04 Apr 2022
04 Apr 2022
Status: this preprint is currently under review for the journal WCD.

Stratospheric Wave Reflection Events Modulate North American Weather Regimes and Cold Spells

Gabriele Messori1,2, Marlene Kretschmer3, Simon H. Lee4, and Vivien Matthias5 Gabriele Messori et al.
  • 1Department of Earth Sciences and Centre of Natural Hazards and Disaster Science (CNDS), Uppsala University, Uppsala, Sweden
  • 2Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 3Department of Meteorology, University of Reading, Reading, UK
  • 4Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA
  • 5Institute for Solar-Terrestrial Physics, German Aerospace Center (DLR), Neustrelitz, Germany

Abstract. The Arctic stratospheric polar vortex is an important driver of mid-latitude cold spells. One proposed coupling mechanism between the stratospheric polar vortex and the troposphere are upward-propagating planetary waves being reflected downward by the polar vortex. However, while the wave reflection mechanism is well-documented, its role in favouring cold spells is still under-explored. Here, we analyse such stratospheric wave reflection events and their impacts on the tropospheric circulation and surface temperatures over North America in winter. We present a physically interpretable regional stratospheric wave reflection detection metric, and identify the tropospheric circulation anomalies associated with prolonged periods of wave reflection, which we term reflection events. In particular, we characterise the tropospheric anomalies through the lens of North American weather regimes. Stratospheric reflection events show a systematic evolution from a Pacific Trough regime – associated on average with positive temperature anomalies and a near-complete absence of anomalously cold temperatures in North America – to an Alaskan Ridge regime, which favours low temperatures over much of the continent. The most striking feature of the stratospheric reflection events is thus a rapid, continental-scale decrease in temperatures. These emerge as continental-scale colds spells by the end of the reflection events. Stratospheric reflection events are thus relevant for tropospheric predictability in a socioeconomic impacts perspective.

Gabriele Messori et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2022-18', Pengfei Zhang, 11 May 2022
    • AC1: 'Reply on RC1', Gabriele Messori, 01 Jul 2022
  • RC2: 'Comment on wcd-2022-18', Anonymous Referee #2, 17 May 2022
    • AC2: 'Reply on RC2', Gabriele Messori, 01 Jul 2022

Gabriele Messori et al.

Gabriele Messori et al.


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Short summary
Over 10 km above the ground, there is a region of the atmosphere called stratosphere. While there is very little air in the stratosphere itself, its interactions with the lower parts of the atmosphere – where we live – can affect the weather. Here we study a specific example of such interaction, whereby processes occurring at the boundary of the stratosphere can lead to a continent-wide drop in temperatures in North America during winter.