Author | Feng Tang
The warming of the Arctic may be the source of extreme winter weather in the United States. Photo courtesy of the research group
In February of this year, a large-scale power outage was caused by the strongest cold current in history. In addition to power outages and the inability to keep warm, extreme weather such as snowfall, ice, freezing rain has also caused nearly half of the total population of 14 million people in Texas to face difficulties in the supply of drinking water, and the food supply chain has also been affected.
What caused this rare winter storm? Isn't the global climate continuously warming? A new study led by University of Massachusetts Lowell, Atmospheric and Environmental Research Corporation (AER) and Israel Hebrew University identified the "source" of the extreme weather-the disturbed polar regions vortex.
Researchers found that the frequency of the polar vortex interference is increasing, which is one of the important reasons for the extreme weather in the United States in winter. The changes in the Arctic may be one of the reasons for this increasing trend. On September 3, this research was published in Science.
The colder and colder winter
Currently,Global warming has basically become a consensus among people. According to data released by the US National Oceanic and Atmospheric Administration recently, the global average temperature in July 2021 broke a record, becoming the hottest July since the meteorological record was established in 1880. Compared with the average temperature of 15.8 degrees Celsius in July in the 20th century, the global land and ocean surface temperature was 0.93 degrees Celsius higher in this July.
On the other hand, many mid-latitudes have experienced "super cold" winters. In January 2021, there was heavy snowfall throughout Spain, affecting more than 400 roads in more than 10 autonomous regions, and 60 roads were closed. At almost the same time, heavy snow fell in many places along the coast of the Sea of Japan. The thickness of the snow in some areas reached more than two meters. The thickness of the snow at the observation point in Joetsu City, Niigata Prefecture reached 2.26 meters. The snow at the observation point of Toyama Prefecture and Fukui Prefecture The thickness of more than 1 meter is more than twice the thickness of snow in previous years.
Soon after, parts of Texas in the southern United States began to experience winter storms, which caused icy roads, blocked roads and extensive power outages. For the first time in history, the National Weather Service issued a "wind chill warning" in southeastern Texas, including Houston. But the people behind Texas residents who are forced to "hug together to keep warm" are in the far North Pole.
paper co-author, Chaim Garfinkel of the Hebrew University said: "Although the global climate is warming, the extreme cold weather in winter in mid-latitudes has increased significantly. There is a long-term contradiction between the two."
"On the one hand, record-setting warm Arctic, low Arctic sea ice, deep snow in Siberia, and complex polar vortex interference; on the other hand, record-breaking coldness in the United States, Europe and Asia, and destruction of Europe and the United States. Sexual snowfall.” Judah Cohen, the correspondent of the paper and director of AER's seasonal forecasting, said that these seemingly contradictory phenomena actually have a physical connection.
The polar vortex is "stretching"
In the past 30 years,The Arctic has experienced the greatest degree of climate change on Earth, including rapid rise in temperature, melting of sea ice, reduced snow cover in spring, and increased snow cover in autumn. The rapid warming of the Arctic relative to the rest of the world is called the Arctic amplification effect. But the extent to which these rapid changes in the Arctic have affected the weather in mid-latitudes has been a topic of intense debate among climate scientists.
"Last winter, the severe cold wave in Texas heated up the debate about whether climate change would lead to more severe winter extreme weather. However, to date, few studies have confirmed that climate change and extreme weather events such as the Texas cold wave There is a physical connection between them. This study proves that global warming does not necessarily protect people from the devastating effects of severe winter weather.” Cohen said.
Previously, most theories about the connection between the Arctic amplification effect and the winter weather in mid-latitudes believed that this approach was either through wavy jets or through the sudden warming of the stratosphere, which had the greatest impact on polar vortices , The most frequently studied content. This study provides convincing evidence that the strongest link between Arctic warming and extreme winter weather in mid-latitudes, at least in the United States, may be derived from a lesser-known and weaker polar region. The vortex "stretches."
Researchers found that the stratospheric polar vortex has a relatively weak or interrupted state, showing a stretched appearance instead of the more typical circular appearance. These changes have been increasing in the satellite era (after 1979). Observational analysis and numerical simulation experiments have shown that changes in the Arctic region, including accelerated warming, melting of sea ice and increased snowfall in Siberia, are conducive to the extension of the polar vortex and the North American region east of Rocky Mountains appears in winter extreme weather.
The reduction of greenhouse gas emissions cannot be relaxed The surface climate changes to the polar stratosphere,Then back to the surface of the United States) highlights the possible wide-ranging effects of climate change. ”
Specifically, more damped jets, larger temperature gradients from the equator to the pole, and less upward wave energy in the troposphere of are conducive to stronger polar vortices in the stratosphere.
However, as the Arctic warms, the melting of the Barents- Kara Sea sea ice warms the northwestern part of Eurasia, and the increase in snowfall in Siberia makes the northeastern part of Eurasia warmer. The cold causes more frequent amplification of jets over Eurasia, which in turn causes the upward atmospheric wave energy to increase.
Under conditions such as the weakening of the zonal wind as the stratosphere height increases, the polar vortices appear to stretch and increase. Wave reflection-upward over Eurasia and downward over North America.
The downward wave energy radiative convergence causes the jet stream over Alaska Bay to move north, the jet stream over North America moves south, and North America The increase in extreme winter weather (cold and snowfall) in the eastern region.
"But all temperature anomalies are relative to their cycles. It does not mean that the winter becomes a whole in the process of the Arctic amplification effect. Colder. "Cohen said in an interview with China Science News.
But Garfinkel said that this study emphasizes that the increase in extreme cold in winter in mid-latitudes should not be used as an excuse to postpone actions to reduce greenhouse gas emissions.
"This research closely combines observational analysis with simulation experiments, which is very important and provides opportunities for the application of new machine learning tools. "
did not participate in the study Amsterdam , Netherlands Free University's Dim Coumou pointed out in a related review article published at the same time,"Future work should further unravel the causal relationship between the Arctic and mid-latitude cold and warm seasons, and pay special attention to extreme weather."
"I think that better understanding and identification of these polar vortex changes can help Asia and the Americas (including China, the United States and Canada) prepare for extreme winter weather. It allows us to predict these events earlier."
Cohen said, "We still need to better understand the causes of these events Mechanism. We plan to expand the modeling research in the next step."
"Chinese Journal of Science" (2021-09-06 2nd edition, the original international title is "Who makes Texas "shiver"")
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