Polar vortex is nothing new. It has recently become popular due to its contribution in USA’s recent extreme cold temperatures in January 2019. Polar vortex can be defined as a large area of low pressure cold air on the poles of the earth. It weakens during the summer and becomes stronger in winters, but has always existed. This article gives more insight into polar vortices facts, how they are formed, why they are dangerous, what causes them to leak and how global warming is related to these.
What is a polar vortex?
The term “vortex” simply means rotation of cold air near the poles. This rotation lets the cold air stay near the poles. In fact, there are two polar vortices, one for each pole. In the north, the polar vortex rotates counter-clockwise and in the south, the polar vortex rotates clockwise. One might say, its properties are similar to that of a cyclone. The rotation is caused by the coriolis force.
The polar vortex extends between the tropopause and the mesosphere, i.e, (20 km – 50 km above the surface of the earth).
How is a polar vortex formed
The polar vortex intensity depends on the temperature difference between the equatorial and polar regions. This is why it is strong in winters and weak in summers. The circle of cold air is contained by jet streams. The jet streams do not let air from the polar vortex interact with the warmer air in the mid-latitudes, which is why the polar vortices are extremely cold.
The role of jet streams –
Jet streams are high speed winds traveling at the speeds ranging between 160 – 320 kmph (100 – 200 mph). And when these jet streams weaken, it causes the polar vortex of cold arctic region break into mid-latitude regions.
The jet streams in the northern hemisphere are also known as “polar nights”. This is essentially because dark months contribute to cold air formation.
How jet streams are formed
During summer, the temperature difference between the mid-latitude regions and the poles is small. In winters, the poles stay devoid of sunlight for months and become frigid cold.
This leads to a drastic temperature difference between air near the poles and the air near the mid-latitudes. These temperature differences cause extreme pressure differences in the stratosphere. The pressure difference and the coriolis force, together combined form “polar night jet streams”.
“There is a common misconception that jetstreams cause the polar vortex to form. However, it is quite the opposite. The jet streams are instead formed as a result of ‘certain’ weather conditions.”
Why is the polar vortex so cold?
The polar jet streams thus formed, leave no way for the warm air to mingle with the colder air near the poles. As a result, the “cold” near the poles intensifies manifold.
What causes the polar vortex to break?
The jet streams exist in the stratosphere and so does the polar vortex. Sometimes, this polar vortex weakens and allows the cold harsh arctic winds reach lower latitudes. This has happened before in 1977, 1982, 1985, 1989, 2014 and now in 2019.
When the temperature in the stratosphere becomes warmer, it weakens the jet stream that contains the polar vortex, thus leading the polar vortex to leak to warmer regions.
A weakened polar vortex splits into distinct areas, each contained by a comparatively disoriented weaker jet stream.
Simply put, it is global warming that is causing the polar vortex to break more frequently over the last few decades.
More facts on polar vortex
- The polar vortex is not limited to the United States. Some parts of Europe and Asia also experience cold waves associated with the polar vortex.
- The polar vortex of the Antarctic south pole is much stronger than the Arctic. This is because the winds in the southern hemisphere are unobstructed, while in the northern hemisphere, the winds are disturbed.
- The deep freeze that gripped the USA and Canada between between January and February 2019 is believed to have been caused due breaking of polar vortex with some areas facing temperatures as low as -56 degrees celsius.
- When the polar vortex leak occurred in 2014, it caused the Niagara falls to freeze.
- Polar vortex is also linked to ozone layer depletion above the South pole. This because, at the temperature of -80 degree celsius, the nitric acid in clouds reacts with chlorofluorocarbons to form chlorine, which destroys the ozone layer. This effect is more severe in the south pole because of stronger polar vortex (thus leading to colder temperature that is optimum for the reaction to take place).
- Some other planets also have polar vortices. These include Jupiter, Venus, Mars, Saturn and Jupiter’s moon, Titan.