Stratospheric warming led to abnormal cold weather

Scientists have found that stratospheric warming led to the abnormal cold weather in the winter of 2020-2021. It influenced polar vortices, jet streams and the temperature of the Arctic Ocean. The research is published in the journal Advances in Atmospheric Sciences.

54.4 ° C is the highest temperature ever recorded on Earth. It was recorded on July 9, 2021 in Death Valley, California. Most interestingly, the record heat came just a few months after record cold weather in the United States and Asia. Could these phenomena be related? An international research team looked at three cases of extreme cold to find out what mechanisms underlie these temperature fluctuations.

“The general question that needs to be answered is why extreme weather events are more likely to occur in the context of warming in recent decades, and whether the increasing warming in the Arctic is playing a leading role. The extreme events of winter 2020-2021 provide a unique opportunity to study which physical processes or mechanisms lead to these events, ”said Xiangdong Zhang of the University of Alaska Fairbanks, the first author of the study.

Researchers studied two record cold outbreaks in China from late December 2020 to mid-January 2021. Beijing and Tiadzin saw their lowest temperatures in 54 years this winter: -19.7 ° C and -19.9 ° C, respectively. Also, scientists turned to the record cold weather in the south of the United States. The Texas cities of Austin and Houston both recorded the lowest temperatures in a century this winter (-13.3 ° C and -8.3 ° C, respectively).

Scientists have compared the 2020-2021 winter to the previous 42 winters. They used observational data and computer models. So the researchers wanted to understand what marine and atmospheric phenomena could underlie extreme weather events. They found that the polar vortex (cold air at low pressure above the poles) and jet stream (air currents moving from west to east) play a key role. These are two atmospheric phenomena that carry cold air from the poles. A sharp rise in temperature in the upper atmosphere, called sudden stratospheric warming, can drastically change their behavior and interactions. This will affect water temperatures in the Arctic Ocean, which in turn will make the weather even more extreme across the Northern Hemisphere.

“The study shows that ocean temperature anomalies, in addition to large-scale atmospheric circulation, can play a key role in extreme weather events, complementing large-scale atmospheric circulation,” said Annette Rimke of the Alfred Wegener Institute at the Center for Polar and Marine Research. Helmholtz.

Scientists note that although one process underlies all the extreme cold weather of the last winter, the cold snap manifested itself in different ways. For example, during the first event in East Asia, cold polar air modulated the jet stream in mid-latitudes, directing the cold air southward. In the second case, the polar vortex split open, deepening the low-pressure region and circulating with the colder Arctic air. And in the case of North America, the polar vortex was also split, but in this case forced the lower atmosphere to settle deeper in the south, putting pressure on the very cold air.

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