Weather throws a curve
Apparently the intense curve of the jet stream can predict the variability of an entire season and it is part of a 4,000 year pattern. Last winter's curvy jet stream in North America resulted in mild western temperatures and harsher cold temperatures in the east. University of Utah researchers reveal that a similar pattern became more pronounced 4,000 years ago, suggesting that it may worsen as Earth's climate warms.
According to geochemist Gabe Bowen, senior author of the study, "If this trend continues, it could contribute to more extreme winter weather events in North America, as experienced this year with warm conditions in California and Alaska and intrusion of cold Arctic air across the eastern USA."
"A sinuous or curvy winter jet stream means unusual warmth in the West, drought conditions in part of the West, and abnormally cold winters in the East and Southeast," adds Bowen. "We saw a good example of extreme wintertime climate that largely fit that pattern this past winter," although typically California is wetter.
The researchers note that scientists have already linked "Greenhouse" gases to the current warming of the Earth’s climate and increased weather extremes predicting the likelihood of their continuance.
But the new study shows that the North American jet stream pattern for wintertime weather extremes is millennia old — "a longstanding and persistent pattern of climate variability," Bowen says. Yet global warming may enhance the pattern making winter weather extremes more frequent or severe or both.
"This is one more reason why we may have more winter extremes in North America, as well as something of a model for what those extremes may look like," Bowen says. Human-caused climate change is reducing equator-to-pole temperature differences; the atmosphere is warming more at the poles than at the equator. Based on what happened in past millennia, that could make a curvy jet stream even more frequent and-or intense than it is now, he says.
Bowen and his co-authors analyzed previously published data on oxygen isotope ratios in lake sediment cores and cave deposits from sites in the eastern and western United States and Canada. Those isotopes were deposited in ancient rainfall and incorporated into calcium carbonate. They reveal jet stream directions during the past 8,000 years, a geological time known as middle and late stages of the Holocene Epoch.
Next, the researchers did computer modeling or simulations of jet stream patterns — both curvy and more direct west to east — to show how changes in those patterns can explain changes in the isotope ratios left by rainfall in the old lake and cave deposits.
Read more at the University of Utah.
Winter covered home image via Shutterstock.