An example of a vortex split leading to a weak polar vortex: the center of the vortex is knocked off the North Pole and slpit in two. The fast flow of westerlies is slowed down, the trajectory is now also north-south and cold air spills out from the polar regions to lower latitudes. The stratospheric warmign is initiated by a perturbatithat emerges from Siberia and splits the polar vortex. Shading shows temperatures and countours the geopotential heights.