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<p>Extreme winter cold-air outbreaks (CAOs) impose substantial societal and economic impacts across the Northern Hemisphere, yet the stratospheric processes that modulate these events—and shape their regional expression—remain incompletely understood. Previous studies relied on cluster-based classifications of polar vortex states, which discretize continuous variability and often emphasize North American impacts. Here, we introduce a, phase-based diagnostic framework that characterizes the evolving geometry of the lower stratospheric polar vortex (LSPV) using amplitude, percentage of longitudinal spatial variance explained by wave-1 and wave-2 components, and their longitudinal phase in 100 hPa geopotential height anomalies. This approach distinguishes displacement (wave-1) and stretching (wave-2) configurations and identifies four recurrent trough orientations over North America, Atlantic, Asia, and Far East. Composite analysis for January–February 1979–2024 shows that these phase-locked configurations are frequently associated with vertically coherent anomaly patterns between 100 hPa and 500 hPa and with distinct surface temperature anomalies. A transition-probability matrix indicates that LSPV trough configurations often reorganize between preferred longitudinal sectors than propagate gradually in longitude. These results show that wave-1 (displacement) and wave-2 (stretching) geometries represent recurrent modes of LSPV variability during January–February, with sector-dependent surface temperature anomalies, providing a framework for understanding the regional structure of CAO-related midlatitude winter circulation patterns.</p>

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Regional structure of the polar vortex via planetary wave phase diagnostics and its link to cold air outbreaks

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月24日

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  • Varunesh Chandra,
  • Muyin Wang,
  • James E. Overland

摘要

Extreme winter cold-air outbreaks (CAOs) impose substantial societal and economic impacts across the Northern Hemisphere, yet the stratospheric processes that modulate these events—and shape their regional expression—remain incompletely understood. Previous studies relied on cluster-based classifications of polar vortex states, which discretize continuous variability and often emphasize North American impacts. Here, we introduce a, phase-based diagnostic framework that characterizes the evolving geometry of the lower stratospheric polar vortex (LSPV) using amplitude, percentage of longitudinal spatial variance explained by wave-1 and wave-2 components, and their longitudinal phase in 100 hPa geopotential height anomalies. This approach distinguishes displacement (wave-1) and stretching (wave-2) configurations and identifies four recurrent trough orientations over North America, Atlantic, Asia, and Far East. Composite analysis for January–February 1979–2024 shows that these phase-locked configurations are frequently associated with vertically coherent anomaly patterns between 100 hPa and 500 hPa and with distinct surface temperature anomalies. A transition-probability matrix indicates that LSPV trough configurations often reorganize between preferred longitudinal sectors than propagate gradually in longitude. These results show that wave-1 (displacement) and wave-2 (stretching) geometries represent recurrent modes of LSPV variability during January–February, with sector-dependent surface temperature anomalies, providing a framework for understanding the regional structure of CAO-related midlatitude winter circulation patterns.