::' ' ; NEWS AN D news and notes Notes El Nino and Climate More Predictable Than Seasonal averages, especially in the Tropics, are Previousl y Thought most predictable because the tropical atmosphere re- Fluctuations in the earth's climate from year to year, sponds directly to slowly varying conditions at the such as those that are associated with El Nino, are earth's surface. Shukla and his colleagues at COLA considerably more predictable than had been previ- have run models of the global climate to show that ously believed, according to a paper appearing in the seasonal mean weather conditions are determined by 23 October issue of Science. The research was jointly sea surface temperature, soil wetness, vegetation, and funded by the National Science Foundation (NSF), snow cover. In particular, variations in sea surface tem- NOAA, and NASA. perature such as those that are associated with El Nino "For more than 30 years, the so-called butterfly ef- can significantly alter weather in the Tropics for an entire season, or longer. fect has been the dominant paradigm for weather fore- casting," says scientist J. Shukla of the George Mason High predictability of the tropical atmosphere can University Center for Ocean-Land-Atmospheric also enhance the predictability of the North American Studies (COLA), lead author of the Science paper. "It region. Shukla said that if changes in the tropical Pa- has now been demonstrated that there are more impor- cific sea surface temperature are large, the seasonal tant exceptions to the butterfly effect and that certain average atmospheric circulation over the North Pacific aspects of climate are far more predictable than pre- and North America is also highly predictable. viously thought." "It is no accident that seasonal predictions made by The butterfly effect is a reference to the chaotic na- several research groups around the world for last win- ture of day-to-day atmospheric fluctuations, explained ter (1997-98) were quite accurate." Shukla pointed Jay Fein, director of NSF's climate dynamics program, out. "Those unprecedented forecasts were just the first examples of the accurate predictions of major El Nino which funds COLA research. Such weather events events. We can expect more such in the future." cannot be predicted precisely beyond one to two weeks in the future. For several decades, the prevailing view in scientific circles was that it was not possible to pre- Voluntee r Science Tea m Soar s Towar d Better dict weather and climate variations beyond this intrin- Weathe r Forecasting sic limit. Research by Shukla and his colleagues at A volunteer team of scientists from the National COLA has shown that, although weather cannot be Center for Atmospheric Research, in Boulder, Colo- predicted beyond a few days away, atmospheric cir- rado, and glider pilots from the Soaring Society of culation and precipitation, averaged for an entire sea- Boulder, spent the past spring exploring an elusive son, are potentially predictable. "Indeed, there is atmospheric phenomenon from a high-performance, predictability in the midst of chaos," Shukla said. "We hybrid aircraft called a motorglider. Supported by the now have a scientific basis for climate prediction, and National Science Foundation and the University Cor- that suggests that the large-scale effects for all future poration for Atmospheric Research, the scientists are major El Nino events should be predictable several now analyzing what was learned about thermal months in advance." waves—the gravity waves that sometimes form above rising columns of warm air called thermals. Thermals are perhaps best known to hawk-watchers, as these air currents are used by hawks, eagles, and other birds of prey, as well as by man-made gliders or sailplanes, to gain altitude in motorless flight. 155 Scott A. Lawrimore 1998 Thermal waves, which have eluded thorough sci- entific measurement until now, may hold one key to 281 6 Vol. 79, No. 72, December 1998
Bulletin of the American Meteorological Society – American Meteorological Society
Published: Dec 1, 1998
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