Preprints
https://doi.org/10.5194/egusphere-2024-667
https://doi.org/10.5194/egusphere-2024-667
07 Mar 2024
 | 07 Mar 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Downward Coupling of Sudden Stratospheric Warmings: Important Role of Synoptic-Scale Waves Demonstrated by ERA5 Reanalysis

Tabea Rahm, Robin Pilch Kedzierski, Martje Hänsch, and Katja Matthes

Abstract. Circulation anomalies accompanying Sudden Stratospheric Warmings (SSWs) can have a significant impact on the troposphere. This surface response is observed for some but not all SSWs, and their downward coupling is not fully understood. We use an existing classification method to separate downward- and non-propagating SSWs (d/nSSWs) in ERA5 reanalysis data for the years 1979–2019. The differences in SSW downward propagation in composites of spatial patterns clearly show that dSSWs dominate the surface regional impacts following SSWs. During dSSWs, the upper-tropospheric jet stream is significantly displaced equatorward. Wave activity analysis shows remarkable differences between d/nSSWs for planetary and synoptic-scale waves. Enhanced stratospheric planetary eddy kinetic energy (EKE) and heat fluxes around the central date of dSSWs are followed by increased synoptic-scale wave activity and even surface coupling for synoptic-scale EKE. An observed significant reduction in upper-tropospheric synoptic-scale momentum fluxes following dSSWs confirms the important role of tropospheric eddy feedbacks for coupling to the surface. Our findings emphasize the role of the lower stratosphere and synoptic-scale waves in coupling the SSW signal to the surface and agree with mechanisms suggested in earlier modeling studies.

Tabea Rahm, Robin Pilch Kedzierski, Martje Hänsch, and Katja Matthes

Status: open (until 18 Apr 2024)

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  • RC1: 'Comment on egusphere-2024-667', Anonymous Referee #1, 29 Mar 2024 reply
  • RC2: 'Comment on egusphere-2024-667', Anonymous Referee #2, 02 Apr 2024 reply
Tabea Rahm, Robin Pilch Kedzierski, Martje Hänsch, and Katja Matthes
Tabea Rahm, Robin Pilch Kedzierski, Martje Hänsch, and Katja Matthes

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Short summary
Sudden Stratospheric Warmings (SSWs) are extreme wintertime events that can impact surface weather. However, a distinct surface response is not observed for every SSW. Here, we classify SSWs that do and do not impact the troposphere in ERA5 reanalysis data. In addition, we evaluate the effects of two kinds of waves: planetary and synoptic-scale. Our findings emphasize that the lower stratosphere and synoptic-scale waves play crucial roles in coupling the SSW signal to the surface.