Context: Meteorologists have blamed a phenomenon called the polar vortex for the bitter cold that has descended on much of the central and eastern United States this week, forcing residents to huddle indoors, closing schools and businesses and cancelling flights.

• The term ‘polar vortex’ has become more commonly used in the past couple of years but the phenomenon has been around forever. There is some debate among scientists about whether polar vortexes have become more frequent and, if so, what effect climate change might be having on them.

What exactly is a polar vortex?

It is described as a whirling cone of low pressure over the poles that is strongest in the winter months due to the increased temperature contrast between the polar regions and the mid-latitudes, such as the US and Europe.

Features:

1. The polar vortex spins in the stratosphere.
2. Usually, when the vortex is strongest, cold air is less-likely to plunge deep into North America or Europe. In other words, it forms a wall that protects the mid-latitudes from cold Arctic air.
3. But occasionally, the polar vortex is disrupted and weakens, due to wave energy propagating upward from the lower atmosphere. When this happens, the stratosphere warms sharply in an event known as sudden stratospheric warming, in just a few days, miles above the Earth’s surface.
4. The warming weakens the polar vortex, shifting its location somewhat south of the pole or, in some instances, ‘splitting’ the vortex up into ‘sister vortices’.

Effects of Polar Vortex:

The split higher up in the atmosphere can give rise to both, sudden and delayed effects, much of which involves declining temperatures and extreme winter weather in the eastern US along with northern and western Europe.

• A sudden stratospheric warming also leads to a warm Arctic not only in the stratosphere but also in the troposphere as well.
• A warmer Arctic, in turn, favours more severe winter weather in the Northern Hemisphere mid-latitudes including the eastern US.