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May 24, 2000

John Bluck

NASA Ames Research Center, Moffett Field, CA

650/604-5026 or 650/604-9000,

Harvey Leifert (contact until May 26 and for media registration)

American Geophysical Union (AGU), Washington, DC


AGU Press Room (contact from May 30 on and for media registration)

Washington Convention Center, 900 9th St. NW

Washington, DC

202/371-5087, fax 202/371-5093,



The culprits in the major ozone loss in the Arctic stratosphere earlier this year were unusually long-lasting polar clouds made of nitric acid crystals, according to preliminary results from an international field experiment.

The new evidence also confirms scientists’ suspicions that an ozone-destroying chemical process not thought to be active over the northern pole is occurring, which could foreshadow greater ozone losses in the future. This research on the ozone-destroying role of polar stratospheric clouds (PSCs) will be presented next week at the American Geophysical Union’s Spring Meeting in Washington, D.C. A news briefing is scheduled for Tuesday, May 30, at 12:15 p.m. EDT in the Washington Convention Center. Three thousand earth scientists are expected at this year’s meeting.

"Even the very small numbers of particles observed in PSCs during our experiment can efficiently remove nitrogen from the stratosphere," said Eric Jensen, a scientist from NASA's Ames Research Center, located in California's Silicon Valley, who will be one of the briefing panelists. "We found that the clouds lasted longer during the 1999/2000 winter than during past winters, allowing greater ozone depletion over the Arctic."

picture of stratospheric clouds Click here to reach links to images of polar stratospheric clouds in high enough resolution for some publications.

Scientists involved in a recent NASA/European Commission field experiment in Sweden will discuss their preliminary results at the briefing. Topics include the formation of PSCs by waves in the atmosphere created by mountain ranges, and indications that "denitrification" may now be taking place over the Arctic, a process that can delay the natural shut-off of ozone-destruction as spring arrives.

The new observations were collected by aircraft, balloons, and satellites during the joint SAGE III Ozone Loss and Validation Experiment (SOLVE) and the European Stratospheric Experiment in Ozone (THESEO), conducted between December 1999 and March 2000.

More information about the NASA-sponsored SOLVE campaign and the European Commission-sponsored THESEO 2000 experiment (including a list of participating institutions) is on the Internet at:

(THESEO 2000) --

In addition to Jensen, participants in the AGU news briefing include: Edward V. Browell, NASA Langley Research Center, Hampton, VA; Ken Carslaw, University of Leeds, United Kingdom; Michael J. Kurylo, NASA’s Upper Atmosphere Research Program, NASA Headquarters, Washington, DC; and Brian Toon, University of Colorado, Boulder, CO.

Video and new data animations will be distributed at the AGU news briefing. Color photographs of polar stratospheric clouds from the recent field experiment are available on the Internet at:



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