New Study Finds Giant Meanders in Jet Stream Responsible for Extreme Winter Weather
A new study published in the Bulletin of the American Meteorological Society suggests that the Earth’s atmosphere is being pushed around in ways that cause long periods of extreme winter cold or wet in certain regions. The study’s authors have identified giant meanders in the global jet stream that bring polar air southward, resulting in frigid or wet conditions over much of North America and Europe for weeks at a time. They have found that these weather waves have doubled in frequency since the 1960s and have become increasingly damaging in recent years.
The research paper, titled “Recent Increase in a Recurrent Pan-Atlantic Wave Pattern Driving Concurrent Wintertime Extremes,” highlights the impact of these meanders on weather patterns. “Even though winters are getting milder on average, it’s happening at the expense of increasingly devastating heat extremes in the warm season,” said Kai Kornhuber, one of the authors of the study. He also emphasized the relevance of cold as a hazard in the present and future, despite global warming.
The jet stream, a fast-moving river of air that circulates the Northern Hemisphere, is generally responsible for separating cold polar air masses from the midlatitudes. However, the study suggests that rapid warming in the Arctic is causing the jet stream to develop larger and more frequent wobbles, destabilizing the system. Under the right conditions, these wobbles can transform into symmetrical waves known as Rossby waves, which lock in place across the globe.
The study focuses on a specific Rossby wave pattern known as wave-4, which consists of four peaks and four matching troughs. When this pattern locks in place, it increases the likelihood of extreme cold or wet conditions in the troughs by three times. At the same time, abnormally warm or dry conditions may develop in the peaks. This phenomenon has been responsible for recent extreme weather events, such as the February 2021 cold wave that affected Canada, the United States, and northern Mexico.
The researchers found that these wave-4 patterns used to occur only once each winter, on average, 50 years ago. However, the frequency has now increased to twice a year. The study also suggests a connection between extreme weather events in North America and Europe, often occurring simultaneously.
The exact mechanisms behind the emergence of wave-4 patterns require further research, but the study’s authors suspect that it starts with periodic changes in oceanic conditions over parts of the Pacific. These changes can trigger a global chain reaction, leading to the formation of the meanders. Understanding this mechanism could potentially improve predictions of extreme cold or wet waves.
While there is growing evidence of a connection between warming climate and meanders that cause heat waves in the summer, the winter wave patterns are still under intense scientific discourse. Further research is necessary to determine the extent of their connection to climate change and how things might evolve in the future.
The findings of this study highlight the increasing significance of these meanders in the jet stream and their impact on extreme winter weather. As climate change continues to alter the Earth’s systems, understanding these patterns becomes crucial for preparedness and mitigation efforts.
Further information about the study can be found in the article “Recent Increase in a Recurrent Pan-Atlantic Wave Pattern Driving Concurrent Wintertime Extremes” published in the Bulletin of the American Meteorological Society.