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Science Briefing

Kevin Trenberth. (Photo by Bob Bumpas)
The most recent El Nino/Southern Oscillation (ENSO) event was the longest one observed in 130 years of records. It warmed parts of the central and eastern tropical Pacific from 1990 to mid-1995. In a paper for Geophysical Research Letters (GRL) published 1 January, CGD's Kevin Trenberth and Timothy Hoar demonstrate how exceptional this long-lived ENSO event was. Using a statistical test, the two scientists found that such an occurrence would be expected only once in about 2,000 years if the climate were unchanging.

El Nino traditionally refers to the periodic warming of Pacific waters off the coasts of Peru and Ecuador. However, this is only part of ENSO, a large and complex interaction between the tropical Pacific and the global atmosphere. It is linked to such atmospheric impacts as drought in Australia and parts of South America and flooding across California and the U.S. Gulf Coast.

Tim Hoar. (Photo by Bob Bumpas)
Kevin and Tim began with a 100-year record of atmospheric pressure at Darwin, Australia. Pressures at Darwin and Tahiti are often used as an index of the Southern Oscillation, since they average higher and lower than normal, respectively, during El Nino. From December 1989 to May 1995, the pressures at Darwin ran 0.94 millibars (about 0.03 inches of mercury) above the 100-year average. Kevin and Tim used an autoregressive moving average model to simulate the seasonal fluctuations at Darwin over a stretch of 1 million years, based on rises and falls observed over the century between 1882 and 1981 (before the most recent ENSO event began).

ENSO events lasting as long as the 1990-95 event occurred only once every 1,000 to 3,000 years in the model. Kevin and Tim also evaluated the overall warm tropical-Pacific conditions for the longer period of 1977-95 and obtained similar results, with a likelihood of occurrence every 1,500 to 2,500 years.

As the authors note in their GRL paper, "These results raise questions about the role of climate change. Is this pattern of change a manifestation of the global warming and related climate change associated with increases in greenhouse gases in the atmosphere? Or is this pattern a natural decadal- timescale variation? We have shown that the latter is highly unlikely."

The GRL paper also notes that the traditional definition of ENSO may need updating. In the 1990-95 event, Pacific water temperatures off South America-- long used to define El Nino--waxed and waned, while those farther west, in the central tropical Pacific, remained above normal. The latter region appears to be tied more closely to ENSO-style atmospheric changes in Australia and the Americas. Water temperatures now are running below normal in both the central and eastern tropical Pacific, heralding a move toward the first La NiNa since 1988-89.

SCD's Visualization Group has cleaned up in two prestigious graphics contests. Its six-minute, high-definition TV (HDTV) video The Visible Human Project has received first prize in the computer graphics section of the Nippon Computer Graphics Association's Grand Prix competition, as well as a distinguished production award. The latter includes a cash prize of 500,000 yen (about $5000). Earlier last summer, the video gained entry into the uppermost tier of the prestigious Animation Festival that takes place at the annual meeting of the Association of Computing Machinery's Special Interest Group on Computer Graphics and Interactive Techniques (SIGGRAPH). The SCD video was shown at Los Angeles' Shrine Auditorium--site of the 1995 Academy Awards--to an appreciative audience estimated at 30,000.

"The movie has been a stunning success and has attracted broad international attention and acclaim," says group head Don Middleton, who coproduced the movie with John Clyne, also in SCD's Visualization Group, and researchers from the University of Colorado's Health Sciences Center in Denver (UCHSC). "It's one of those unique situations where science and technology take center stage- -and people take notice. As an added benefit, the demanding requirements of the digital HDTV production resulted in a major advance in our own animation production capability."

The Visible Man is a 39-year-old Texan who willed his body to science before his execution for murder. Using a custom-made device, researchers at the UCHSC sliced his body into one-millimeter-thick sections and digitally photographed it at each stage. The result was an unprecedented data set allowing three- dimensional views and dissections from any angle. NCAR hosted the data set in 1995 on behalf of the National Library of Medicine. Medical schools, researchers, and many others transferred a remarkable 300 gigabytes of the data over the Internet during 1995. The Visible Woman recently debuted (sans SCD involvement), with three times the resolution of her male counterpart.

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Edited by Bob Henson, bhenson@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Thu Mar 30 11:41:07 MST 2000