WASHINGTON — The jet stream — America’s stormy-weather maker — is creeping northward and weakening, new research shows.
That potentially means less rain in the already dry South and Southwest and more storms in the North. And it could also translate into more and stronger hurricanes since the jet stream suppresses their formation. The study’s authors said they have to do more research to pinpoint specific consequences.
From 1979 to 2001, the Northern Hemisphere’s jet stream moved northward on average at a rate of about 1.25 miles a year, according to a paper published today in the journal Geophysical Research Letters. The authors suspect global warming is the cause but have yet to prove it.
The jet stream is a high-speed, constantly shifting river of air about 30,000 feet above the ground that guides storm systems and cool air around the globe. And when it moves away from a region, high pressure and clear skies predominate.
Two other jet streams in the Southern Hemisphere are also shifting poleward, the study found.
The northern jet stream “is the dominant thing that creates weather systems for the United States,” said study co-author Ken Caldeira, a climate scientist at the Carnegie Institution of Washington in Stanford, Calif. “Basically look south of where you are and that’s probably a good guess of what your weather may be like in a few decades.”
The study’s authors and other scientists suggest that the widening of Earth’s tropical belt — a development documented last year — is pushing the three jet streams toward the poles.
A rate of 1.25 miles a year “doesn’t sound like much, but that works out to about 18 feet per day,” Caldeira said.
The jet stream also factors into bumpy air travel. It is a cause of clear air turbulence that airline pilots try to avoid by tracking where the jet stream is.
Warmer globally, average in U.S.
On Thursday it was also reported that last month was the warmest March on record over land surfaces of the world and the second warmest overall worldwide.
For the United States, however, it was just an average March, the National Oceanic and Atmospheric Administra-tion reported.
NOAA’s National Climatic Data Center said high temperatures over much of Asia pulled the worldwide land temperature up to an average of 40.8 degrees Fahrenheit (4.9 degrees Celsius), 3.2 degrees (1.8 C) warmer than the average in the 20th century.
While Asia had its greatest January snow cover this year, warm March readings caused a rapid melt and March snow cover on the continent was a record low.
Global ocean temperatures were the 13th warmest on record, with a weakening of the La Niña conditions that cool the tropical Pacific Ocean.
Overall land and sea surface temperatures for the world were second highest in 129 years of record keeping, trailing only 2002, the agency said.
The climate center said that for the 48 contiguous United States it was about average, ranking as the 63rd warmest March in 113 years of record keeping.
The average temperature for the U.S. in March was 42 degrees, 0.4 degrees below the 20th-century mean.
The snowpack declined in many parts of the West in March, but the Western snowpack remains the best in more than a decade thanks to heavy snowfall from December through February.
