02 Mar 2022
02 Mar 2022
Status: a revised version of this preprint is currently under review for the journal WCD.

Stratospheric wave driving events as an alternative to sudden stratospheric sudden warmings

Thomas Reichler1 and Martin Jucker2,3 Thomas Reichler and Martin Jucker
  • 1Department of Atmospheric Sciences, University of Utah, Salt Lake City, 84112, USA
  • 2Climate Change Research Center, the University of New South Wales, Sydney, NSW, Australia
  • 3Australian Research Council Center of Excellence for Climate Extremes, Sydney, NSW, Australia

Abstract. Natural variations in the strength of the northern stratospheric polar vortex, so-called polar vortex events, help to improve sub-seasonal to seasonal (S2S) predictions of winter climate. Past research on polar vortex events has been largely focused on stratospheric sudden warming events (SSWs), a class of relatively strong weakenings of the polar vortex. SSWs are defined when the polar vortex reverses its normal westerly wind direction. In this study, however, we use an alternative definition, based on the weighted time-integrated upward wave activity flux at the lower stratosphere prior to the onset of the events. We use a long control simulation with a stratosphere-resolving model and the ERA5 reanalysis to compare various aspects of the wave activity definition with traditional SSWs over the Arctic. About half of the wave events are identical to SSWs, while the other half create on average more robust surface signals than the SSWs that do not concur with the wave events. There exist several other advantages over traditional SSWs: the wave activity flux definition creates more robust surface signals, captures with one simple criterium a variety of different event types, lengthens the prediction horizon of the surface response, and can be more meaningfully applied over the southern hemisphere. We therefore conclude that that the wave driving represents a useful early indicator for stratospheric polar vortex events, which exploits the stratospheric potential for creating predictable surface signals better than SSWs.

Thomas Reichler and Martin Jucker

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-2022-13', Amy Butler, 30 Mar 2022
  • RC2: 'Comment on wcd-2022-13', Anonymous Referee #2, 30 Mar 2022
  • AC1: 'Comment on wcd-2022-13', Thomas Reichler, 25 Apr 2022

Thomas Reichler and Martin Jucker

Thomas Reichler and Martin Jucker


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Short summary
Variations in the stratospheric polar vortex, so-called vortex events, can improve predictions of surface weather and climate. There are various ways to detect such events, and here we use the amount of wave energy that propagates into the stratosphere. The the new definition is tested against so-called stratospheric sudden warmings (SSWs). We find that the wave definition has important advantages over SSWs, for example in terms of a stronger surface response that follows the events.