Stratosphere–Troposphere Coupling During Cold Air Outbreaks in the Eastern United States

Cold air outbreaks (CAOs) are extreme weather events characterized by the equatorward displacement of polar air. This study investigates CAOs occurring along the East Coast of the US and establishes that approximately 16% are driven by stratosphere‐troposphere coupling through wave dynamics. Using ERA5 data, we show that daily surface air temperature anomalies are significantly associated with the EOF2 of stratospheric variability at 10 hPa as determined by linear regression. Wave activity flux analysis indicates that approximately 14 days prior to the CAO onset, distortion of the polar vortex generates downward propagating planetary waves. As the waves reach the mid‐troposphere (500 hPa), they enhance the horizontal convergence of wave activity which interacts with the polar jet stream, extending it fartherer south and thus triggering a CAO at the surface. The 14‐day between the stratospheric triggering and the onset has potential to increase the sub‐seasonal to seasonal predictability of these events.