程度上再现平流层信息可用期间的SSW频率。将指数延伸到1850年表明，SSW事件的频率表现出年代际变化，如在20世纪后半叶所观察到的。还发现，20世纪90年代初，很少有SSW事件被观察到的时期，可能是自1850年以来最长的SSW事件的缺席。
Sudden stratospheric warming (SSW) events can exhibit long-lasting surface impacts that promise improvements in medium-range to seasonal predictability. Their surface impact is dominated by the negative phase of the North Atlantic Oscillation (NAO). Hence, the question arises if stratospheric variability, and in particular the frequency of SSW events, can in turn be estimated from surface NAO conditions. This is especially relevant for the period before frequent upper air observations became available, while daily surface observations of the NAO date back to 1850. The surface impact is here quantified by NAO characteristics that are commonly observed after SSW events: a switch from a positive to a negative NAO and an extended persistence of the negative NAO, termed NAO events. Two thirds of SSW events are found to be followed by either a persistence or switch NAO event, and a quarter of SSW events are followed by both. On the other hand, less than 25% of winter surface NAO events are preceded by a SSW event. Based on these findings, an index purely based on surface NAO observations is derived that estimates SSW frequency for the satellite era and extends it back to 1850, indicating that decadal stratospheric variability was present for the entire time series, with no significant trend. The minimum in SSW frequency in the 1990s is found to be coincident with the longest absence of NAO events since 1850, indicating that the early 1990s may constitute the longest absence of SSW events for the 150-year record.Plain Language Summary Extreme events in the stratosphere, so-called sudden stratospheric warming (SSW) events, have long-lasting impacts on the weather over the North Atlantic that can be characterized by variability in the North Atlantic Oscillation (NAO). While daily observations of the NAO date back to 1850, estimates of SSW event frequency only go back to the 1950s. This study explores to what extent the frequency of SSW events can be estimated from surface NAO variability as a first step toward reconstructing SSW frequency before the 1950s. It is found that characteristic effects in the surface NAO that typically occur after SSW events are only associated with SSW events in about a quarter of all cases. Nevertheless, an index can be generated entirely based on surface information that can to a good extent reproduce the SSW frequency for the period for which information for the stratosphere is available. Extending the index back to 1850 indicates that the frequency of SSW events exhibited decadal variability, as observed in the second half of the twentieth century. It is also found that the early 1990s, a period where very few SSW events were observed, was likely the longest absence of SSW events since 1850.