Our study reframes our understanding of stratosphere-troposphere interactions, traditionally thought to be confined within individual hemispheres, by introducing a novel cross-hemispheric link. We demonstrate that strong boreal winter Arctic stratospheric polar vortex (APV) boosts the transmission of upper tropospheric waves from Northern Hemisphere’s mid-high latitudes to the equator. Facilitated by the tropical central and eastern Pacific’s “westerly bridge”, these waves reach Southern Hemisphere’s mid-high latitudes. The entire process shows a “semicircular road”. Waves reaching the Southern Hemisphere affect the circulation through wave-flow interaction, causing a southward swing of the Southern Hemispheric westerly jet center. This displacement weakens the subtropical jet and strengthens the polar jet, resulting in increased subtropical precipitation and decreased mid-latitude precipitation in the Southern Hemisphere during austral summer. Correspondingly, a weak APV may lead to the opposite result. Our findings underscore APV’s broader impact on the tropospheric atmosphere, extending beyond prior knowledge.

Stratospheric Polar Vortex