The Polar Vortex

Source: National Geographic

BY SARAH GIBBENS 30 JANUARY 2019

HOW THE POLAR VORTEX CREATED RECORD SUBZERO TEMPERATURES IN THE MIDWEST

Some states are seeing temperatures colder than the Arctic.

WHILE AUSTRALIANS BRACE THE HEATwaves of this year’s summer, there is no doubt that reading the winter forecasts in the United States sends a chill down our spine

In some regions of the United States, temperatures are dropping below freezing, and some portions of the Midwest are experiencing temperatures below 40 degrees Celcius and a mind-blowing wind chill of 59 degrees below zero thanks to the polar vortex. Accuweather predicts the Midwestern states will experience the extreme temperatures until later this week and cautions against stepping outside with any exposed skin. In these record-shattering temperatures, frostbite can occur after only a few minutes.

A BLAST OF ARCTIC AIR

What is the polar vortex, the doomsday-sounding weather pattern blamed for these frigid conditions?

The term refers to a swirling mass of Arctic air that hovers around the north pole all year. Its swirling eddies spin counterclockwise, and during winter months in the Northern Hemisphere, these eddies grow longer and dip farther south.

When the vortex grows, these cold swirls of air are transported south by the polar jet stream (also called the polar front). Moving from west to east, the polar jet stream hovers farther north in the summer and farther south in the winter, altered by changing seasonal sunlight. Along with its subtropical jet stream counterpart in the south, these two fronts play a determining role in seasonal weather changes.

Intermittent blasts of cold polar vortex air happen when the vortex becomes less stable, circulating in waves rather than a tight circle. According to the National Oceanic and Atmospheric Administration, denser cold air in the north and warm air currents moving south can all cause the vortex to become unstable. The more unstable the vortex becomes, the more likely it is that parts of North America, Europe, and Asia feel stray blasts of Arctic weather.

WILL CLIMATE CHANGE MAKE THE VORTEX MORE UNSTABLE?

Scientists are only recently beginning to understand how a climate changed by warming temperatures may lead to colder winters.

One study published last March in the journal Nature Communications found a link between warmer Arctic air and colder US winters, particularly in the northeastern part of the country.

WHAT IS THE POLAR VORTEX?

In a press release about the research, study author Jennifer Francis said, “Warm temperatures in the Arctic cause the jet stream to take these wild swings, and when it swings farther south, that causes cold air to reach farther south. These swings tend to hang around for a while, so the weather we have in the eastern United States, whether it’s cold or warm, tends to stay with us longer.”

One theory for why this might occur focuses on the stability of jet streams. These westerly winds are propelled by the difference between cold air in the north and warm air in the tropics. Without this strong difference, jet streams could become weaker, concluded a paper published last October.

Though global temperatures are rising, climate change could lead to more erratic, extreme weather conditions. In parts of the Midwest and Northeast experiencing these temperature drops, the risk of hypothermia makes an unstable vortex potentially deadly.