A planetary-scale mid- to high-latitude circumpolar cyclonic circulation, extending from the middle troposphere to the stratosphere. The Northern Hemisphere vortex often features two centers—one near Baffin Island and the other over northeast Siberia—with analogous circumpolar asymmetry atypical in the Southern Hemisphere. (emphasis mine)
Why does the Northern Hemisphere polar vortex often have two centers, as opposed to one for the Southern? I gather that this may have something to do with the Arctic vortex being elongated in shape, but this leads to the question of why it is elongated? Does it have something to do with the terrain features below?