How the polar vortex fuels intense winter weather in the USGetty ImagesHere’s how the polar vortex, and climate change, influence extremely cold winter weather in the US.Intense snowy wintry weather in the US has been fuelled by activity of the polar vortex, slipping down to engulf large parts of the country. Early January’s winter storm prompted seven states to declare states of emergency, with flights suspended, businesses shuttered and one area in New York recording 6.25ft (1.9m) of snowfall in just 24 hours. Another wave of Arctic air has kept temperatures lower than average through to the middle of January, and parts of the Midwest to the Appalachians and Atlantic Seaboard are expecting further wintry storms.This blast of cold weather is due to activity of the polar vortex.What is the polar vortex?The polar vortex, or Arctic polar vortex, is a ring of strong westerly winds that form between 10 and 30 miles (16-48km) above the North Pole every winter, enclosing a large pool of extremely cold air. The stronger the winds, the more air inside is isolated from warmer areas. When the vortex is stable, the polar jet stream shifts northward, helping to keep the coldest air within the Arctic.However, when this stable scenario breaks down, it can mean an intense cold snap at mid-latitudes, where the US lies. When the vortex weakens, its pattern of winds changes from a circular ring to a wavy band that loops further south. This unleashes the cold weather normally retained at the pole further to the south. The polar vortex doesn’t always influence the weather in the mid-latitudes, but when it does the effects can be extreme.Noaa”[The early January] cold outbreak and the one through the 16 January are basically broken off pieces of the polar vortex,” Brett Anderson, senior meteorologist at AccuWeather, tells the BBC. “[It’s] like a large chunk of ice that breaks off of a glacier and floats southward with the current – with the current being the jet stream winds.” Does climate change affect the polar vortex? It is not known whether climate change will affect the polar vortex, says Amy Butler, an atmospheric scientist at the National Oceanic and Atmospheric Administration, and an expert on the polar vortex. There are several reasons why it is so hard to predict whether polar vortexes will strengthen or weaken in years to come. “There are many things that can change the strength of the polar vortex,” Butler says. Sea ice is one of them – some models suggest melting sea ice may have a weakening effect on the vortex. However, warming in the upper layers of the atmosphere can potentially strengthen the vortex. Regional changes in sea surface temperatures could also influence the vortex.”For these reasons, models show no agreement in what will happen to the Northern Hemisphere polar vortex in the future,” says Butler.How are winter storms changing in the US?In many parts of the US, total snowfall has decreased since official records began in the 1
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