Recent relevance: Tens of millions of Americans braved Arctic-like temperatures on Thursday as low as minus 49 degrees Celsius that paralysed the U.S. Midwest and were blamed for 21 deaths. The cold has been blamed on a phenomenon called the ‘polar vortex’.

What is the polar vortex?

Meteorologist Mark Chenard said a polar vortex refers to the upper level jet stream that circulates around both the North and South Poles, keeping the coldest air there. When that jet stream occasionally weakens and buckles it disrupts weather patterns — bumping warmer air into Alaska and pushing cold winds down into the U.S.

It’s a band of strong winds, high up in the atmosphere that keeps bitterly cold air locked around the Arctic region. This circulation isn’t considered a single storm, or even a weather pattern as such.

Why is it affecting the US?

Occasionally, the vortex can become distorted and meander far further south than normal. The phenomenon became widely known to Americans during a particularly frigid spell in 2014.

Is this weather event linked to climate change?

There’s some evidence that 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.

Source: The Guardian