The polar vortex, a swirl of low-pressure air six miles up in the atmosphere, blasted much of the American Midwest and Northeast in late January 2019 with temperatures cold enough to bring on frostbite within minutes. 

Polar vortex :-

• The polar vortex is a great gyre of air that forms each winter and circulates above the North Pole, way up in the stratosphere.
• The polar vortex forms every winter because of the temperature difference between the equator and the poles.
• In the polar stratosphere, sunlight basically gets cut off during the late fall and early winter and that makes it really cold, while the equator remains quite warm.
• A jet forms to balance this temperature difference. This jet is what is called the polar vortex or the polar night jet. It flows in a complete circle around the pole, 10 kilometers or a little over six miles above the Earth’s surface. 
• Impact :-–
  • The polar vortex hitting the U.S. led severely cold temperatures that cancelled flights, closed schools and left dangerous conditions around the country .

Polar vortex is due to climate change :-

• The term “polar vortex” has been around since the late 1940s. It forms every winter and breaks up in the spring. But for the last 20 years or so, the polar vortex has been very, very disturbed in the middle of winter.
• Increasing carbon dioxide in the atmosphere cools the polar stratosphere, which could increase the temperature difference between the pole and the equator and strengthen the polar vortex.
• There’s also some model evidence that the waves that are propagating upwards in the troposphere are getting more energetic as the planet warms, leading to a more perturbed polar stratosphere.
• There’s some evidencethat the jet stream, a meandering air current that flows over North America and Europe, is slowing and becoming wavier as the planet warms. The jet stream interacts with the polar vortex, helping bring numbing temperatures further south.
• Scientists also point to a complex sequence of events involving sea ice, which is rapidly diminishing in the Arctic.
  • As the ice retreats, summertime heat is absorbed by the dark ocean that lies underneath. This heat is released into the atmosphere during winter, spurring winds that can disrupt the polar vortex.
  • Scientists have observed that more and more Arctic sea iceis melting during the summer months. As the ice melts, the Arctic Ocean warms, and radiates that excess heat back to the atmosphere in winter. Because that heat somewhat reduces the contrast between the Arctic air and the atmosphere in regions farther south, it reduces

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  the intensity of the winds that form the barrier between the two areas. That, in turn, weakens and disrupts the polar vortex.