Study Identifies Jet-Stream Pattern That Locks In Extreme Winter Cold, Wet Spellshttps://phys.org/news/2023-10-jet-stream-pattern-extreme-winter-cold.html
Researchers say they have identified giant meanders in the global jet stream that bring polar air southward, locking in frigid or wet conditions concurrently over much of North America and Europe, often for weeks at a time. Such weather waves, they say, have doubled in frequency since the 1960s. In just the last few years, they have killed hundreds of people and paralyzed energy and transport systems.
The new paper, titled
"Recent Increase in a Recurrent Pan-Atlantic Wave Pattern Driving Concurrent Wintertime Extremes," appears this week in the
Bulletin of the American Meteorological Society.In a 2019 study, Kornhuber and colleagues showed that a repeating Rossby wave pattern known as a wave-7—that is, seven giant peaks and seven matching troughs spanning the globe—draws warm, dry air from the subtropics up to the midlatitudes, causing concurrent summer heat waves and droughts in predictable parts of North America, Europe and Asia. These can cause widespread, simultaneous crop losses in important breadbasket regions, the study said.
https://iopscience.iop.org/article/10.1088/1748-9326/ab13bfThe newer paper shows more or less the other side of the coin. A winter pattern known as a wave-4—globally, four peaks and four matching troughs—tends to lock in place. The authors say that when this happens, the chances of extreme cold or wet in the trough triples. At the same time, abnormally warm or dry conditions may develop in the peaks.
The most recent major wave-4 iteration brought a February 2021 cold wave to much of Canada, the United States and even northern Mexico. Temperatures fell as much as 50 degrees F below average as far south as the U.S. Gulf Coast. Parts of the Deep South saw rare snowfall. Hardest hit was Texas, where record cold paralyzed natural gas pipelines and other energy infrastructure, knocking out much of the electricity grid and causing homes and businesses to go dark and freeze.
All told, at least 278 people were killed directly or indirectly by the cold wave, and there was nearly $200 billion in damage. A similar though less destructive event caused a January-February 2019 cold snap in the eastern United States, killing more than 20 people.
The same pattern often hits on the other side of the Atlantic at the same time, usually most most extreme in southwestern Europe and Scandinavia. The January-February 2019 event brought extreme low temperatures to both southern France and Sweden. At the same time, by sweeping in moist air from the Atlantic, it caused extreme precipitation and flooding across many areas in central and eastern Europe. Similar events took place in Europe in 2013 and 2018.
The researchers say that 50 years ago, such concurrent waves took hold on average only once each winter. The numbers vary year to year, but now the average has risen to twice a year.
Kai Kornhuber et al,
Recent Increase in a Recurrent Pan-Atlantic Wave Pattern Driving Concurrent Wintertime Extremes,
Bulletin of the American Meteorological Society (2023).
https://journals.ametsoc.org/view/journals/bams/104/9/BAMS-D-21-0295.1.xml
