Lengthy droughts tied to long-lived La Ninas. (Long, Dry Spells).A new study of persistent droughts that occurred in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. during the past 3 centuries suggests that those dry spells may be associated with prolonged instances of the climate phenomenon known as La Nina. That occurs when sea-surface temperatures in the central Pacific are cooler than average. La Nina events typically bring drier-than-normal conditions to the southwestern United States, says Edward R. Cook of the Lamont-Doherty Earth Observatory Lamont-Doherty Earth Observatory (LDEO) is a world-class research institution specializing in the Earth sciences and is part of Columbia University. The current director of Lamont is G. Michael Purdy. in Palisades Palisades, cliffs along the west bank of the Hudson River, NE N.J. and SE N.Y., extending from N of Jersey City, N.J., to the vicinity of Piermont, N.Y., with a general altitude of from 350 ft to 550 ft (107–168 m). , N.Y. In the 20th century, each La Nina typically didn't last more than 2 years. However, new analyses of coral taken from the central Pacific indicate that the sea-surface temperatures there were significantly lower than normal from 1855 to 1863. That period lines up with the driest decade in Texas since 1700, as recorded in tree rings, says Cook. Trees farther north, along the edges of the Great Plains, also chronicle a drought beginning in 1855 that was worse than the one that afflicted af·flict tr.v. af·flict·ed, af·flict·ing, af·flicts To inflict grievous physical or mental suffering on. [Middle English afflighten, from afflight, the region during the Dust Bowl of the 1930s. Other widespread droughts that coincided with extended La Ninas stretched from 1703 to 1709 and from 1818 to 1824. Several additional dry spells--including ones in the 1730s, 1750s, 1890s, and 1950s--overlap but slightly lag corresponding La Nina periods in the central Pacific, Cook notes. He and his colleagues report their findings in an upcoming issue of Geophysical Research Letters Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or . The team's analyses suggest that La Nina is merely one of the factors that influence precipitation in the Southwest and Great Plains. The so-called Pacific Decadal Oscillation The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N. , an approximately 20-year-long cycle in ocean temperatures in the northern Pacific, seems to play a significant role as well, says Cook. A mild drought in the Southwest, which began in 1879, ended in 1884--the same time that ocean temperatures in the northern Pacific swung from slightly below normal to much above normal--even though La Nina conditions persisted until 1888. Climate data recorded in living organisms such as trees and coral are particularly important because they enable researchers to examine conditions prevalent in a region before scientific measurements were available, says Gregory J. McCabe, a climatologist cli·ma·tol·o·gy n. The meteorological study of climates and their phenomena. cli  ma·to·log at the U.S. Geological Survey in Denver. The new study should help fill in more pieces of Earth's climate puzzle, he notes.
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