Robust asymmetry of the future Arctic polar vortex is driven by tropical Pacific warming

Abstract The wintertime Arctic stratospheric polar vortex is characterized by a circumpolar westerly jet, confining the coldest temperatures over the Arctic. The future stratosphere is globally dominated by a strong radiative cooling due to the increase in greenhouse gases, enhancing the Arctic cooling. However, we find that over North America, the Arctic stratospheric cooling is suppressed or rather warming occurs, whereas over Eurasia stratospheric cooling is most pronounced, leading to an asymmetric polar vortex, based on 21st century climate model simulations. There are many causes that drive polar vortex variability, such as Arctic sea ice loss, and midlatitude and tropical Pacific warming, which make future projections highly uncertain. Our model simulations demonstrate that tropical warming induces the asymmetric polar vortex. The eastern equatorial Pacific warming causes eastward-shifted teleconnection, which strengthens the polar vortex over Eurasia and weakens over North America by enhancing the vertical wave propagation into the stratosphere. The asymmetric polar vortex is projected to markedly develop in the 2030s, and so could also affect winter surface climate over mid- to high-latitudes of Eurasia in the near future.