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Arctic scientists are poring over data coming in from the vast, normally frozen region, after the North Pole's version of a heat wave swept across the area for the past week. Not only was the region near the North Pole the warmest it has been during the month of February since at least the 1950s, but one of the northernmost land-based weather stations, known as Cape Morris Jesup, exceeded the freezing mark on an unprecedented nine separate days during the month.

On Feb. 25, that weather station remained above freezing for about 24 hours, which is virtually unheard of during February, when there is no sunlight reaching the ground there. Arctic sea ice in the Bering Sea and to the north of Greenland actually declined during February, a time when sea ice usually expands toward its seasonal maximum in early to mid-March.

SEE ALSO:'Beast from the East' brings snow to UK, mainland Europe along with frigid temperatures

Scientists interviewed for this story say that the Arctic warming event, technically known as a warm air intrusion, may be a common feature of the Arctic climate, as comparatively mild and moist air from the midlatitudes is transported north by storm systems. However, this event was not like the others, researchers said.

In Greenland, monitoring stations registered unprecedented warmth at the top of the world's largest island.

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"I think it's fair to say that this event is unprecedented in our record -- both in terms of the magnitude and (for Kap Morris Jesup at least) the duration," said Ruth Mottram, a climate scientist at the Danish Meteorological Institute, in a Twitter message, using the Danish spelling for Cape Morris Jessup. "The warm event at KMJ is not record breaking in terms of the highest ever recorded temperature in February, but that event in 2011 was very short-lived compared to what we have seen this year...," she said. "A prolonged period like this has definitely not been seen before."

She said some of the warmth in northern Greenland was likely due to downsloping winds known as Foehn winds, which can increase air temperatures. But that doesn't explain the warmth in the Arctic overall, when compared to average February conditions. "But when we look at the high Arctic overall, the temperature record since 1958 has never seen a warm spike of this magnitude in February," she said. "Having said that, the last few winters have seen similar events of very warm air coming in to the Arctic , though not nearly as large in magnitude," Mottram said.

Temperature departures from average on Feb. 26, 2018, showing the red splotch of warmth across the Arctic.Credit: climate reanalyzer.

"I'm pretty surprised by quite how large the temperature anomaly is this year and how persistent." Noting cold temperatures on the west side of Greenland, Mottram emphasized that this was a weather event that was superimposed on top of rising average temperatures in the Arctic. The rising baseline makes it easier to attain all-time record highs, like a rising basketball floor making it more likely that a player will be able to dunk the ball in the net.

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A study published in 2017 found that these types of warming events have been increasing in frequency and duration during winter as the Arctic continues to warm at more than twice the rate of the rest of the globe.

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"What’s exactly driving these changes is not clear, but having storm tracks move further north (i.e. the North Atlantic storm track) may be tied to the northward retreat of the ice edge," said Julienne Stroeve, a senior research scientist at the National Snow and Ice Data Center in Boulder, Colorado, in an email.

"Thus, while having temperatures exceed freezing during winter is not uncommon, but it may be becoming more common as the climate changes and the ice edge continues to retreat."

Stroeve said that it's not just summer and fall sea ice showing steep declines, but that this is occurring year round now. "What it shows us too is that the winter sea ice is now also starting to respond as every winter now for the past 4 winters has been more extreme than the year before in terms of record low sea ice," she said.

The Arctic heat wave -- though most wouldn't consider temperatures in the mid 30s to low 40s Fahrenheit to be "hot," this the Arctic in the dead of winter -- has its roots in a weather system that pumped mild and unusually moist air into the Arctic from the Atlantic, while another storm system did the same from the Pacific side of the Arctic. Winds blew from the southeast off the east coast of Greenland for the past week, driving this mild and moist air northward, toward the North Pole, where temperatures were about 45 degrees Fahrenheit higher than average for this time of year.

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The warm air intrusion followed two other related and noteworthy weather events, a sudden warming of the stratosphere, known as a sudden stratospheric warming event, and a splitting of the polar vortex. These are both complex phenomena, but a sudden stratospheric warming event typically occurs when energy from the lower atmosphere travels upwards, and this can disrupt the area of low pressure and high westerly winds that comprise the polar vortex.

One area of the vortex wound up in the Western U.S., while the other went to Eurasia, where it's helping to cause an Arctic outbreak in Europe known as the "Beast from the East." The net result of these events was that the ultra-cold air typically found in the Arctic during February drained out of the region, as if someone opened the Northern Hemisphere's freezer door and left it ajar.

Daily 2 meter surface air temperature for the Arctic averaged above 80°N. Individual years from 1958-2017 are shown by the sequential blue/purple to yellow lines. 2018 is indicated by the red line. The white line shows the average temperature.Credit: zack labe

Zack Labe, a climate scientist at the University of California at Irvine, has a knack for creating compelling visuals of Arctic sea ice trends and air temperatures. His data corroborate this narrative, and this analogy, showing a sharp and persistent spike in air temperatures during February to the north of 80 degrees North Latitude.

"The duration of this warmth is remarkable and a common feature of the last several winters," Labe said in a Twitter message. He said that while warm air intrusions occur every winter, this one is unusual for occurring during February, lasting longer than a week, and for "the extent/magnitude of the moisture transport into the Arctic."

"I think the takeaway is that the dramatic wintertime warming of the Arctic continues in addition to a long-term trend in decreasing sea ice. These effects, along with others, have significant physical, environmental, social, and political consequences for the Arctic and beyond," he said.

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