Although sudden stratospheric warmings (SSWs) can improve subseasonal-to-seasonal forecasts, it is unclear whether the two types of SSW - displacements and splits - have different near-surface effects. To examine the longer-term (i.e., multi-week lead) tropospheric response to displacements and splits, we utilize an intermediate-complexity model and impose wave-1 and wave-2 stratospheric heating perturbations spun-off from a control run. At longer lags, the tropospheric response is found to be insensitive to both the wavenumber and location of the imposed heating, in agreement with freely evolving displacements and splits identified in the control run. At shorter lags, however, large differences are found between displacements and splits in both the control run and the different wavenumber-forced events. In particular, in the control run, the free-running splits have an immediate barotropic response throughout the stratosphere and troposphere whereas displacements take 1–2 weeks before a near-surface response becomes evident. Interestingly, this barotropic response found during CTRL splits is not captured by the barotropically forced wave-2 events, indicating that the zonal-mean tropospheric circulation is somehow coupled with the generation of the wave-2 splits. It is also found that in the control run, displacements yield stronger Polar-Cap temperature anomalies than splits, yet both still yield similar magnitude tropospheric responses. Hence, the strength of the stratospheric warming is not the only governing factor in the surface response. Overall, SSW classification based on vortex morphology may be useful for subseasonal but not seasonal tropospheric prediction.
Bibliographical noteFunding Information:
The authors wish to thank Ed Gerber and an anonymous reviewer whose in‐depth reviews have led to a much‐improved manuscript. I. P. White is also thankful for useful conversations with Chen Schwartz. The authors acknowledge the support of a European Research Council starting grant under the European Union Horizon 2020 research and innovation program (Grant 677756). J. Cohen is supported by the US National Science Foundation grant PLR‐1901352. M. Jucker is supported by the ARC Centre of Excellence for Climate Extremes under Grant CE170100023 and ARC Grant FL150100035. J. Rao also acknowledges support from the National Natural Science Foundation of China (41705024).
© 2021. The Authors.
- Idealized modeling
- Northern Annular Mode
- polar vortex
- stratosphere-troposphere coupling
- sudden stratospheric warmings
- thermal forcing