Maarg Manthan · Topic 5.21

Polar Vortex and Its Relationship with Ozone Depletion

Geography › Climatology · Topic 5.21

The polar vortex is a large area of low pressure and cold air that surrounds each pole in the stratosphere and the upper troposphere, kept in place by strong westerly winds. The Antarctic vortex is stronger and more stable than the Arctic one. Inside the winter vortex, extreme cold forms polar stratospheric clouds, on which chlorine from human-made chemicals destroys ozone when sunlight returns in spring, producing the Antarctic ozone hole. Weak or disturbed Arctic vortices can send cold air south and cause cold waves in mid-latitudes.

7 min read · UPSC Prelims · Geography · Climatology

At a Glance

Polar vortex Cold low-pressure region around each pole
Stronger vortex Antarctic
Ozone hole Antarctic spring, September to October
Cause of hole CFCs and polar stratospheric clouds
Treaty Montreal Protocol, 1987
Exam link UPSC Prelims, Geography: Climatology

Where Does It Fit?

This topic closes the group on atmospheric disturbances with a feature of the high atmosphere. It links the winter weather of the middle latitudes with the ozone layer, which connects the macro on climatology to the study of the environment. Previous topic: Temperate (Extra-Tropical) Cyclones: Air Masses, Fronts, Origin and Development. Next topic: El Niño and La Niña: ENSO and the Indian Ocean Dipole Effect.

What Is the Polar Vortex?

In short: the polar vortex is a permanent ring of strong winds that fences in a pool of very cold air over each pole.

The polar vortex is a large-scale cyclonic circulation around the poles, in the middle and upper troposphere and in the stratosphere. It is a permanent feature, but it is strongest in winter. During the polar night, there is no sunlight at the pole, so the air cools greatly, while the air in the mid-latitudes is warmer. The sharp temperature contrast produces a very strong westerly flow, called the polar night jet, at around 50 to 60 degrees latitude and 20 to 50 km height, as in Jet Streams: Permanent and Temporary Types and Their Impact on Weather. The ring of wind keeps the cold air confined over the Arctic. The vortex is not new, and it is not a storm, and it is not a feature of the surface weather. It is a tight circulation high above, whose changes affect the weather below.

Feature	Arctic polar vortex	Antarctic polar vortex
Stability	Weaker and distorted by mountains and land-sea contrasts in the northern hemisphere	Stronger and more stable, as the southern hemisphere has few mountains and land masses
Breakdown	Often in winter, by sudden stratospheric warming	Late spring, in November or December
Ozone	Modest ozone loss in cold years	Deep ozone loss each spring, the ozone hole

What Is a Sudden Stratospheric Warming and How Does It Affect the Weather?

In some winters, large Rossby waves from the troposphere rise into the stratosphere and disturb the vortex, as in Jet Streams: Permanent and Temporary Types and Their Impact on Weather. The temperature of the polar stratosphere can rise by 30 to 50 degrees Celsius within days, which is called a sudden stratospheric warming. The westerly winds slow, reverse or break up, and the vortex can be displaced from the pole or split into two lobes. The disturbance can travel down to the troposphere over the following weeks and weaken the jet stream there. The Arctic Oscillation, an index of the pressure difference between the Arctic and the mid-latitudes, then turns negative, and the cold air that is no longer enclosed can flow south in a cold wave.

United States: the severe cold waves of January 2014 and 2019 and of February 2021 in Texas, which overloaded the power grid, were linked to a disturbed vortex.
Europe and Asia: the cold spell of the Beast from the East in February and March 2018 followed a stratospheric warming.
Not every case: a weak vortex does not always bring cold waves, and a strong one can also be followed by cold weather, so forecasters treat the warming as a signal that raises the chances and not as a sure prediction.

How Is the Polar Vortex Linked to the Ozone Hole?

The Antarctic polar vortex is strong and isolates the air above the continent in winter. Temperatures drop below minus 78 degrees Celsius, and polar stratospheric clouds form. On the surface of these cloud particles, chlorine and bromine from man-made chemicals such as CFCs are converted into forms that destroy ozone when sunlight returns in spring, so that the ozone hole forms each year, usually reaching its maximum in September and October. The hole is slowly shrinking since the Montreal Protocol of 1987 phased out ozone-depleting substances, and scientists expect the ozone layer over Antarctica to recover to 1980 levels around the 2060s. The ozone layer itself is described in Structure of the Atmosphere: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.

What Are the Ozone Hole and the Montreal Protocol?

Discovery: in 1985 scientists of the British Antarctic Survey, Joseph Farman, Brian Gardiner and Jonathan Shanklin, reported a large fall in spring ozone over Antarctica, now known as the ozone hole.
Cause: chlorine and bromine from human-made chemicals, mainly chlorofluorocarbons (CFCs) and halons, reach the stratosphere. In the dark polar winter, ice crystals of polar stratospheric clouds form inside the vortex, and on their surface the chemicals are turned into forms that destroy ozone when sunlight returns in spring.
Timing: the hole is deepest in September and October. Its largest area, about 28 million sq km, was recorded around 2000, and holes in recent years have been smaller, though they still vary from year to year.
Arctic: the Arctic vortex is weaker and warmer, so ozone loss is smaller, but severe losses occurred in 2011 and 2020.
Response: the Montreal Protocol of 1987 phased out CFCs and other ozone-depleting substances, and the Kigali Amendment of 2016 phases down hydrofluorocarbons, which damage the climate. UN assessments expect the ozone layer to recover to 1980 levels around 2040 for most of the world, around 2045 over the Arctic and around 2066 over Antarctica, if the rules are followed.

The ozone layer lies in the stratosphere, described in Structure of the Atmosphere: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.

Is Climate Change Affecting the Polar Vortex?

The Arctic has warmed about two to four times faster than the global average, which is called Arctic amplification. Some studies suggest that the loss of sea ice weakens the vortex and favours cold outbreaks in the mid-latitudes, but other studies find little or no link, so the matter is still open and needs to be reported with caution. The overall winter is still warming, and cold waves are becoming less frequent even if some are severe. For India, the polar vortex has no direct impact, but changes in the upper-level waves can modify the track and strength of western disturbances, as in Temperate (Extra-Tropical) Cyclones: Air Masses, Fronts, Origin and Development, and the Arctic Oscillation has been linked in studies to cold waves in north India. As an analytical point, the polar vortex story is a good example of how a warming planet does not mean that every winter is warmer, and why weather and climate should be distinguished.

Why Is This Topic Important?

Current affairs Cold waves and ozone
Concepts Vortex, jets and oscillation
Climate Arctic amplification debate

What Came Next?

The next topic explains El Niño, La Niña and the Indian Ocean Dipole. Next topic: El Niño and La Niña: ENSO and the Indian Ocean Dipole Effect.

Key People and Terms

Polar vortex Cold cyclonic circulation over the pole
Polar night jet Stratospheric westerly jet
Sudden stratospheric warming Abrupt warming that disrupts the vortex
Arctic Oscillation Pressure index of the Arctic
Ozone hole Springtime ozone loss over Antarctica
Arctic amplification Faster warming of the Arctic

Exam Corner

Points to Remember

The polar vortex spins anticlockwise in the north.
Sudden stratospheric warming can split it.
Negative Arctic Oscillation allows cold outbreaks.
The Antarctic vortex causes the ozone hole.
The Montreal Protocol was signed in 1987.

Do Not Confuse With

Polar vortex and polar cyclone Permanent large circulation versus individual storms
Arctic and Antarctic vortex Weaker and distorted versus strong and stable
Weather and climate A cold wave versus long-term warming

Memory Hook

The ring holds the cold; break the ring and the Arctic walks south.

Mains Angle

Questions link the vortex with extreme weather. These points add depth.

Mechanism Wave disruption of the vortex
Impact Cold waves, ozone hole
Debate Arctic warming link uncertain

A Question You May Face

An original practice question, not a past paper question.

“What is the polar vortex? Explain how its disturbance can cause cold waves in mid-latitudes and how it is related to the ozone hole.”

How to Answer

Define Cold ring of winds.
Disruption Stratospheric warming.
Effects Cold waves and ozone.
Debate Climate link uncertain.

GS Relevance

Prelims: polar vortex, ozone hole, Montreal Protocol, causes of cold waves. GS Paper 1: atmosphere; GS Paper 3: environment.

Frequently Asked Questions

What is the polar vortex?

The polar vortex is a large region of cold, low pressure air surrounded by strong westerly winds, which circulates around each pole. It is strongest in winter in the stratosphere, and it normally keeps the very cold air confined to the polar region.

What is a sudden stratospheric warming?

A sudden stratospheric warming is a rapid rise of temperature in the polar stratosphere, by tens of degrees within a few days, caused by upward-moving atmospheric waves. It weakens, displaces or splits the polar vortex, and can lead to cold outbreaks in the middle latitudes weeks later.

Does the polar vortex cause cold waves?

The polar vortex itself is always there, but when it is disturbed and weakened, the jet stream becomes wavy and cold Arctic air can move south to North America, Europe and Asia. Not every weak vortex causes a cold wave, so the link raises the probability only.

How is the polar vortex related to the ozone hole?

The strong Antarctic polar vortex isolates the air above Antarctica in winter, allowing very low temperatures and polar stratospheric clouds. On their surfaces, chlorine and bromine compounds destroy ozone when sunlight returns in spring, which creates the ozone hole each September and October.

Does the polar vortex affect India?

The polar vortex has no direct effect on India, but changes in upper-level waves and the Arctic Oscillation can modify the strength and track of western disturbances. Some studies connect a negative Arctic Oscillation with cold waves in north India, though the link is complicated.

PYQ Practice — Statement Analysis

1 The polar vortex is strongest in the winter stratosphere.

True

The polar night makes the contrast greatest.

2 The Antarctic polar vortex is less stable than the Arctic one.

False

It is stronger and more stable.

3 Sudden stratospheric warming can weaken or split the polar vortex.