Winter temperatures in the North America (NA) exhibit evident intraseasonal variation, which has become more pronounced under global climate change. In particular, the wintertime relationship between NA temperatures and long-lasting positive sea surface temperature anomalies (SSTAs) in the Northeast Pacific (NEP), known as warm blobs, has been hotly debated in recent years. However, their relationship on intraseasonal timescales remains unclear. Using reanalysis data and an Atmospheric General Circulation Model, this study reveals that the intraseasonal variation of atmospheric circulation is the primary factor to induce intraseasonal temperature anomalies in NA after classifying warm SSTA events based on their different evolutions. Moreover, the atmospheric circulation anomalies over the mid-to-high-latitude regions are in part contributed by the feedback of NEP warm SSTAs to the atmosphere. Specifically, for early-winter warm SSTA events (peaking in November), there are two intraseasonal reversals in geopotential height anomalies over the NEP and NA, corresponding to a “cold-warm-cold” temperature change in NA. However, for mid-winter warm SSTA events (peaking in January), the atmospheric circulation pattern is relatively stable, mainly characterized by a “west high-east low” dipole, associated with persistent cold anomalies in NA. Then, the role of warm SSTAs over the NEP in the intraseasonal temperature variation is generally verified by the numerical simulations. Hence, although the NEP warm SSTAs may not be the dominant driver of the intraseasonal variations of winter NA temperatures, we emphasize the implication of their evolutionary differences in reflecting the NA temperature variations, which contributes to better predictability.

中文翻译：

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北美冬季气温与东北太平洋暖海面温度的季节内关系


北美 （NA） 的冬季温度表现出明显的季节内变化，在全球气候变化下变得更加明显。特别是，NA 温度与东北太平洋 （NEP） 的长期正海面温度异常 （SSTA）（称为暖斑点）之间的冬季关系近年来一直受到激烈争论。然而，它们在季节内时间尺度上的关系仍不清楚。利用再分析数据和大气环流模型，本研究揭示了在根据温暖的 SSTA 事件的不同演变进行分类后，大气环流的季节内变化是诱发 NA 季节内温度异常的主要因素。此外，中高纬度地区的大气环流异常部分是由 NEP 暖 SSTA 对大气的反馈造成的。具体来说，对于初冬温暖的 SSTA 事件（在 11 月达到峰值），NEP 和 NA 上的位势高度异常存在两次季节内反转，对应于 NA 中的“冷-暖-冷”温度变化。然而，对于隆冬温暖的海温事件（在 1 月达到峰值），大气环流模式相对稳定，主要以“西高东低”偶极子为特征，与 NA 持续的寒冷异常有关。然后，通常通过数值模拟验证暖 SSTA 对 NEP 在季节内温度变化中的作用。因此，尽管 NEP 暖 SSTA 可能不是冬季 NA 温度季节内变化的主要驱动因素，但我们强调它们的进化差异在反映 NA 温度变化方面的意义，这有助于更好的可预测性。