Question of the Day #328

"Polar vortex death toll rises to 21 as US cold snap continues"
From the headline of this article at BBC News.

上記の文で、polar vortexの意味は？
In the sentence above, what does "polar vortex" mean?

答えは、コメントに書いてください。
Write your answer in the Comments.

明日、ここに答えを書きます。
I will add the answer and other remarks here tomorrow.

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解答

意味：
英辞郎によると、


極渦

とありますが、最近の天気予報で時々耳にする「寒冷渦」の極端に強いものと考えていいと思います。したがって、わかりやすくするために北半球の場合は「北極寒冷渦」と言ってもいいのではないかと思います。
ちなみに、vortexの複数形はvorticesまたはvortexesですが前者の方が一般的です。

Answer

According to AccuWeather:

A polar vortex is a large pocket of very cold air, typically the coldest air in the Northern Hemisphere, which sits over the polar region during the winter season.
The frigid air can find its way into the United States when the polar vortex is pushed farther south, occasionally reaching southern Canada and the northern Plains, Midwest and northeastern portions of the United States.

Examples

• A displaced polar vortex is causing Arctic temperatures across the United States.
• There are two polar vortices in the Earth's atmosphere, one overlying each Pole.
• Variations in the strength of the polar vortex in the upper stratosphere may influence surface climate.
• Lower pressure leads to the contraction of the polar vortex, which moves the frontal systems further south.
• This year the winter polar vortices have been particularly persistent in the Arctic.