Euro‐Atlantic regimes are typically identified using either the latitude of the North Atlantic jet or clustering algorithms in the phase space of 500‐hPa geopotential (Z500). However, while robust trimodality is visibly apparent in jet latitude indices, Z500 clusters require highly sensitive significance tests to distinguish them from autocorrelated noise. This leads to considerable decadal variability in regime patterns, confounding many potential applications. A clear‐cut choice of the optimal number of regimes is also hard to justify. We argue that the jet speed, a near‐Gaussian distribution projecting strongly onto the Z500 field, is the source of these difficulties. Once its influence is removed, the phase space becomes visibly non‐Gaussian, and clustering algorithms easily recover three regimes, closely corresponding to the jet latitude modes. Further analysis supports the existence of two additional blocking regimes, corresponding to a tilted and split jet. All five regimes are approximately stationary across the twentieth century.

中文翻译：

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喷气速度的变化掩盖了欧洲大西洋政权的结构

通常使用北大西洋急流的纬度或在500-hPa地势（Z500）相空间中的聚类算法来确定欧洲-大西洋政权。但是，尽管在喷气纬度指数中明显表现出强大的三峰性，但Z500集群需要进行高度敏感的显着性测试，以将其与自相关噪声区分开。这导致了政权模式中相当大的年代际变化，混淆了许多潜在的应用。明确选择最佳方案数量也很难成立。我们认为，喷射速度是Z500场上强烈投射的近高斯分布，是造成这些困难的原因。消除影响后，相空间就明显变为非高斯分布，并且聚类算法轻松恢复了三种状态，紧密对应于喷气纬度模式 进一步的分析支持存在两个额外的阻塞方案，分别对应于倾斜和分开的射流。在整个20世纪中，所有五个政权都是大致固定的。