【Indonesia】

It's coming.

The Indonesiapolar vortex -- a spinning mass of winter-chilled Arctic air -- has become wobbly and weak. It's expected to slosh down and blanket a considerable part of the East Coast and Midwest with frigid polar air beginning this weekend, bringing sub zero temperaturesto some Midwestern places.

"We're gonna freeze," John Martin, an atmospheric scientist at the University of Wisconsin-Madison, said in an interview.

The polar vortex typically lives in the high Arctic each winter. So why does this mass of frigid air sometimes swirl so far down south and away from its home?

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The polar vortex can be envisioned as a miles-high mass of rotating cold air. It forms during the winter when the most northern regions on Earth go months with little sunlight. In the absence of light and solar energy, the temperature plummets. That's why the polar vortex is also called the "polar night jet," explained Martin.

This frigid vortex of air can often stay strong and locked in the northern reaches throughout the winter, as the Arctic region's greater mass of cold air holds the polar vortex in place.

"It's almost like a fence that holds it in," Gabriel Filippelli, a professor of earth sciences at Indiana University-Purdue University Indianapolis, said in an interview.

But not always.

Weather, or waves of air, are liable to push the polar vortex around.

"It's always susceptible to having waves bump into it," said Martin.

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This fickle weather occurs in the lowest part of the atmosphere, the troposphere, which spans from sea level to about six miles above the surface. There's a lot of warmer weather moving around at this level, which Martin describes as a "parade of activity."

Weather from the troposphere can collide with and pierce into the Arctic's cold fence of frigid air, unleashing the polar vortex into the U.S. and other places, like Europe.

"When that fence destabilizes there’s very little that will keep it [the polar vortex] from gushing down into the Midwest," said Filippelli, noting that he lives in the "core" of the predicted polar blast.

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Sometimes, this warmer, invading air will split the polar vortex apart, like a "band of warm air just cutting right through the puddle of cold air," said Martin.

This allows the polar vortex to simultaneously spread to different places, like the U.S. and Europe.

What's next?

Now that the polar vortex has been unleashed, the U.S. will likely be subjected to repeated blasts of cold air throughout the winter, said Filippelli.

Martin is already looking two weeks ahead to the end of January, in which longer-term forecasts predict even colder temperatures.

"It's gonna be cold," he said.

But eventually, as winter wanes and the sun rises over the Arctic, the polar vortex "decays away into nothing," said Martin. It dies.

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Then, atmospheric scientists can look back at the 2019 polar vortex event and see the different factors that ultimately contributed to the breaching of the Arctic's formidable front of cold air.

"The details almost always unravel after the fact," Martin said. "We don’t know yet exactly the underlying cause."

But Filippelli said it's likely that warming surface temperatures in the Arctic might contribute to the destabilization of the polar vortex. Because it's locked into a vicious warming cycle the region is warming over twice as fast as the rest of the planet. Warm air melts bright white, reflective sea ice, which then allows the vast, dark open ocean to absorb more heat, and release more heat. This means more relatively warm air that can potentially destabilize the cold, fenced-in Arctic.

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Though Filipelli notes that other atmospheric factorsare at play too, he emphasizes that "climate change just enhances the impact."

Meanwhile, the National Weather Service will be watching as the polar vortex misbehaves. While these government meteorologists aren't getting paid for their work, they are vigilantly observing the freezing mass of polar air as it spreads southward, blanketing the U.S. in an extreme chill.

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