Picture: Cloud vortex. Credit: Neenu Vimalkumar unsplash

The polar vortex – a strong jet that circumnavigates the stratospheric winter Pole at ∼10–50 km – is known to influence surface weather. In particular, when the polar vortex becomes highly disturbed in events known as sudden stratospheric warmings, a downward influence on the surface is observed.

Recent studies have debated whether the two types of sudden stratospheric warming – displacement events when the vortex is displaced off the Pole and split events when the vortex splits into two smaller vortices – have differing near-surface impacts.

Using an idealised model, CLEX researchers examined the near‐surface response to imposed stratospheric (longitudinally asymmetric) displacement‐ and split‐like events. They found that on seasonal timescales (i.e., approximately longer than 3–4 weeks), the surface response was insensitive to displacements and splits. However, on subseasonal timescales (less than a month), clear differences are apparent, with splits initially leading to a stronger surface response and displacements taking 1–2 weeks for a response to develop. Further, varying the location of both the displacement‐ and split‐type forcing does not yield appreciably different tropospheric responses.

Overall, the study suggests that knowledge of the sudden stratospheric warming type is useful for subseasonal weather prediction but may not be useful in improving weather prediction on seasonal timescales.

  • Paper: White, I. P., Garfinkel, C. I., Cohen, J., Jucker, M., & Rao, J. (2021). The impact of split and displacement sudden stratospheric warmings on the troposphere. Journal of Geophysical Research: Atmospheres, 126, e2020JD033989. https://doi.org/10.1029/2020JD033989