Monday, December 05, 2016

Weakening polar vortex may yield longer, harsher winters in North America

By Michael Kuhne

Longer, harsher winters may be in store for the portions of North America as the polar vortex continues to weaken and shifts, according to a new study.

The polar vortex is a large pocket of frigid air that hovers above the polar regions, and is most prominent in the winter months.

Researchers at China's Lanzhou University penned the study, which was published in Nature Climate Change last month.

Lanzhou researchers found that a loss of sea ice in the Arctic regions due to rising temperatures in the Barents-Kara seas, along with an increase in snow cover over Europe and Asia, has caused the polar vortex to weaken. The pocket of cold air has in turn shifted toward Eurasia.

This movement could lead to colder and possibly extended winter seasons for portions of North America and Eurasia, according to the study.


The polar vortex in winter can extend well into the atmosphere and at times be more than 100,000 feet deep, AccuWeather Senior Meteorologist Bob Smerbeck said.

A weaker polar vortex allows the stratosphere, or a distant part of the Earth's atmosphere, to warm, while a stronger one prevents that process, according to Vallee.

"The stratospheric vortex typically governs the tropospheric vortex [in the lower part of the Earth's atmosphere] during the winter months and is based on polar heating and cooling," Vallee said.

"As the stratosphere warms in winter, it can reverse the wind direction below it," he said.

This could block high pressure systems from taking shape in the high latitudes of the Earth, which would increase opportunities for cold in the mid-latitudes.

According to Smerbeck, the southern shift could bring the other end of the polar vortex toward eastern North America, yielding colder winters for the region.

"There are other factors that determine where the vortex sets up," Smerbeck said. "The warm blob over the north Pacific in winter 2013-2014 and the unusually warm waters along the west coast of North America [for the] 2014-2015 winter contributed to a southward dip in the vortex across eastern North America and cold winters in the central and eastern U.S."

Smerbeck said there is a lot of research still being conducted,


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