Midlatitude heatwave variability modulated by a shifting storm track

Both the circulation response to climate change as well as internal atmospheric variability are marked by a meridional displacement of the extratropical storm track. It remains to be quantified how such changes in the storm track modulate the occurrence of heatwaves. We combine a composite analysis of reanalysis data with idealized model experiments to investigate the response in heatwave frequency to variations in the storm track latitude in two different datasets. In the idealized model, a forced poleward storm track shift leads to an increase in upper-tropospheric Rossby wave phase speed, and vice versa, which in turn reduces and increases heatwave frequency and duration across the mid-latitudes. A similar relationship between storm track latitude, Rossby wave phase speed, and heatwave duration is found for internal variability in reanalysis data. However, in reanalysis, a reduction in phase speed does not necessarily lead to an increased heatwave frequency due to geographically phase-locked wave trains induced by zonal asymmetries. These results shed new light on the dynamical drivers for heat extremes.