What is a polar vortex, the weather event that causes winter storms in the US? | Weather news

The United States is experiencing severe winter storms that are likely to affect more than 60 million people in the eastern part of the country. The ongoing cold spell, which could drop the mercury to -50C (-60F), is caused by the southward expansion of the polar vortex – an area of ​​extremely cold, rotating air around the Arctic.

Freezing temperatures could extend as far south as the Gulf Coast and the Florida peninsula in the US.

The polar vortex mainly affects countries located in the middle to high latitudes of the Northern Hemisphere. These regions are particularly susceptible to extreme cold events.

What is a polar vortex?

The polar vortex rotates counterclockwise around the North Pole with wind speeds of about 250 km/h.

There are two types of polar vortices – tropospheric and stratospheric.

The tropospheric polar vortex occurs in the lowest layer of the atmosphere where most weather phenomena occur. The vortex creates milder weather in northern latitudes.

The polar vortex we are currently observing is a stratospheric polar vortex that usually occurs about 10-30 miles (16-48 km) above the Earth's surface and forms in the fall but disappears in the spring of each year.

When the stratospheric polar vortex is in a steady state, cold arctic air is confined to the polar regions.

But when it is in a weakened state, the cold winds expand beyond the circumpolar region and extend south to Florida.

Warm air rising from the lower atmosphere weakens the polar vortex, allowing it to spread more widely. This upward movement of warm air can be triggered by significant weather patterns or phenomena, such as strong winds in mountainous regions or changes in tropical climate systems.

Both types of polar vortex are important to global atmospheric circulation and climate regulation.

Do we experience cold polar vortexes all the time?

The extreme cold from the weakened polar vortex, although seasonal and cyclical in nature, is not an annual phenomenon. In fact, the term polar vortex did not become a popular public term until 2014.

The polar vortex of 2013-14. brought record-breaking cold and snowfall across Canada and the eastern United States, plunging the regions into one of the coldest winters on record.

Major metropolitan areas including New York, Philadelphia and Chicago were covered in snow, with accumulations ranking among the top 10 highest in their recorded histories.

According to an article published by NASA in 2015, the 2013-14 polar vortex. has resulted in 92.5 percent of the Great Lakes being covered in ice, the second largest ice sheet observed by satellite. The surface of Lake Michigan froze to an unprecedented 93.3 percent on March 8, 2014, marking the highest ice cover ever recorded for this Great Lake.

In 2014 many news outlets and weather reports extensively discussed this atmospheric pattern, making it a household name. The extreme cold not only attracted public attention, but also provided a widely available explanation for severe weather conditions, cementing the polar vortex within the cultural zeitgeist as a key factor in understanding winter climate patterns in the Northern Hemisphere.

Is climate change affecting the polar vortex?

Researchers are trying to understand the effect of climate change on the intensity or frequency of cooler temperatures due to the polar vortex. Some evidence suggests that climate change may affect the polar vortex.

“It makes sense that the polar vortex is not as strong because of global warming because the planet is not warming evenly. It warms more at the pole, generally reducing the strength of the polar vortex and the jet stream and making it more susceptible to being displaced and sent toward us,” Stephen Decker, director of the Undergraduate Program in Meteorology at Rutgers University, said last February.

Global warming makes the polar vortex weaker because the Earth is not heating up equally everywhere. The North Pole is warming faster than other places, which weakens the polar vortex and the jet stream, a fast-moving stream of air in the atmosphere. This makes it easier for the vortex to be displaced and bring colder air to many regions, including Europe and northern Asia.

“The change warms higher latitudes and reduces the temperature difference between warmer mid-latitudes and polar regions. This weakens and destabilizes the polar jet stream, causing it to sink into lower latitudes, carrying polar air further south,” wrote Paul Ulrich, associate professor of regional climate modeling at UC Davis, in 2021. article.