A poleward storm track shift reduces mid-latitude heatwave frequency: insights from an idealized atmospheric model

Abstract. Recent decades have seen a global increase in hot extremes, yet the role of changes in the atmospheric circulation in driving this trend remains unclear. While previous studies focused on the amplitude of planetary and synoptic-scale waves for explaining the frequency and persistence of temperature extremes, we here investigate the influence of the storm track position. Specifically, we conduct a suite of idealized model experiments with the dry dynamical core of the ICON model, where thermal forcing in the tropics or the polar regions alters the characteristics of the extratropical storm track. In these simulations, the storm track is associated with a mid-latitude minimum in the frequency of persistent temperature extremes. The underlying relationship between the zonal phase speed of synoptic-scale waves and storm track characteristics is assessed through spectral analysis of upper-tropospheric meridional wind. A poleward-shifted storm track is associated with a strengthened eddy-driven jet, an increase in phase speed, and a reduction in heatwave frequency. Reanalysis data for the Southern Hemisphere, where ozone depletion and greenhouse gas emissions have caused a poleward storm track shift, reveals a mid-latitude minimum in heatwave frequency reminiscent of the idealized model. While the phase speed of synoptic-scale waves has continuously increased from the 1980s to the present, we cannot find evidence that this development has influenced the persistence of Southern Hemisphere mid-latitude temperature extremes, potentially due to differences in the climatological-mean spectrum between the idealized model and reanalysis. The mechanism may, on the other hand, be relevant for the future evolution of extreme events in the Northern Hemisphere under the joint influence of Arctic amplification and the expansion of the tropics.