Preprints
https://doi.org/10.5194/egusphere-2025-3017
https://doi.org/10.5194/egusphere-2025-3017
08 Jul 2025
 | 08 Jul 2025
Status: this preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).

Transient Flow Patterns of an Annular-like Stratospheric Polar Vortex

Huw Davies and Michael Sprenger

Abstract. A two-component study is undertaken of flow features associated with the wintertime polar-night vortex at upper-stratospheric levels. First, three cursory case studies are presented based upon reanalysis data. They suggest that: – (a) sub-planetary scale flow features are pervasive, tend to occur near the periphery of the vortex, and are associated with the vortex’s predilection to develop a structure akin to an annular-like band of enhanced potential vorticity; (b) planetary scale flow features are influenced by, and can significantly distort such a band. Second, theoretical considerations and numerical model simulations of perturbations of an annular band of enhanced absolute vorticity using a non-divergent barotropic model on a polar β-plane yield results consistent both with the occurrence of the sub-planetary scale features, and with the possible rapid reconfiguration of a pre-conditioned planetary scale flow. The latter result bears comparison with the occurrence of a sudden stratospheric warming event via a synergetic combination of strong planetary-scale Rossby-wave forcing from below acting upon the vortex’s annular potential vorticity band.

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Huw Davies and Michael Sprenger

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-3017', Anonymous Referee #1, 17 Aug 2025 reply
    • AC1: 'Reply on RC1', Huw Davies, 26 Aug 2025 reply
Huw Davies and Michael Sprenger
Huw Davies and Michael Sprenger

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Short summary
The Stratospheric Polar Vortex (SPV) with its accompanying strong circumpolar jet is a dominant feature of the wintertime stratosphere. Evidence is presented that the SPV’s periphery often possesses distinctive sub-planetary scale features. The scale and dynamics of the features are linked to the break-up of an annular band of strong vorticity at the SPV’s periphery, and the latter’s aggregation into one or two vortices due to forcing from below bears comparison to Sudden Stratospheric Warming.
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