Polar vortex

The polar vortex is a band of strong stratospheric winds that circles the Arctic (and Antarctic) poles, confining cold polar air within the polar regions and separating it from warmer mid-latitude air. The vortex is not a single coherent structure but a dynamical equilibrium maintained by the temperature gradient between the pole and the equator. When the vortex is strong, the Arctic Oscillation is typically positive and the Icelandic Low is deep and stable. When the vortex weakens or fragments — a phenomenon known as sudden stratospheric warming — Arctic air can spill southward, disrupting mid-latitude weather patterns. The polar vortex is the stratosphere's answer to the troposphere's jet stream: both are critical transitions in the atmosphere's angular momentum budget, and both are sensitive to perturbations from below and above.