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This is because stratospheric warming is occurring at high altitudes above the North Pole, causing temperatures to rise.

That, in turn, could result in cold air pushing south toward the U.S in a couple of weeks, although it remains uncertain where exactly the Arctic air will fall and for how long.
How the polar vortex works. (CNN)

The polar vortex is simply a low-pressure system that spins cold air around the polar regions of the globe.

But the system can sometimes leave the North Pole.

In doing so, it releases cool air much further south in regions like North America and Europe.

The polar vortex is located in the stratosphere, about 18 miles above the Earth’s surface, which is well above the jet stream, where airplanes fly and where it occurs most of the time.

But upheavals and disruptions in the flow and location of the polar vortex, like what we’re seeing in early 2021, can influence air movement and the weather below it.

And scientists are watching current events closely for clues about when and where impacts will occur.

What is the polar vortex?

Although the term “polar vortex” has caught on on social media in recent years, the concept is not new.

It is a staple food for the polar regions every year.

“In some winters, it remains quite unflappable. In other winters (like this), it can be severely disrupted or weakened,” Jason Furtado, assistant professor at the University of Oklahoma School of Meteorology, said by email.

“Understanding what is happening to the polar vortex is one of several characteristics of our climate that helps meteorologists understand what to expect in winter weather for the next two to six weeks.”

When the low pressure polar system is strong, it keeps the jet stream traveling around the Earth in a very circular path and keeps the Arctic air concentrated near the Pole.

But when that system weakens, parts of the vortex break and elongate, causing cold air to move south.

When that low pressure system is weaker, the jet stream also does not have enough force to maintain its usual path.

It is that disruption in the jet stream that has a direct correlation with our climate closest to the surface.

“When the stratospheric polar vortex is strong, the jet stream tends to move further north, which keeps the air cool in the Arctic and allows for relatively milder conditions across much of the United States and Eurasia,” Furtado said.

The polar vortex appears to be in motion. This is because stratospheric warming is occurring at high altitudes above the North Pole, causing temperatures to rise. ((AWI – Steffen Graupner))

A common reason the polar vortex leaves its usual location is due to a sudden change in warmer air, known as sudden stratospheric warming, or SSW. This weakens the polar vortex and allows it to move.

“When the polar vortex is weak, or an SSW event occurs, then the jet stream will tend to weaken, move further south and become ‘more wavy,'” Furtado said.

“The effect of these changes is that warmer-than-normal air moves into the Arctic, cooler weather enters North America and Europe / Asia, and more extreme weather and storms generally in the mid-latitudes.”

The jet stream is the main storm path in the mid-latitudes of the northern hemisphere, dividing cooler air to the north and warmer air to the south.

Because the polar vortex is physically disconnected from where most of the weather occurs, it often has a more indirect impact on daily weather.

Cold air is denser, so it sinks, allowing warm air from the SSW to remain in the stratosphere and cooler air to sink to lower levels near the surface.

That downward sinking air results in sections of the polar vortex pushing toward lower latitudes in North America, Europe, and Asia.

Recently, an SSW caused the polar vortex to start moving away from the North Pole.

But it remains a question where that cold air will end for the next week or two.

What makes this SSW so special is its intensity, which increases the chances of hitting the northern hemisphere.

It is important to note that an interruption in the polar vortex does not generate immediate changes in the climate. Instead, its effects are often delayed.

“In the stratosphere, the polar vortex normally regains its strength within a couple of weeks of the peak of the event,” Furtado said.

“However, in the troposphere, the effects of the SSW event can last up to eight weeks.

“So these events, which can evolve rapidly, can have lasting impacts on winter weather patterns in the troposphere.

“Another thing to keep in mind: even with strong SSW events, there is still no certainty that the US will see direct hits.

“We actually had two events in the recent past that show this contrast. There was a major SSW event in February 2018 and one in January 2019, and the after effects of each were very different.”

Temperature forecast for January 16, 2021. (CNN)

Furtado said there was cold and stormy weather across much of central and eastern North America after the 2018 event, but minimal effects were felt in North America after the 2019 event.

So there is no need to panic about this recent event.

But it’s certainly something we need to keep an eye on for the next seven to 14 days.

How climate change plays a role

If you have a warming Earth, then it would only make sense for more frequent sudden stratospheric warming events to occur, right?

The answer is complex, mainly because no one lives at the North Pole except Santa, which makes long-term historical weather data very difficult to come by.

But this does not mean that climate change is not affecting the polar vortex.

“We know from observations that the Arctic region is warming at a much faster rate than other parts of the world (we call it Arctic amplification),” Furtado said.

“The impact of Arctic amplification is twofold. First, since the Arctic is getting very hot, when cold air outbreaks occur in North America and Europe / Asia, they are not as cold as decades ago.

“The second effect (although currently debated in the scientific community) is that a warmer Arctic is also weakening the stratospheric polar vortex on average.”

This is why, in theory, a weaker polar vortex should be easier to disrupt, allowing for more frequent SSW events.

Food to go? Although a warming planet may mean that the total number of snowstorms worldwide may decrease, those that do occur could produce much larger snow accumulations.

Fire, flood, snow

Fire, Snow, Heat Waves, and Storms: The Weather Extremes of 2020


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