Helena Joyce
The polar vortex is a large area of low pressure and cold air surrounding the Earth's poles. It is always present near the poles, but its strength varies depending on the temperature difference between the equator and the poles, with the greatest temperature differences leading to the strongest winds. The polar vortex is strongest during the winter, when it can expand, sending cold air southward with the jet stream. This expansion can cause extremely cold temperatures in parts of North America, Europe, and Asia. The polar vortex can also influence the jet stream, a band of strong wind that separates warmer, mid-latitude air and colder, polar air. When the polar vortex is strong, the jet stream tends to stay farther north, resulting in colder temperatures in the Arctic and milder weather in the mid-latitudes. When the polar vortex weakens, the jet stream can become wavy, allowing warm air to enter the Arctic and cold air to sink into the mid-latitudes.
| Characteristics | Values |
|---|---|
| Definition | A large region of cold, rotating air surrounding both of Earth's polar regions |
| Formation | Forms in the stratosphere during autumn when Arctic or Antarctic temperatures cool rapidly as the polar night begins |
| Strength | Strongest in winter due to a redistribution of heat from the tropics; weakest in summer |
| Impact on Weather | Can cause extreme cold air outbreaks in the mid-latitudes when it weakens, shifts, or breaks down |
| Role in Climate Change | May be linked to global warming and extreme winter weather |
| Interaction with Jet Stream | Influences the polar jet stream, which separates warmer mid-latitude air and colder polar air |
| Speed | High-speed, cyclonically rotating winds with speeds of 15-50 km/h |
| Altitude | Occurs at altitudes between 10-30 miles above the North Pole |
| Disruptions | Occasional "sudden stratospheric warming" events can disrupt the polar vortex, causing temperature spikes and wind reversals |
| Visibility | Popularized by the media during extreme weather events, bringing attention to a long-existing weather feature |
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What You'll Learn
- The polar vortex is a large area of cold air surrounding Earth's poles
- The polar vortex strengthens in winter, weakening in summer
- Sudden stratospheric warming events can disrupt the polar vortex
- When the polar vortex weakens, cold air is pushed southwards?
- The polar vortex can cause extreme cold weather outbreaks
The polar vortex is a large area of cold air surrounding Earth's poles
The polar vortex is not a surface-level phenomenon. Weather forecasters study it by observing conditions tens of thousands of feet above the Earth's surface. When the polar vortex expands, it can send cold air southward, leading to extremely cold temperatures in regions that do not usually experience such low temperatures. This southward movement of cold air is facilitated by the jet stream, a band of strong winds that typically keeps colder air north and warmer air south.
The jet stream is influenced by the polar vortex. When the polar vortex is strong, the jet stream tends to exhibit a more zonal flow, with less meandering. However, when the polar vortex weakens, the jet stream becomes wavier, allowing warm air to enter the Arctic and cold air to sink into the mid-latitudes. This can result in cold air outbreaks in regions such as the Southern Plains, the Gulf Coast, and the central United States.
Occasionally, the polar vortex can be disrupted by "sudden stratospheric warming" events, caused by large-scale atmospheric waves known as Rossby waves. These waves can weaken the polar vortex and, in some cases, reverse the direction of its winds. While these disruptions can lead to cold air outbreaks, they do not always result in extreme winter weather. The polar vortex's influence on winter weather in the mid-latitudes is complex and dependent on various factors.
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The polar vortex strengthens in winter, weakening in summer
The polar vortex is a large area of low pressure and cold air surrounding both of the Earth's poles. It is always present near the poles, but the term "vortex" refers to the counter-clockwise flow of air that helps keep the colder air near the poles. The polar vortex is strongest in winter due to a redistribution of heat from the tropics. During the winter, the winds that make up the polar vortex blow from west to east. The stronger the winds, the more the air inside is isolated from warmer latitudes, and the colder it gets.
In spring, as the Earth's tilt changes and the poles receive more sunlight, the direction of the winds changes to blow from east to west. The winds also become weaker as a result of less heat wafting from the tropics to the pole. The Arctic polar vortex breaks down during spring as the polar night ends. The polar vortex is also influenced by sudden stratospheric warming (SSW) events, which can cause the vortex to weaken, slow its spin, or even split entirely in two. These events happen when large-scale atmospheric waves, called Rossby waves, get pushed into the stratosphere from below, triggering sudden spikes in temperature.
When the polar vortex is strong, the polar jet stream tends to stay farther north and exhibit a more zonal flow, with less meandering. The polar jet stream occurs in the troposphere, at altitudes between 5-9 miles above the surface, and plays a much larger role in our day-to-day winter weather in the mid-latitudes than the polar vortex. When the polar vortex weakens, the jet stream becomes wavy, bulging south and allowing Arctic air to flow down across North America and Eurasia, causing temperatures to plummet across the affected areas.
The weakening of the polar vortex in summer is due to its dependence on the temperature difference between the equator and the poles. As the poles warm, the temperature difference decreases, causing the polar vortex to weaken. This weakening can have dramatic effects, as small amounts of heating or cooling in the polar vortex can trigger or delay downwelling, altering the Gulf Stream Current of the Atlantic and the speed of other ocean currents.
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Sudden stratospheric warming events can disrupt the polar vortex
The polar vortex is a large region of cold, rotating air that encircles the Earth's polar regions. The polar vortex strengthens in the winter and weakens in the summer due to its dependence on the temperature difference between the equator and the poles. The stronger the winds, the more the air inside is isolated from warmer latitudes, and the colder it gets.
Sudden stratospheric warming (SSW) events are a significant disruption to the polar vortex. These events occur when large-scale atmospheric waves, called Rossby waves, are pushed into the stratosphere from below, triggering sudden spikes in temperature. Rossby waves can "break" on top of the polar vortex, weakening it and, in extreme cases, reversing the direction of its winds. This leads to cold air descending and warming rapidly.
When the polar vortex is disrupted, the stratosphere warms quickly and intensely. The polar vortex can be displaced off the pole, or it can split into two smaller vortices. This allows cold air that was bottled up near the polar cap to escape and expand into the middle latitudes, such as the United States, Europe, and parts of Asia. This can result in colder-than-average temperatures in these regions.
The impacts of SSWs are not guaranteed and are not necessarily experienced everywhere. However, disruptions to the polar vortex can communicate down to the troposphere and disrupt the jet stream, which plays a significant role in winter weather in the mid-latitudes. When the jet stream is disrupted, it can bring colder-than-normal Arctic air down to the mid-latitudes.
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When the polar vortex weakens, cold air is pushed southwards
The polar vortex is a large area of low pressure and cold air surrounding both of the Earth's poles. It is always present near the poles, but its strength varies depending on the season. The polar vortex is strongest during the winter due to a redistribution of heat from the tropics, and it weakens in the summer because of the reduced temperature difference between the equator and the poles.
When the polar vortex weakens, it can break into two or more smaller vortices, and the polar jet stream often becomes wavy. This waviness allows warm air to enter the Arctic and cold air to sink into the mid-latitudes. The weakened low-pressure system may also cause a portion of the system to break off, which can lead to colder temperatures in regions like the United States, Europe, and Asia. This occurs when the jet stream, no longer constrained by the low-pressure system, becomes wavy and allows a collection of cold air to push southwards.
The weakening of the polar vortex can be caused by "sudden stratospheric warming" events, which happen when large-scale atmospheric waves, called Rossby waves, are pushed into the stratosphere, triggering spikes in temperature. These events can disrupt the usual west-to-east winds of the polar vortex, and in some cases, reverse them entirely. While minor warmings are common and typically do not affect surface temperatures, major warmings can cause the polar vortex to weaken and shift southwards.
The polar vortex's influence on winter weather in the mid-latitudes is not constant, but when it does have an effect, the results can be extreme. For example, the polar vortex has been linked to outbreaks of extremely cold weather in the Southern Plains and Gulf Coast of the United States, as well as in parts of Europe and Asia. These cold air outbreaks can cause temperatures to drop significantly, leading to freezing conditions and impacting the daily lives of those in affected regions.
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The polar vortex can cause extreme cold weather outbreaks
The polar vortex is a large area of low pressure and cold air surrounding both of Earth's poles. It is always present near the poles, but its strength varies depending on the season. The polar vortex is strongest during the winter due to a redistribution of heat from the tropics, and it weakens during the summer as a result of less heat wafting from the tropics to the poles. The term "vortex" refers to the counter-clockwise flow of air that helps keep colder air near the poles.
During winter in the northern hemisphere, the polar vortex occasionally expands, sending cold air southward with the jet stream. This expansion occurs regularly during winter and is often associated with large outbreaks of Arctic air in the United States, Europe, and Asia. These cold air outbreaks can cause extremely cold temperatures in regions that do not typically experience such low temperatures.
The polar vortex can influence winter weather in the mid-latitudes, and when it does, the effects can be extreme. When the polar vortex is strong, the polar jet stream tends to stay farther north, resulting in colder temperatures in the Arctic and milder weather in the mid-latitudes. However, when the polar vortex weakens, shifts, or breaks down, it can lead to disruptions in the polar jet stream, allowing warm air to enter the Arctic and cold air to sink into the mid-latitudes.
Occasional sudden stratospheric warming events can cause the polar vortex to weaken or even reverse its direction. These events occur when large-scale atmospheric waves, known as Rossby waves, are pushed into the stratosphere, triggering spikes in temperature. The disruption of the polar vortex can lead to extreme cold weather outbreaks in the mid-latitudes of the United States or Eurasia a few weeks later.
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Frequently asked questions
A polar vortex is a large area of low pressure and cold air surrounding both of the Earth’s poles. It is always present near the poles, but it strengthens in the winter due to a redistribution of heat from the tropics.
The polar vortex traps pollution by keeping the jet stream travelling around the Earth in a circular path. The jet stream is a band of strong wind that plays a key role in keeping colder air north and warmer air south. When the polar vortex weakens, the jet stream becomes wavy and rambling, allowing warm air to flood into the Arctic and cold air to sink into the mid-latitudes.
A polar vortex weakens when large-scale atmospheric waves, called Rossby waves, get pushed into the stratosphere from below, triggering sudden spikes in temperature. These waves can break on top of the polar vortex, weakening it and sometimes reversing the direction of its winds.
When the polar vortex weakens, it can cause extremely cold temperatures in the mid-latitudes, leading to cold air outbreaks. It can also result in warmer temperatures in the Arctic, as the polar jet stream shifts northward.
It is not uncommon for the polar vortex to weaken. On average, it occurs about every other year in the Arctic. However, it takes unusual conditions for the vortex to weaken significantly or migrate far south.
