The Impact of Split and Displacement Sudden Stratospheric Warmings on the Troposphere

Abstract:

It is understood that sudden stratospheric warmings (SSWs) can improve subseasonal to seasonal forecasts due to their near-surface impacts. However, it is not known whether the two types of SSW - splits and displacements - have different surface effects. To answer this, we utilise an intermediate-complexity model and impose wave-1 and wave-2 heating perturbations to the polar stratosphere to examine the ensuing near-surface response. The evolution of displacements and splits in a control run are compared with the wave-1 and wave-2 forced events. Overall it is found that there is little difference in the near-surface response to splits and displacements either in the control run or the forced events suggesting that SSW classification based on vortex morphology may not be useful in determining the tropospheric response. We also vary the phasing of the imposed perturbations to test whether the surface response is sensitive to the location of the vortex anomalies. It is found that the phasing of the wave-1 forcing is important for the near-surface response, with a heating over the North Pacific yielding an overall weaker tropospheric jet shift than a heating over Northern Europe. However, the location of the wave-2 forcing is seemingly unimportant for the near-surface response. An examination into the reasons for the differences, or lack of, are also explored.