The winter North Atlantic Oscillation (NAO), one of the leading modes of atmospheric variability in the Northern Hemisphere and key driver of surface climate anomalies, was long considered to be spatially stable. Yet, its northern center-of-action – the Icelandic Low (IL) – shifted eastward in the late 1970s compared to the preceding decades of the mid-20th century. The responsible processes are still uncertain, particularly after the decline of the positive NAO trend in the 21st century. Here, we present observational and model evidence that the NAO-IL moves naturally alternating between two preferential locations, west/east of Iceland, with no need for changes in anthropogenic forcing or low-frequency oceanic variability. These recurrent longitudinal displacements of the NAO pattern appear linked to zonal changes in the fluctuations (not mean-state) of transient-eddy activity, emphasizing the relevance of internal atmospheric variability, and could represent a major source of uncertainty in regional climate prediction and projection.

冬季北大西洋涛动 （NAO） 是北半球大气变率的主要模式之一，也是地表气候异常的关键驱动因素，长期以来一直被认为在空间上是稳定的。然而，与 20 世纪中叶的前几十年相比，它的北部活动中心——冰岛低压 （IL）——在 1970 年代后期向东移动。负责的过程仍然不确定，尤其是在 21 世纪积极 NAO 趋势下降之后。在这里，我们提供了观测和模型证据，表明 NAO-IL 在冰岛西部/东部两个优先位置之间自然交替移动，不需要人为强迫或低频海洋变化的变化。NAO 型的这些反复纵向位移似乎与瞬态涡流活动波动（而不是平均状态）的纬向变化有关，强调了内部大气变率的相关性，并可能代表区域气候预测和预测不确定性的主要来源。