最近、北極の上の空（成層圏）で大きな変化がありました。
Recently, a major change has occurred in the stratosphere over the Arctic.
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This change is due to the weakening of the polar vortex—an air current that traps cold air over the Arctic.
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When the polar vortex weakens, cold air moves southward, spreading to America, Europe, and even Asia.
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Currently, the temperature in the stratosphere is rising rapidly, and this phenomenon is called Sudden Stratospheric Warming SSW.
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When this phenomenon occurs, the polar vortex weakens further, and cold air may spread over a wider area.
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In America, there are many hot days this month, but it might suddenly get cold from now on.
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According to experts, such a major change as this is extremely rare.
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Especially, it is unusual for this phenomenon to occur in November.
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At present, it is still unclear whether a severe cold wave will occur, but December may be colder than usual and there is a possibility of heavier snowfall.
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Furthermore, it is believed that accurately understanding changes in the polar vortex will improve the accuracy of weather forecasts.
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However, the satellites used to observe the stratosphere are gradually aging, and the decreasing amount of data is also becoming a problem.
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We will need to continue paying close attention to trends in the polar regions.
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