Polar Vortex

• Weather experts are predicting an extremely cold January and February for the North eastern United States due to low polar vortex. Extreme cold has become cause of concern as low polar vortex has been alleged earlier for drop in temperatures along the mid-latitudes, in United States and Europe.
• similar cold outbreaks had occurred in the past, including notable outbreaks in 1977, 1982, 1985, 1989 and 2014

What is Polar Vortex?

• The stratospheric polar vortex is a large-scale region of air that is contained by a strong west-to-east jet stream that circles the polar region. This jet stream is usually referred to as the polar night jet.
• The polar vortex extends from the tropopause (the dividing line between the stratosphere and troposphere) through the stratosphere and into the mesosphere (above 50 km). Low values of ozone and cold temperatures are associated with the air inside the 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.
• Often when the polar vortex is strong, temperatures are mild in the mid-latitudes across the Eastern US and Northern Eurasia; and when the vortex is weak, temperatures tend to be cold across the Eastern US and northern Europe and Asia.

 What is Strong Polar Vortex?

• Strong polar vortex is the more common state of vortex which creates strong low pressure in the Arctic region.
• Because of the pressure difference between the Arctic and mid-latitudes, air flows into low pressure and this confines the cold air to high latitudes closer to the Arctic. Therefore it is often mild across the Eastern US, Europe and East Asia during winters when the polar vortex is strong. During strong polar vortex, the air flow is fast and in a direction from west to east.
• Low pressure in the Arctic region is referred to as the positive phase of the Arctic Oscillation (AO), which is also known as the North Atlantic Oscillation (NAO).

Weak polar vortex                                  

• 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.
• 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’.
• 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.

Is Polar vortex recent phenomena and confined to particular region?

• It is not a recent phenomenon. It has been tormenting the Earth’s northern regions for well over four billion years.
• Weather forecasters examine the polar vortex by looking at conditions tens of thousands of feet up in the atmosphere.
• This is not confined to the United States. Portions of Europe and Asia also experience cold surges connected to the polar vortex.

Is global warming responsible for weakening of polar vortex?

• It is being hypothesised that the weakening of polar vortex is a result of global warming. Warming leads to melting of polar ice during summer months. The melting ice warms the Arctic Ocean and the heat is radiated back to the atmosphere.
• In the absence of global warming, there used to be a substantial difference between the temperatures at the poles and in the mid latitudes.
• As more and more ice melts in the coming years, more such events can be expected. But very little research on this is available as ice melting is a recent phenomenon.
•  IPCC (Intergovernmental Panel on Climate Change) report says that the polar vortex is expected to become smaller in the coming years.