The Pacific-North American teleconnection (PNA) is one of the most important atmospheric modes in the Northern Hemisphere in modern climate. Through the PNA teleconnection, climate variations in the tropical Pacific have significant impacts on North America. However, whether there existed the PNA-like mode in the deep-time climate and how it evolved remain unknown. Here, we study the evolution of the PNA in the past 70 million years, using simulation results with the fully coupled Community Earth System Model version 1.2.2 (CESM1.2.2). Our simulation results show that there existed a PNA-like mode (referred to as PNA in this study) in the Cenozoic, but with different strengths and pathways. The strengths of the PNA were weaker over 70–40 million years ago (Ma) than that of the present, while it is comparable to the present over 30–10 Ma. Diagnosis indicates that the weaker strengths and distorted pathways of the PNA before ∼40 Ma are due to weaker meridional temperature gradients in warmer climates, which causes weakened extratropical westerly jet and altered extratropical waveguide of planetary-scale stationary waves. After ∼40 Ma, Earth climate became much colder, entering into the icehouse climate. Thus, the PNA pattern is close to the present state.

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新生代太平洋-北美遥相关

太平洋-北美遥相关（PNA）是现代气候下北半球最重要的大气模式之一。通过 PNA 遥连，热带太平洋的气候变化对北美产生重大影响。然而，深时气候中是否存在类PNA模式以及它是如何演化的仍然未知。在这里，我们使用完全耦合的社区地球系统模型版本 1.2.2 (CESM1.2.2) 的模拟结果来研究 PNA 在过去 7000 万年的演变。我们的模拟结果表明，新生代存在类PNA模式（本研究中简称为PNA），但强度和路径不同。 70-4000万年前（Ma）PNA的强度比现在弱，但30-10 Ma以上与现在相当。诊断表明，~40 Ma之前PNA强度减弱和路径扭曲是由于气候变暖时经向温度梯度减弱，导致温带西风急流减弱和行星尺度驻波温带波导改变。 ～40 Ma后，地球气候变得更加寒冷，进入冰室气候。因此，PNA 模式接近当前状态。