for National Geographic News
Earth's jet streams—high-altitude winds that influence storm direction—may be changing due to global warming, possibly making it easier for hurricanes to form, a new study says.
Jet streams in both the Northern and Southern Hemispheres have moved toward the poles and are slightly higher now than they were in 1979, according to analyses of data collected between 1979 to 2001.
Researchers also discovered that the jet stream in the Northern Hemisphere, which can affect the formation of hurricanes over the Atlantic Ocean, is a little weaker than it was two decades ago.
More studies are needed to conclusively link the shifts to global warming, the scientists say.
(Related: "Hurricanes Have Doubled Due to Global Warming, Study Says" [July 30, 2007].)
When upper-level winds are present during the hurricane season, the gusts can create wind shear, which greatly inhibits storm formation.
That's because winds blow across the top of the hurricane, preventing the storm's circulation from gaining the momentum it needs to develop more power. The jet stream also sometimes steers storms away from the U.S. mainland.
But without these upper-level winds to inhibit the storms' development, stronger and more plentiful Atlantic hurricanes could form and make landfall in the U.S.
However the possible effects of jet stream shifts on hurricanes is only briefly mentioned in the study and is "all speculation," said study co-author Christina Archer, a meteorologist at the Carnegie Institution's Department for Global Ecology in Stanford, California.
Archer and colleague Ken Caldeira, also of Carnegie, published their research recently in the journal Geophysical Research Letters.
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