Abstract Applying the daily ERA-interim reanalysis data from 1979 to 2016, we found that widespread cold (warm) wintertime extreme events in Northern Europe occurred most frequently in winter 1984–1985 (2006–2007). These events often persisted for multiple days, and their primary drivers were the pattern of atmospheric large-scale circulation, the direction of surface wind and the downward longwave radiation. Widespread cold extremes were favoured by the Scandinavian Pattern and Ural Blocking, associated with advection of continental air-masses from the east, clear skies and negative anomalies in downward longwave radiation. In the case of widespread warm extremes, a centre of low pressure was typically located over the Barents Sea and a centre of high pressure over Central Europe, which caused south-westerly winds to dominate over Northern Europe, bringing warm, cloudy air masses to Northern Europe. Applying Self-Organizing Maps, we found out that thermodynamic processes explained 80% (64%) of the decreasing (increasing) trend in the occurrence of extreme cold (warm) events. The trends were due to a combined effect of climate warming and internal variability of the system. Changes in cases with a high-pressure centre over Iceland were important for the decreased occurrence of cold extremes over Northern Europe, with contribution from increasing downward long-wave radiation and south-westerly winds. The largest contribution to the increased occurrence of widespread warm extremes originated from warming and increased occurrence of the Icelandic low.

中文翻译：

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1979-2016 年北欧冬季极端温度的发生和驱动因素

摘要 应用 1979 年至 2016 年的每日 ERA-临时再分析数据，我们发现北欧广泛的冷（暖）冬季极端事件最常发生在 1984 年至 1985 年（2006 年至 2007 年）冬季。这些事件往往持续数天，其主要驱动因素是大气大尺度环流模式、地表风向和向下长波辐射。斯堪的纳维亚模式和乌拉尔阻塞有利于广泛的极端寒冷，这与来自东部的大陆气团的平流、晴朗的天空和向下长波辐射的负异常有关。在普遍的极端暖和的情况下，低压中心通常位于巴伦支海上空，高压中心位于中欧上空，这导致西南风在北欧占据主导地位，将温暖多云的气团带到北欧。应用自组织图，我们发现热力学过程解释了极端冷（暖）事件发生的减少（增加）趋势的 80%（64%）。这些趋势是由于气候变暖和系统内部变异的综合影响。冰岛高压中心案例的变化对于减少北欧极端寒冷事件的发生很重要，这是向下长波辐射和西南风增加的贡献。对广泛发生的极端温暖事件增加的最大贡献源于变暖和冰岛低压发生的增加。我们发现热力学过程解释了 80% (64%) 的极端冷（暖）事件发生的减少（增加）趋势。这些趋势是由于气候变暖和系统内部变异的综合影响。冰岛高压中心案例的变化对于减少北欧极端寒冷事件的发生很重要，这是向下长波辐射和西南风增加的贡献。对广泛发生的极端温暖事件增加的最大贡献源于变暖和冰岛低压发生的增加。我们发现热力学过程解释了 80% (64%) 的极端冷（暖）事件发生的减少（增加）趋势。这些趋势是由于气候变暖和系统内部变异的综合影响。冰岛高压中心案例的变化对于减少北欧极端寒冷事件的发生很重要，这是向下长波辐射和西南风增加的贡献。对广泛发生的极端温暖事件增加的最大贡献源于变暖和冰岛低压发生的增加。冰岛高压中心案例的变化对于减少北欧极端寒冷事件的发生很重要，这是向下长波辐射和西南风增加的贡献。对广泛发生的极端温暖事件增加的最大贡献源于变暖和冰岛低压发生的增加。冰岛高压中心案例的变化对于减少北欧极端寒冷事件的发生很重要，这是向下长波辐射和西南风增加的贡献。对广泛发生的极端温暖事件增加的最大贡献源于变暖和冰岛低压发生的增加。