Utilizing ERA5 data, this study provides evidence that both the winter-mean state and subseasonal variability (SSV) of the warm Arctic-cold Eurasia (WACE) pattern significantly influence the frequency of cold extremes in Eurasia. The positive phase of winter-mean WACE (WACE_Mean) or a stronger SSV of WACE (WACE_SSV) corresponds to a higher occurrence of cold extremes over central Eurasia and East Asia. Furthermore, the study reveals that the impact of WACE_Mean on the cold extremes is modulated by WACE_SSV. During years characterized by a positive WACE_Mean and enhanced WACE_SSV, the associated winter-mean anticyclonic anomalies, combined with amplified subseasonal circulation fluctuations over the northern Eurasia continent, contribute to a significant increase in the blocking frequency over the Ural–Siberia region. This, in turn, contributes to an intensified occurrence of cold extremes in central Eurasia and East Asia. In contrast, during the years with a positive WACE_Mean but reduced WACE_SSV, in the absence of significant changes in the subseasonal circulation fluctuations, the winter-mean anticyclonic anomalies over the northern Eurasia continent do not exert a significant impact on Ural–Siberian blocking frequency by themselves. Consequently, there are no notable anomalies in the frequency of cold extremes over central Eurasia and East Asia. Finally, this study reveals that the differences in the distribution of the frequency anomalies in the blocking between the two sets of years are attributed to the constructive and destructive superposition of anomalies in subseasonal circulation fluctuations related to the WACE_Mean and WACE_SSV.

中文翻译：

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次季节变率对冬季平均暖北极-冷欧亚大陆格局对欧亚极寒事件的影响的调节

利用 ERA5 数据，本研究提供的证据表明，温暖的北极-寒冷欧亚大陆 (WACE) 模式的冬季平均状态和次季节变化 (SSV) 显着影响欧亚大陆极端寒冷的频率。冬季平均 WACE (WACE _Mean ) 的正相位或更强的 WACE SSV (WACE _SSV ) 对应于欧亚大陆中部和东亚地区极端寒冷事件的发生率较高。此外，研究表明 WACE_平均值对极端寒冷的影响受到 WACE _{SSV 的}调节。在WACE_平均值为正值和WACE _SSV增强的年份中，相关的冬季平均反气旋异常，加上欧亚大陆北部次季节环流波动的放大，导致乌拉尔-西伯利亚地区的阻塞频率显着增加。这反过来又导致欧亚大陆中部和东亚极端寒冷事件的加剧。相比之下，在WACE_平均值为正但WACE _SSV降低的年份，在次季节环流波动没有显着变化的情况下，欧亚大陆北部冬季平均反气旋异常对乌拉尔—西伯利亚阻塞没有产生显着影响频率由自己决定。因此，欧亚大陆中部和东亚极端寒冷天气的频率没有明显异常。最后，本研究揭示了两组年份之间阻塞频率异常分布的差异归因于与WACE _Mean和WACE _SSV相关的次季节环流波动异常的相长和相消叠加。