Arctic sea ice decline, increasing successive sudden stratospheric warmings and cold northern hemisphere continents

The frequency of successive sudden stratospheric warming events has markedly increased since 2000s. Using multimodel experiments it is demonstrated that reduced sea ice leads to higher frequencies of successive warming events. The decline in Arctic sea ice corresponds to a reduction in the refractive index in the mid-to-high latitude stratosphere, changing the waveguide and enhancing poleward planetary-wave propagation. Decomposition of the refractive index reveals variations in the meridional gradient of potential vorticity are the dominant factor. Under reduced sea ice conditions, increased successive sudden warmings still produce persistent downward influences on surface weather, resulting in broader cold temperature anomalies across Northern Hemisphere continents. Further analysis of multimodel experiments confirms a significant negative correlation between Arctic sea ice and sudden warming frequency, ruling out greenhouse gases alone as the cause of the observed trend. As the Arctic warming reshapes stratospheric variability, the cold anomalies over some spots may not diminish.