During the initial days of January 2025, the United States (US) was facing severe winter storms that had an impact of over 60 million people in the eastern part of the country. The storms caused temperatures to plummet as low as about –50 °C. Weather alerts were issued in 30 states, with seven of them declaring emergencies. This extreme weather has been driven by the southward expansion of the polar vortex, a region of intense cold and rotating air around the Arctic. The polar vortex mainly impacts countries located in the mid to high latitudes of the Northern Hemisphere, which are especially vulnerable to severe cold weather conditions.
Polar Vortex
What is it? The polar vortex is a vast area of low pressure and cold air that surrounds both the Arctic and Antarctic poles of the Earth. The term ‘vortex’ refers to the counter-clockwise flow of air that helps keep the cold air confined to the poles. It is always present near the poles, although it weakens in the summer and strengthens in the winter.
Types There are two types of polar vortexes—tropospheric and stratospheric.
The tropospheric polar vortex occurs at the lowest layer of the atmosphere, extending up to 10–15 km, where most weather phenomena take place. This vortex creates milder weather across northern latitudes.
Stratospheric polar vortex is the one which typically occurs about 16–48 km above the Earth’s surface. When the stratospheric polar vortex is in a stable state, frigid Arctic air is confined to the polar regions. However, when it is in a weakened state, the chilly winds expand beyond its circular North Pole region and extend as far south as Florida.
Both forms of the polar vortex play a key role in global atmospheric circulation and climate control.
Impacts Disruptions in the polar vortex can lead to shifts in atmospheric circulation, triggering events like heavy snowfall, ice storms, and blizzards. When cold Arctic air is pushed south, it can collide with warmer, moister air from the mid-latitudes, setting up ideal conditions for winter storms.
In the US, this can lead to major snowstorms, such as the 2010 Snowmageddon. A weakened vortex can also cause the jet stream to dip south, bringing cold air to lower latitudes, resulting in an Arctic blast. Beyond North America, Europe has also experienced severe cold waves tied to polar vortex disruptions, as seen in 2018.
This disruption can accelerate ozone depletion, especially over Antarctica, contributing to the ozone hole's formation. In India, a weakened vortex may bring more western disturbances, leading to snowfall in the western Himalayas and colder temperatures in northern regions.
Structure and Dynamics of Polar Vortex
The polar vortex is a massive storm that exists in the middle and upper layers of the atmosphere, typically centered around the Arctic Circle. During the cold season in the Northern Hemisphere, it usually intensifies near the North Pole. Storms, including the polar vortex, often forming along zones where there are significant temperature contrasts, which helps fuel strengthening during the winter months.
The temperature difference between the tropics and the Arctic Circle grows as a result of the reduced sunlight over the polar region during the fall and early winter months. The growing temperature contrast is what drives the strengthening of the polar vortex. When the polar vortex is intense, the westerly winds around the Arctic Circle also stay strong, preventing the coldest air from escaping and keeping it confined near the North Pole. As the vortex weakens, some of the cold Arctic air can break off and move southward, bringing a surge of cold weather.
This occurs because when the polar vortex is strong and stable, it helps maintain the jet stream’s circular path around the planet. Without the strong low-pressure system of the polar vortex, the jet stream loses the force needed to maintain its usual path and becomes wavy and erratic. When high-pressure systems interfere, pockets of cold air can break off and push south, bringing the rest of the polar vortex system along with it.
Polar Jet Stream and Polar Vortex
Jet streams are narrow, fast-moving air currents found in the upper atmosphere, usually at altitudes of about 30,000 feet. Polar jet stream acts as a boundary between warmer air from the mid-latitudes and colder air from the poles.
People often mistake the polar vortex for the polar jet stream, but there are some differences. In simple terms, the polar vortex is a mass of cold air, while the polar jet stream is a fast-moving wind pattern that can influence the movement of the vortex and affect weather on the ground.
Disturbances in the Polar Vortex and Extreme Cold Events
Typically, when the polar vortex is strong in the north, westerly winds flow across much of the US and southern Canada, generally between the mid-latitudes of 30° and 60° north. However, at times, storms in these regions can intensify enough to disrupt and shift the westerly winds. Storms can intensify to the point where they push warmer air northward, weakening the polar vortex and causing the strong winds around the Arctic Circle to weaken. When this occurs, it can trigger a chain reaction that allows Arctic air to escape southward, reaching the mid-latitudes.
While storms over the US and Canada can lead to temperature fluctuations, including occasional warm spells and brief bursts of Arctic air, the polar vortex must significantly weaken for major outbreaks of Arctic air that persist for several days or weeks.
Each weakening of the polar vortex and its associated Arctic outbreaks may subside as the vortex weakens and then stabilises or strengthens again. However, other intensely cold outbreaks can intensify when a slightly weakened vortex weakens further, causing a significant southward push of Arctic air.
Polar Vortex and Climate Change
Researchers have been investigating how climate change influences the intensity and frequency of colder temperatures linked to the polar vortex. Scientists are still studying the exact effects of climate change on the polar vortex, particularly whether rising temperatures are causing the low-pressure system to weaken or shift more often. Some data indicate that climate change could be impacting the behaviour of the polar vortex.
Global warming is weakening the polar vortex because Earth is not warming uniformly. The North Pole is warming at a much faster rate than other areas, which disrupts the polar vortex and the jet stream. As a result, the vortex has become more vulnerable to shifting, allowing colder air to spill in the regions like Europe and North Asia.
According to the National Oceanic and Atmospheric Administration, the Arctic is warming much faster than other parts of the planet, and the reduced temperature difference that helps maintain the stability of the polar vortex leads to a weaker jet stream. The warming of higher latitudes reduces the temperature difference between the warmer mid-latitudes and the polar regions. This weakens and destabilises the polar jet stream causing it to dip further south and bring cold polar air into lower latitudes.
Several factors can impact the strength of the polar vortex, with sea ice being one of them. Some models suggest that melting sea ice could weaken the vortex. On the other hand, warming in the upper layers of the atmosphere might strengthen it. Additionally, regional shifts in the sea surface temperatures could also play a role. Because of these varying influences, models do not agree on how the Northern Hemisphere polar vortex will behave in the future.
Recent studies have highlighted a rise in instances where the polar vortex has shifted into densely populated areas. Scientists are gaining a clearer understanding of why this occurs with many pointing to climate change as a contributing factor. There is evidence suggesting that the jet stream is slowing down and becoming more wavy as the planet warms. This change in the jet stream affects the polar vortex, helping to push frigid temperatures further south.
Scientists also highlight a complex chain of events involving the rapidly shrinking sea ice in the Arctic. As the ice melts, the darker ocean beneath absorbs more heat during the summer. This heat is then released into the atmosphere in winter, driving winds that can disrupt the polar vortex.
The research on polar vortex and climate change is still ongoing and while the scientists have not reached on definitive conclusions yet, there is growing support for this idea. It is a rapidly developing and highly debated area of study.
Conclusion
The polar vortex is a crucial atmospheric feature that plays a significant role in shaping weather patterns, especially during the winter months. Understanding the dynamics of the polar vortex is critical for predicting extreme weather events and better preparing for the impacts of climate change.
As the Arctic continues to warm, there is concern that polar vortex disruptions could become more frequent and intense, leading to an increase in extreme cold events and altered weather patterns. The ongoing study of the polar vortex and its relationship with climate change will be essential in forecasting and managing the effects of these disruptive weather events in the future.
By gaining a better understanding of the polar vortex, scientists, meteorologists, and policymakers can work together to mitigate the impacts of extreme cold events and adapt to the changing climate.
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