Regional Structure of the Polar Vortex via Planetary Wave Phase Diagnostics and Its Link to Cold Air Outbreaks

Extreme winter cold-air outbreaks (CAOs) disrupt societies and economies across the Northern Hemisphere, yet the stratospheric pathways that organize these events—and their regional expression—remain incompletely understood. While prior studies often emphasize North American impacts using cluster-based approaches, disruptions of the lower stratospheric polar vortex (LSPV)—through displacement or stretching—can shape weather across the wider subarctic and midlatitudes. We present a framework to diagnose daily LSPV variability using the variance, amplitude and longitudinal phase of zonal wave-1 and wave-2 spectral components derived from 100 hPa geopotential height anomalies. Applying zonal harmonic decomposition on band-averaged geopotential height anomalies at100 hPa, we separate SPV structure into wave-1 (displacement) and wave-2 (stretching) modes. This analysis reveals four persistent, regionally anchored vortex trough phase orientations—over North America, the Atlantic, Asia, and the Far East—that reflect quasi-stationary planetary wave geometry and recurring large-scale weather regimes. Composite analysis demonstrates vertically coherent structures extending from the lower stratosphere to the surface, with distinct 500 hPa trough anomalies and associated surface CAOs. A transition probability matrix show that the SPV undergoes rapid spatial reorganization rather than slow longitudinal advection. These results demonstrate that vortex displacement and stretching are fundamental, recurring features of Arctic and subarctic atmospheric variability, providing a new approach for diagnosing and predicting midlatitude extremes under ongoing Arctic amplification.