Preprints
https://doi.org/10.5194/wcd-2022-43
https://doi.org/10.5194/wcd-2022-43
 
26 Jul 2022
26 Jul 2022
Status: this preprint is currently under review for the journal WCD.

The role of Rossby waves in polar weather and climate

Tim Woollings1, Camille Li2, Marie Drouard1,3, Etienne Dunn-Sigouin4, Karim A. Elmestekawy1, Momme Hell5, Brian Hoskins6, Cheikh Mbengue1,7, Matthew Patterson1, and Thomas Spengler2 Tim Woollings et al.
  • 1Atmospheric, Oceanic and Planetary Physics, Parks Rd, Oxford, OX1 3PU, UK
  • 2Geophysical Institute, University of Bergen, and Bjerknes Centre for Climate Research, Bergen, Norway
  • 3Earth Physics and Astrophysics Department, Universidad Complutense de Madrid, Spain
  • 4NORCE Norwegian Research Centre AS and Bjerknes Centre for Climate Research, Bergen Norway
  • 5Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
  • 6Grantham Institute, Imperial College London, London, UK, and Department of Meteorology, University of Reading, Reading, UK
  • 7Climate Modeling Alliance, California Institute of Technology, Pasadena, California, USA

Abstract. Recent Arctic warming has fuelled interest in the weather and climate of the polar regions and how this interacts with lower latitudes. Several interesting theories of polar-midlatitude linkages involves Rossby wave propagation as a key process even though the meridional gradient in planetary vorticity, crucial for these waves, is weak at high latitudes. Here we review some basic theory and suggest that Rossby waves can indeed explain some features of polar variability, especially when relative vorticity gradients are present.

We suggest that large-scale polar flow can be conceptualised as a mix of geostrophic turbulence and Rossby wave propagation, as in the mid-latitudes, but with the balance tipped further in favour of turbulent flow. Hence, isolated vortices often dominate but some wavelike features remain. As an example, quasi-stationary or weakly westward-propagating subpolar anomalies emerge from statistical analysis of observed data, and these are consistent with some role for wave propagation. The noted persistence of polar cyclones and anticyclones is attributed in part to the weakened effects of wave dispersion, the mechanism responsible for the decay of mid-latitude anomalies in downstream development. We also suggest that the vortex-dominated nature of polar dynamics encourages the emergence of annular mode structures in principal component analyses of extratropical circulation.

Finally, we consider how Rossby waves may be triggered from high latitudes. The linear mechanisms known to balance localised heating at lower latitudes are shown to be less efficient in the polar regions. Instead, we suggest the direct response to sea ice loss often manifests as a heat low, with radiative cooling balancing the heating. If the relative vorticity gradient is favourable this does have the potential to trigger a Rossby wave response, although this will often be weak compared to waves forced from lower latitudes.

Tim Woollings et al.

Status: open (until 10 Sep 2022)

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Tim Woollings et al.

Tim Woollings et al.

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Short summary
This paper investigates large scale atmospheric variability in polar regions, specifically the balance between large scale turbulence and Rossby wave activity. The polar regions are relatively more dominated by turbulence than lower latitudes, but Rossby waves are found to play a role and can even be triggered from high latitudes under certain conditions. Features such as cyclone lifetimes, high-latitude blocks and annular modes are discussed from this perspective.